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// Package msgutil provides utility for JSON message with uint32le header
package msgutil
import (
"bytes"
"encoding/binary"
"encoding/json"
"fmt"
"io"
)
const (
maxLength = 1 << 16
)
func MarshalToWriter(w io.Writer, x interface{}) (int, error) {
b, err := json.Marshal(x)
if err != nil {
return 0, err
}
if len(b) > maxLength {
return 0, fmt.Errorf("bad message length: %d (max: %d)", len(b), maxLength)
}
h := make([]byte, 4)
binary.LittleEndian.PutUint32(h, uint32(len(b)))
return w.Write(append(h, b...))
}
func UnmarshalFromReader(r io.Reader, x interface{}) (int, error) {
hdr := make([]byte, 4)
n, err := r.Read(hdr)
if err != nil {
return n, err
}
if n != 4 {
return n, fmt.Errorf("read %d bytes, expected 4 bytes", n)
}
bLen := binary.LittleEndian.Uint32(hdr)
if bLen > maxLength || bLen < 1 {
return n, fmt.Errorf("bad message length: %d (max: %d)", bLen, maxLength)
}
b := make([]byte, bLen)
n, err = r.Read(b)
if err != nil {
return 4 + n, err
}
if n != int(bLen) {
return 4 + n, fmt.Errorf("read %d bytes, expected %d bytes", n, bLen)
}
return 4 + n, json.Unmarshal(b, x)
}
func Marshal(x interface{}) ([]byte, error) {
var b bytes.Buffer
_, err := MarshalToWriter(&b, x)
return b.Bytes(), err
}
func Unmarshal(b []byte, x interface{}) error {
n, err := UnmarshalFromReader(bytes.NewReader(b), x)
if n != len(b) {
return fmt.Errorf("read %d bytes, expected %d bytes", n, len(b))
}
return err
}
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