jsonapi: add lexer option to keep token ownership

Commit 0785d1b8b adds support for libpq as a JSON client, but
allocations for string tokens can still be leaked during parsing
failures. This is tricky to fix for the object_field semantic callbacks:
the field name must remain valid until the end of the object, but if a
parsing error is encountered partway through, object_field_end() won't
be invoked and the client won't get a chance to free the field name.

This patch adds a flag to switch the ownership of parsed tokens to the
lexer. When this is enabled, the client must make a copy of any tokens
it wants to persist past the callback lifetime, but the lexer will
handle necessary cleanup on failure.

Backend uses of the JSON parser don't need to use this flag, since the
parser's allocations will occur in a short lived memory context.

A -o option has been added to test_json_parser_incremental to exercise
the new setJsonLexContextOwnsTokens() API, and the test_json_parser TAP
tests make use of it. (The test program now cleans up allocated memory,
so that tests can be usefully run under leak sanitizers.)

Author: Jacob Champion

Discussion: https://postgr.es/m/CAOYmi+kb38EciwyBQOf9peApKGwraHqA7pgzBkvoUnw5BRfS1g@mail.gmail.com

1 files changed, 30 insertions, 7 deletions

diff --git a/src/test/modules/test_json_parser/test_json_parser_incremental.c b/src/test/modules/test_json_parser/test_json_parser_incremental.c
index 294e5f74eac..0b02b5203bf 100644
--- a/src/test/modules/test_json_parser/test_json_parser_incremental.c
+++ b/src/test/modules/test_json_parser/test_json_parser_incremental.c
@@ -18,6 +18,10 @@
  * If the -s flag is given, the program does semantic processing. This should
  * just mirror back the json, albeit with white space changes.
  *
+ * If the -o flag is given, the JSONLEX_CTX_OWNS_TOKENS flag is set. (This can
+ * be used in combination with a leak sanitizer; without the option, the parser
+ * may leak memory with invalid JSON.)
+ *
  * The argument specifies the file containing the JSON input.
  *
  *-------------------------------------------------------------------------
@@ -72,6 +76,8 @@ static JsonSemAction sem = {
 	.scalar = do_scalar
 };
 
+static bool lex_owns_tokens = false;
+
 int
 main(int argc, char **argv)
 {
@@ -88,10 +94,11 @@ main(int argc, char **argv)
 	char	   *testfile;
 	int			c;
 	bool		need_strings = false;
+	int			ret = 0;
 
 	pg_logging_init(argv[0]);
 
-	while ((c = getopt(argc, argv, "c:s")) != -1)
+	while ((c = getopt(argc, argv, "c:os")) != -1)
 	{
 		switch (c)
 		{
@@ -100,6 +107,9 @@ main(int argc, char **argv)
 				if (chunk_size > BUFSIZE)
 					pg_fatal("chunk size cannot exceed %d", BUFSIZE);
 				break;
+			case 'o':			/* switch token ownership */
+				lex_owns_tokens = true;
+				break;
 			case 's':			/* do semantic processing */
 				testsem = &sem;
 				sem.semstate = palloc(sizeof(struct DoState));
@@ -112,7 +122,7 @@ main(int argc, char **argv)
 
 	if (optind < argc)
 	{
-		testfile = pg_strdup(argv[optind]);
+		testfile = argv[optind];
 		optind++;
 	}
 	else
@@ -122,6 +132,7 @@ main(int argc, char **argv)
 	}
 
 	makeJsonLexContextIncremental(&lex, PG_UTF8, need_strings);
+	setJsonLexContextOwnsTokens(&lex, lex_owns_tokens);
 	initStringInfo(&json);
 
 	if ((json_file = fopen(testfile, PG_BINARY_R)) == NULL)
@@ -160,7 +171,8 @@ main(int argc, char **argv)
 			if (result != JSON_INCOMPLETE)
 			{
 				fprintf(stderr, "%s\n", json_errdetail(result, &lex));
-				exit(1);
+				ret = 1;
+				goto cleanup;
 			}
 			resetStringInfo(&json);
 		}
@@ -172,15 +184,21 @@ main(int argc, char **argv)
 			if (result != JSON_SUCCESS)
 			{
 				fprintf(stderr, "%s\n", json_errdetail(result, &lex));
-				exit(1);
+				ret = 1;
+				goto cleanup;
 			}
 			if (!need_strings)
 				printf("SUCCESS!\n");
 			break;
 		}
 	}
+
+cleanup:
 	fclose(json_file);
-	exit(0);
+	freeJsonLexContext(&lex);
+	free(json.data);
+
+	return ret;
 }
 
 /*
@@ -230,7 +248,8 @@ do_object_field_start(void *state, char *fname, bool isnull)
 static JsonParseErrorType
 do_object_field_end(void *state, char *fname, bool isnull)
 {
-	/* nothing to do really */
+	if (!lex_owns_tokens)
+		free(fname);
 
 	return JSON_SUCCESS;
 }
@@ -291,6 +310,9 @@ do_scalar(void *state, char *token, JsonTokenType tokentype)
 	else
 		printf("%s", token);
 
+	if (!lex_owns_tokens)
+		free(token);
+
 	return JSON_SUCCESS;
 }
 
@@ -343,7 +365,8 @@ usage(const char *progname)
 {
 	fprintf(stderr, "Usage: %s [OPTION ...] testfile\n", progname);
 	fprintf(stderr, "Options:\n");
-	fprintf(stderr, "  -c chunksize      size of piece fed to parser (default 64)n");
+	fprintf(stderr, "  -c chunksize      size of piece fed to parser (default 64)\n");
+	fprintf(stderr, "  -o                set JSONLEX_CTX_OWNS_TOKENS for leak checking\n");
 	fprintf(stderr, "  -s                do semantic processing\n");
 
 }