Use extensible buffers to assemble command lines

This makes use of StringInfo to assemble command lines, instead of
using fixed-size buffers and the (remote) possibility of "command too
long" errors.  Also makes the code a bit simpler.

This covers the test driver programs pg_regress and
pg_isolation_regress.

Similar to the changes done for pg_rewind in a33e17f210.

Discussion: https://www.postgresql.org/message-id/2be4fee5-738f-4749-b9f8-b452032c7ade%40eisentraut.org

src/test/isolation/isolation_main.c

@@ -12,6 +12,7 @@
 
 #include "postgres_fe.h"
 
+#include "lib/stringinfo.h"
 #include "pg_regress.h"
 
 char		saved_argv0[MAXPGPATH];
@@ -34,8 +35,7 @@ isolation_start_test(const char *testname,
 	char		infile[MAXPGPATH];
 	char		outfile[MAXPGPATH];
 	char		expectfile[MAXPGPATH];
-	char		psql_cmd[MAXPGPATH * 3];
-	size_t		offset = 0;
+	StringInfoData psql_cmd;
 	char	   *appnameenv;
 
 	/* need to do the path lookup here, check isolation_init() for details */
@@ -75,34 +75,23 @@ isolation_start_test(const char *testname,
 	add_stringlist_item(resultfiles, outfile);
 	add_stringlist_item(expectfiles, expectfile);
 
+	initStringInfo(&psql_cmd);
+
 	if (launcher)
-	{
-		offset += snprintf(psql_cmd + offset, sizeof(psql_cmd) - offset,
-						   "%s ", launcher);
-		if (offset >= sizeof(psql_cmd))
-		{
-			fprintf(stderr, _("command too long\n"));
-			exit(2);
-		}
-	}
+		appendStringInfo(&psql_cmd, "%s ", launcher);
 
-	offset += snprintf(psql_cmd + offset, sizeof(psql_cmd) - offset,
-					   "\"%s\" \"dbname=%s\" < \"%s\" > \"%s\" 2>&1",
-					   isolation_exec,
-					   dblist->str,
-					   infile,
-					   outfile);
-	if (offset >= sizeof(psql_cmd))
-	{
-		fprintf(stderr, _("command too long\n"));
-		exit(2);
-	}
+	appendStringInfo(&psql_cmd,
+					 "\"%s\" \"dbname=%s\" < \"%s\" > \"%s\" 2>&1",
+					 isolation_exec,
+					 dblist->str,
+					 infile,
+					 outfile);
 
 	appnameenv = psprintf("isolation/%s", testname);
 	setenv("PGAPPNAME", appnameenv, 1);
 	free(appnameenv);
 
-	pid = spawn_process(psql_cmd);
+	pid = spawn_process(psql_cmd.data);
 
 	if (pid == INVALID_PID)
 	{
@@ -113,6 +102,8 @@ isolation_start_test(const char *testname,
 
 	unsetenv("PGAPPNAME");
 
+	pfree(psql_cmd.data);
+
 	return pid;
 }
 

src/test/regress/pg_regress_main.c

@@ -18,6 +18,7 @@
 
 #include "postgres_fe.h"
 
+#include "lib/stringinfo.h"
 #include "pg_regress.h"
 
 /*
@@ -34,8 +35,7 @@ psql_start_test(const char *testname,
 	char		infile[MAXPGPATH];
 	char		outfile[MAXPGPATH];
 	char		expectfile[MAXPGPATH];
-	char		psql_cmd[MAXPGPATH * 3];
-	size_t		offset = 0;
+	StringInfoData psql_cmd;
 	char	   *appnameenv;
 
 	/*
@@ -62,40 +62,29 @@ psql_start_test(const char *testname,
 	add_stringlist_item(resultfiles, outfile);
 	add_stringlist_item(expectfiles, expectfile);
 
+	initStringInfo(&psql_cmd);
+
 	if (launcher)
-	{
-		offset += snprintf(psql_cmd + offset, sizeof(psql_cmd) - offset,
-						   "%s ", launcher);
-		if (offset >= sizeof(psql_cmd))
-		{
-			fprintf(stderr, _("command too long\n"));
-			exit(2);
-		}
-	}
+		appendStringInfo(&psql_cmd, "%s ", launcher);
 
 	/*
 	 * Use HIDE_TABLEAM to hide different AMs to allow to use regression tests
 	 * against different AMs without unnecessary differences.
 	 */
-	offset += snprintf(psql_cmd + offset, sizeof(psql_cmd) - offset,
-					   "\"%s%spsql\" -X -a -q -d \"%s\" %s < \"%s\" > \"%s\" 2>&1",
-					   bindir ? bindir : "",
-					   bindir ? "/" : "",
-					   dblist->str,
-					   "-v HIDE_TABLEAM=on -v HIDE_TOAST_COMPRESSION=on",
-					   infile,
-					   outfile);
-	if (offset >= sizeof(psql_cmd))
-	{
-		fprintf(stderr, _("command too long\n"));
-		exit(2);
-	}
+	appendStringInfo(&psql_cmd,
+					 "\"%s%spsql\" -X -a -q -d \"%s\" %s < \"%s\" > \"%s\" 2>&1",
+					 bindir ? bindir : "",
+					 bindir ? "/" : "",
+					 dblist->str,
+					 "-v HIDE_TABLEAM=on -v HIDE_TOAST_COMPRESSION=on",
+					 infile,
+					 outfile);
 
 	appnameenv = psprintf("pg_regress/%s", testname);
 	setenv("PGAPPNAME", appnameenv, 1);
 	free(appnameenv);
 
-	pid = spawn_process(psql_cmd);
+	pid = spawn_process(psql_cmd.data);
 
 	if (pid == INVALID_PID)
 	{
@@ -106,6 +95,8 @@ psql_start_test(const char *testname,
 
 	unsetenv("PGAPPNAME");
 
+	pfree(psql_cmd.data);
+
 	return pid;
 }