Unicode escapes with any backend encoding

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Unicode escapes with any backend encoding

Tom Lane-2
I threatened to do this in another thread [1], so here it is.

This patch removes the restriction that the server encoding must
be UTF-8 in order to write any Unicode escape with a value outside
the ASCII range.  Instead, we'll allow the notation and convert to
the server encoding if that's possible.  (If it isn't, of course
you get an encoding conversion failure.)

In the cases that were already supported, namely ASCII characters
or UTF-8 server encoding, this should be only immeasurably slower
than before.  Otherwise, it calls the appropriate encoding conversion
procedure, which of course will take a little time.  But that's
better than failing, surely.

One way in which this is slightly less good than before is that
you no longer get a syntax error cursor pointing at the problematic
escape when conversion fails.  If we were really excited about that,
something could be done with setting up an errcontext stack entry.
But that would add a few cycles, so I wasn't sure whether to do it.

Grepping for other direct uses of unicode_to_utf8(), I notice that
there are a couple of places in the JSON code where we have a similar
restriction that you can only write a Unicode escape in UTF8 server
encoding.  I'm not sure whether these same semantics could be
applied there, so I didn't touch that.

Thoughts?

                        regards, tom lane

[1] https://www.postgresql.org/message-id/flat/CACPNZCvaoa3EgVWm5yZhcSTX6RAtaLgniCPcBVOCwm8h3xpWkw%40mail.gmail.com


diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index c908e0b..e134877 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -189,6 +189,23 @@ UPDATE "my_table" SET "a" = 5;
     ampersands.  The length limitation still applies.
    </para>
 
+   <para>
+    Quoting an identifier also makes it case-sensitive, whereas
+    unquoted names are always folded to lower case.  For example, the
+    identifiers <literal>FOO</literal>, <literal>foo</literal>, and
+    <literal>"foo"</literal> are considered the same by
+    <productname>PostgreSQL</productname>, but
+    <literal>"Foo"</literal> and <literal>"FOO"</literal> are
+    different from these three and each other.  (The folding of
+    unquoted names to lower case in <productname>PostgreSQL</productname> is
+    incompatible with the SQL standard, which says that unquoted names
+    should be folded to upper case.  Thus, <literal>foo</literal>
+    should be equivalent to <literal>"FOO"</literal> not
+    <literal>"foo"</literal> according to the standard.  If you want
+    to write portable applications you are advised to always quote a
+    particular name or never quote it.)
+   </para>
+
    <indexterm>
      <primary>Unicode escape</primary>
      <secondary>in identifiers</secondary>
@@ -230,7 +247,8 @@ U&amp;"d!0061t!+000061" UESCAPE '!'
     The escape character can be any single character other than a
     hexadecimal digit, the plus sign, a single quote, a double quote,
     or a whitespace character.  Note that the escape character is
-    written in single quotes, not double quotes.
+    written in single quotes, not double quotes,
+    after <literal>UESCAPE</literal>.
    </para>
 
    <para>
@@ -239,32 +257,18 @@ U&amp;"d!0061t!+000061" UESCAPE '!'
    </para>
 
    <para>
-    The Unicode escape syntax works only when the server encoding is
-    <literal>UTF8</literal>.  When other server encodings are used, only code
-    points in the ASCII range (up to <literal>\007F</literal>) can be
-    specified.  Both the 4-digit and the 6-digit form can be used to
+    Either the 4-digit or the 6-digit escape form can be used to
     specify UTF-16 surrogate pairs to compose characters with code
     points larger than U+FFFF, although the availability of the
     6-digit form technically makes this unnecessary.  (Surrogate
-    pairs are not stored directly, but combined into a single
-    code point that is then encoded in UTF-8.)
+    pairs are not stored directly, but are combined into a single
+    code point.)
    </para>
 
    <para>
-    Quoting an identifier also makes it case-sensitive, whereas
-    unquoted names are always folded to lower case.  For example, the
-    identifiers <literal>FOO</literal>, <literal>foo</literal>, and
-    <literal>"foo"</literal> are considered the same by
-    <productname>PostgreSQL</productname>, but
-    <literal>"Foo"</literal> and <literal>"FOO"</literal> are
-    different from these three and each other.  (The folding of
-    unquoted names to lower case in <productname>PostgreSQL</productname> is
-    incompatible with the SQL standard, which says that unquoted names
-    should be folded to upper case.  Thus, <literal>foo</literal>
-    should be equivalent to <literal>"FOO"</literal> not
-    <literal>"foo"</literal> according to the standard.  If you want
-    to write portable applications you are advised to always quote a
-    particular name or never quote it.)
+    If the server encoding is not UTF-8, the Unicode code point identified
+    by one of these escape sequences is converted to the actual server
+    encoding; an error is reported if that's not possible.
    </para>
   </sect2>
 
@@ -427,25 +431,11 @@ SELECT 'foo'      'bar';
     <para>
      It is your responsibility that the byte sequences you create,
      especially when using the octal or hexadecimal escapes, compose
-     valid characters in the server character set encoding.  When the
-     server encoding is UTF-8, then the Unicode escapes or the
+     valid characters in the server character set encoding.
+     A useful alternative is to use Unicode escapes or the
      alternative Unicode escape syntax, explained
-     in <xref linkend="sql-syntax-strings-uescape"/>, should be used
-     instead.  (The alternative would be doing the UTF-8 encoding by
-     hand and writing out the bytes, which would be very cumbersome.)
-    </para>
-
-    <para>
-     The Unicode escape syntax works fully only when the server
-     encoding is <literal>UTF8</literal>.  When other server encodings are
-     used, only code points in the ASCII range (up
-     to <literal>\u007F</literal>) can be specified.  Both the 4-digit and
-     the 8-digit form can be used to specify UTF-16 surrogate pairs to
-     compose characters with code points larger than U+FFFF, although
-     the availability of the 8-digit form technically makes this
-     unnecessary.  (When surrogate pairs are used when the server
-     encoding is <literal>UTF8</literal>, they are first combined into a
-     single code point that is then encoded in UTF-8.)
+     in <xref linkend="sql-syntax-strings-uescape"/>; then the server
+     will check that the character conversion is possible.
     </para>
 
     <caution>
@@ -524,16 +514,23 @@ U&amp;'d!0061t!+000061' UESCAPE '!'
     </para>
 
     <para>
-     The Unicode escape syntax works only when the server encoding is
-     <literal>UTF8</literal>.  When other server encodings are used, only
-     code points in the ASCII range (up to <literal>\007F</literal>)
-     can be specified.  Both the 4-digit and the 6-digit form can be
-     used to specify UTF-16 surrogate pairs to compose characters with
-     code points larger than U+FFFF, although the availability of the
-     6-digit form technically makes this unnecessary.  (When surrogate
-     pairs are used when the server encoding is <literal>UTF8</literal>, they
-     are first combined into a single code point that is then encoded
-     in UTF-8.)
+     To include the escape character in the string literally, write
+     it twice.
+    </para>
+
+    <para>
+     Either the 4-digit or the 6-digit escape form can be used to
+     specify UTF-16 surrogate pairs to compose characters with code
+     points larger than U+FFFF, although the availability of the
+     6-digit form technically makes this unnecessary.  (Surrogate
+     pairs are not stored directly, but are combined into a single
+     code point.)
+    </para>
+
+    <para>
+     If the server encoding is not UTF-8, the Unicode code point identified
+     by one of these escape sequences is converted to the actual server
+     encoding; an error is reported if that's not possible.
     </para>
 
     <para>
@@ -546,11 +543,6 @@ U&amp;'d!0061t!+000061' UESCAPE '!'
      parameter is set to off, this syntax will be rejected with an
      error message.
     </para>
-
-    <para>
-     To include the escape character in the string literally, write it
-     twice.
-    </para>
    </sect3>
 
    <sect3 id="sql-syntax-dollar-quoting">
diff --git a/src/backend/parser/parser.c b/src/backend/parser/parser.c
index 1bf1144..e88a5e0 100644
--- a/src/backend/parser/parser.c
+++ b/src/backend/parser/parser.c
@@ -292,7 +292,7 @@ hexval(unsigned char c)
  return 0; /* not reached */
 }
 
-/* is Unicode code point acceptable in database's encoding? */
+/* is Unicode code point acceptable? */
 static void
 check_unicode_value(pg_wchar c, int pos, core_yyscan_t yyscanner)
 {
@@ -302,12 +302,6 @@ check_unicode_value(pg_wchar c, int pos, core_yyscan_t yyscanner)
  (errcode(ERRCODE_SYNTAX_ERROR),
  errmsg("invalid Unicode escape value"),
  scanner_errposition(pos, yyscanner)));
-
- if (c > 0x7F && GetDatabaseEncoding() != PG_UTF8)
- ereport(ERROR,
- (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8"),
- scanner_errposition(pos, yyscanner)));
 }
 
 /* is 'escape' acceptable as Unicode escape character (UESCAPE syntax) ? */
@@ -338,18 +332,30 @@ str_udeescape(const char *str, char escape,
  const char *in;
  char   *new,
    *out;
+ size_t new_len;
  pg_wchar pair_first = 0;
 
  /*
- * This relies on the subtle assumption that a UTF-8 expansion cannot be
- * longer than its escaped representation.
+ * Guesstimate that result will be no longer than input, but allow enough
+ * padding for Unicode conversion.
  */
- new = palloc(strlen(str) + 1);
+ new_len = strlen(str) + MAX_UNICODE_EQUIVALENT_STRING + 1;
+ new = palloc(new_len);
 
  in = str;
  out = new;
  while (*in)
  {
+ /* Enlarge string if needed */
+ size_t out_dist = out - new;
+
+ if (out_dist > new_len - (MAX_UNICODE_EQUIVALENT_STRING + 1))
+ {
+ new_len *= 2;
+ new = repalloc(new, new_len);
+ out = new + out_dist;
+ }
+
  if (in[0] == escape)
  {
  if (in[1] == escape)
@@ -390,8 +396,8 @@ str_udeescape(const char *str, char escape,
  pair_first = unicode;
  else
  {
- unicode_to_utf8(unicode, (unsigned char *) out);
- out += pg_mblen(out);
+ pg_unicode_to_server(unicode, (unsigned char *) out);
+ out += strlen(out);
  }
  in += 5;
  }
@@ -431,8 +437,8 @@ str_udeescape(const char *str, char escape,
  pair_first = unicode;
  else
  {
- unicode_to_utf8(unicode, (unsigned char *) out);
- out += pg_mblen(out);
+ pg_unicode_to_server(unicode, (unsigned char *) out);
+ out += strlen(out);
  }
  in += 8;
  }
@@ -457,13 +463,6 @@ str_udeescape(const char *str, char escape,
  goto invalid_pair;
 
