Add backend-only appendStringInfoStringQuoted

This provides a mechanism to emit literal values in informative
messages, such as query parameters.  The new code is more complex than
what it replaces, primarily because it wants to be more efficient.
It also has the (currently unused) additional optional capability of
specifying a maximum size to print.

The new function lives out of common/stringinfo.c so that frontend users
of that file need not pull in unnecessary multibyte-encoding support
code.

Author: Álvaro Herrera and Alexey Bashtanov, after a suggestion from Andres Freund
Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/20190920203905.xkv5udsd5dxfs6tr@alap3.anarazel.de

3 files changed, 88 insertions, 0 deletions

diff --git a/src/backend/utils/mb/Makefile b/src/backend/utils/mb/Makefile
index 18dd758cfe8..cd4a016449e 100644
--- a/src/backend/utils/mb/Makefile
+++ b/src/backend/utils/mb/Makefile
@@ -16,6 +16,7 @@ OBJS = \
 	conv.o \
 	encnames.o \
 	mbutils.o \
+	stringinfo_mb.o \
 	wchar.o \
 	wstrcmp.o \
 	wstrncmp.o
diff --git a/src/backend/utils/mb/README b/src/backend/utils/mb/README
index c9bc6e6f8d6..7495ca5db23 100644
--- a/src/backend/utils/mb/README
+++ b/src/backend/utils/mb/README
@@ -9,6 +9,7 @@ wchar.c:	mostly static functions and a public table for mb string and
 		multibyte conversion
 mbutils.c:	public functions for the backend only.
 		requires conv.c and wchar.c
+stringinfo_mb.c: public backend-only multibyte-aware stringinfo functions
 wstrcmp.c:	strcmp for mb
 wstrncmp.c:	strncmp for mb
 win866.c:	a tool to generate KOI8 <--> CP866 conversion table
diff --git a/src/backend/utils/mb/stringinfo_mb.c b/src/backend/utils/mb/stringinfo_mb.c
new file mode 100644
index 00000000000..51bb051206e
--- /dev/null
+++ b/src/backend/utils/mb/stringinfo_mb.c
@@ -0,0 +1,86 @@
+/*-------------------------------------------------------------------------
+ *
+ * stringinfo_mb.c
+ *		Multibyte encoding-aware additional StringInfo facilites
+ *
+ * This is separate from common/stringinfo.c so that frontend users
+ * of that file need not pull in unnecessary multibyte-encoding support
+ * code.
+ *
+ *
+ * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/utils/mb/stringinfo_mb.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "mb/stringinfo_mb.h"
+#include "mb/pg_wchar.h"
+
+
+/*
+ * appendStringInfoStringQuoted
+ *
+ * Append up to maxlen characters from s to str, or the whole input string if
+ * maxlen <= 0, adding single quotes around it and doubling all single quotes.
+ * Add an ellipsis if the copy is incomplete.
+ */
+void
+appendStringInfoStringQuoted(StringInfo str, const char *s, int maxlen)
+{
+	char	   *copy = NULL;
+	const char *chunk_search_start,
+			   *chunk_copy_start,
+			   *chunk_end;
+	int			slen;
+	bool		ellipsis;
+
+	Assert(str != NULL);
+
+	slen = strlen(s);
+	if (maxlen > 0 && maxlen < slen)
+	{
+		int		finallen = pg_mbcliplen(s, slen, maxlen);
+
+		copy = pnstrdup(s, finallen);
+		chunk_search_start = copy;
+		chunk_copy_start = copy;
+
+		ellipsis = true;
+	}
+	else
+	{
+		chunk_search_start = s;
+		chunk_copy_start = s;
+
+		ellipsis = false;
+	}
+
+	appendStringInfoCharMacro(str, '\'');
+
+	while ((chunk_end = strchr(chunk_search_start, '\'')) != NULL)
+	{
+		/* copy including the found delimiting ' */
+		appendBinaryStringInfoNT(str,
+								 chunk_copy_start,
+								 chunk_end - chunk_copy_start + 1);
+
+		/* in order to double it, include this ' into the next chunk as well */
+		chunk_copy_start = chunk_end;
+		chunk_search_start = chunk_end + 1;
+	}
+
+	/* copy the last chunk and terminate */
+	if (ellipsis)
+		appendStringInfo(str, "%s...'", chunk_copy_start);
+	else
+		appendStringInfo(str, "%s'", chunk_copy_start);
+
+	if (copy)
+		pfree(copy);
+}