Remove dependency to StringInfo in xlogbackup.{c.h}

This was used as the returned result type of the generated contents for
the backup_label and backup history files.  This is replaced by a simple
string, reducing the cleanup burden of all the callers of
build_backup_content().

Reviewed-by: Bharath Rupireddy
Discussion: https://postgr.es/m/YzERvNPaZivHEKZJ@paquier.xyz

src/backend/access/transam/xlog.c

@@ -8711,7 +8711,7 @@ do_pg_backup_stop(BackupState *state, bool waitforarchive)
 	}
 	else
 	{
-		StringInfo	history_file;
+		char	   *history_file;
 
 		/*
 		 * Write the backup-end xlog record
@@ -8751,8 +8751,7 @@ do_pg_backup_stop(BackupState *state, bool waitforarchive)
 
 		/* Build and save the contents of the backup history file */
 		history_file = build_backup_content(state, true);
-		fprintf(fp, "%s", history_file->data);
+		fprintf(fp, "%s", history_file);
-		pfree(history_file->data);
 		pfree(history_file);
 
 		if (fflush(fp) || ferror(fp) || FreeFile(fp))

src/backend/access/transam/xlogbackup.c

@@ -23,15 +23,16 @@
  * When ishistoryfile is true, it creates the contents for a backup history
  * file, otherwise it creates contents for a backup_label file.
  *
- * Returns the result generated as a palloc'd StringInfo.
+ * Returns the result generated as a palloc'd string.
  */
-StringInfo
+char *
 build_backup_content(BackupState *state, bool ishistoryfile)
 {
 	char		startstrbuf[128];
 	char		startxlogfile[MAXFNAMELEN]; /* backup start WAL file */
 	XLogSegNo	startsegno;
 	StringInfo	result = makeStringInfo();
+	char	   *data;
 
 	Assert(state != NULL);
 
@@ -76,5 +77,8 @@ build_backup_content(BackupState *state, bool ishistoryfile)
 		appendStringInfo(result, "STOP TIMELINE: %u\n", state->stoptli);
 	}
 
-	return result;
+	data = result->data;
+	pfree(result);
+
+	return data;
 }

src/backend/access/transam/xlogfuncs.c

@@ -130,7 +130,7 @@ pg_backup_stop(PG_FUNCTION_ARGS)
 	Datum		values[PG_BACKUP_STOP_V2_COLS] = {0};
 	bool		nulls[PG_BACKUP_STOP_V2_COLS] = {0};
 	bool		waitforarchive = PG_GETARG_BOOL(0);
-	StringInfo	backup_label;
+	char	   *backup_label;
 	SessionBackupState status = get_backup_status();
 
 	/* Initialize attributes information in the tuple descriptor */
@@ -153,7 +153,7 @@ pg_backup_stop(PG_FUNCTION_ARGS)
 	backup_label = build_backup_content(backup_state, false);
 
 	values[0] = LSNGetDatum(backup_state->stoppoint);
-	values[1] = CStringGetTextDatum(backup_label->data);
+	values[1] = CStringGetTextDatum(backup_label);
 	values[2] = CStringGetTextDatum(tablespace_map->data);
 
 	/* Deallocate backup-related variables */
@@ -162,7 +162,6 @@ pg_backup_stop(PG_FUNCTION_ARGS)
 	pfree(tablespace_map->data);
 	pfree(tablespace_map);
 	tablespace_map = NULL;
-	pfree(backup_label->data);
 	pfree(backup_label);
 
 	/* Returns the record as Datum */

src/backend/backup/basebackup.c

@@ -317,15 +317,14 @@ perform_base_backup(basebackup_options *opt, bbsink *sink)
 			{
 				struct stat statbuf;
 				bool		sendtblspclinks = true;
-				StringInfo	backup_label;
+				char	   *backup_label;
 
 				bbsink_begin_archive(sink, "base.tar");
 
 				/* In the main tar, include the backup_label first... */
 				backup_label = build_backup_content(backup_state, false);
 				sendFileWithContent(sink, BACKUP_LABEL_FILE,
-									backup_label->data, &manifest);
+									backup_label, &manifest);
-				pfree(backup_label->data);
 				pfree(backup_label);
 
 				/* Then the tablespace_map file, if required... */

src/include/access/xlogbackup.h

@@ -15,7 +15,6 @@
 #define XLOG_BACKUP_H
 
 #include "access/xlogdefs.h"
-#include "lib/stringinfo.h"
 #include "pgtime.h"
 
 /* Structure to hold backup state. */
@@ -36,7 +35,7 @@ typedef struct BackupState
 	pg_time_t	stoptime;		/* backup stop time */
 } BackupState;
 
-extern StringInfo build_backup_content(BackupState *state,
+extern char *build_backup_content(BackupState *state,
-									   bool ishistoryfile);
+								  bool ishistoryfile);
 
 #endif							/* XLOG_BACKUP_H */