  *out = '\0';
-
- /*
- * We could skip pg_verifymbstr if we didn't process any non-7-bit-ASCII
- * codes; but it's probably not worth the trouble, since this isn't likely
- * to be a performance-critical path.
- */
- pg_verifymbstr(new, out - new, false);
  return new;
 
 invalid_pair:
diff --git a/src/backend/parser/scan.l b/src/backend/parser/scan.l
index 84c7391..3903df8 100644
--- a/src/backend/parser/scan.l
+++ b/src/backend/parser/scan.l
@@ -1226,19 +1226,18 @@ process_integer_literal(const char *token, YYSTYPE *lval)
 static void
 addunicode(pg_wchar c, core_yyscan_t yyscanner)
 {
- char buf[8];
+ char buf[MAX_UNICODE_EQUIVALENT_STRING + 1];
 
  /* See also check_unicode_value() in parser.c */
  if (c == 0 || c > 0x10FFFF)
  yyerror("invalid Unicode escape value");
- if (c > 0x7F)
- {
- if (GetDatabaseEncoding() != PG_UTF8)
- yyerror("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8");
- yyextra->saw_non_ascii = true;
- }
- unicode_to_utf8(c, (unsigned char *) buf);
- addlit(buf, pg_mblen(buf), yyscanner);
+
+ /*
+ * We expect that pg_unicode_to_server() will complain about any
+ * unconvertible code point, so we don't have to set saw_non_ascii.
+ */
+ pg_unicode_to_server(c, (unsigned char *) buf);
+ addlit(buf, strlen(buf), yyscanner);
 }
 
 static unsigned char
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 3808c30..a2d2a0b 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -2086,26 +2086,6 @@ map_sql_identifier_to_xml_name(const char *ident, bool fully_escaped,
 
 
 /*
- * Map a Unicode codepoint into the current server encoding.
- */
-static char *
-unicode_to_sqlchar(pg_wchar c)
-{
- char utf8string[8]; /* need room for trailing zero */
- char   *result;
-
- memset(utf8string, 0, sizeof(utf8string));
- unicode_to_utf8(c, (unsigned char *) utf8string);
-
- result = pg_any_to_server(utf8string, strlen(utf8string), PG_UTF8);
- /* if pg_any_to_server didn't strdup, we must */
- if (result == utf8string)
- result = pstrdup(result);
- return result;
-}
-
-
-/*
  * Map XML name to SQL identifier; see SQL/XML:2008 section 9.3.
  */
 char *
@@ -2125,10 +2105,12 @@ map_xml_name_to_sql_identifier(const char *name)
  && isxdigit((unsigned char) *(p + 5))
  && *(p + 6) == '_')
  {
+ char cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];
  unsigned int u;
 
  sscanf(p + 2, "%X", &u);
- appendStringInfoString(&buf, unicode_to_sqlchar(u));
+ pg_unicode_to_server(u, (unsigned char *) cbuf);
+ appendStringInfoString(&buf, cbuf);
  p += 6;
  }
  else
diff --git a/src/backend/utils/mb/mbutils.c b/src/backend/utils/mb/mbutils.c
index 5d7cc74..7d90ac9 100644
--- a/src/backend/utils/mb/mbutils.c
+++ b/src/backend/utils/mb/mbutils.c
@@ -68,6 +68,13 @@ static FmgrInfo *ToServerConvProc = NULL;
 static FmgrInfo *ToClientConvProc = NULL;
 
 /*
+ * This variable stores the conversion function to convert from UTF-8
+ * to the server encoding.  It's NULL if the server encoding *is* UTF-8,
+ * or if we lack a conversion function for this.
+ */
+static FmgrInfo *Utf8ToServerConvProc = NULL;
+
+/*
  * These variables track the currently-selected encodings.
  */
 static const pg_enc2name *ClientEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];
@@ -273,6 +280,8 @@ SetClientEncoding(int encoding)
 void
 InitializeClientEncoding(void)
 {
+ int current_server_encoding;
+
  Assert(!backend_startup_complete);
  backend_startup_complete = true;
 
@@ -289,6 +298,35 @@ InitializeClientEncoding(void)
  pg_enc2name_tbl[pending_client_encoding].name,
  GetDatabaseEncodingName())));
  }
+
+ /*
+ * Also look up the UTF8-to-server conversion function if needed.  Since
+ * the server encoding is fixed within any one backend process, we don't
+ * have to do this more than once.
+ */
+ current_server_encoding = GetDatabaseEncoding();
+ if (current_server_encoding != PG_UTF8 &&
+ current_server_encoding != PG_SQL_ASCII)
+ {
+ Oid utf8_to_server_proc;
+
+ Assert(IsTransactionState());
+ utf8_to_server_proc =
+ FindDefaultConversionProc(PG_UTF8,
+  current_server_encoding);
+ /* If there's no such conversion, just leave the pointer as NULL */
+ if (OidIsValid(utf8_to_server_proc))
+ {
+ FmgrInfo   *finfo;
+
+ finfo = (FmgrInfo *) MemoryContextAlloc(TopMemoryContext,
+ sizeof(FmgrInfo));
+ fmgr_info_cxt(utf8_to_server_proc, finfo,
+  TopMemoryContext);
+ /* Set Utf8ToServerConvProc only after data is fully valid */
+ Utf8ToServerConvProc = finfo;
+ }
+ }
 }
 
 /*
@@ -752,6 +790,73 @@ perform_default_encoding_conversion(const char *src, int len,
  return result;
 }
 
+/*
+ * Convert a single Unicode code point into a string in the server encoding.
+ *
+ * The code point given by "c" is converted and stored at *s, which must
+ * have at least MAX_UNICODE_EQUIVALENT_STRING+1 bytes available.
+ * The output will have a trailing '\0'.  Throws error if the conversion
+ * cannot be performed.
+ *
+ * Note that this relies on having previously looked up any required
+ * conversion function.  That's partly for speed but mostly because the parser
+ * may call this outside any transaction, or in an aborted transaction.
+ */
+void
+pg_unicode_to_server(pg_wchar c, unsigned char *s)
+{
+ unsigned char c_as_utf8[MAX_MULTIBYTE_CHAR_LEN + 1];
+ int c_as_utf8_len;
+ int server_encoding;
+
+ /*
+ * Complain if invalid Unicode code point.  The choice of errcode here is
+ * debatable, but really our caller should have checked this anyway.
+ */
+ if (c == 0 || c > 0x10FFFF)
+ ereport(ERROR,
+ (errcode(ERRCODE_SYNTAX_ERROR),
+ errmsg("invalid Unicode code point")));
+
+ /* Otherwise, if it's in ASCII range, conversion is trivial */
+ if (c <= 0x7F)
+ {
+ s[0] = (unsigned char) c;
+ s[1] = '\0';
+ return;
+ }
+
+ /* If the server encoding is UTF-8, we just need to reformat the code */
+ server_encoding = GetDatabaseEncoding();
+ if (server_encoding == PG_UTF8)
+ {
+ unicode_to_utf8(c, s);
+ s[pg_utf_mblen(s)] = '\0';
+ return;
+ }
+
+ /* For all other cases, we must have a conversion function available */
+ if (Utf8ToServerConvProc == NULL)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("conversion between %s and %s is not supported",
+ pg_enc2name_tbl[PG_UTF8].name,
+ GetDatabaseEncodingName())));
+
+ /* Construct UTF-8 source string */
+ unicode_to_utf8(c, c_as_utf8);
+ c_as_utf8_len = pg_utf_mblen(c_as_utf8);
+ c_as_utf8[c_as_utf8_len] = '\0';
+
+ /* Convert, or throw error if we can't */
+ FunctionCall5(Utf8ToServerConvProc,
+  Int32GetDatum(PG_UTF8),
+  Int32GetDatum(server_encoding),
+  CStringGetDatum(c_as_utf8),
+  CStringGetDatum(s),
+  Int32GetDatum(c_as_utf8_len));
+}
+
 
 /* convert a multibyte string to a wchar */
 int
diff --git a/src/include/mb/pg_wchar.h b/src/include/mb/pg_wchar.h
index 7fb5fa4..2daf301 100644
--- a/src/include/mb/pg_wchar.h
+++ b/src/include/mb/pg_wchar.h
@@ -316,6 +316,15 @@ typedef enum pg_enc
 #define MAX_CONVERSION_GROWTH  4
 
 /*
+ * Maximum byte length of the string equivalent to any one Unicode code point,
+ * in any backend encoding.  The current value assumes that a 4-byte UTF-8
+ * character might expand by MAX_CONVERSION_GROWTH, which is a huge
+ * overestimate.  But in current usage we don't allocate large multiples of
+ * this, so there's little point in being stingy.
+ */
+#define MAX_UNICODE_EQUIVALENT_STRING 16
+
+/*
  * Table for mapping an encoding number to official encoding name and
  * possibly other subsidiary data.  Be careful to check encoding number
  * before accessing a table entry!
@@ -602,6 +611,8 @@ extern char *pg_server_to_client(const char *s, int len);
 extern char *pg_any_to_server(const char *s, int len, int encoding);
 extern char *pg_server_to_any(const char *s, int len, int encoding);
 
+extern void pg_unicode_to_server(pg_wchar c, unsigned char *s);
+
 extern unsigned short BIG5toCNS(unsigned short big5, unsigned char *lc);
 extern unsigned short CNStoBIG5(unsigned short cns, unsigned char lc);
 
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Re: Unicode escapes with any backend encoding

Andrew Dunstan-8
On Tue, Jan 14, 2020 at 10:02 AM Tom Lane <[hidden email]> wrote:
>

>
> Grepping for other direct uses of unicode_to_utf8(), I notice that
> there are a couple of places in the JSON code where we have a similar
> restriction that you can only write a Unicode escape in UTF8 server
> encoding.  I'm not sure whether these same semantics could be
> applied there, so I didn't touch that.
>


Off the cuff I'd be inclined to say we should keep the text escape
rules the same. We've already extended the JSON standard y allowing
non-UTF8 encodings.

cheers

andrew


--
Andrew Dunstan                https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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Re: Unicode escapes with any backend encoding

Tom Lane-2
Andrew Dunstan <[hidden email]> writes:
> On Tue, Jan 14, 2020 at 10:02 AM Tom Lane <[hidden email]> wrote:
>> Grepping for other direct uses of unicode_to_utf8(), I notice that
>> there are a couple of places in the JSON code where we have a similar
>> restriction that you can only write a Unicode escape in UTF8 server
>> encoding.  I'm not sure whether these same semantics could be
>> applied there, so I didn't touch that.

> Off the cuff I'd be inclined to say we should keep the text escape
> rules the same. We've already extended the JSON standard y allowing
> non-UTF8 encodings.

Right.  I'm just thinking though that if you can write "é" literally
in a JSON string, even though you're using LATIN1 not UTF8, then why
not allow writing that as "\u00E9" instead?  The latter is arguably
truer to spec.

However, if JSONB collapses "\u00E9" to LATIN1 "é", that would be bad,
unless we have a way to undo it on printout.  So there might be
some more moving parts here than I thought.

