Make json_error_t opaque

All decoding functions now accept a json_error_t** parameter and set
it to point to a heap-allocated json_error_t structure if an error
occurs. The contents of json_error_t are no longer exposed directly, a
few functions to do it have been added instead. If an error occurs,
the user must free the json_error_t value.

This makes it possible to enhance the error reporting facilities in
the future without breaking ABI compatibility with older versions.

This is a backwards incompatible change.

doc/apiref.rst

@@ -715,74 +715,93 @@ affect especially the behavior of the decoder.
 
 .. type:: json_error_t
 
-   This data structure is used to return information on decoding
+   This opaque structure is used to return information on errors from
-   errors from the decoding functions. Its definition is repeated
+   the decoding functions. See below for more discussion on error
-   here::
+   reporting.
 
-      #define JSON_ERROR_TEXT_LENGTH  160
+The following functions perform the JSON decoding:
 
-      typedef struct {
+.. function:: json_t *json_loads(const char *input, size_t flags, json_error_t **error)
-          char text[JSON_ERROR_TEXT_LENGTH];
-          int line;
-      } json_error_t;
-
-   *line* is the line number on which the error occurred, or -1 if
-   this information is not available. *text* contains the error
-   message (in UTF-8), or an empty string if a message is not
-   available.
-
-   The normal usef of :type:`json_error_t` is to allocate it normally
-   on the stack, and pass a pointer to a decoding function. Example::
-
-      int main() {
-          json_t *json;
-          json_error_t error;
-
-          json = json_load_file("/path/to/file.json", 0, &error);
-          if(!json) {
-              /* the error variable contains error information */
-          }
-          ...
-      }
-
-   Also note that if the decoding succeeded (``json != NULL`` in the
-   above example), the contents of ``error`` are unspecified.
-
-   All decoding functions also accept *NULL* as the
-   :type:`json_error_t` pointer, in which case no error information
-   is returned to the caller.
-
-The following functions perform the actual JSON decoding.
-
-.. function:: json_t *json_loads(const char *input, size_t flags, json_error_t *error)
 
    .. refcounting:: new
 
    Decodes the JSON string *input* and returns the array or object it
-   contains, or *NULL* on error, in which case *error* is filled with
+   contains, or *NULL* on error. If *error* is non-*NULL*, it's used
-   information about the error. See above for discussion on the
+   to return error information. See below for more discussion on error
-   *error* parameter. *flags* is currently unused, and should be set
+   reporting. *flags* is currently unused, and should be set to 0.
-   to 0.
 
-.. function:: json_t *json_loadf(FILE *input, size_t flags, json_error_t *error)
+.. function:: json_t *json_loadf(FILE *input, size_t flags, json_error_t **error)
 
    .. refcounting:: new
 
    Decodes the JSON text in stream *input* and returns the array or
-   object it contains, or *NULL* on error, in which case *error* is
+   object it contains, or *NULL* on error. If *error* is non-*NULL*,
-   filled with information about the error. See above for discussion
+   it's used to return error information. See below for more
-   on the *error* parameter. *flags* is currently unused, and should
+   discussion on error reporting. *flags* is currently unused, and
-   be set to 0.
+   should be set to 0.
 
-.. function:: json_t *json_load_file(const char *path, size_t flags, json_error_t *error)
+.. function:: json_t *json_load_file(const char *path, size_t flags, json_error_t **error)
 
    .. refcounting:: new
 
    Decodes the JSON text in file *path* and returns the array or
-   object it contains, or *NULL* on error, in which case *error* is
+   object it contains, or *NULL* on error. If *error* is non-*NULL*,
-   filled with information about the error. See above for discussion
+   it's used to return error information. See below for more
-   on the *error* parameter. *flags* is currently unused, and should
+   discussion on error reporting. *flags* is currently unused, and
-   be set to 0.
+   should be set to 0.
+
+
+The :type:`json_error_t` parameter, that all decoding function accept
+as their last parameter, is used to return information on decoding
+errors to the caller. It is used by having a ``json_error_t *``
+variable and passing a pointer to this variable to a decoding
+function. Example::
+
+   int main() {
+       json_t *json;
+       json_error_t *error;
+
+       json = json_load_file("/path/to/file.json", 0, &error);
+       if(!json) {
+           /* the error variable contains error information */
+           fprintf(stderr, "Decoding error occured on line %d: %s\n", json_error_line(error), json_error_msg(error));
+           free(error);
+       }
+
+       /* ... */
+   }
+
+Note that **the caller must free the error structure** after use if a
+decoding error occurs. If decoding is succesfully finished, *error* is
+simply set to *NULL* by the decoding function.
+
+All decoding functions also accept *NULL* as the :type:`json_error_t`
+pointer, in which case no error information is returned to the caller.
+Example::
+
+   int main() {
+       json_t *json;
+
+       json = json_load_file("/path/to/file.json", 0, NULL);
+       if(!json) {
+           /* A decoding error occured but no error information is available */
+       }
+
+       /* ... */
+   }
+
+:type:`json_error_t` is totally opaque and must be queried using the
+following functions:
+
+.. function:: const char *json_error_msg(const json_error_t *error)
+
+   Return a pointer to an UTF-8 encoded string that describes the
+   error in human-readable text, or *NULL* if *error* is *NULL*.
+
+.. function:: int json_error_line(const json_error_t *error)
+
+   Return the line numer on which the error occurred, or -1 if this
+   information is not available or if *error* is *NULL*.
 
