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|
package eventstream
import (
"bytes"
"encoding/binary"
"hash/crc32"
)
const preludeLen = 8
const preludeCRCLen = 4
const msgCRCLen = 4
const minMsgLen = preludeLen + preludeCRCLen + msgCRCLen
const maxPayloadLen = 1024 * 1024 * 16 // 16MB
const maxHeadersLen = 1024 * 128 // 128KB
const maxMsgLen = minMsgLen + maxHeadersLen + maxPayloadLen
var crc32IEEETable = crc32.MakeTable(crc32.IEEE)
// A Message provides the eventstream message representation.
type Message struct {
Headers Headers
Payload []byte
}
func (m *Message) rawMessage() (rawMessage, error) {
var raw rawMessage
if len(m.Headers) > 0 {
var headers bytes.Buffer
if err := encodeHeaders(&headers, m.Headers); err != nil {
return rawMessage{}, err
}
raw.Headers = headers.Bytes()
raw.HeadersLen = uint32(len(raw.Headers))
}
raw.Length = raw.HeadersLen + uint32(len(m.Payload)) + minMsgLen
hash := crc32.New(crc32IEEETable)
binaryWriteFields(hash, binary.BigEndian, raw.Length, raw.HeadersLen)
raw.PreludeCRC = hash.Sum32()
binaryWriteFields(hash, binary.BigEndian, raw.PreludeCRC)
if raw.HeadersLen > 0 {
hash.Write(raw.Headers)
}
// Read payload bytes and update hash for it as well.
if len(m.Payload) > 0 {
raw.Payload = m.Payload
hash.Write(raw.Payload)
}
raw.CRC = hash.Sum32()
return raw, nil
}
type messagePrelude struct {
Length uint32
HeadersLen uint32
PreludeCRC uint32
}
func (p messagePrelude) PayloadLen() uint32 {
return p.Length - p.HeadersLen - minMsgLen
}
func (p messagePrelude) ValidateLens() error {
if p.Length == 0 || p.Length > maxMsgLen {
return LengthError{
Part: "message prelude",
Want: maxMsgLen,
Have: int(p.Length),
}
}
if p.HeadersLen > maxHeadersLen {
return LengthError{
Part: "message headers",
Want: maxHeadersLen,
Have: int(p.HeadersLen),
}
}
if payloadLen := p.PayloadLen(); payloadLen > maxPayloadLen {
return LengthError{
Part: "message payload",
Want: maxPayloadLen,
Have: int(payloadLen),
}
}
return nil
}
type rawMessage struct {
messagePrelude
Headers []byte
Payload []byte
CRC uint32
}
|
