Adjust pg_parse_json() so that it does not directly ereport().

Instead, it now returns a value indicating either success or the
type of error which occurred. The old behavior is still available
by calling pg_parse_json_or_ereport(). If the new interface is
used, an error can be thrown by passing the return value of
pg_parse_json() to json_ereport_error().

pg_parse_json() can still elog() in can't-happen cases, but it
seems like that issue is best handled separately.

Adjust json_lex() and json_count_array_elements() to return an
error code, too.

This is all in preparation for making the backend's json parser
available to frontend code.

Reviewed and/or tested by Mark Dilger and Andrew Dunstan.

Discussion: http://postgr.es/m/CA+TgmoYfOXhd27MUDGioVh6QtpD0C1K-f6ObSA10AWiHBAL5bA@mail.gmail.com

Author: robertmhaas

src/backend/utils/adt/json.c

@@ -81,7 +81,7 @@ json_in(PG_FUNCTION_ARGS)
 
 	/* validate it */
 	lex = makeJsonLexContext(result, false);
-	pg_parse_json(lex, &nullSemAction);
+	pg_parse_json_or_ereport(lex, &nullSemAction);
 
 	/* Internal representation is the same as text, for now */
 	PG_RETURN_TEXT_P(result);
@@ -128,7 +128,7 @@ json_recv(PG_FUNCTION_ARGS)
 
 	/* Validate it. */
 	lex = makeJsonLexContextCstringLen(str, nbytes, false);
-	pg_parse_json(lex, &nullSemAction);
+	pg_parse_json_or_ereport(lex, &nullSemAction);
 
 	PG_RETURN_TEXT_P(cstring_to_text_with_len(str, nbytes));
 }
@@ -1337,12 +1337,15 @@ json_typeof(PG_FUNCTION_ARGS)
 	JsonLexContext *lex;
 	JsonTokenType tok;
 	char	   *type;
+	JsonParseErrorType	result;
 
 	json = PG_GETARG_TEXT_PP(0);
 	lex = makeJsonLexContext(json, false);
 
 	/* Lex exactly one token from the input and check its type. */
-	json_lex(lex);
+	result = json_lex(lex);
+	if (result != JSON_SUCCESS)
+		json_ereport_error(result, lex);
 	tok = lex->token_type;
 	switch (tok)
 	{