                        regards, tom lane


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Re: Unicode escapes with any backend encoding

Tom Lane-2
I wrote:
> Andrew Dunstan <[hidden email]> writes:
>> On Tue, Jan 14, 2020 at 10:02 AM Tom Lane <[hidden email]> wrote:
>>> Grepping for other direct uses of unicode_to_utf8(), I notice that
>>> there are a couple of places in the JSON code where we have a similar
>>> restriction that you can only write a Unicode escape in UTF8 server
>>> encoding.  I'm not sure whether these same semantics could be
>>> applied there, so I didn't touch that.

>> Off the cuff I'd be inclined to say we should keep the text escape
>> rules the same. We've already extended the JSON standard y allowing
>> non-UTF8 encodings.

> Right.  I'm just thinking though that if you can write "é" literally
> in a JSON string, even though you're using LATIN1 not UTF8, then why
> not allow writing that as "\u00E9" instead?  The latter is arguably
> truer to spec.
> However, if JSONB collapses "\u00E9" to LATIN1 "é", that would be bad,
> unless we have a way to undo it on printout.  So there might be
> some more moving parts here than I thought.

On third thought, what would be so bad about that?  Let's suppose
I write:

        INSERT ... values('{"x": "\u00E9"}'::jsonb);

and the jsonb parsing logic chooses to collapse the backslash to
the represented character, i.e., "é".  Why should it matter whether
the database encoding is UTF8 or LATIN1?  If I am using UTF8
client encoding, I will see the "é" in UTF8 encoding either way,
because of output encoding conversion.  If I am using LATIN1
client encoding, I will see the "é" in LATIN1 either way --- or
at least, I will if the database encoding is UTF8.  Right now I get
an error for that when the database encoding is LATIN1 ... but if
I store the "é" as literal "é", it works, either way.  So it seems
to me that this error is just useless pedantry.  As long as the DB
encoding can represent the desired character, it should be transparent
to users.

                        regards, tom lane


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Re: Unicode escapes with any backend encoding

Chapman Flack
On 1/14/20 10:10 AM, Tom Lane wrote:
> to me that this error is just useless pedantry.  As long as the DB
> encoding can represent the desired character, it should be transparent
> to users.

That's my position too.

Regards,
-Chap


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Re: Unicode escapes with any backend encoding

Andrew Dunstan-8
On Wed, Jan 15, 2020 at 4:25 AM Chapman Flack <[hidden email]> wrote:
>
> On 1/14/20 10:10 AM, Tom Lane wrote:
> > to me that this error is just useless pedantry.  As long as the DB
> > encoding can represent the desired character, it should be transparent
> > to users.
>
> That's my position too.
>


and mine.

cheers

andrew


--
Andrew Dunstan                https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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Re: Unicode escapes with any backend encoding

Tom Lane-2
Andrew Dunstan <[hidden email]> writes:
> On Wed, Jan 15, 2020 at 4:25 AM Chapman Flack <[hidden email]> wrote:
>> On 1/14/20 10:10 AM, Tom Lane wrote:
>>> to me that this error is just useless pedantry.  As long as the DB
>>> encoding can represent the desired character, it should be transparent
>>> to users.

>> That's my position too.

> and mine.

I'm confused --- yesterday you seemed to be against this idea.
Have you changed your mind?

I'll gladly go change the patch if people are on board with this.

                        regards, tom lane


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Re: Unicode escapes with any backend encoding

Chapman Flack
On 1/14/20 4:25 PM, Tom Lane wrote:

> Andrew Dunstan <[hidden email]> writes:
>> On Wed, Jan 15, 2020 at 4:25 AM Chapman Flack <[hidden email]> wrote:
>>> On 1/14/20 10:10 AM, Tom Lane wrote:
>>>> to me that this error is just useless pedantry.  As long as the DB
>>>> encoding can represent the desired character, it should be transparent
>>>> to users.
>
>>> That's my position too.
>
>> and mine.
>
> I'm confused --- yesterday you seemed to be against this idea.
> Have you changed your mind?
>
> I'll gladly go change the patch if people are on board with this.

Hmm, well, let me clarify for my own part what I think I'm agreeing
with ... perhaps it's misaligned with something further upthread.

In an ideal world (which may be ideal in more ways than are in scope
for the present discussion) I would expect to see these principles:

1. On input, whether a Unicode escape is or isn't allowed should
   not depend on any encoding settings. It should be lexically
   allowed always, and if it represents a character that exists
   in the server encoding, it should mean that character. If it's
   not representable in the storage format, it should produce an
   error that says that.

2. If it happens that the character is representable in both the
   storage encoding and the client encoding, it shouldn't matter
   whether it arrives literally as an é or as an escape. Either
   should get stored on disk as the same bytes.

3. On output, as long as the character is representable in the client
   encoding, there is nothing to worry about. It will be sent as its
   representation in the client encoding (which may be different bytes
   than its representation in the server encoding).

4. If a character to be output isn't in the client encoding, it
   will be datatype-dependent whether there is any way to escape.
   For example, xml_out could produce &#x????; forms, and json_out
   could produce \u???? forms.

5. If the datatype being output has no escaping rules available
   (as would be the case for an ordinary text column, say), then
   the unrepresentable character has to be reported in an error.
   (Encoding conversions often have the option of substituting
   a replacement character like ? but I don't believe a DBMS has
   any business making such changes to data, unless by explicit
   opt-in. If it can't give you the data you wanted, it should
   say "here's why I can't give you that.")

6. While 'text' in general provides no escaping mechanism, some
   functions that produce text may still have that option. For
   example, quote_literal and quote_ident could conceivably
   produce the U&'...' or U&"..." forms, respectively, if
   the argument contains characters that won't go in the client
   encoding.

I understand that on the way from 1 to 6 I will have drifted
further from what's discussed in this thread; for example, I bet
that quote_literal/quote_ident never produce U& forms now, and
that no one is proposing to change that, and I'm pretending not
to notice the question of how astonishing such behavior could be.
(Not to mention, how would they know whether they are returning
a value that's destined to go across the client encoding, rather
than to be used in a purely server-side expression? Maybe distinct
versions of those functions could take an encoding argument, and
produce the U& forms when the content won't go in the specified
encoding. That would avoid astonishing changes to existing functions.)

Regards,
-Chap


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Re: Unicode escapes with any backend encoding

Andrew Dunstan-8
In reply to this post by Tom Lane-2
On Wed, Jan 15, 2020 at 7:55 AM Tom Lane <[hidden email]> wrote:

>
> Andrew Dunstan <[hidden email]> writes:
> > On Wed, Jan 15, 2020 at 4:25 AM Chapman Flack <[hidden email]> wrote:
> >> On 1/14/20 10:10 AM, Tom Lane wrote:
> >>> to me that this error is just useless pedantry.  As long as the DB
> >>> encoding can represent the desired character, it should be transparent
> >>> to users.
>
> >> That's my position too.
>
> > and mine.
>
> I'm confused --- yesterday you seemed to be against this idea.
> Have you changed your mind?
>
> I'll gladly go change the patch if people are on board with this.
>
>

Perhaps I expressed myself badly. What I meant was that we should keep
the json and text escape rules in sync, as they are now. Since we're
changing the text rules to allow resolvable non-ascii unicode escapes
in non-utf8 locales, we should do the same for json.

cheers

andrew


--
Andrew Dunstan                https://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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Re: Unicode escapes with any backend encoding

Tom Lane-2
Andrew Dunstan <[hidden email]> writes:
> Perhaps I expressed myself badly. What I meant was that we should keep
> the json and text escape rules in sync, as they are now. Since we're
> changing the text rules to allow resolvable non-ascii unicode escapes
> in non-utf8 locales, we should do the same for json.

Got it.  I'll make the patch do that in a little bit.

                        regards, tom lane


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Re: Unicode escapes with any backend encoding

Tom Lane-2
I wrote:
> Andrew Dunstan <[hidden email]> writes:
>> Perhaps I expressed myself badly. What I meant was that we should keep
>> the json and text escape rules in sync, as they are now. Since we're
>> changing the text rules to allow resolvable non-ascii unicode escapes
>> in non-utf8 locales, we should do the same for json.

> Got it.  I'll make the patch do that in a little bit.

OK, here's v2, which brings JSONB into the fold and also makes some
effort to produce an accurate error cursor for invalid Unicode escapes.
As it's set up, we only pay the extra cost of setting up an error
context callback when we're actually processing a Unicode escape,
so I think that's an acceptable cost.  (It's not much of a cost,
anyway.)

The callback support added here is pretty much a straight copy-and-paste
of the existing functions setup_parser_errposition_callback() and friends.
That's slightly annoying --- we could perhaps merge those into one.
But I didn't see a good common header to put such a thing into, so
I just did it like this.

Another note is that we could use the additional scanner infrastructure
to produce more accurate error pointers for other cases where we're
whining about a bad escape sequence, or some other sub-part of a lexical
token.  I think that'd likely be a good idea, since the existing cursor
placement at the start of the token isn't too helpful if e.g. you're
dealing with a very long string constant.  But to keep this focused,
I only touched the behavior for Unicode escapes.  The rest could be
done as a separate patch.

This also mops up after 7f380c59 by making use of the new pg_wchar.c
exports is_utf16_surrogate_first() etc everyplace that they're relevant
(which is just the JSON code I was touching anyway, as it happens).
I also made a bit of an effort to ensure test coverage of all the
code touched in that patch and this one.

                        regards, tom lane


diff --git a/doc/src/sgml/json.sgml b/doc/src/sgml/json.sgml
index 6ff8751..0f0d0c6 100644
--- a/doc/src/sgml/json.sgml
+++ b/doc/src/sgml/json.sgml
@@ -61,8 +61,8 @@
  </para>
 
  <para>
-  <productname>PostgreSQL</productname> allows only one character set
-  encoding per database.  It is therefore not possible for the JSON
+  RFC 7159 specifies that JSON strings should be encoded in UTF8.
+  It is therefore not possible for the JSON
   types to conform rigidly to the JSON specification unless the database
   encoding is UTF8. Attempts to directly include characters that
   cannot be represented in the database encoding will fail; conversely,
@@ -77,13 +77,13 @@
   regardless of the database encoding, and are checked only for syntactic
   correctness (that is, that four hex digits follow <literal>\u</literal>).
   However, the input function for <type>jsonb</type> is stricter: it disallows
-  Unicode escapes for non-ASCII characters (those above <literal>U+007F</literal>)
-  unless the database encoding is UTF8.  The <type>jsonb</type> type also
+  Unicode escapes for characters that cannot be represented in the database
+  encoding.  The <type>jsonb</type> type also
   rejects <literal>\u0000</literal> (because that cannot be represented in
   <productname>PostgreSQL</productname>'s <type>text</type> type), and it insists
   that any use of Unicode surrogate pairs to designate characters outside
   the Unicode Basic Multilingual Plane be correct.  Valid Unicode escapes
-  are converted to the equivalent ASCII or UTF8 character for storage;
+  are converted to the equivalent single character for storage;
   this includes folding surrogate pairs into a single character.
  </para>
 
