Returns the associated value of *string* as a null terminated UTF-8
encoded string, or *NULL* if *string* is not a JSON string.
+ The retuned value is read-only and must not be modified or freed by
+ the user. It is valid as long as *string* exists, i.e. as long as
+ its reference count has not dropped to zero.
+
.. function:: int json_string_set(const json_t *string, const char *value)
Sets the associated value of *string* to *value*. *value* must be a
}
+Error reporting
+===============
+
+Jansson uses a single struct type to pass error information to the
+user. See sections :ref:`apiref-decoding`, :ref:`apiref-pack` and
+:ref:`apiref-unpack` for functions that pass error information using
+this struct.
+
+.. type:: json_error_t
+
+ .. member:: char text[]
+
+ The error message (in UTF-8), or an empty string if a message is
+ not available.
+
+ .. member:: char source[]
+
+ Source of the error. This can be (a part of) the file name or a
+ special identifier in angle brackers (e.g. ``<string>``).
+
+ .. member:: int line
+
+ The line number on which the error occurred.
+
+ .. member:: int column
+
+ The column on which the error occurred. Note that this is the
+ *character column*, not the byte column, i.e. a multibyte UTF-8
+ character counts as one column.
+
+ .. member:: size_t position
+
+ The position in bytes from the start of the input. This is
+ useful for debugging Unicode encoding problems.
+
+The normal use of :type:`json_error_t` is to allocate it on the stack,
+and pass a pointer to a 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 call succeeded (``json != NULL`` in the above
+example), the contents of ``error`` are unspecified.
+
+All functions also accept *NULL* as the :type:`json_error_t` pointer,
+in which case no error information is returned to the caller.
+
+
Encoding
========
above. Returns 0 on success and -1 on error.
+.. _apiref-decoding:
+
Decoding
========
Decodes the JSON string *input* and returns the array or object it
contains, or *NULL* on error, in which case *error* is filled with
- information about the error. See above for discussion on the
- *error* parameter. *flags* is currently unused, and should be set
- to 0.
+ information about the error. *flags* is currently unused, and
+ should be set to 0.
.. function:: json_t *json_loadf(FILE *input, size_t flags, json_error_t *error)
Decodes the JSON text in stream *input* and returns the array or
object it contains, or *NULL* on error, in which case *error* is
- filled with information about the error. See above for discussion
- on the *error* parameter. *flags* is currently unused, and should
- be set to 0.
+ filled with information about the error. *flags* is currently
+ unused, and should be set to 0.
.. function:: json_t *json_load_file(const char *path, size_t flags, json_error_t *error)
Decodes the JSON text in file *path* and returns the array or
object it contains, or *NULL* on error, in which case *error* is
- filled with information about the error. See above for discussion
- on the *error* parameter. *flags* is currently unused, and should
- be set to 0.
+ filled with information about the error. *flags* is currently
+ unused, and should be set to 0.
-.. type:: json_error_t
- This data structure is used to return information on decoding
- errors from the decoding functions.
+.. _apiref-pack:
- .. member:: const char *text
+Building Values
+===============
- The error message (in UTF-8), or an empty string if a message is
- not available.
+This sectinon describes functions that help to create, or *pack*,
+complex JSON values, especially nested objects and arrays. Value
+building is based on a *format string* that is used to tell the
+functions about the expected arguments.
- .. member:: int line
+For example, the format string ``"i"`` specifies a single integer
+value, while the format string ``"[ssb]"`` or the equivalent ``"[s, s,
+b]"`` specifies an array value with two integers and a boolean as its
+items::
- The line number on which the error occurred, or -1 if this
- information is not available.
+ /* Create the JSON integer 42 */
+ json_pack("i", 42);
- .. member:: int column
+ /* Create the JSON array ["foo", "bar", true] */
+ json_pack("[ssb]", "foo", "bar", 1);
+
+Here's the full list of format characters. The type in parentheses
+denotes the resulting JSON type, and the type in brackets (if any)
+denotes the C type that is expected as the corresponding argument.
+
+``s`` (string) [const char \*]
+ Convert a NULL terminated UTF-8 string to a JSON string.
+
+``n`` (null)
+ Output a JSON null value. No argument is consumed.
+
+``b`` (boolean) [int]
+ Convert a C :type:`int` to JSON boolean value. Zero is converted
+ to ``false`` and non-zero to ``true``.
+
+``i`` (integer) [int]
+ Convert a C :type:`int` to JSON integer.
+
+``I`` (integer) [json_int_t]
+ Convert a C :type:`json_int_t` to JSON integer.
+
+``f`` (real) [double]
+ Convert a C :type:`double` to JSON real.
+
+``o`` (any value) [json_t \*]
+ Output any given JSON value as-is. If the value is added to an
+ array or object, the reference to the value passed to ``o`` is
+ stealed by the container.
+
+``O`` (any value) [json_t \*]
+ Like ``o``, but the argument's reference count is incremented.
