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