@@ -96,9 +96,8 @@
    not <type>jsonb</type>. The fact that the <type>json</type> input function does
    not make these checks may be considered a historical artifact, although
    it does allow for simple storage (without processing) of JSON Unicode
-   escapes in a non-UTF8 database encoding.  In general, it is best to
-   avoid mixing Unicode escapes in JSON with a non-UTF8 database encoding,
-   if possible.
+   escapes in a database encoding that does not support the represented
+   characters.
   </para>
  </note>
 
@@ -144,8 +143,8 @@
        <row>
         <entry><type>string</type></entry>
         <entry><type>text</type></entry>
-        <entry><literal>\u0000</literal> is disallowed, as are non-ASCII Unicode
-         escapes if database encoding is not UTF8</entry>
+        <entry><literal>\u0000</literal> is disallowed, as are Unicode escapes
+         representing characters not available in the database encoding</entry>
        </row>
        <row>
         <entry><type>number</type></entry>
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index c908e0b..e134877 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -189,6 +189,23 @@ UPDATE "my_table" SET "a" = 5;
     ampersands.  The length limitation still applies.
    </para>
 
+   <para>
+    Quoting an identifier also makes it case-sensitive, whereas
+    unquoted names are always folded to lower case.  For example, the
+    identifiers <literal>FOO</literal>, <literal>foo</literal>, and
+    <literal>"foo"</literal> are considered the same by
+    <productname>PostgreSQL</productname>, but
+    <literal>"Foo"</literal> and <literal>"FOO"</literal> are
+    different from these three and each other.  (The folding of
+    unquoted names to lower case in <productname>PostgreSQL</productname> is
+    incompatible with the SQL standard, which says that unquoted names
+    should be folded to upper case.  Thus, <literal>foo</literal>
+    should be equivalent to <literal>"FOO"</literal> not
+    <literal>"foo"</literal> according to the standard.  If you want
+    to write portable applications you are advised to always quote a
+    particular name or never quote it.)
+   </para>
+
    <indexterm>
      <primary>Unicode escape</primary>
      <secondary>in identifiers</secondary>
@@ -230,7 +247,8 @@ U&amp;"d!0061t!+000061" UESCAPE '!'
     The escape character can be any single character other than a
     hexadecimal digit, the plus sign, a single quote, a double quote,
     or a whitespace character.  Note that the escape character is
-    written in single quotes, not double quotes.
+    written in single quotes, not double quotes,
+    after <literal>UESCAPE</literal>.
    </para>
 
    <para>
@@ -239,32 +257,18 @@ U&amp;"d!0061t!+000061" UESCAPE '!'
    </para>
 
    <para>
-    The Unicode escape syntax works only when the server encoding is
-    <literal>UTF8</literal>.  When other server encodings are used, only code
-    points in the ASCII range (up to <literal>\007F</literal>) can be
-    specified.  Both the 4-digit and the 6-digit form can be used to
+    Either the 4-digit or the 6-digit escape form can be used to
     specify UTF-16 surrogate pairs to compose characters with code
     points larger than U+FFFF, although the availability of the
     6-digit form technically makes this unnecessary.  (Surrogate
-    pairs are not stored directly, but combined into a single
-    code point that is then encoded in UTF-8.)
+    pairs are not stored directly, but are combined into a single
+    code point.)
    </para>
 
    <para>
-    Quoting an identifier also makes it case-sensitive, whereas
-    unquoted names are always folded to lower case.  For example, the
-    identifiers <literal>FOO</literal>, <literal>foo</literal>, and
-    <literal>"foo"</literal> are considered the same by
-    <productname>PostgreSQL</productname>, but
-    <literal>"Foo"</literal> and <literal>"FOO"</literal> are
-    different from these three and each other.  (The folding of
-    unquoted names to lower case in <productname>PostgreSQL</productname> is
-    incompatible with the SQL standard, which says that unquoted names
-    should be folded to upper case.  Thus, <literal>foo</literal>
-    should be equivalent to <literal>"FOO"</literal> not
-    <literal>"foo"</literal> according to the standard.  If you want
-    to write portable applications you are advised to always quote a
-    particular name or never quote it.)
+    If the server encoding is not UTF-8, the Unicode code point identified
+    by one of these escape sequences is converted to the actual server
+    encoding; an error is reported if that's not possible.
    </para>
   </sect2>
 
@@ -427,25 +431,11 @@ SELECT 'foo'      'bar';
     <para>
      It is your responsibility that the byte sequences you create,
      especially when using the octal or hexadecimal escapes, compose
-     valid characters in the server character set encoding.  When the
-     server encoding is UTF-8, then the Unicode escapes or the
+     valid characters in the server character set encoding.
+     A useful alternative is to use Unicode escapes or the
      alternative Unicode escape syntax, explained
-     in <xref linkend="sql-syntax-strings-uescape"/>, should be used
-     instead.  (The alternative would be doing the UTF-8 encoding by
-     hand and writing out the bytes, which would be very cumbersome.)
-    </para>
-
-    <para>
-     The Unicode escape syntax works fully only when the server
-     encoding is <literal>UTF8</literal>.  When other server encodings are
-     used, only code points in the ASCII range (up
-     to <literal>\u007F</literal>) can be specified.  Both the 4-digit and
-     the 8-digit form can be used to specify UTF-16 surrogate pairs to
-     compose characters with code points larger than U+FFFF, although
-     the availability of the 8-digit form technically makes this
-     unnecessary.  (When surrogate pairs are used when the server
-     encoding is <literal>UTF8</literal>, they are first combined into a
-     single code point that is then encoded in UTF-8.)
+     in <xref linkend="sql-syntax-strings-uescape"/>; then the server
+     will check that the character conversion is possible.
     </para>
 
     <caution>
@@ -524,16 +514,23 @@ U&amp;'d!0061t!+000061' UESCAPE '!'
     </para>
 
     <para>
-     The Unicode escape syntax works only when the server encoding is
-     <literal>UTF8</literal>.  When other server encodings are used, only
-     code points in the ASCII range (up to <literal>\007F</literal>)
-     can be specified.  Both the 4-digit and the 6-digit form can be
-     used to specify UTF-16 surrogate pairs to compose characters with
-     code points larger than U+FFFF, although the availability of the
-     6-digit form technically makes this unnecessary.  (When surrogate
-     pairs are used when the server encoding is <literal>UTF8</literal>, they
-     are first combined into a single code point that is then encoded
-     in UTF-8.)
+     To include the escape character in the string literally, write
+     it twice.
+    </para>
+
+    <para>
+     Either the 4-digit or the 6-digit escape form can be used to
+     specify UTF-16 surrogate pairs to compose characters with code
+     points larger than U+FFFF, although the availability of the
+     6-digit form technically makes this unnecessary.  (Surrogate
+     pairs are not stored directly, but are combined into a single
+     code point.)
+    </para>
+
+    <para>
+     If the server encoding is not UTF-8, the Unicode code point identified
+     by one of these escape sequences is converted to the actual server
+     encoding; an error is reported if that's not possible.
     </para>
 
     <para>
@@ -546,11 +543,6 @@ U&amp;'d!0061t!+000061' UESCAPE '!'
      parameter is set to off, this syntax will be rejected with an
      error message.
     </para>
-
-    <para>
-     To include the escape character in the string literally, write it
-     twice.
-    </para>
    </sect3>
 
    <sect3 id="sql-syntax-dollar-quoting">
diff --git a/src/backend/parser/parser.c b/src/backend/parser/parser.c
index 1bf1144..22c9479 100644
--- a/src/backend/parser/parser.c
+++ b/src/backend/parser/parser.c
@@ -292,22 +292,15 @@ hexval(unsigned char c)
  return 0; /* not reached */
 }
 
-/* is Unicode code point acceptable in database's encoding? */
+/* is Unicode code point acceptable? */
 static void
-check_unicode_value(pg_wchar c, int pos, core_yyscan_t yyscanner)
+check_unicode_value(pg_wchar c)
 {
  /* See also addunicode() in scan.l */
  if (c == 0 || c > 0x10FFFF)
  ereport(ERROR,
  (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("invalid Unicode escape value"),
- scanner_errposition(pos, yyscanner)));
-
- if (c > 0x7F && GetDatabaseEncoding() != PG_UTF8)
- ereport(ERROR,
- (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8"),
- scanner_errposition(pos, yyscanner)));
+ errmsg("invalid Unicode escape value")));
 }
 
 /* is 'escape' acceptable as Unicode escape character (UESCAPE syntax) ? */
@@ -338,20 +331,39 @@ str_udeescape(const char *str, char escape,
  const char *in;
  char   *new,
    *out;
+ size_t new_len;
  pg_wchar pair_first = 0;
+ ScannerCallbackState scbstate;
 
  /*
- * This relies on the subtle assumption that a UTF-8 expansion cannot be
- * longer than its escaped representation.
+ * Guesstimate that result will be no longer than input, but allow enough
+ * padding for Unicode conversion.
  */
- new = palloc(strlen(str) + 1);
+ new_len = strlen(str) + MAX_UNICODE_EQUIVALENT_STRING + 1;
+ new = palloc(new_len);
 
  in = str;
  out = new;
  while (*in)
  {
+ /* Enlarge string if needed */
+ size_t out_dist = out - new;
+
+ if (out_dist > new_len - (MAX_UNICODE_EQUIVALENT_STRING + 1))
+ {
+ new_len *= 2;
+ new = repalloc(new, new_len);
+ out = new + out_dist;
+ }
+
  if (in[0] == escape)
  {
+ /*
+ * Any errors reported while processing this escape sequence will
+ * have an error cursor pointing at the escape.
+ */
+ setup_scanner_errposition_callback(&scbstate, yyscanner,
+   in - str + position + 3); /* 3 for U&" */
  if (in[1] == escape)
  {
  if (pair_first)
@@ -370,9 +382,7 @@ str_udeescape(const char *str, char escape,
  (hexval(in[2]) << 8) +
  (hexval(in[3]) << 4) +
  hexval(in[4]);
- check_unicode_value(unicode,
- in - str + position + 3, /* 3 for U&" */
- yyscanner);
+ check_unicode_value(unicode);
  if (pair_first)
  {
  if (is_utf16_surrogate_second(unicode))
@@ -390,8 +400,8 @@ str_udeescape(const char *str, char escape,
  pair_first = unicode;
  else
  {
- unicode_to_utf8(unicode, (unsigned char *) out);
- out += pg_mblen(out);
+ pg_unicode_to_server(unicode, (unsigned char *) out);
+ out += strlen(out);
  }
  in += 5;
  }
@@ -411,9 +421,7 @@ str_udeescape(const char *str, char escape,
  (hexval(in[5]) << 8) +
  (hexval(in[6]) << 4) +
  hexval(in[7]);
- check_unicode_value(unicode,
- in - str + position + 3, /* 3 for U&" */
- yyscanner);
+ check_unicode_value(unicode);
  if (pair_first)
  {
  if (is_utf16_surrogate_second(unicode))
@@ -431,17 +439,18 @@ str_udeescape(const char *str, char escape,
  pair_first = unicode;
  else
  {
- unicode_to_utf8(unicode, (unsigned char *) out);
- out += pg_mblen(out);
+ pg_unicode_to_server(unicode, (unsigned char *) out);
+ out += strlen(out);
  }
  in += 8;
  }
  else
  ereport(ERROR,
  (errcode(ERRCODE_SYNTAX_ERROR),
- errmsg("invalid Unicode escape value"),
- scanner_errposition(in - str + position + 3, /* 3 for U&" */
- yyscanner)));
+ errmsg("invalid Unicode escape"),
+ errhint("Unicode escapes must be \\XXXX or \\+XXXXXX.")));
+
+ cancel_scanner_errposition_callback(&scbstate);
  }
  else
  {
@@ -457,15 +466,13 @@ str_udeescape(const char *str, char escape,
  goto invalid_pair;
 
