Make StringInfo available to frontend code.

There's plenty places in frontend code that could benefit from a
string buffer implementation. Some because it yields simpler and
faster code, and some others because of the desire to share code
between backend and frontend.

While there is a string buffer implementation available to frontend
code, libpq's PQExpBuffer, it is clunkier than stringinfo, it
introduces a libpq dependency, doesn't allow for sharing between
frontend and backend code, and has a higher API/ABI stability
requirement due to being exposed via libpq.

Therefore it seems best to just making StringInfo being usable by
frontend code. There's not much to do for that, except for rewriting
two subsequent elog/ereport calls into others types of error
reporting, and deciding on a maximum string length.

For the maximum string size I decided to privately define MaxAllocSize
to the same value as used in the backend. It seems likely that we'll
want to reconsider this for both backend and frontend code in the not
too far away future.

For now I've left stringinfo.h in lib/, rather than common/, to reduce
the likelihood of unnecessary breakage. We could alternatively decide
to provide a redirecting stringinfo.h in lib/, or just not provide
compatibility.

Author: Andres Freund
Reviewed-By: Kyotaro Horiguchi, Daniel Gustafsson
Discussion: https://postgr.es/m/20190920051857.2fhnvhvx4qdddviz@alap3.anarazel.de

src/backend/lib/Makefile

@@ -23,6 +23,5 @@ OBJS = \
 	knapsack.o \
 	pairingheap.o \
 	rbtree.o \
-	stringinfo.o
 
 include $(top_srcdir)/src/backend/common.mk

src/bin/pg_waldump/compat.c

@@ -20,7 +20,6 @@
 
 #include <time.h>
 
-#include "lib/stringinfo.h"
 #include "utils/datetime.h"
 
 /* copied from timestamp.c */
@@ -63,29 +62,3 @@ timestamptz_to_str(TimestampTz dt)
 
 	return buf;
 }
-
-/*
- * Provide a hacked up compat layer for StringInfos so xlog desc functions can
- * be linked/called.
- */
-void
-appendStringInfo(StringInfo str, const char *fmt,...)
-{
-	va_list		args;
-
-	va_start(args, fmt);
-	vprintf(fmt, args);
-	va_end(args);
-}
-
-void
-appendStringInfoString(StringInfo str, const char *string)
-{
-	appendStringInfo(str, "%s", string);
-}
-
-void
-appendStringInfoChar(StringInfo str, char ch)
-{
-	appendStringInfo(str, "%c", ch);
-}

src/bin/pg_waldump/pg_waldump.c

@@ -514,6 +514,7 @@ XLogDumpDisplayRecord(XLogDumpConfig *config, XLogReaderState *record)
 	int			block_id;
 	uint8		info = XLogRecGetInfo(record);
 	XLogRecPtr	xl_prev = XLogRecGetPrev(record);
+	StringInfoData s;
 
 	XLogDumpRecordLen(record, &rec_len, &fpi_len);
 
@@ -530,8 +531,10 @@ XLogDumpDisplayRecord(XLogDumpConfig *config, XLogReaderState *record)
 	else
 		printf("desc: %s ", id);
 
-	/* the desc routine will printf the description directly to stdout */
+	initStringInfo(&s);
-	desc->rm_desc(NULL, record);
+	desc->rm_desc(&s, record);
+	printf("%s", s.data);
+	pfree(s.data);
 
 	if (!config->bkp_details)
 	{

src/common/Makefile

@@ -67,6 +67,7 @@ OBJS_COMMON = \
 	saslprep.o \
 	scram-common.o \
 	string.o \
+	stringinfo.o \
 	unicode_norm.o \
 	username.o \
 	wait_error.o

