Add a json_tokener_get_parse_end() function to replace direct access of tok->char_offset.

json_tokener.c

@@ -15,6 +15,7 @@
 
 #include "config.h"
 
+#include <assert.h>
 #include <math.h>
 #include "math_compat.h"
 #include <stdio.h>
@@ -225,7 +226,7 @@ struct json_object* json_tokener_parse_verbose(const char *str,
    )
 
 /* ADVANCE_CHAR() macro:
- *   Incrementes str & tok->char_offset.
+ *   Increments str & tok->char_offset.
  *   For convenience of existing conditionals, returns the old value of c (0 on eof)
  *   Implicit inputs:  c var
  */
@@ -995,3 +996,10 @@ void json_tokener_set_flags(struct json_tokener *tok, int flags)
 {
 	tok->flags = flags;
 }
+
+size_t json_tokener_get_parse_end(struct json_tokener *tok)
+{
+	assert(tok->char_offset >= 0); /* Drop this line when char_offset becomes a size_t */
+	return (size_t)tok->char_offset;
+}
+

json_tokener.h

@@ -79,17 +79,46 @@ struct json_tokener_srec
 
 #define JSON_TOKENER_DEFAULT_DEPTH 32
 
+/**
+ * Internal state of the json parser.
+ * Do not access any fields of this structure directly.
+ * Its definition is published due to historical limitations
+ * in the json tokener API, and will be changed to be an opaque
+ * type in the future.
+ */
 struct json_tokener
 {
   char *str;
   struct printbuf *pb;
-  int max_depth, depth, is_double, st_pos, char_offset;
+  int max_depth, depth, is_double, st_pos;
+  /**
+   * See json_tokener_get_parse_end()
+   */
+  int char_offset;
   enum json_tokener_error err;
   unsigned int ucs_char;
   char quote_char;
   struct json_tokener_srec *stack;
   int flags;
 };
+
+/**
+ * Return the offset of the byte after the last byte parsed
+ * relative to the start of the most recent string passed in
+ * to json_tokener_parse_ex().  i.e. this is where parsing
+ * would start again if the input contains another JSON object
+ * after the currently parsed one.
+ *
+ * Note that when multiple parse calls are issued, this is *not* the
+ * total number of characters parsed.
+ *
+ * In the past this would have been accessed as tok->char_offset.
+ *
+ * See json_tokener_parse_ex() for an example of how to use this.
+ */
+size_t json_tokener_get_parse_end(struct json_tokener *tok);
+
+
 /**
  * @deprecated Unused in json-c code
  */
@@ -160,13 +189,13 @@ JSON_EXPORT void json_tokener_set_flags(struct json_tokener *tok, int flags);
  * the type with json_object_is_type() or json_object_get_type() before using
  * the object.
  *
- * @b XXX this shouldn't use internal fields:
  * Trailing characters after the parsed value do not automatically cause an
  * error.  It is up to the caller to decide whether to treat this as an
  * error or to handle the additional characters, perhaps by parsing another
  * json value starting from that point.
  *
- * Extra characters can be detected by comparing the tok->char_offset against
+ * Extra characters can be detected by comparing the value returned by
+ * json_tokener_get_parse_end() against
  * the length of the last len parameter passed in.
  *
  * The tokener does \b not maintain an internal buffer so the caller is
@@ -194,7 +223,7 @@ if (jerr != json_tokener_success)
 	fprintf(stderr, "Error: %s\n", json_tokener_error_desc(jerr));
 	// Handle errors, as appropriate for your application.
 }
-if (tok->char_offset < stringlen) // XXX shouldn't access internal fields
+if (json_tokener_get_parse_end(tok) < stringlen)
 {
 	// Handle extra characters after parsed object as desired.
 	// e.g. issue an error, parse another object from that point, etc...

tests/test_parse.c

@@ -334,7 +334,7 @@ static void test_incremental_parse()
 		int this_step_ok = 0;
 		struct incremental_step *step = &incremental_steps[ii];
 		int length = step->length;
-		int expected_char_offset = step->char_offset;
+		size_t expected_char_offset;
 
 		if (step->reset_tokener & 2)
 			json_tokener_set_flags(tok, JSON_TOKENER_STRICT);
@@ -343,8 +343,10 @@ static void test_incremental_parse()
 
 		if (length == -1)
 			length = strlen(step->string_to_parse);
-		if (expected_char_offset == -1)
+		if (step->char_offset == -1)
 			expected_char_offset = length;
+		else
+			expected_char_offset = step->char_offset;
 
 		printf("json_tokener_parse_ex(tok, %-12s, %3d) ... ",
 			step->string_to_parse, length);
@@ -359,9 +361,9 @@ static void test_incremental_parse()
 			else if (jerr != step->expected_error)
 				printf("ERROR: got wrong error: %s\n",
 				       json_tokener_error_desc(jerr));
-			else if (tok->char_offset != expected_char_offset)
-				printf("ERROR: wrong char_offset %d != expected %d\n",
-				       tok->char_offset,
+			else if (json_tokener_get_parse_end(tok) != expected_char_offset)
+				printf("ERROR: wrong char_offset %zu != expected %zu\n",
+				       json_tokener_get_parse_end(tok),
 				       expected_char_offset);
 			else
 			{
@@ -377,9 +379,9 @@ static void test_incremental_parse()
 			      strncmp(step->string_to_parse, "null", 4) == 0))
 				printf("ERROR: expected valid object, instead: %s\n",
 				       json_tokener_error_desc(jerr));
-			else if (tok->char_offset != expected_char_offset)
-				printf("ERROR: wrong char_offset %d != expected %d\n",
-				       tok->char_offset,
+			else if (json_tokener_get_parse_end(tok) != expected_char_offset)
+				printf("ERROR: wrong char_offset %zu != expected %zu\n",
+				       json_tokener_get_parse_end(tok),
 				       expected_char_offset);
 			else
 			{