  *out = '\0';
+ return new;
 
  /*
- * We could skip pg_verifymbstr if we didn't process any non-7-bit-ASCII
- * codes; but it's probably not worth the trouble, since this isn't likely
- * to be a performance-critical path.
+ * We might get here with the error callback active, or not.  Call
+ * scanner_errposition to make sure an error cursor appears; if the
+ * callback is active, this is duplicative but harmless.
  */
- pg_verifymbstr(new, out - new, false);
- return new;
-
 invalid_pair:
  ereport(ERROR,
  (errcode(ERRCODE_SYNTAX_ERROR),
diff --git a/src/backend/parser/scan.l b/src/backend/parser/scan.l
index 84c7391..685aa84 100644
--- a/src/backend/parser/scan.l
+++ b/src/backend/parser/scan.l
@@ -106,6 +106,18 @@ const uint16 ScanKeywordTokens[] = {
  */
 #define ADVANCE_YYLLOC(delta)  ( *(yylloc) += (delta) )
 
+/*
+ * Sometimes, we do want yylloc to point into the middle of a token; this is
+ * useful for instance to throw an error about an escape sequence within a
+ * string literal.  But if we find no error there, we want to revert yylloc
+ * to the token start, so that that's the location reported to the parser.
+ * Use PUSH_YYLLOC/POP_YYLLOC to save/restore yylloc around such code.
+ * (Currently the implied "stack" is just one location, but someday we might
+ * need to nest these.)
+ */
+#define PUSH_YYLLOC() (yyextra->save_yylloc = *(yylloc))
+#define POP_YYLLOC() (*(yylloc) = yyextra->save_yylloc)
+
 #define startlit() ( yyextra->literallen = 0 )
 static void addlit(char *ytext, int yleng, core_yyscan_t yyscanner);
 static void addlitchar(unsigned char ychar, core_yyscan_t yyscanner);
@@ -605,8 +617,18 @@ other .
 <xe>{xeunicode} {
  pg_wchar c = strtoul(yytext + 2, NULL, 16);
 
+ /*
+ * For consistency with other productions, issue any
+ * escape warning with cursor pointing to start of string.
+ * We might want to change that, someday.
+ */
  check_escape_warning(yyscanner);
 
+ /* Remember start of overall string token ... */
+ PUSH_YYLLOC();
+ /* ... and set the error cursor to point at this esc seq */
+ SET_YYLLOC();
+
  if (is_utf16_surrogate_first(c))
  {
  yyextra->utf16_first_part = c;
@@ -616,10 +638,18 @@ other .
  yyerror("invalid Unicode surrogate pair");
  else
  addunicode(c, yyscanner);
+
+ /* Restore yylloc to be start of string token */
+ POP_YYLLOC();
  }
 <xeu>{xeunicode} {
  pg_wchar c = strtoul(yytext + 2, NULL, 16);
 
+ /* Remember start of overall string token ... */
+ PUSH_YYLLOC();
+ /* ... and set the error cursor to point at this esc seq */
+ SET_YYLLOC();
+
  if (!is_utf16_surrogate_second(c))
  yyerror("invalid Unicode surrogate pair");
 
@@ -627,12 +657,21 @@ other .
 
  addunicode(c, yyscanner);
 
+ /* Restore yylloc to be start of string token */
+ POP_YYLLOC();
+
  BEGIN(xe);
  }
-<xeu>. { yyerror("invalid Unicode surrogate pair"); }
-<xeu>\n { yyerror("invalid Unicode surrogate pair"); }
-<xeu><<EOF>> { yyerror("invalid Unicode surrogate pair"); }
+<xeu>. |
+<xeu>\n |
+<xeu><<EOF>> {
+ /* Set the error cursor to point at missing esc seq */
+ SET_YYLLOC();
+ yyerror("invalid Unicode surrogate pair");
+ }
 <xe,xeu>{xeunicodefail} {
+ /* Set the error cursor to point at malformed esc seq */
+ SET_YYLLOC();
  ereport(ERROR,
  (errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
  errmsg("invalid Unicode escape"),
@@ -1029,12 +1068,13 @@ other .
  * scanner_errposition
  * Report a lexer or grammar error cursor position, if possible.
  *
- * This is expected to be used within an ereport() call.  The return value
+ * This is expected to be used within an ereport() call, or via an error
+ * callback such as setup_scanner_errposition_callback().  The return value
  * is a dummy (always 0, in fact).
  *
  * Note that this can only be used for messages emitted during raw parsing
- * (essentially, scan.l and gram.y), since it requires the yyscanner struct
- * to still be available.
+ * (essentially, scan.l, parser.c, and gram.y), since it requires the
+ * yyscanner struct to still be available.
  */
 int
 scanner_errposition(int location, core_yyscan_t yyscanner)
@@ -1051,6 +1091,62 @@ scanner_errposition(int location, core_yyscan_t yyscanner)
 }
 
 /*
+ * Error context callback for inserting scanner error location.
+ *
+ * Note that this will be called for *any* error occurring while the
+ * callback is installed.  We avoid inserting an irrelevant error location
+ * if the error is a query cancel --- are there any other important cases?
+ */
+static void
+scb_error_callback(void *arg)
+{
+ ScannerCallbackState *scbstate = (ScannerCallbackState *) arg;
+
+ if (geterrcode() != ERRCODE_QUERY_CANCELED)
+ (void) scanner_errposition(scbstate->location, scbstate->yyscanner);
+}
+
+/*
+ * setup_scanner_errposition_callback
+ * Arrange for non-scanner errors to report an error position
+ *
+ * Sometimes the scanner calls functions that aren't part of the scanner
+ * subsystem and can't reasonably be passed the yyscanner pointer; yet
+ * we would like any errors thrown in those functions to be tagged with an
+ * error location.  Use this function to set up an error context stack
+ * entry that will accomplish that.  Usage pattern:
+ *
+ * declare a local variable "ScannerCallbackState scbstate"
+ * ...
+ * setup_scanner_errposition_callback(&scbstate, yyscanner, location);
+ * call function that might throw error;
+ * cancel_scanner_errposition_callback(&scbstate);
+ */
+void
+setup_scanner_errposition_callback(ScannerCallbackState *scbstate,
+   core_yyscan_t yyscanner,
+   int location)
+{
+ /* Setup error traceback support for ereport() */
+ scbstate->yyscanner = yyscanner;
+ scbstate->location = location;
+ scbstate->errcallback.callback = scb_error_callback;
+ scbstate->errcallback.arg = (void *) scbstate;
+ scbstate->errcallback.previous = error_context_stack;
+ error_context_stack = &scbstate->errcallback;
+}
+
+/*
+ * Cancel a previously-set-up errposition callback.
+ */
+void
+cancel_scanner_errposition_callback(ScannerCallbackState *scbstate)
+{
+ /* Pop the error context stack */
+ error_context_stack = scbstate->errcallback.previous;
+}
+
+/*
  * scanner_yyerror
  * Report a lexer or grammar error.
  *
@@ -1226,19 +1322,21 @@ process_integer_literal(const char *token, YYSTYPE *lval)
 static void
 addunicode(pg_wchar c, core_yyscan_t yyscanner)
 {
- char buf[8];
+ ScannerCallbackState scbstate;
+ char buf[MAX_UNICODE_EQUIVALENT_STRING + 1];
 
  /* See also check_unicode_value() in parser.c */
  if (c == 0 || c > 0x10FFFF)
  yyerror("invalid Unicode escape value");
- if (c > 0x7F)
- {
- if (GetDatabaseEncoding() != PG_UTF8)
- yyerror("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8");
- yyextra->saw_non_ascii = true;
- }
- unicode_to_utf8(c, (unsigned char *) buf);
- addlit(buf, pg_mblen(buf), yyscanner);
+
+ /*
+ * We expect that pg_unicode_to_server() will complain about any
+ * unconvertible code point, so we don't have to set saw_non_ascii.
+ */
+ setup_scanner_errposition_callback(&scbstate, yyscanner, *(yylloc));
+ pg_unicode_to_server(c, (unsigned char *) buf);
+ cancel_scanner_errposition_callback(&scbstate);
+ addlit(buf, strlen(buf), yyscanner);
 }
 
 static unsigned char
diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index 458505a..62b97f5 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -831,10 +831,10 @@ json_lex_string(JsonLexContext *lex)
  }
  if (lex->strval != NULL)
  {
- char utf8str[5];
- int utf8len;
-
- if (ch >= 0xd800 && ch <= 0xdbff)
+ /*
+ * Combine surrogate pairs.
+ */
+ if (is_utf16_surrogate_first(ch))
  {
  if (hi_surrogate != -1)
  ereport(ERROR,
@@ -843,10 +843,10 @@ json_lex_string(JsonLexContext *lex)
  "json"),
  errdetail("Unicode high surrogate must not follow a high surrogate."),
  report_json_context(lex)));
- hi_surrogate = (ch & 0x3ff) << 10;
+ hi_surrogate = ch;
  continue;
  }
- else if (ch >= 0xdc00 && ch <= 0xdfff)
+ else if (is_utf16_surrogate_second(ch))
  {
  if (hi_surrogate == -1)
  ereport(ERROR,
@@ -854,7 +854,7 @@ json_lex_string(JsonLexContext *lex)
  errmsg("invalid input syntax for type %s", "json"),
  errdetail("Unicode low surrogate must follow a high surrogate."),
  report_json_context(lex)));
- ch = 0x10000 + hi_surrogate + (ch & 0x3ff);
+ ch = surrogate_pair_to_codepoint(hi_surrogate, ch);
  hi_surrogate = -1;
  }
 
@@ -866,12 +866,8 @@ json_lex_string(JsonLexContext *lex)
  report_json_context(lex)));
 
  /*
- * For UTF8, replace the escape sequence by the actual
- * utf8 character in lex->strval. Do this also for other
- * encodings if the escape designates an ASCII character,
- * otherwise raise an error.
+ * Add the represented character to lex->strval.
  */
-
  if (ch == 0)
  {
  /* We can't allow this, since our TEXT type doesn't */
@@ -881,30 +877,13 @@ json_lex_string(JsonLexContext *lex)
  errdetail("\\u0000 cannot be converted to text."),
  report_json_context(lex)));
  }
- else if (GetDatabaseEncoding() == PG_UTF8)
- {
- unicode_to_utf8(ch, (unsigned char *) utf8str);
- utf8len = pg_utf_mblen((unsigned char *) utf8str);
- appendBinaryStringInfo(lex->strval, utf8str, utf8len);
- }
- else if (ch <= 0x007f)
- {
- /*
- * This is the only way to designate things like a
- * form feed character in JSON, so it's useful in all
- * encodings.
- */
- appendStringInfoChar(lex->strval, (char) ch);
- }
  else
  {
- ereport(ERROR,
- (errcode(ERRCODE_UNTRANSLATABLE_CHARACTER),
- errmsg("unsupported Unicode escape sequence"),
- errdetail("Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8."),
- report_json_context(lex)));
- }
+ char cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];
 
