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<h1 id="json">JSON</h1>
<p>JSON is a data interchange format. The description of this format can be found from IETF RFC 4627.</p>
<h2 id="description">Description</h2>
<p>This package helps in converting between C data types and JSON data objects. It supports both encoding and decoding.</p>
<h2 id="data-structures">Data structures</h2>
<h3 id="encoding">Encoding</h3>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #177500">/* Encoding functions */</span>
<span style="color: #A90D91">typedef</span> <span style="color: #A90D91">int</span> (<span style="color: #000000">*json_write_func_t</span>)(<span style="color: #A90D91">void</span> <span style="color: #000000">*buf</span>, <span style="color: #A90D91">char</span> <span style="color: #000000">*data</span>,
<span style="color: #A90D91">int</span> <span style="color: #000000">len</span>);
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_encoder</span> {
<span style="color: #000000">json_write_func_t</span> <span style="color: #000000">je_write</span>;
<span style="color: #A90D91">void</span> <span style="color: #000000">*je_arg</span>;
<span style="color: #A90D91">int</span> <span style="color: #000000">je_wr_commas:</span><span style="color: #1C01CE">1</span>;
<span style="color: #A90D91">char</span> <span style="color: #000000">je_encode_buf</span>[<span style="color: #1C01CE">64</span>];
};
</code></pre></div>
<p>Here's the data structure encoder funtions use, and it must be initialized by the caller. The key element is <em>je_write</em>, which is a function pointer which gets called whenever encoding routine is ready with encoded data. The element <em>je_arg</em> is passed to <em>je_write</em> as the first argument. The rest of the structure contents are for internal state management.
This function should collect all the data encoder function generates. It can collect this data to a flat buffer, chain of mbufs or even stream through.</p>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #177500">/**</span>
<span style="color: #177500"> * For encode. The contents of a JSON value to encode.</span>
<span style="color: #177500"> */</span>
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_value</span> {
<span style="color: #A90D91">uint8_t</span> <span style="color: #000000">jv_pad1</span>;
<span style="color: #A90D91">uint8_t</span> <span style="color: #000000">jv_type</span>;
<span style="color: #A90D91">uint16_t</span> <span style="color: #000000">jv_len</span>;
<span style="color: #A90D91">union</span> {
<span style="color: #A90D91">uint64_t</span> <span style="color: #000000">u</span>;
<span style="color: #A90D91">float</span> <span style="color: #000000">fl</span>;
<span style="color: #A90D91">char</span> <span style="color: #000000">*str</span>;
<span style="color: #A90D91">struct</span> {
<span style="color: #A90D91">char</span> <span style="color: #000000">**keys</span>;
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_value</span> <span style="color: #000000">**values</span>;
} <span style="color: #000000">composite</span>;
} <span style="color: #000000">jv_val</span>;
};
</code></pre></div>
<p>This data structure is filled with data to be encoded. It is best to fill this using the macros <em>JSON_VALUE_STRING()</em> or <em>JSON_VALUE_STRINGN()</em> when value is string, <em>JSON_VALUE_INT()</em> when value is an integer, and so forth.</p>
<h3 id="decoding">Decoding</h3>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #177500">/* when you implement a json buffer, you must implement these functions */</span>
<span style="color: #177500">/* returns the next character in the buffer or &#39;\0&#39;*/</span>
<span style="color: #A90D91">typedef</span> <span style="color: #A90D91">char</span> (<span style="color: #000000">*json_buffer_read_next_byte_t</span>)(<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_buffer</span> <span style="color: #000000">*</span>);
<span style="color: #177500">/* returns the previous character in the buffer or &#39;\0&#39; */</span>
<span style="color: #A90D91">typedef</span> <span style="color: #A90D91">char</span> (<span style="color: #000000">*json_buffer_read_prev_byte_t</span>)(<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_buffer</span> <span style="color: #000000">*</span>);
<span style="color: #177500">/* returns the number of characters read or zero */</span>
<span style="color: #A90D91">typedef</span> <span style="color: #A90D91">int</span> (<span style="color: #000000">*json_buffer_readn_t</span>)(<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_buffer</span> <span style="color: #000000">*</span>, <span style="color: #A90D91">char</span> <span style="color: #000000">*buf</span>, <span style="color: #A90D91">int</span> <span style="color: #000000">n</span>);
