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authorLorry Tar Creator <lorry-tar-importer@baserock.org>2014-12-02 09:01:21 +0000
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+
+JSMN
+====
+
+jsmn (pronounced like 'jasmine') is a minimalistic JSON parser in C. It can be
+easily integrated into resource-limited or embedded projects.
+
+You can find more information about JSON format at [json.org][1]
+
+Library sources are available at [bitbucket.org/zserge/jsmn][2]
+
+The web page with some information about jsmn can be found at
+[http://zserge.com/jsmn.html][3]
+
+Philosophy
+----------
+
+Most JSON parsers offer you a bunch of functions to load JSON data, parse it
+and extract any value by its name. jsmn proves that checking the correctness of
+every JSON packet or allocating temporary objects to store parsed JSON fields
+often is an overkill.
+
+JSON format itself is extremely simple, so why should we complicate it?
+
+jsmn is designed to be **robust** (it should work fine even with erroneous
+data), **fast** (it should parse data on the fly), **portable** (no superfluous
+dependencies or non-standard C extensions). An of course, **simplicity** is a
+key feature - simple code style, simple algorithm, simple integration into
+other projects.
+
+Features
+--------
+
+* compatible with C89
+* no dependencies (even libc!)
+* highly portable (tested on x86/amd64, ARM, AVR)
+* about 200 lines of code
+* extremely small code footprint
+* API contains only 2 functions
+* no dynamic memory allocation
+* incremental single-pass parsing
+* library code is covered with unit-tests
+
+Design
+------
+
+The rudimentary jsmn object is a **token**. Let's consider a JSON string:
+
+ '{ "name" : "Jack", "age" : 27 }'
+
+It holds the following tokens:
+
+* Object: `{ "name" : "Jack", "age" : 27}` (the whole object)
+* Strings: `"name"`, `"Jack"`, `"age"` (keys and some values)
+* Number: `27`
+
+In jsmn, tokens do not hold any data, but point to token boundaries in JSON
+string instead. In the example above jsmn will create tokens like: Object
+[0..31], String [3..7], String [12..16], String [20..23], Number [27..29].
+
+Every jsmn token has a type, which indicates the type of corresponding JSON
+token. jsmn supports the following token types:
+
+* Object - a container of key-value pairs, e.g.:
+ `{ "foo":"bar", "x":0.3 }`
+* Array - a sequence of values, e.g.:
+ `[ 1, 2, 3 ]`
+* String - a quoted sequence of chars, e.g.: `"foo"`
+* Primitive - a number, a boolean (`true`, `false`) or `null`
+
+Besides start/end positions, jsmn tokens for complex types (like arrays
+or objects) also contain a number of child items, so you can easily follow
+object hierarchy.
+
+This approach provides enough information for parsing any JSON data and makes
+it possible to use zero-copy techniques.
+
+Install
+-------
+
+To clone the repository you should have mercurial installed. Just run:
+
+ $ hg clone http://bitbucket.org/zserge/jsmn jsmn
+
+Repository layout is simple: jsmn.c and jsmn.h are library files; demo.c is an
+example of how to use jsmn (it is also used in unit tests); test.sh is a test
+script. You will also find README, LICENSE and Makefile files inside.
+
+To build the library, run `make`. It is also recommended to run `make test`.
+Let me know, if some tests fail.
+
+If build was successful, you should get a `libjsmn.a` library.
+The header file you should include is called `"jsmn.h"`.
+
+API
+---
+
+Token types are described by `jsmntype_t`:
+
+ typedef enum {
+ JSMN_PRIMITIVE = 0,
+ JSMN_OBJECT = 1,
+ JSMN_ARRAY = 2,
+ JSMN_STRING = 3
+ } jsmntype_t;
+
+**Note:** Unlike JSON data types, primitive tokens are not divided into
+numbers, booleans and null, because one can easily tell the type using the
+first character:
+
+* <code>'t', 'f'</code> - boolean
+* <code>'n'</code> - null
+* <code>'-', '0'..'9'</code> - number
+
+Token is an object of `jsmntok_t` type:
+
+ typedef struct {
+ jsmntype_t type; // Token type
+ int start; // Token start position
+ int end; // Token end position
+ int size; // Number of child (nested) tokens
+ } jsmntok_t;
+
+**Note:** string tokens point to the first character after
+the opening quote and the previous symbol before final quote. This was made
+to simplify string extraction from JSON data.
+
+All job is done by `jsmn_parser` object. You can initialize a new parser using:
+
+ struct jsmn_parser parser;
+ jsmntok_t tokens[10];
+
+ // js - pointer to JSON string
+ // tokens - an array of tokens available
+ // 10 - number of tokens available
+ jsmn_init_parser(&parser, js, tokens, 10);
+
+This will create a parser, that can parse up to 10 JSON tokens from `js` string.
+
+Later, you can use `jsmn_parse(&parser)` function to process JSON string with the parser.
+If something goes wrong, you will get an error. Error will be one of these:
+
+* `JSMN_SUCCESS` - everything went fine. String was parsed
+* `JSMN_ERROR_INVAL` - bad token, JSON string is corrupted
+* `JSMN_ERROR_NOMEM` - not enough tokens, JSON string is too large
+* `JSMN_ERROR_PART` - JSON string is too short, expecting more JSON data
+
+If you get `JSON_ERROR_NOMEM`, you can re-allocate more tokens and call
+`jsmn_parse` once more. If you read json data from the stream, you can
+periodically call `jsmn_parse` and check if return value is `JSON_ERROR_PART`.
+You will get this error until you reach the end of JSON data.
+
+Other info
+----------
+
+This software is distributed under [MIT license](http://www.opensource.org/licenses/mit-license.php),
+ so feel free to integrate it in your commercial products.
+
+[1]: http://www.json.org/
+[2]: https://bitbucket.org/zserge/jsmn/wiki/Home
+[3]: http://zserge.com/jsmn.html