Basics

note

Client protocol reference is in progress.

Most examples are only in Go.

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.

note

Signed varint is not used.

String

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

info

Validate length to prevent OOM:

0 ≤ len < MAX

Encode

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...)

Decode

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!

Hex dump

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

Base64

DUhlbGxvLCB3b3JsZCE

Go

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

Integers

tip

ClickHouse uses Little Endian for fixed size 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

Hex dump

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

Base64

6AMAAAAAAAA

Boolean

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