src/common/stringinfo.c

@@ -2,21 +2,34 @@
  *
  * stringinfo.c
  *
- * StringInfo provides an indefinitely-extensible string data type.
+ * StringInfo provides an extensible string data type (currently limited to a
- * It can be used to buffer either ordinary C strings (null-terminated text)
+ * length of 1GB).  It can be used to buffer either ordinary C strings
- * or arbitrary binary data.  All storage is allocated with palloc().
+ * (null-terminated text) or arbitrary binary data.  All storage is allocated
+ * with palloc() (falling back to malloc in frontend code).
  *
  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	  src/backend/lib/stringinfo.c
+ *	  src/common/stringinfo.c
  *
  *-------------------------------------------------------------------------
  */
+
+#ifndef FRONTEND
+
 #include "postgres.h"
+#include "utils/memutils.h"
+
+#else
+
+#include "postgres_fe.h"
+
+/* It's possible we could use a different value for this in frontend code */
+#define MaxAllocSize	((Size) 0x3fffffff) /* 1 gigabyte - 1 */
+
+#endif
 
 #include "lib/stringinfo.h"
-#include "utils/memutils.h"
 
 
 /*
@@ -261,10 +274,10 @@ appendBinaryStringInfoNT(StringInfo str, const char *data, int datalen)
  * can save some palloc overhead by enlarging the buffer before starting
  * to store data in it.
  *
- * NB: because we use repalloc() to enlarge the buffer, the string buffer
+ * NB: In the backend, because we use repalloc() to enlarge the buffer, the
- * will remain allocated in the same memory context that was current when
+ * string buffer will remain allocated in the same memory context that was
- * initStringInfo was called, even if another context is now current.
+ * current when initStringInfo was called, even if another context is now
- * This is the desired and indeed critical behavior!
+ * current.  This is the desired and indeed critical behavior!
  */
 void
 enlargeStringInfo(StringInfo str, int needed)
@@ -276,13 +289,29 @@ enlargeStringInfo(StringInfo str, int needed)
 	 * an overflow or infinite loop in the following.
 	 */
 	if (needed < 0)				/* should not happen */
+	{
+#ifndef FRONTEND
 		elog(ERROR, "invalid string enlargement request size: %d", needed);
+#else
+		fprintf(stderr, "invalid string enlargement request size: %d\n", needed);
+		exit(EXIT_FAILURE);
+#endif
+	}
 	if (((Size) needed) >= (MaxAllocSize - (Size) str->len))
+	{
+#ifndef FRONTEND
 		ereport(ERROR,
 				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
 				 errmsg("out of memory"),
 				 errdetail("Cannot enlarge string buffer containing %d bytes by %d more bytes.",
 						   str->len, needed)));
+#else
+		fprintf(stderr,
+				_("out of memory\n\nCannot enlarge string buffer containing %d bytes by %d more bytes.\n"),
+				str->len, needed);
+		exit(EXIT_FAILURE);
+#endif
+	}
 
 	needed += str->len + 1;		/* total space required now */
 

src/include/lib/stringinfo.h

@@ -3,9 +3,10 @@
  * stringinfo.h
  *	  Declarations/definitions for "StringInfo" functions.
  *
- * StringInfo provides an indefinitely-extensible string data type.
+ * StringInfo provides an extensible string data type (currently limited to a
- * It can be used to buffer either ordinary C strings (null-terminated text)
+ * length of 1GB).  It can be used to buffer either ordinary C strings
- * or arbitrary binary data.  All storage is allocated with palloc().
+ * (null-terminated text) or arbitrary binary data.  All storage is allocated
+ * with palloc() (falling back to malloc in frontend code).
  *
  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California

src/tools/msvc/Mkvcbuild.pm

@@ -123,7 +123,7 @@ sub mkvcbuild
 	  base64.c config_info.c controldata_utils.c d2s.c exec.c f2s.c file_perm.c ip.c
 	  keywords.c kwlookup.c link-canary.c md5.c
 	  pg_lzcompress.c pgfnames.c psprintf.c relpath.c rmtree.c
-	  saslprep.c scram-common.c string.c unicode_norm.c username.c
+	  saslprep.c scram-common.c string.c stringinfo.c unicode_norm.c username.c
 	  wait_error.c);
 
 	if ($solution->{options}->{openssl})