+ pg_unicode_to_server(ch, (unsigned char *) cbuf);
+ appendStringInfoString(lex->strval, cbuf);
+ }
  }
  }
  else if (lex->strval != NULL)
diff --git a/src/backend/utils/adt/jsonpath_scan.l b/src/backend/utils/adt/jsonpath_scan.l
index 70681b7..be0a2cf 100644
--- a/src/backend/utils/adt/jsonpath_scan.l
+++ b/src/backend/utils/adt/jsonpath_scan.l
@@ -486,13 +486,6 @@ hexval(char c)
 static void
 addUnicodeChar(int ch)
 {
- /*
- * For UTF8, replace the escape sequence by the actual
- * utf8 character in lex->strval. Do this also for other
- * encodings if the escape designates an ASCII character,
- * otherwise raise an error.
- */
-
  if (ch == 0)
  {
  /* We can't allow this, since our TEXT type doesn't */
@@ -501,40 +494,20 @@ addUnicodeChar(int ch)
  errmsg("unsupported Unicode escape sequence"),
   errdetail("\\u0000 cannot be converted to text.")));
  }
- else if (GetDatabaseEncoding() == PG_UTF8)
- {
- char utf8str[5];
- int utf8len;
-
- unicode_to_utf8(ch, (unsigned char *) utf8str);
- utf8len = pg_utf_mblen((unsigned char *) utf8str);
- addstring(false, utf8str, utf8len);
- }
- else if (ch <= 0x007f)
- {
- /*
- * This is the only way to designate things like a
- * form feed character in JSON, so it's useful in all
- * encodings.
- */
- addchar(false, (char) ch);
- }
  else
  {
- ereport(ERROR,
- (errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
- errmsg("invalid input syntax for type %s", "jsonpath"),
- errdetail("Unicode escape values cannot be used for code "
-   "point values above 007F when the server encoding "
-   "is not UTF8.")));
+ char cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];
+
+ pg_unicode_to_server(ch, (unsigned char *) cbuf);
+ addstring(false, cbuf, strlen(cbuf));
  }
 }
 
-/* Add unicode character and process its hi surrogate */
+/* Add unicode character, processing any surrogate pairs */
 static void
 addUnicode(int ch, int *hi_surrogate)
 {
- if (ch >= 0xd800 && ch <= 0xdbff)
+ if (is_utf16_surrogate_first(ch))
  {
  if (*hi_surrogate != -1)
  ereport(ERROR,
@@ -542,10 +515,10 @@ addUnicode(int ch, int *hi_surrogate)
  errmsg("invalid input syntax for type %s", "jsonpath"),
  errdetail("Unicode high surrogate must not follow "
    "a high surrogate.")));
- *hi_surrogate = (ch & 0x3ff) << 10;
+ *hi_surrogate = ch;
  return;
  }
- else if (ch >= 0xdc00 && ch <= 0xdfff)
+ else if (is_utf16_surrogate_second(ch))
  {
  if (*hi_surrogate == -1)
  ereport(ERROR,
@@ -553,7 +526,7 @@ addUnicode(int ch, int *hi_surrogate)
  errmsg("invalid input syntax for type %s", "jsonpath"),
  errdetail("Unicode low surrogate must follow a high "
    "surrogate.")));
- ch = 0x10000 + *hi_surrogate + (ch & 0x3ff);
+ ch = surrogate_pair_to_codepoint(*hi_surrogate, ch);
  *hi_surrogate = -1;
  }
  else if (*hi_surrogate != -1)
diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
index 3808c30..a2d2a0b 100644
--- a/src/backend/utils/adt/xml.c
+++ b/src/backend/utils/adt/xml.c
@@ -2086,26 +2086,6 @@ map_sql_identifier_to_xml_name(const char *ident, bool fully_escaped,
 
 
 /*
- * Map a Unicode codepoint into the current server encoding.
- */
-static char *
-unicode_to_sqlchar(pg_wchar c)
-{
- char utf8string[8]; /* need room for trailing zero */
- char   *result;
-
- memset(utf8string, 0, sizeof(utf8string));
- unicode_to_utf8(c, (unsigned char *) utf8string);
-
- result = pg_any_to_server(utf8string, strlen(utf8string), PG_UTF8);
- /* if pg_any_to_server didn't strdup, we must */
- if (result == utf8string)
- result = pstrdup(result);
- return result;
-}
-
-
-/*
  * Map XML name to SQL identifier; see SQL/XML:2008 section 9.3.
  */
 char *
@@ -2125,10 +2105,12 @@ map_xml_name_to_sql_identifier(const char *name)
  && isxdigit((unsigned char) *(p + 5))
  && *(p + 6) == '_')
  {
+ char cbuf[MAX_UNICODE_EQUIVALENT_STRING + 1];
  unsigned int u;
 
  sscanf(p + 2, "%X", &u);
- appendStringInfoString(&buf, unicode_to_sqlchar(u));
+ pg_unicode_to_server(u, (unsigned char *) cbuf);
+ appendStringInfoString(&buf, cbuf);
  p += 6;
  }
  else
diff --git a/src/backend/utils/mb/mbutils.c b/src/backend/utils/mb/mbutils.c
index 5d7cc74..7d90ac9 100644
--- a/src/backend/utils/mb/mbutils.c
+++ b/src/backend/utils/mb/mbutils.c
@@ -68,6 +68,13 @@ static FmgrInfo *ToServerConvProc = NULL;
 static FmgrInfo *ToClientConvProc = NULL;
 
 /*
+ * This variable stores the conversion function to convert from UTF-8
+ * to the server encoding.  It's NULL if the server encoding *is* UTF-8,
+ * or if we lack a conversion function for this.
+ */
+static FmgrInfo *Utf8ToServerConvProc = NULL;
+
+/*
  * These variables track the currently-selected encodings.
  */
 static const pg_enc2name *ClientEncoding = &pg_enc2name_tbl[PG_SQL_ASCII];
@@ -273,6 +280,8 @@ SetClientEncoding(int encoding)
 void
 InitializeClientEncoding(void)
 {
+ int current_server_encoding;
+
  Assert(!backend_startup_complete);
  backend_startup_complete = true;
 
@@ -289,6 +298,35 @@ InitializeClientEncoding(void)
  pg_enc2name_tbl[pending_client_encoding].name,
  GetDatabaseEncodingName())));
  }
+
+ /*
+ * Also look up the UTF8-to-server conversion function if needed.  Since
+ * the server encoding is fixed within any one backend process, we don't
+ * have to do this more than once.
+ */
+ current_server_encoding = GetDatabaseEncoding();
+ if (current_server_encoding != PG_UTF8 &&
+ current_server_encoding != PG_SQL_ASCII)
+ {
+ Oid utf8_to_server_proc;
+
+ Assert(IsTransactionState());
+ utf8_to_server_proc =
+ FindDefaultConversionProc(PG_UTF8,
+  current_server_encoding);
+ /* If there's no such conversion, just leave the pointer as NULL */
+ if (OidIsValid(utf8_to_server_proc))
+ {
+ FmgrInfo   *finfo;
+
+ finfo = (FmgrInfo *) MemoryContextAlloc(TopMemoryContext,
+ sizeof(FmgrInfo));
+ fmgr_info_cxt(utf8_to_server_proc, finfo,
+  TopMemoryContext);
+ /* Set Utf8ToServerConvProc only after data is fully valid */
+ Utf8ToServerConvProc = finfo;
+ }
+ }
 }
 
 /*
@@ -752,6 +790,73 @@ perform_default_encoding_conversion(const char *src, int len,
  return result;
 }
 
+/*
+ * Convert a single Unicode code point into a string in the server encoding.
+ *
+ * The code point given by "c" is converted and stored at *s, which must
+ * have at least MAX_UNICODE_EQUIVALENT_STRING+1 bytes available.
+ * The output will have a trailing '\0'.  Throws error if the conversion
+ * cannot be performed.
+ *
+ * Note that this relies on having previously looked up any required
+ * conversion function.  That's partly for speed but mostly because the parser
+ * may call this outside any transaction, or in an aborted transaction.
+ */
+void
+pg_unicode_to_server(pg_wchar c, unsigned char *s)
+{
+ unsigned char c_as_utf8[MAX_MULTIBYTE_CHAR_LEN + 1];
+ int c_as_utf8_len;
+ int server_encoding;
+
+ /*
+ * Complain if invalid Unicode code point.  The choice of errcode here is
+ * debatable, but really our caller should have checked this anyway.
+ */
+ if (c == 0 || c > 0x10FFFF)
+ ereport(ERROR,
+ (errcode(ERRCODE_SYNTAX_ERROR),
+ errmsg("invalid Unicode code point")));
+
+ /* Otherwise, if it's in ASCII range, conversion is trivial */
+ if (c <= 0x7F)
+ {
+ s[0] = (unsigned char) c;
+ s[1] = '\0';
+ return;
+ }
+
+ /* If the server encoding is UTF-8, we just need to reformat the code */
+ server_encoding = GetDatabaseEncoding();
+ if (server_encoding == PG_UTF8)
+ {
+ unicode_to_utf8(c, s);
+ s[pg_utf_mblen(s)] = '\0';
+ return;
+ }
+
+ /* For all other cases, we must have a conversion function available */
+ if (Utf8ToServerConvProc == NULL)
+ ereport(ERROR,
+ (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+ errmsg("conversion between %s and %s is not supported",
+ pg_enc2name_tbl[PG_UTF8].name,
+ GetDatabaseEncodingName())));
+
+ /* Construct UTF-8 source string */
+ unicode_to_utf8(c, c_as_utf8);
+ c_as_utf8_len = pg_utf_mblen(c_as_utf8);
+ c_as_utf8[c_as_utf8_len] = '\0';
+
+ /* Convert, or throw error if we can't */
+ FunctionCall5(Utf8ToServerConvProc,
+  Int32GetDatum(PG_UTF8),
+  Int32GetDatum(server_encoding),
+  CStringGetDatum(c_as_utf8),
+  CStringGetDatum(s),
+  Int32GetDatum(c_as_utf8_len));
+}
+
 
 /* convert a multibyte string to a wchar */
 int
diff --git a/src/include/mb/pg_wchar.h b/src/include/mb/pg_wchar.h
index 7fb5fa4..2daf301 100644
--- a/src/include/mb/pg_wchar.h
+++ b/src/include/mb/pg_wchar.h
@@ -316,6 +316,15 @@ typedef enum pg_enc
 #define MAX_CONVERSION_GROWTH  4
 
