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features/binary_formats/cbor/index.md
+30
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@@ -124,6 +124,36 @@ Output:
0xa2 0x67 0x63 0x6f 0x6d 0x70 0x61 0x63 0x74 0xf5 0x66 0x73 0x63 0x68 0x65 0x6d 0x61 0x00
```
### Byte layout
Consider the following JSON value (shown formatted for readability):
```
{
"id": 300,
"name": "json",
"pi": 3.14,
"tags": [
"a",
"b"
]
}
```
`to_cbor` encodes it to 39 bytes (shown in hexadecimal; the encoding contains no whitespace). The colors mark the role of each byte: type/marker length/count/size data.
| JSON | Bytes | Meaning |
| ----------------- | ----------------------------------- | -------------------------------------------------------------------------------------------------------- |
| `{` | A4 | map with 4 key/value pairs |
| `"id": 300,` | 62 69 64 19 01 2C | key: text string of length 2, then its UTF-8 bytes; value: unsigned integer, 2 bytes follow (big-endian) |
| `"name": "json",` | 64 6E 61 6D 65 64 6A 73 6F 6E | key: text string of length 4; value: text string of length 4 |
| `"pi": 3.14,` | 62 70 69 FB 40 09 1E B8 51 EB 85 1F | key: text string of length 2; value: double-precision float (IEEE 754, big-endian) |
| `"tags": [` | 64 74 61 67 73 82 | key: text string of length 4; value: array with 2 elements |
| `"a",` | 61 61 | text string of length 1 |
| `"b"` | 61 62 | text string of length 1 |
| `]` | | no end marker: the element count was given up front |
| `}` | | no end marker: the member count was given up front |
## Deserialization
The library maps CBOR types to JSON value types as follows: