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// Package pktline implements reading payloads form pkt-lines and encoding
// pkt-lines from payloads.
package pktline
import (
"bytes"
"errors"
"fmt"
"io"
)
// An Encoder writes pkt-lines to an output stream.
type Encoder struct {
w io.Writer
}
const (
// MaxPayloadSize is the maximum payload size of a pkt-line in bytes.
MaxPayloadSize = 65516
)
var (
// FlushPkt are the contents of a flush-pkt pkt-line.
FlushPkt = []byte{'0', '0', '0', '0'}
// Flush is the payload to use with the Encode method to encode a flush-pkt.
Flush = []byte{}
// FlushString is the payload to use with the EncodeString method to encode a flush-pkt.
FlushString = ""
// ErrPayloadTooLong is returned by the Encode methods when any of the
// provided payloads is bigger than MaxPayloadSize.
ErrPayloadTooLong = errors.New("payload is too long")
)
// NewEncoder returns a new encoder that writes to w.
func NewEncoder(w io.Writer) *Encoder {
return &Encoder{
w: w,
}
}
// Flush encodes a flush-pkt to the output stream.
func (e *Encoder) Flush() error {
_, err := e.w.Write(FlushPkt)
return err
}
// Encode encodes a pkt-line with the payload specified and write it to
// the output stream. If several payloads are specified, each of them
// will get streamed in their own pkt-lines.
func (e *Encoder) Encode(payloads ...[]byte) error {
for _, p := range payloads {
if err := e.encodeLine(p); err != nil {
return err
}
}
return nil
}
func (e *Encoder) encodeLine(p []byte) error {
if len(p) > MaxPayloadSize {
return ErrPayloadTooLong
}
if bytes.Equal(p, Flush) {
return e.Flush()
}
n := len(p) + 4
if _, err := e.w.Write(asciiHex16(n)); err != nil {
return err
}
_, err := e.w.Write(p)
return err
}
// Returns the hexadecimal ascii representation of the 16 less
// significant bits of n. The length of the returned slice will always
// be 4. Example: if n is 1234 (0x4d2), the return value will be
// []byte{'0', '4', 'd', '2'}.
func asciiHex16(n int) []byte {
var ret [4]byte
ret[0] = byteToASCIIHex(byte(n & 0xf000 >> 12))
ret[1] = byteToASCIIHex(byte(n & 0x0f00 >> 8))
ret[2] = byteToASCIIHex(byte(n & 0x00f0 >> 4))
ret[3] = byteToASCIIHex(byte(n & 0x000f))
return ret[:]
}
// turns a byte into its hexadecimal ascii representation. Example:
// from 11 (0xb) to 'b'.
func byteToASCIIHex(n byte) byte {
if n < 10 {
return '0' + n
}
return 'a' - 10 + n
}
// EncodeString works similarly as Encode but payloads are specified as strings.
func (e *Encoder) EncodeString(payloads ...string) error {
for _, p := range payloads {
if err := e.Encode([]byte(p)); err != nil {
return err
}
}
return nil
}
// Encodef encodes a single pkt-line with the payload formatted as
// the format specifier. The rest of the arguments will be used in
// the format string.
func (e *Encoder) Encodef(format string, a ...interface{}) error {
return e.EncodeString(
fmt.Sprintf(format, a...),
)
}
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