 
 Equality

src/jansson.h

@@ -168,18 +168,19 @@ json_t *json_copy(json_t *value);
 json_t *json_deep_copy(json_t *value);
 
 
+/* error reporting */
+
+typedef struct json_error_t json_error_t;
+
+const char *json_error_msg(const json_error_t *error);
+int json_error_line(const json_error_t *error);
+
+
 /* loading, printing */
 
-#define JSON_ERROR_TEXT_LENGTH  160
+json_t *json_loads(const char *input, size_t flags, json_error_t **error);
-
+json_t *json_loadf(FILE *input, size_t flags, json_error_t **error);
-typedef struct {
+json_t *json_load_file(const char *path, size_t flags, json_error_t **error);
-    char text[JSON_ERROR_TEXT_LENGTH];
-    int line;
-} json_error_t;
-
-json_t *json_loads(const char *input, size_t flags, json_error_t *error);
-json_t *json_loadf(FILE *input, size_t flags, json_error_t *error);
-json_t *json_load_file(const char *path, size_t flags, json_error_t *error);
 
 #define JSON_INDENT(n)      (n & 0x1F)
 #define JSON_COMPACT        0x20

src/load.c

@@ -60,53 +60,71 @@ typedef struct {
 
 /*** error reporting ***/
 
-static void error_init(json_error_t *error)
+#define JSON_ERROR_MSG_LENGTH 160
+
+struct json_error_t {
+  char msg[JSON_ERROR_MSG_LENGTH];
+  int line;
+};
+
+const char *json_error_msg(const json_error_t *error)
 {
-    if(error)
+    return error ? error->msg : NULL;
-    {
-        error->text[0] = '\0';
-        error->line = -1;
-    }
 }
 
-static void error_set(json_error_t *error, const lex_t *lex,
+int json_error_line(const json_error_t *error)
+{
+    return error ? error->line : -1;
+}
+
+static void error_init(json_error_t **error)
+{
+    if(error)
+        *error = NULL;
+}
+
+static void error_set(json_error_t **error, const lex_t *lex,
                       const char *msg, ...)
 {
     va_list ap;
-    char text[JSON_ERROR_TEXT_LENGTH];
+    char text[JSON_ERROR_MSG_LENGTH];
 
-    if(!error || error->text[0] != '\0') {
+    if(!error || *error) {
-        /* error already set */
+        /* error not given or already set */
         return;
     }
 
+    *error = malloc(sizeof(json_error_t));
+    if(!(*error))
+        return;
+
     va_start(ap, msg);
-    vsnprintf(text, JSON_ERROR_TEXT_LENGTH, msg, ap);
+    vsnprintf(text, JSON_ERROR_MSG_LENGTH, msg, ap);
     va_end(ap);
 
     if(lex)
     {
         const char *saved_text = strbuffer_value(&lex->saved_text);
-        error->line = lex->line;
+        (*error)->line = lex->line;
         if(saved_text && saved_text[0])
         {
             if(lex->saved_text.length <= 20) {
-                snprintf(error->text, JSON_ERROR_TEXT_LENGTH,
+                snprintf((*error)->msg, JSON_ERROR_MSG_LENGTH,
                          "%s near '%s'", text, saved_text);
             }
             else
-                snprintf(error->text, JSON_ERROR_TEXT_LENGTH, "%s", text);
+                snprintf((*error)->msg, JSON_ERROR_MSG_LENGTH, "%s", text);
         }
         else
         {
-            snprintf(error->text, JSON_ERROR_TEXT_LENGTH,
+            snprintf((*error)->msg, JSON_ERROR_MSG_LENGTH,
                      "%s near end of file", text);
         }
     }
     else
     {
-        error->line = -1;
+        (*error)->line = -1;
-        snprintf(error->text, JSON_ERROR_TEXT_LENGTH, "%s", text);
+        snprintf((*error)->msg, JSON_ERROR_MSG_LENGTH, "%s", text);
     }
 }
 
@@ -124,7 +142,7 @@ stream_init(stream_t *stream, get_func get, eof_func eof, void *data)
     stream->buffer_pos = 0;
 }
 
-static char stream_get(stream_t *stream, json_error_t *error)
+static char stream_get(stream_t *stream, json_error_t **error)
 {
     char c;
 
@@ -182,7 +200,7 @@ static void stream_unget(stream_t *stream, char c)
 }
 
 
-static int lex_get(lex_t *lex, json_error_t *error)
+static int lex_get(lex_t *lex, json_error_t **error)
 {
     return stream_get(&lex->stream, error);
 }
@@ -197,7 +215,7 @@ static void lex_save(lex_t *lex, char c)
     strbuffer_append_byte(&lex->saved_text, c);
 }
 