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_buffer</span> {
<span style="color: #000000">json_buffer_readn_t</span> <span style="color: #000000">jb_readn</span>;
<span style="color: #000000">json_buffer_read_next_byte_t</span> <span style="color: #000000">jb_read_next</span>;
<span style="color: #000000">json_buffer_read_prev_byte_t</span> <span style="color: #000000">jb_read_prev</span>;
};
</code></pre></div>
<p>Function pointers within this structure are used by decoder when it is reading in more data to decode.</p>
<div class="codehilite" style="background: #ffffff"><pre style="line-height: 125%;"><span></span><code><span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_attr_t</span> {
<span style="color: #A90D91">char</span> <span style="color: #000000">*attribute</span>;
<span style="color: #000000">json_type</span> <span style="color: #000000">type</span>;
<span style="color: #A90D91">union</span> {
<span style="color: #A90D91">int</span> <span style="color: #000000">*integer</span>;
<span style="color: #A90D91">unsigned</span> <span style="color: #A90D91">int</span> <span style="color: #000000">*uinteger</span>;
<span style="color: #A90D91">double</span> <span style="color: #000000">*real</span>;
<span style="color: #A90D91">char</span> <span style="color: #000000">*string</span>;
<span style="color: #A90D91">bool</span> <span style="color: #000000">*boolean</span>;
<span style="color: #A90D91">char</span> <span style="color: #000000">*character</span>;
<span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_array_t</span> <span style="color: #000000">array</span>;
<span style="color: #A90D91">size_t</span> <span style="color: #000000">offset</span>;
} <span style="color: #000000">addr</span>;
<span style="color: #A90D91">union</span> {
<span style="color: #A90D91">int</span> <span style="color: #000000">integer</span>;
<span style="color: #A90D91">unsigned</span> <span style="color: #A90D91">int</span> <span style="color: #000000">uinteger</span>;
<span style="color: #A90D91">double</span> <span style="color: #000000">real</span>;
<span style="color: #A90D91">bool</span> <span style="color: #000000">boolean</span>;
<span style="color: #A90D91">char</span> <span style="color: #000000">character</span>;
<span style="color: #A90D91">char</span> <span style="color: #000000">*check</span>;
} <span style="color: #000000">dflt</span>;
<span style="color: #A90D91">size_t</span> <span style="color: #000000">len</span>;
<span style="color: #A90D91">const</span> <span style="color: #A90D91">struct</span> <span style="color: #3F6E75">json_enum_t</span> <span style="color: #000000">*map</span>;
<span style="color: #A90D91">bool</span> <span style="color: #000000">nodefault</span>;
};
</code></pre></div>
<p>This structure tells the decoder about a particular name/value pair. Structure must be filled in before calling the decoder routine <em>json_read_object()</em>.</p>
<table>
<thead>
<tr>
<th>Element</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>attribute</td>
<td>Name of the value</td>
</tr>
<tr>
<td>type</td>
<td>The type of the variable; see enum json_type</td>
</tr>
<tr>
<td>addr</td>
<td>Contains the address where value should be stored</td>
</tr>
<tr>
<td>dflt</td>
<td>Default value to fill in, if this name is not found</td>
</tr>
<tr>
<td>len</td>
<td>Max number of bytes to read in for value</td>
</tr>
<tr>
<td>nodefault</td>
<td>If set, default value is not copied name</td>
</tr>
</tbody>
</table>
<h2 id="list-of-functions">List of Functions</h2>
<p>Functions for encoding:</p>
<table>
<thead>
<tr>
<th>Function</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><a href="../json_encode_object_start/">json_encode_object_start</a></td>
<td>This function starts the encoded JSON object.</td>
</tr>
<tr>
<td><a href="../json_encode_object_key/">json_encode_object_key</a></td>
<td>This function writes out a name for a field, followed by ":" character.</td>
</tr>
<tr>
<td><a href="../json_encode_object_entry/">json_encode_object_entry</a></td>
<td>This function writes out a name for a field, followed by ":" character, and the value itself.</td>
</tr>
<tr>
<td><a href="../json_encode_object_finish/">json_encode_object_finish</a></td>
<td>This function finalizes the encoded JSON object.</td>
</tr>
</tbody>
</table>
<p>Functions for decoding:</p>
<table>
<thead>
<tr>
<th>Function</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><a href="../json_read_object/">json_read_object</a></td>
<td>This function reads in JSON data stream, while looking for name/value pairs described in given attribites.</td>
</tr>
</tbody>
</table>
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