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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"
)
// Encoder provides EventStream message encoding.
type Encoder struct {
w io.Writer
logger aws.Logger
headersBuf *bytes.Buffer
}
// NewEncoder initializes and returns an Encoder to encode Event Stream
// messages to an io.Writer.
func NewEncoder(w io.Writer, opts ...func(*Encoder)) *Encoder {
e := &Encoder{
w: w,
headersBuf: bytes.NewBuffer(nil),
}
for _, opt := range opts {
opt(e)
}
return e
}
// EncodeWithLogger adds a logger to be used by the encode when decoding
// stream events.
func EncodeWithLogger(logger aws.Logger) func(*Encoder) {
return func(d *Encoder) {
d.logger = logger
}
}
// Encode encodes a single EventStream message to the io.Writer the Encoder
// was created with. An error is returned if writing the message fails.
func (e *Encoder) Encode(msg Message) (err error) {
e.headersBuf.Reset()
writer := e.w
if e.logger != nil {
encodeMsgBuf := bytes.NewBuffer(nil)
writer = io.MultiWriter(writer, encodeMsgBuf)
defer func() {
logMessageEncode(e.logger, encodeMsgBuf, msg, err)
}()
}
if err = EncodeHeaders(e.headersBuf, msg.Headers); err != nil {
return err
}
crc := crc32.New(crc32IEEETable)
hashWriter := io.MultiWriter(writer, crc)
headersLen := uint32(e.headersBuf.Len())
payloadLen := uint32(len(msg.Payload))
if err = encodePrelude(hashWriter, crc, headersLen, payloadLen); err != nil {
return err
}
if headersLen > 0 {
if _, err = io.Copy(hashWriter, e.headersBuf); err != nil {
return err
}
}
if payloadLen > 0 {
if _, err = hashWriter.Write(msg.Payload); err != nil {
return err
}
}
msgCRC := crc.Sum32()
return binary.Write(writer, binary.BigEndian, msgCRC)
}
func logMessageEncode(logger aws.Logger, msgBuf *bytes.Buffer, msg Message, encodeErr error) {
w := bytes.NewBuffer(nil)
defer func() { logger.Log(w.String()) }()
fmt.Fprintf(w, "Message to encode:\n")
encoder := json.NewEncoder(w)
if err := encoder.Encode(msg); err != nil {
fmt.Fprintf(w, "Failed to get encoded message, %v\n", err)
}
if encodeErr != nil {
fmt.Fprintf(w, "Encode error: %v\n", encodeErr)
return
}
fmt.Fprintf(w, "Raw message:\n%s\n", hex.Dump(msgBuf.Bytes()))
}
func encodePrelude(w io.Writer, crc hash.Hash32, headersLen, payloadLen uint32) error {
p := messagePrelude{
Length: minMsgLen + headersLen + payloadLen,
HeadersLen: headersLen,
}
if err := p.ValidateLens(); err != nil {
return err
}
err := binaryWriteFields(w, binary.BigEndian,
p.Length,
p.HeadersLen,
)
if err != nil {
return err
}
p.PreludeCRC = crc.Sum32()
err = binary.Write(w, binary.BigEndian, p.PreludeCRC)
if err != nil {
return err
}
return nil
}
// EncodeHeaders writes the header values to the writer encoded in the event
// stream format. Returns an error if a header fails to encode.
func EncodeHeaders(w io.Writer, headers Headers) error {
for _, h := range headers {
hn := headerName{
Len: uint8(len(h.Name)),
}
copy(hn.Name[:hn.Len], h.Name)
if err := hn.encode(w); err != nil {
return err
}
if err := h.Value.encode(w); err != nil {
return err
}
}
return nil
}
func binaryWriteFields(w io.Writer, order binary.ByteOrder, vs ...interface{}) error {
for _, v := range vs {
if err := binary.Write(w, order, v); err != nil {
return err
}
}
return nil
}
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