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package eventstream
import (
"bytes"
"encoding/binary"
"encoding/hex"
"encoding/json"
"fmt"
"hash"
"hash/crc32"
"io"
"github.com/aws/aws-sdk-go/aws"
)
// Decoder provides decoding of an Event Stream messages.
type Decoder struct {
r io.Reader
logger aws.Logger
}
// NewDecoder initializes and returns a Decoder for decoding event
// stream messages from the reader provided.
func NewDecoder(r io.Reader) *Decoder {
return &Decoder{
r: r,
}
}
// Decode attempts to decode a single message from the event stream reader.
// Will return the event stream message, or error if Decode fails to read
// the message from the stream.
func (d *Decoder) Decode(payloadBuf []byte) (m Message, err error) {
reader := d.r
if d.logger != nil {
debugMsgBuf := bytes.NewBuffer(nil)
reader = io.TeeReader(reader, debugMsgBuf)
defer func() {
logMessageDecode(d.logger, debugMsgBuf, m, err)
}()
}
crc := crc32.New(crc32IEEETable)
hashReader := io.TeeReader(reader, crc)
prelude, err := decodePrelude(hashReader, crc)
if err != nil {
return Message{}, err
}
if prelude.HeadersLen > 0 {
lr := io.LimitReader(hashReader, int64(prelude.HeadersLen))
m.Headers, err = decodeHeaders(lr)
if err != nil {
return Message{}, err
}
}
if payloadLen := prelude.PayloadLen(); payloadLen > 0 {
buf, err := decodePayload(payloadBuf, io.LimitReader(hashReader, int64(payloadLen)))
if err != nil {
return Message{}, err
}
m.Payload = buf
}
msgCRC := crc.Sum32()
if err := validateCRC(reader, msgCRC); err != nil {
return Message{}, err
}
return m, nil
}
// UseLogger specifies the Logger that that the decoder should use to log the
// message decode to.
func (d *Decoder) UseLogger(logger aws.Logger) {
d.logger = logger
}
func logMessageDecode(logger aws.Logger, msgBuf *bytes.Buffer, msg Message, decodeErr error) {
w := bytes.NewBuffer(nil)
defer func() { logger.Log(w.String()) }()
fmt.Fprintf(w, "Raw message:\n%s\n",
hex.Dump(msgBuf.Bytes()))
if decodeErr != nil {
fmt.Fprintf(w, "Decode error: %v\n", decodeErr)
return
}
rawMsg, err := msg.rawMessage()
if err != nil {
fmt.Fprintf(w, "failed to create raw message, %v\n", err)
return
}
decodedMsg := decodedMessage{
rawMessage: rawMsg,
Headers: decodedHeaders(msg.Headers),
}
fmt.Fprintf(w, "Decoded message:\n")
encoder := json.NewEncoder(w)
if err := encoder.Encode(decodedMsg); err != nil {
fmt.Fprintf(w, "failed to generate decoded message, %v\n", err)
}
}
func decodePrelude(r io.Reader, crc hash.Hash32) (messagePrelude, error) {
var p messagePrelude
var err error
p.Length, err = decodeUint32(r)
if err != nil {
return messagePrelude{}, err
}
p.HeadersLen, err = decodeUint32(r)
if err != nil {
return messagePrelude{}, err
}
if err := p.ValidateLens(); err != nil {
return messagePrelude{}, err
}
preludeCRC := crc.Sum32()
if err := validateCRC(r, preludeCRC); err != nil {
return messagePrelude{}, err
}
p.PreludeCRC = preludeCRC
return p, nil
}
func decodePayload(buf []byte, r io.Reader) ([]byte, error) {
w := bytes.NewBuffer(buf[0:0])
_, err := io.Copy(w, r)
return w.Bytes(), err
}
func decodeUint8(r io.Reader) (uint8, error) {
type byteReader interface {
ReadByte() (byte, error)
}
if br, ok := r.(byteReader); ok {
v, err := br.ReadByte()
return uint8(v), err
}
var b [1]byte
_, err := io.ReadFull(r, b[:])
return uint8(b[0]), err
}
func decodeUint16(r io.Reader) (uint16, error) {
var b [2]byte
bs := b[:]
_, err := io.ReadFull(r, bs)
if err != nil {
return 0, err
}
return binary.BigEndian.Uint16(bs), nil
}
func decodeUint32(r io.Reader) (uint32, error) {
var b [4]byte
bs := b[:]
_, err := io.ReadFull(r, bs)
if err != nil {
return 0, err
}
return binary.BigEndian.Uint32(bs), nil
}
func decodeUint64(r io.Reader) (uint64, error) {
var b [8]byte
bs := b[:]
_, err := io.ReadFull(r, bs)
if err != nil {
return 0, err
}
return binary.BigEndian.Uint64(bs), nil
}
func validateCRC(r io.Reader, expect uint32) error {
msgCRC, err := decodeUint32(r)
if err != nil {
return err
}
if msgCRC != expect {
return ChecksumError{}
}
return nil
}
|
