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features/binary_formats/messagepack.md
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@@ -114,6 +114,41 @@ specification:
```
### Byte layout
Consider the following JSON value (shown formatted for readability):
```json
{
"id": 300,
"name": "json",
"pi": 3.14,
"tags": [
"a",
"b"
]
}
```
`to_msgpack` encodes it to 39 bytes (shown in hexadecimal; the encoding contains no whitespace). The colors mark the role of each byte: <span class="bl bl-t">type/marker</span> <span class="bl bl-l">length/count/size</span> <span class="bl bl-d">data</span>.
<div class="byte-layout" markdown="0"><table>
<thead><tr><th>JSON</th><th>Bytes</th><th>Meaning</th></tr></thead><tbody>
<tr><td><code>{</code></td><td><span class="bl bl-t">84</span></td><td>map with 4 key/value pairs</td></tr>
<tr><td><code>&quot;id&quot;: 300,</code></td><td><span class="bl bl-t">A2</span> <span class="bl bl-d">69 64</span> <span class="bl bl-t">CD</span> <span class="bl bl-d">01 2C</span></td><td>key: fixstr of length 2, then its UTF-8 bytes; value: uint 16 (big-endian)</td></tr>
<tr><td><code>&quot;name&quot;: &quot;json&quot;,</code></td><td><span class="bl bl-t">A4</span> <span class="bl bl-d">6E 61 6D 65</span> <span class="bl bl-t">A4</span> <span class="bl bl-d">6A 73 6F 6E</span></td><td>key: fixstr of length 4; value: fixstr of length 4</td></tr>
<tr><td><code>&quot;pi&quot;: 3.14,</code></td><td><span class="bl bl-t">A2</span> <span class="bl bl-d">70 69</span> <span class="bl bl-t">CB</span> <span class="bl bl-d">40 09 1E B8 51 EB 85 1F</span></td><td>key: fixstr of length 2; value: float 64 (IEEE 754, big-endian)</td></tr>
<tr><td><code>&quot;tags&quot;: [</code></td><td><span class="bl bl-t">A4</span> <span class="bl bl-d">74 61 67 73</span> <span class="bl bl-t">92</span></td><td>key: fixstr of length 4; value: fixarray with 2 elements</td></tr>
<tr><td><code>&quot;a&quot;,</code></td><td><span class="bl bl-t">A1</span> <span class="bl bl-d">61</span></td><td>fixstr of length 1</td></tr>
<tr><td><code>&quot;b&quot;</code></td><td><span class="bl bl-t">A1</span> <span class="bl bl-d">62</span></td><td>fixstr of length 1</td></tr>
<tr><td><code>]</code></td><td></td><td>no end marker: the element count was given up front</td></tr>
<tr><td><code>}</code></td><td></td><td>no end marker: the member count was given up front</td></tr>
</tbody></table></div>
## Deserialization
The library maps MessagePack types to JSON value types as follows: