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opack.go
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opack.go
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package opack
import (
"bytes"
"fmt"
"io"
)
func Encode(m map[string]interface{}) ([]byte, error) {
buf := bytes.NewBuffer(nil)
err := encodeDict(buf, m)
if err != nil {
return nil, err
}
return buf.Bytes(), nil
}
func encodeDict(w io.Writer, d map[string]interface{}) error {
l := len(d)
if l > 0xF {
return fmt.Errorf("%d exceeds max size of 0xF", l)
}
b := 0xE0 | uint8(l)
_, err := w.Write([]byte{b})
if err != nil {
return err
}
for k, e := range d {
err := encodeString(w, k)
if err != nil {
return err
}
switch t := e.(type) {
case string:
err := encodeString(w, e.(string))
if err != nil {
return err
}
case []byte:
err := encodeData(w, e.([]byte))
if err != nil {
return err
}
default:
return fmt.Errorf("can't encode type %s", t)
}
}
return nil
}
func encodeString(w io.Writer, s string) error {
err := writeLengthBasedIdentifier(w, 0x40, len(s))
if err != nil {
return err
}
_, err = w.Write([]byte(s))
return err
}
func encodeData(w io.Writer, b []byte) error {
err := writeLengthBasedIdentifier(w, 0x70, len(b))
if err != nil {
return err
}
_, err = w.Write(b)
return err
}
func createIdentifierWithLength(t byte, l int) ([]byte, error) {
if l <= 0xF {
return []byte{t | byte(l)}, nil
} else if l < 0x20 {
inc := t + (1 << 4)
return []byte{inc | (byte(l) & 0xF)}, nil
} else if l <= 0xFF {
inc := (t + (2 << 4)) | 0x1
return []byte{inc, byte(l)}, nil
} else {
return nil, fmt.Errorf("string too long: %d", l)
}
}
func writeLengthBasedIdentifier(w io.Writer, t byte, l int) error {
id, err := createIdentifierWithLength(t, l)
if err != nil {
return err
}
_, err = w.Write(id)
return err
}