# Protocol Data Types

## List of Possible Types

Unknown type:

|                                         |                          |
| --------------------------------------- | ------------------------ |
| [byte<1>](#fixed-length-bytes)          | Fixed-length bytes       |
| [byte\<lenenc>](#length-encoded-bytes)  | Length-encoded bytes     |
| [byte\<EOF>](#end-of-file-length-bytes) | End-of-file length bytes |

Integer type:

|                                          |                         |
| ---------------------------------------- | ----------------------- |
| [int<1>](#fixed-length-integers)         | Fixed-length integers   |
| [int\<lenenc>](#length-encoded-integers) | Length-encoded integers |

String type:

|                                             |                            |
| ------------------------------------------- | -------------------------- |
| [string\<fix>](#fixed-length-strings)       | Fixed-length strings       |
| [string\<NUL>](#null-terminated-strings)    | Null-terminated strings    |
| [string\<lenenc>](#length-encoded-strings)  | Length-encoded strings     |
| [string\<EOF>](#end-of-file-length-strings) | End-of-file length strings |

### Fixed-Length Bytes

The notation is `byte`*`<n>`*, where *`<n>`* is a positive integer. A fixed-length byte stores the value in a series of `n` bytes.

### Length-Encoded Bytes

The notation is `byte<lenenc>`. Length-encoded bytes are prefixed by a length-encoded integer which describes the length of the byte value, followed by the bytes value.

### End of File Length Bytes

The notation is `byte<EOF>`. Bytes whose length is calculated by the packet remaining length.

### Fixed-Length Integers

Notation is `int`*`<n>`*, where *`<n>`* is a positive integer. A fixed-length integer stores the value in a series of `n` bytes. The least significant byte is always the first byte (little-endian format).

#### Example

An `int<4>` with value of `2` is stored as `02 00 00 00` .

### Length-Encoded Integers

The notation is `int<lenenc>`. An integer which depending on its value is represented by `n` bytes.

The first byte represents the size of the integer, depending on the value of the first byte:

* < `0xFB` - Integer value is this a 1-byte integer
* `0xFB` - `NULL` value
* `0xFC` - Integer value is encoded in the next 2 bytes (3 bytes total)
* `0xFD` - Integer value is encoded in the next 3 bytes (4 bytes total)
* `0xFE` - Integer value is encoded in the next 8 bytes (9 bytes total)

### Fixed-Length Strings

The notation is `string<fix>`. Fixed-length strings have a known hardcoded length.

### Null-Terminated Strings

The notation is `string<NUL>`. Null-terminated strings have a variable size and are terminated by a `0x00` character.

### Length-Encoded Strings

The notation is `string<lenenc>`. Length-encoded strings are prefixed by a length-encoded integer which describes the length of the string, followed by the string value.

#### Example

An string of 512 "a" is encoded in 515 bytes:

{% code overflow="wrap" %}

```
fc 00 02 97 97 97 97 97 97 97 97 97 97 97 97 97	² .. a a a a a a a a a a a a a
```

{% endcode %}

The `NULL` value is encoded using null (`0xfb`) length.

An empty value is encoded with a 0 (`0x00`) length.

### End of File Length Strings

The notation is `string<EOF>`.

Strings whose length is calculated by the packet remaining length. For an example, see the [COM\_STMT\_PREPARE](/docs/server/reference/clientserver-protocol/3-binary-protocol-prepared-statements/com_stmt_prepare.md) packet.

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