 /*
+ * Maximum byte length of the string equivalent to any one Unicode code point,
+ * in any backend encoding.  The current value assumes that a 4-byte UTF-8
+ * character might expand by MAX_CONVERSION_GROWTH, which is a huge
+ * overestimate.  But in current usage we don't allocate large multiples of
+ * this, so there's little point in being stingy.
+ */
+#define MAX_UNICODE_EQUIVALENT_STRING 16
+
+/*
  * Table for mapping an encoding number to official encoding name and
  * possibly other subsidiary data.  Be careful to check encoding number
  * before accessing a table entry!
@@ -602,6 +611,8 @@ extern char *pg_server_to_client(const char *s, int len);
 extern char *pg_any_to_server(const char *s, int len, int encoding);
 extern char *pg_server_to_any(const char *s, int len, int encoding);
 
+extern void pg_unicode_to_server(pg_wchar c, unsigned char *s);
+
 extern unsigned short BIG5toCNS(unsigned short big5, unsigned char *lc);
 extern unsigned short CNStoBIG5(unsigned short cns, unsigned char lc);
 
diff --git a/src/include/parser/scanner.h b/src/include/parser/scanner.h
index 7a0e5e5..a27352a 100644
--- a/src/include/parser/scanner.h
+++ b/src/include/parser/scanner.h
@@ -99,9 +99,13 @@ typedef struct core_yy_extra_type
  int literallen; /* actual current string length */
  int literalalloc; /* current allocated buffer size */
 
+ /*
+ * Random assorted scanner state.
+ */
  int state_before_str_stop; /* start cond. before end quote */
  int xcdepth; /* depth of nesting in slash-star comments */
  char   *dolqstart; /* current $foo$ quote start string */
+ YYLTYPE save_yylloc; /* one-element stack for PUSH_YYLLOC() */
 
  /* first part of UTF16 surrogate pair for Unicode escapes */
  int32 utf16_first_part;
@@ -116,6 +120,14 @@ typedef struct core_yy_extra_type
  */
 typedef void *core_yyscan_t;
 
+/* Support for scanner_errposition_callback function */
+typedef struct ScannerCallbackState
+{
+ core_yyscan_t yyscanner;
+ int location;
+ ErrorContextCallback errcallback;
+} ScannerCallbackState;
+
 
 /* Constant data exported from parser/scan.l */
 extern PGDLLIMPORT const uint16 ScanKeywordTokens[];
@@ -129,6 +141,10 @@ extern void scanner_finish(core_yyscan_t yyscanner);
 extern int core_yylex(core_YYSTYPE *lvalp, YYLTYPE *llocp,
    core_yyscan_t yyscanner);
 extern int scanner_errposition(int location, core_yyscan_t yyscanner);
+extern void setup_scanner_errposition_callback(ScannerCallbackState *scbstate,
+   core_yyscan_t yyscanner,
+   int location);
+extern void cancel_scanner_errposition_callback(ScannerCallbackState *scbstate);
 extern void scanner_yyerror(const char *message, core_yyscan_t yyscanner) pg_attribute_noreturn();
 
 #endif /* SCANNER_H */
diff --git a/src/test/regress/expected/json_encoding.out b/src/test/regress/expected/json_encoding.out
index d8d34f4..f343f74 100644
--- a/src/test/regress/expected/json_encoding.out
+++ b/src/test/regress/expected/json_encoding.out
@@ -1,4 +1,19 @@
+--
 -- encoding-sensitive tests for json and jsonb
+--
+-- We provide expected-results files for UTF8 (json_encoding.out)
+-- and for SQL_ASCII (json_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
+\endif
+SELECT getdatabaseencoding();           -- just to label the results files
+ getdatabaseencoding
+---------------------
+ UTF8
+(1 row)
+
 -- first json
 -- basic unicode input
 SELECT '"\u"'::json; -- ERROR, incomplete escape
diff --git a/src/test/regress/expected/json_encoding_1.out b/src/test/regress/expected/json_encoding_1.out
index 79ed78e..e2fc131 100644
--- a/src/test/regress/expected/json_encoding_1.out
+++ b/src/test/regress/expected/json_encoding_1.out
@@ -1,4 +1,19 @@
+--
 -- encoding-sensitive tests for json and jsonb
+--
+-- We provide expected-results files for UTF8 (json_encoding.out)
+-- and for SQL_ASCII (json_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
+\endif
+SELECT getdatabaseencoding();           -- just to label the results files
+ getdatabaseencoding
+---------------------
+ SQL_ASCII
+(1 row)
+
 -- first json
 -- basic unicode input
 SELECT '"\u"'::json; -- ERROR, incomplete escape
@@ -33,9 +48,7 @@ SELECT '"\uaBcD"'::json; -- OK, uppercase and lower case both OK
 
 -- handling of unicode surrogate pairs
 select json '{ "a":  "\ud83d\ude04\ud83d\udc36" }' -> 'a' as correct_in_utf8;
-ERROR:  unsupported Unicode escape sequence
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
-CONTEXT:  JSON data, line 1: { "a":...
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 select json '{ "a":  "\ud83d\ud83d" }' -> 'a'; -- 2 high surrogates in a row
 ERROR:  invalid input syntax for type json
 DETAIL:  Unicode high surrogate must not follow a high surrogate.
@@ -84,9 +97,7 @@ select json '{ "a":  "null \\u0000 escape" }' as not_an_escape;
 (1 row)
 
 select json '{ "a":  "the Copyright \u00a9 sign" }' ->> 'a' as correct_in_utf8;
-ERROR:  unsupported Unicode escape sequence
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
-CONTEXT:  JSON data, line 1: { "a":...
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 select json '{ "a":  "dollar \u0024 character" }' ->> 'a' as correct_everywhere;
  correct_everywhere
 --------------------
@@ -144,18 +155,14 @@ CONTEXT:  JSON data, line 1: ...
 -- use octet_length here so we don't get an odd unicode char in the
 -- output
 SELECT octet_length('"\uaBcD"'::jsonb::text); -- OK, uppercase and lower case both OK
-ERROR:  unsupported Unicode escape sequence
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: SELECT octet_length('"\uaBcD"'::jsonb::text);
                             ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
-CONTEXT:  JSON data, line 1: ...
 -- handling of unicode surrogate pairs
 SELECT octet_length((jsonb '{ "a":  "\ud83d\ude04\ud83d\udc36" }' -> 'a')::text) AS correct_in_utf8;
-ERROR:  unsupported Unicode escape sequence
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: SELECT octet_length((jsonb '{ "a":  "\ud83d\ude04\ud83d\udc3...
                                    ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
-CONTEXT:  JSON data, line 1: { "a":...
 SELECT jsonb '{ "a":  "\ud83d\ud83d" }' -> 'a'; -- 2 high surrogates in a row
 ERROR:  invalid input syntax for type json
 LINE 1: SELECT jsonb '{ "a":  "\ud83d\ud83d" }' -> 'a';
@@ -182,11 +189,9 @@ DETAIL:  Unicode low surrogate must follow a high surrogate.
 CONTEXT:  JSON data, line 1: { "a":...
 -- handling of simple unicode escapes
 SELECT jsonb '{ "a":  "the Copyright \u00a9 sign" }' as correct_in_utf8;
-ERROR:  unsupported Unicode escape sequence
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: SELECT jsonb '{ "a":  "the Copyright \u00a9 sign" }' as corr...
                      ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
-CONTEXT:  JSON data, line 1: { "a":...
 SELECT jsonb '{ "a":  "dollar \u0024 character" }' as correct_everywhere;
      correct_everywhere      
 -----------------------------
@@ -212,11 +217,9 @@ SELECT jsonb '{ "a":  "null \\u0000 escape" }' as not_an_escape;
 (1 row)
 
 SELECT jsonb '{ "a":  "the Copyright \u00a9 sign" }' ->> 'a' as correct_in_utf8;
-ERROR:  unsupported Unicode escape sequence
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: SELECT jsonb '{ "a":  "the Copyright \u00a9 sign" }' ->> 'a'...
                      ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
-CONTEXT:  JSON data, line 1: { "a":...
 SELECT jsonb '{ "a":  "dollar \u0024 character" }' ->> 'a' as correct_everywhere;
  correct_everywhere
 --------------------
diff --git a/src/test/regress/expected/json_encoding_2.out b/src/test/regress/expected/json_encoding_2.out
new file mode 100644
index 0000000..4fc8f02
--- /dev/null
+++ b/src/test/regress/expected/json_encoding_2.out
@@ -0,0 +1,9 @@
+--
+-- encoding-sensitive tests for json and jsonb
+--
+-- We provide expected-results files for UTF8 (json_encoding.out)
+-- and for SQL_ASCII (json_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
diff --git a/src/test/regress/expected/jsonpath_encoding.out b/src/test/regress/expected/jsonpath_encoding.out
index ecffe09..7cbfb6a 100644
--- a/src/test/regress/expected/jsonpath_encoding.out
+++ b/src/test/regress/expected/jsonpath_encoding.out
@@ -1,4 +1,19 @@
+--
 -- encoding-sensitive tests for jsonpath
+--
+-- We provide expected-results files for UTF8 (jsonpath_encoding.out)
+-- and for SQL_ASCII (jsonpath_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
+\endif
+SELECT getdatabaseencoding();           -- just to label the results files
+ getdatabaseencoding
+---------------------
+ UTF8
+(1 row)
+
 -- checks for double-quoted values
 -- basic unicode input
 SELECT '"\u"'::jsonpath; -- ERROR, incomplete escape
diff --git a/src/test/regress/expected/jsonpath_encoding_1.out b/src/test/regress/expected/jsonpath_encoding_1.out
index c8cc217..005136c 100644
--- a/src/test/regress/expected/jsonpath_encoding_1.out
+++ b/src/test/regress/expected/jsonpath_encoding_1.out
@@ -1,4 +1,19 @@
+--
 -- encoding-sensitive tests for jsonpath
+--
+-- We provide expected-results files for UTF8 (jsonpath_encoding.out)
+-- and for SQL_ASCII (jsonpath_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
+\endif
+SELECT getdatabaseencoding();           -- just to label the results files
+ getdatabaseencoding
+---------------------
+ SQL_ASCII
+(1 row)
+
 -- checks for double-quoted values
 -- basic unicode input
 SELECT '"\u"'::jsonpath; -- ERROR, incomplete escape
@@ -19,16 +34,14 @@ LINE 1: SELECT '"\u0000"'::jsonpath;
                ^
 DETAIL:  \u0000 cannot be converted to text.
 SELECT '"\uaBcD"'::jsonpath; -- OK, uppercase and lower case both OK
-ERROR:  invalid input syntax for type jsonpath
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: SELECT '"\uaBcD"'::jsonpath;
                ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
 -- handling of unicode surrogate pairs
 select '"\ud83d\ude04\ud83d\udc36"'::jsonpath as correct_in_utf8;
-ERROR:  invalid input syntax for type jsonpath
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: select '"\ud83d\ude04\ud83d\udc36"'::jsonpath as correct_in_...
                ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
 select '"\ud83d\ud83d"'::jsonpath; -- 2 high surrogates in a row
 ERROR:  invalid input syntax for type jsonpath
 LINE 1: select '"\ud83d\ud83d"'::jsonpath;
@@ -51,10 +64,9 @@ LINE 1: select '"\ude04X"'::jsonpath;
 DETAIL:  Unicode low surrogate must follow a high surrogate.
 --handling of simple unicode escapes
 select '"the Copyright \u00a9 sign"'::jsonpath as correct_in_utf8;
-ERROR:  invalid input syntax for type jsonpath
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: select '"the Copyright \u00a9 sign"'::jsonpath as correct_in...
                ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
 select '"dollar \u0024 character"'::jsonpath as correct_everywhere;
   correct_everywhere  
 ----------------------
@@ -98,16 +110,14 @@ LINE 1: SELECT '$."\u0000"'::jsonpath;
                ^
 DETAIL:  \u0000 cannot be converted to text.
 SELECT '$."\uaBcD"'::jsonpath; -- OK, uppercase and lower case both OK
-ERROR:  invalid input syntax for type jsonpath
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: SELECT '$."\uaBcD"'::jsonpath;
                ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
 -- handling of unicode surrogate pairs
 select '$."\ud83d\ude04\ud83d\udc36"'::jsonpath as correct_in_utf8;
-ERROR:  invalid input syntax for type jsonpath
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: select '$."\ud83d\ude04\ud83d\udc36"'::jsonpath as correct_i...
                ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
 select '$."\ud83d\ud83d"'::jsonpath; -- 2 high surrogates in a row
 ERROR:  invalid input syntax for type jsonpath
 LINE 1: select '$."\ud83d\ud83d"'::jsonpath;
@@ -130,10 +140,9 @@ LINE 1: select '$."\ude04X"'::jsonpath;
 DETAIL:  Unicode low surrogate must follow a high surrogate.
 --handling of simple unicode escapes
 select '$."the Copyright \u00a9 sign"'::jsonpath as correct_in_utf8;
-ERROR:  invalid input syntax for type jsonpath
+ERROR:  conversion between UTF8 and SQL_ASCII is not supported
 LINE 1: select '$."the Copyright \u00a9 sign"'::jsonpath as correct_...
                ^
-DETAIL:  Unicode escape values cannot be used for code point values above 007F when the server encoding is not UTF8.
 select '$."dollar \u0024 character"'::jsonpath as correct_everywhere;
    correct_everywhere  
 ------------------------
diff --git a/src/test/regress/expected/jsonpath_encoding_2.out b/src/test/regress/expected/jsonpath_encoding_2.out
new file mode 100644
index 0000000..bb71bfe
--- /dev/null
+++ b/src/test/regress/expected/jsonpath_encoding_2.out
@@ -0,0 +1,9 @@
+--
+-- encoding-sensitive tests for jsonpath
+--
+-- We provide expected-results files for UTF8 (jsonpath_encoding.out)
+-- and for SQL_ASCII (jsonpath_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index 60cb861..6c4443a 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -35,6 +35,12 @@ SELECT U&'d!0061t\+000061' UESCAPE '!' AS U&"d*0061t\+000061" UESCAPE '*';
  dat\+000061
 (1 row)
 
+SELECT U&'a\\b' AS "a\b";
+ a\b
+-----
+ a\b
+(1 row)
+
 SELECT U&' \' UESCAPE '!' AS "tricky";
  tricky
 --------
@@ -48,13 +54,15 @@ SELECT 'tricky' AS U&"\" UESCAPE '!';
 (1 row)
 
 SELECT U&'wrong: \061';
-ERROR:  invalid Unicode escape value
+ERROR:  invalid Unicode escape
 LINE 1: SELECT U&'wrong: \061';
                          ^
+HINT:  Unicode escapes must be \XXXX or \+XXXXXX.
 SELECT U&'wrong: \+0061';
-ERROR:  invalid Unicode escape value
+ERROR:  invalid Unicode escape
 LINE 1: SELECT U&'wrong: \+0061';
                          ^
+HINT:  Unicode escapes must be \XXXX or \+XXXXXX.
 SELECT U&'wrong: +0061' UESCAPE +;
 ERROR:  UESCAPE must be followed by a simple string literal at or near "+"
 LINE 1: SELECT U&'wrong: +0061' UESCAPE +;
@@ -63,6 +71,77 @@ SELECT U&'wrong: +0061' UESCAPE '+';
 ERROR:  invalid Unicode escape character at or near "'+'"
 LINE 1: SELECT U&'wrong: +0061' UESCAPE '+';
                                         ^
+SELECT U&'wrong: \db99';
+ERROR:  invalid Unicode surrogate pair
+LINE 1: SELECT U&'wrong: \db99';
+                              ^
+SELECT U&'wrong: \db99xy';
+ERROR:  invalid Unicode surrogate pair
+LINE 1: SELECT U&'wrong: \db99xy';
+                              ^
+SELECT U&'wrong: \db99\\';
+ERROR:  invalid Unicode surrogate pair
+LINE 1: SELECT U&'wrong: \db99\\';
+                              ^
+SELECT U&'wrong: \db99\0061';
+ERROR:  invalid Unicode surrogate pair
+LINE 1: SELECT U&'wrong: \db99\0061';
+                              ^
+SELECT U&'wrong: \+00db99\+000061';
+ERROR:  invalid Unicode surrogate pair
+LINE 1: SELECT U&'wrong: \+00db99\+000061';
+                                 ^
+SELECT U&'wrong: \+2FFFFF';
+ERROR:  invalid Unicode escape value
+LINE 1: SELECT U&'wrong: \+2FFFFF';
+                         ^
+-- while we're here, check the same cases in E-style literals
+SELECT E'd\u0061t\U00000061' AS "data";
+ data
+------
+ data
+(1 row)
+
+SELECT E'a\\b' AS "a\b";
+ a\b
+-----
+ a\b
+(1 row)
+
+SELECT E'wrong: \u061';
+ERROR:  invalid Unicode escape
+LINE 1: SELECT E'wrong: \u061';
+                        ^
+HINT:  Unicode escapes must be \uXXXX or \UXXXXXXXX.
+SELECT E'wrong: \U0061';
+ERROR:  invalid Unicode escape
+LINE 1: SELECT E'wrong: \U0061';
+                        ^
+HINT:  Unicode escapes must be \uXXXX or \UXXXXXXXX.
+SELECT E'wrong: \udb99';
+ERROR:  invalid Unicode surrogate pair at or near "'"
+LINE 1: SELECT E'wrong: \udb99';
+                              ^
+SELECT E'wrong: \udb99xy';
+ERROR:  invalid Unicode surrogate pair at or near "x"
+LINE 1: SELECT E'wrong: \udb99xy';
+                              ^
+SELECT E'wrong: \udb99\\';
+ERROR:  invalid Unicode surrogate pair at or near "\"
+LINE 1: SELECT E'wrong: \udb99\\';
+                              ^
+SELECT E'wrong: \udb99\u0061';
+ERROR:  invalid Unicode surrogate pair at or near "\u0061"
+LINE 1: SELECT E'wrong: \udb99\u0061';
+                              ^
+SELECT E'wrong: \U0000db99\U00000061';
+ERROR:  invalid Unicode surrogate pair at or near "\U00000061"
+LINE 1: SELECT E'wrong: \U0000db99\U00000061';
+                                  ^
+SELECT E'wrong: \U002FFFFF';
+ERROR:  invalid Unicode escape value at or near "\U002FFFFF"
+LINE 1: SELECT E'wrong: \U002FFFFF';
+                        ^
 SET standard_conforming_strings TO off;
 SELECT U&'d\0061t\+000061' AS U&"d\0061t\+000061";
 ERROR:  unsafe use of string constant with Unicode escapes
diff --git a/src/test/regress/sql/json_encoding.sql b/src/test/regress/sql/json_encoding.sql
index 87a2d56..d7fac69 100644
--- a/src/test/regress/sql/json_encoding.sql
+++ b/src/test/regress/sql/json_encoding.sql
@@ -1,5 +1,16 @@
-
+--
 -- encoding-sensitive tests for json and jsonb
+--
+
+-- We provide expected-results files for UTF8 (json_encoding.out)
+-- and for SQL_ASCII (json_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
+\endif
+
+SELECT getdatabaseencoding();           -- just to label the results files
 
 -- first json
 
diff --git a/src/test/regress/sql/jsonpath_encoding.sql b/src/test/regress/sql/jsonpath_encoding.sql
index 3a23b72..55d9e30 100644
--- a/src/test/regress/sql/jsonpath_encoding.sql
+++ b/src/test/regress/sql/jsonpath_encoding.sql
@@ -1,5 +1,16 @@
-
+--
 -- encoding-sensitive tests for jsonpath
+--
+
+-- We provide expected-results files for UTF8 (jsonpath_encoding.out)
+-- and for SQL_ASCII (jsonpath_encoding_1.out).  Skip otherwise.
+SELECT getdatabaseencoding() NOT IN ('UTF8', 'SQL_ASCII')
+       AS skip_test \gset
+\if :skip_test
+\quit
+\endif
+
+SELECT getdatabaseencoding();           -- just to label the results files
 
 -- checks for double-quoted values
 
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index c5cd151..3e28cd1 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -21,6 +21,7 @@ SET standard_conforming_strings TO on;
 
 SELECT U&'d\0061t\+000061' AS U&"d\0061t\+000061";
 SELECT U&'d!0061t\+000061' UESCAPE '!' AS U&"d*0061t\+000061" UESCAPE '*';
+SELECT U&'a\\b' AS "a\b";
 
 SELECT U&' \' UESCAPE '!' AS "tricky";
 SELECT 'tricky' AS U&"\" UESCAPE '!';
@@ -30,6 +31,25 @@ SELECT U&'wrong: \+0061';
 SELECT U&'wrong: +0061' UESCAPE +;
 SELECT U&'wrong: +0061' UESCAPE '+';
 
+SELECT U&'wrong: \db99';
+SELECT U&'wrong: \db99xy';
+SELECT U&'wrong: \db99\\';
+SELECT U&'wrong: \db99\0061';
+SELECT U&'wrong: \+00db99\+000061';
+SELECT U&'wrong: \+2FFFFF';
+
+-- while we're here, check the same cases in E-style literals
+SELECT E'd\u0061t\U00000061' AS "data";
+SELECT E'a\\b' AS "a\b";
+SELECT E'wrong: \u061';
+SELECT E'wrong: \U0061';
+SELECT E'wrong: \udb99';
+SELECT E'wrong: \udb99xy';
+SELECT E'wrong: \udb99\\';
+SELECT E'wrong: \udb99\u0061';
+SELECT E'wrong: \U0000db99\U00000061';
+SELECT E'wrong: \U002FFFFF';
+
 SET standard_conforming_strings TO off;
 
 SELECT U&'d\0061t\+000061' AS U&"d\0061t\+000061";