-static int lex_get_save(lex_t *lex, json_error_t *error)
+static int lex_get_save(lex_t *lex, json_error_t **error)
 {
     char c = stream_get(&lex->stream, error);
     lex_save(lex, c);
@@ -245,7 +263,7 @@ static int32_t decode_unicode_escape(const char *str)
     return value;
 }
 
-static void lex_scan_string(lex_t *lex, json_error_t *error)
+static void lex_scan_string(lex_t *lex, json_error_t **error)
 {
     char c;
     const char *p;
@@ -407,7 +425,7 @@ out:
 #define json_strtoint     strtol
 #endif
 
-static int lex_scan_number(lex_t *lex, char c, json_error_t *error)
+static int lex_scan_number(lex_t *lex, char c, json_error_t **error)
 {
     const char *saved_text;
     char *end;
@@ -504,7 +522,7 @@ out:
     return -1;
 }
 
-static int lex_scan(lex_t *lex, json_error_t *error)
+static int lex_scan(lex_t *lex, json_error_t **error)
 {
     char c;
 
@@ -610,9 +628,9 @@ static void lex_close(lex_t *lex)
 
 /*** parser ***/
 
-static json_t *parse_value(lex_t *lex, json_error_t *error);
+static json_t *parse_value(lex_t *lex, json_error_t **error);
 
-static json_t *parse_object(lex_t *lex, json_error_t *error)
+static json_t *parse_object(lex_t *lex, json_error_t **error)
 {
     json_t *object = json_object();
     if(!object)
@@ -677,7 +695,7 @@ error:
     return NULL;
 }
 
-static json_t *parse_array(lex_t *lex, json_error_t *error)
+static json_t *parse_array(lex_t *lex, json_error_t **error)
 {
     json_t *array = json_array();
     if(!array)
@@ -717,7 +735,7 @@ error:
     return NULL;
 }
 
-static json_t *parse_value(lex_t *lex, json_error_t *error)
+static json_t *parse_value(lex_t *lex, json_error_t **error)
 {
     json_t *json;
 
@@ -772,7 +790,7 @@ static json_t *parse_value(lex_t *lex, json_error_t *error)
     return json;
 }
 
-static json_t *parse_json(lex_t *lex, json_error_t *error)
+static json_t *parse_json(lex_t *lex, json_error_t **error)
 {
     error_init(error);
 
@@ -811,7 +829,7 @@ static int string_eof(void *data)
     return (stream->data[stream->pos] == '\0');
 }
 
-json_t *json_loads(const char *string, size_t flags, json_error_t *error)
+json_t *json_loads(const char *string, size_t flags, json_error_t **error)
 {
     lex_t lex;
     json_t *result;
@@ -838,7 +856,7 @@ out:
     return result;
 }
 
-json_t *json_loadf(FILE *input, size_t flags, json_error_t *error)
+json_t *json_loadf(FILE *input, size_t flags, json_error_t **error)
 {
     lex_t lex;
     json_t *result;
@@ -863,7 +881,7 @@ out:
     return result;
 }
 
-json_t *json_load_file(const char *path, size_t flags, json_error_t *error)
+json_t *json_load_file(const char *path, size_t flags, json_error_t **error)
 {
     json_t *result;
     FILE *fp;

test/bin/json_process.c

@@ -31,7 +31,7 @@ int main(int argc, char *argv[])
     size_t flags = 0;
 
     json_t *json;
-    json_error_t error;
+    json_error_t *error;
 
     if(argc != 1) {
         fprintf(stderr, "usage: %s\n", argv[0]);
@@ -61,7 +61,10 @@ int main(int argc, char *argv[])
 
     json = json_loadf(stdin, 0, &error);
     if(!json) {
-        fprintf(stderr, "%d\n%s\n", error.line, error.text);
+        fprintf(stderr, "%d\n%s\n",
+                json_error_line(error),
+                json_error_msg(error));
+        free(error);
         return 1;
     }
 

test/suites/api/check-exports

@@ -47,6 +47,8 @@ json_object_iter_set_new
 json_dumps
 json_dumpf
 json_dump_file
+json_error_line
+json_error_msg
 json_loads
 json_loadf
 json_load_file

test/suites/api/test_load.c

@@ -12,13 +12,16 @@
 int main()
 {
     json_t *json;
-    json_error_t error;
+    json_error_t *error;
 
     json = json_load_file("/path/to/nonexistent/file.json", 0, &error);
-    if(error.line != -1)
+    if(json)
+      fail("json_load didn't return an error!");
+    if(json_error_line(error) != -1)
         fail("json_load_file returned an invalid line number");
-    if(strcmp(error.text, "unable to open /path/to/nonexistent/file.json: No such file or directory") != 0)
+    if(strcmp(json_error_msg(error), "unable to open /path/to/nonexistent/file.json: No such file or directory") != 0)
         fail("json_load_file returned an invalid error message");
 
+    free(error);
     return 0;
 }