Basics | ClickHouse Docs

This document describes binary protocol for ClickHouse TCP clients.

Varint

For lengths, packet codes and other cases the unsigned varint encoding is used. Use binary.PutUvarint and binary.ReadUvarint.

String

Variable length strings are encoded as (length, value), where length is varint and value is utf8 string.

s := "Hello, world!"

// Writing string length as uvarint.
buf := make([]byte, binary.MaxVarintLen64)
n := binary.PutUvarint(buf, uint64(len(s)))
buf = buf[:n]

// Writing string value.
buf = append(buf, s...)

r := bytes.NewReader([]byte{
    0xd, 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x2c,
    0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x21,
})

// Read length.
n, err := binary.ReadUvarint(r)
if err != nil {
        panic(err)
}

// Check n to prevent OOM or runtime exception in make().
const maxSize = 1024 * 1024 * 10 // 10 MB
if n > maxSize || n < 0 {
    panic("invalid n")
}

buf := make([]byte, n)
if _, err := io.ReadFull(r, buf); err != nil {
        panic(err)
}

fmt.Println(string(buf))
// Hello, world!

00000000  0d 48 65 6c 6c 6f 2c 20  77 6f 72 6c 64 21        |.Hello, world!|

DUhlbGxvLCB3b3JsZCE

data := []byte{
    0xd, 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x2c,
    0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x21,
}

Integers

Int32

v := int32(1000)

// Encode.
buf := make([]byte, 8)
binary.LittleEndian.PutUint32(buf, uint32(v))

// Decode.
d := int32(binary.LittleEndian.Uint32(buf))
fmt.Println(d) // 1000

00000000  e8 03 00 00 00 00 00 00                           |........|

6AMAAAAAAAA

Boolean

Booleans are represented by single byte, 1 is true and 0 is false.