+ This is useful if you pack into an array or object and want to
+ keep the reference for the JSON value consumed by ``O`` to
+ yourself.
+
+``[fmt]`` (array)
+ Build an array with contents from the inner format string. ``fmt``
+ may contain objects and arrays, i.e. recursive value building is
+ supported.
+
+``{fmt}`` (object)
+ Build an object with contents from the inner format string
+ ``fmt``. The first, third, etc. format character represent a key,
+ and must be ``s`` (as object keys are always strings). The second,
+ fourth, etc. format character represent a value. Any value may be
+ an object or array, i.e. recursive value building is supported.
+
+The following functions compose the value building API:
+
+.. function:: json_t *json_pack(const char *fmt, ...)
+
+ .. refcounting:: new
+
+ Build a new JSON value according to the format string *fmt*. For
+ each format character (except for ``{}[]n``), one argument is
+ consumed and used to build the corresponding value. Returns *NULL*
+ on error.
+
+.. function:: json_t *json_pack_ex(json_error_t *error, size_t flags, const char *fmt, ...)
+ json_t *json_vpack_ex(json_error_t *error, size_t flags, const char *fmt, va_list ap)
+
+ .. refcounting:: new
+
+ Like :func:`json_pack()`, but an in the case of an error, an error
+ message is written to *error*, if it's not *NULL*. The *flags*
+ parameter is currently unused and should be set to 0.
- The character column on which the error occurred, or -1 if this
- information is not available.
+ As only the errors in format string (and out-of-memory errors) can
+ be caught by the packer, these two functions are most likely only
+ useful for debugging format strings.
- .. member:: const char *source
+More examples::
- Source of the error. This is (a part of) the file name when
- using :func:`json_load_file()`, or a special identifier in angle
- brackets otherwise (e.g. ``<string>``).
+ /* Build an empty JSON object */
+ json_pack("{}");
- The normal use of :type:`json_error_t` is to allocate it on the
- stack, and pass a pointer to a decoding function. Example::
+ /* Build the JSON object {"foo": 42, "bar": 7} */
+ json_pack("{sisb}", "foo", 42, "bar", 7);
- int main() {
- json_t *json;
- json_error_t error;
+ /* Like above, ':', ',' and whitespace are ignored */
+ json_pack("{s:i, s:b}", "foo", 42, "bar", 7);
- json = json_load_file("/path/to/file.json", 0, &error);
- if(!json) {
- /* the error variable contains error information */
- }
- ...
- }
+ /* Build the JSON array [[1, 2], {"cool": true}] */
+ json_pack("[[i,i],{s:b]]", 1, 2, "cool", 1);
- 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.
+.. _apiref-unpack:
+
+Parsing and Validating Values
+=============================
+
+This sectinon describes functions that help to validate complex values
+and extract, or *unpack*, data from them. Like :ref:`building values
+<apiref-pack>`, this is also based on format strings.
+
+While a JSON value is unpacked, the type specified in the format
+string is checked to match that of the JSON value. This is the
+validation part of the process. In addition to this, the unpacking
+functions can also check that all items of arrays and objects are
+unpacked. This check be enabled with the format character ``!`` or by
+using the flag ``JSON_STRICT``. See below for details.
+
+Here's the full list of format characters. The type in parentheses
+denotes the JSON type, and the type in brackets (if any) denotes the C
+type whose address should be passed.
+
+``s`` (string) [const char \*]
+ Convert a JSON string to a pointer to a NULL terminated UTF-8
+ string.
+
+``n`` (null)
+ Expect a JSON null value. Nothing is extracted.
+
+``b`` (boolean) [int]
+ Convert a JSON boolean value to a C :type:`int`, so that ``true``
+ is converted to 1 and ``false`` to 0.
+
+``i`` (integer) [int]
+ Convert a JSON integer to C :type:`int`.
+
+``I`` (integer) [json_int_t]
+ Convert a JSON integer to C :type:`json_int_t`.
+
+``f`` (real) [double]
+ Convert a JSON real to C :type:`double`.
+
+``F`` (integer or real) [double]
+ Convert a JSON number (integer or real) to C :type:`double`.
+
+``o`` (any value) [json_t \*]
+ Store a JSON value with no conversion to a :type:`json_t` pointer.
+
+``O`` (any value) [json_t \*]
+ Like ``O``, but the JSON value's reference count is incremented.
+
+``[fmt]`` (array)
+ Convert each item in the JSON array according to the inner format
+ string. ``fmt`` may contain objects and arrays, i.e. recursive
+ value extraction is supporetd.
+
+``{fmt}`` (object)
+ Convert each item in the JSON object according to the inner format
+ string ``fmt``. The first, third, etc. format character represent
+ a key, and must be ``s``. The corresponding argument to unpack
+ functions is read as the object key. The second fourth, etc.
+ format character represent a value and is written to the address
+ given as the corresponding argument. **Note** that every other
+ argument is read from and every other is written to.
+
+ ``fmt`` may contain objects and arrays as values, i.e. recursive
+ value extraction is supporetd.
+
+``!``
+ This special format character is used to enable the check that
+ all object and array items are accessed, on a per-value basis. It
+ must appear inside an array or object as the last format character
+ before the closing bracket or brace. To enable the check globally,
+ use the ``JSON_STRICT`` unpacking flag.
+
+``*``
+ This special format character is the opposite of ``!``. If the
+ ``JSON_STRICT`` flag is used, ``*`` can be used to disable the
+ strict check on a per-value basis. It must appear inside an array
+ or object as the last format character before the closing bracket
+ or brace.
+
+The following functions compose the parsing and validation API:
+
+.. function:: int json_unpack(json_t *root, const char *fmt, ...)
+
+ Validate and unpack the JSON value *root* according to the format
+ string *fmt*. Returns 0 on success and -1 on failure.
+
+.. function:: int json_unpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, ...)
+ int json_vunpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, va_list ap)
+
+ Validate and unpack the JSON value *root* according to the format
+ string *fmt*. If an error occurs and *error* is not *NULL*, write
+ error information to *error*. *flags* can be used to control the
+ behaviour of the unpacker, see below for the flags. Returns 0 on
+ success and -1 on failure.
+
+The following unpacking flags are available:
+
+``JSON_STRICT``
+ Enable the extra validation step checking that all object and
+ array items are unpacked. This is equivalent to appending the
+ format character ``!`` to the end of every array and object in the
+ format string.
+
+``JSON_VALIDATE_ONLY``
+ Don't extract any data, just validate the JSON value against the
+ given format string. Note that object keys must still be specified
+ after the format string.
+
+Examples::
+
+ /* root is the JSON integer 42 */
+ int myint;
+ json_unpack(root, "i", &myint);
+ assert(myint == 42);
+
+ /* root is the JSON object {"foo": "bar", "quux": true} */
+ const char *str;
+ int boolean;
+ json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
+ assert(strcmp(str, "bar") == 0 && boolean == 1);
+
+ /* root is the JSON array [[1, 2], {"baz": null} */
+ json_error_t error;
+ json_unpack_ex(root, &error, JSON_VALIDATE_ONLY, "[[i,i], {s:n}]", "baz");
+ /* returns 0 for validation success, nothing is extracted */
+
+ /* root is the JSON array [1, 2, 3, 4, 5] */
+ int myint1, myint2;
+ json_unpack(root, "[ii!]", &myint1, &myint2);
+ /* returns -1 for failed validation */
Equality
.. refcounting:: new
Returns a deep copy of *value*, or *NULL* on error.
+
+
+Custom Memory Allocation
+========================
+
+By default, Jansson uses :func:`malloc()` and :func:`free()` for
+memory allocation. These functions can be overridden if custom
+behavior is needed.
+
+.. type:: json_malloc_t
+
+ A typedef for a function pointer with :func:`malloc()`'s
+ signature::
+
+ typedef void *(*json_malloc_t)(size_t);
+
+.. type:: json_free_t
+
+ A typedef for a function pointer with :func:`free()`'s
+ signature::
+
+ typedef void (*json_free_t)(void *);
+
+.. function:: void json_set_alloc_funcs(json_malloc_t malloc_fn, json_free_t free_fn)
+
+ Use *malloc_fn* instead of :func:`malloc()` and *free_fn* instead
+ of :func:`free()`. This function has to be called before any other
+ Jansson's API functions to ensure that all memory operations use
+ the same functions.
+
+Examples:
+
+Use the `Boehm's conservative garbage collector`_ for memory
+operations::
+
+ json_set_alloc_funcs(GC_malloc, GC_free);
+
+.. _Boehm's conservative garbage collector: http://www.hpl.hp.com/personal/Hans_Boehm/gc/
+
+Allow storing sensitive data (e.g. passwords or encryption keys) in
+JSON structures by zeroing all memory when freed::
+
+ static void *secure_malloc(size_t size)
+ {
+ /* Store the memory area size in the beginning of the block */
+ void *ptr = malloc(size + 8);
+ *((size_t *)ptr) = size;
+ return ptr + 8;
+ }
+
+ static void secure_free(void *ptr)
+ {
+ size_t size;
+
+ ptr -= 8;
+ size = *((size_t *)ptr);
+
+ guaranteed_memset(ptr, 0, size);
+ free(ptr);
+ }
+
+ int main()
+ {
+ json_set_alloc_funcs(secure_malloc, secure_free);
+ /* ... */
+ }
+
+For more information about the issues of storing sensitive data in
+memory, see
+http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/protect-secrets.html.
+The page also examplains the :func:`guaranteed_memset()` function used
+in the example and gives a sample implementation for it.
projects / jansson.git / blobdiff