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codec.go
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codec.go
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package minq
import (
"bytes"
"fmt"
"io"
"reflect"
"runtime"
"strconv"
"strings"
"unicode"
)
const (
codecDefaultSize = ^uintptr(0)
)
func uintEncode(buf *bytes.Buffer, v reflect.Value, encodingSize uintptr) error {
size := v.Type().Size()
if encodingSize != codecDefaultSize {
if encodingSize > size {
return fmt.Errorf("Requested a length longer than the native type")
}
size = encodingSize
}
uintEncodeInt(buf, v.Uint(), size)
return nil
}
func uintEncodeInt(buf *bytes.Buffer, val uint64, size uintptr) {
// Now encode the low-order bytes of the value.
for b := size; b > 0; b -= 1 {
buf.WriteByte(byte(val >> ((b - 1) * 8)))
}
}
// isVarint determines if the field is a varint. This reads the mint/syntax tag
// for the field, but only supports a simple "varint".
func isVarint(f reflect.StructField) bool {
return f.Tag.Get("tls") == "varint"
}
func varintEncode(buf *bytes.Buffer, v uint64) {
switch {
case v < (uint64(1) << 6):
uintEncodeInt(buf, v, 1)
case v < (uint64(1) << 14):
uintEncodeInt(buf, v|(1<<14), 2)
case v < (uint64(1) << 30):
uintEncodeInt(buf, v|(2<<30), 4)
case v < (uint64(1) << 62):
uintEncodeInt(buf, v|(3<<62), 8)
default:
panic("varint value is too large")
}
}
func arrayEncode(buf *bytes.Buffer, v reflect.Value) error {
b := v.Bytes()
logf(logTypeCodec, "Encoding array length=%d", len(b))
buf.Write(b)
return nil
}
// Check to see if fields
func ignoreField(name string) bool {
return unicode.IsLower(rune(name[0]))
}
// Length specifications are of the form:
//
// lengthbits: "B:L1,L2,...LN
//
// where B is the rightmost bit of the length bits and
// L_n are the various lengths (in bytes) indicated by
// the bit values in sequence. N must be a power of 2
// and the right number of bytes is drawn to compute it.
type lengthSpec struct {
rightBit uint
numBits uint
values []int
}
func parseLengthSpecification(spec string) (*lengthSpec, error) {
spl := strings.Split(spec, ":")
assert(len(spl) == 2)
// Rightmost bit.
p, err := strconv.ParseUint(spl[0], 10, 8)
if err != nil {
return nil, err
}
bitr := uint(p)
vals := strings.Split(spl[1], ",")
// Figure out how many bits we need.
nvals := int(1)
var bits int
for bits = 1; bits <= 8; bits++ {
nvals <<= 1
if nvals == len(vals) {
break
}
}
assert(bits < 9)
// Now compute the values
valArr := make([]int, nvals)
for i, v := range vals {
valArr[i], err = strconv.Atoi(v)
if err != nil {
return nil, err
}
}
return &lengthSpec{
bitr,
uint(bits),
valArr,
}, nil
}
func computeLengthFromSpec(t byte, f reflect.StructField) uintptr {
st := f.Tag.Get("lengthbits")
if st == "" {
return codecDefaultSize
}
spec, err := parseLengthSpecification(st)
assert(err == nil)
mask := byte(0)
bit := uint(0)
for ; bit < spec.numBits; bit++ {
mask |= (1 << bit)
}
idx := int(t >> (spec.rightBit - 1) & mask)
return uintptr(spec.values[idx])
}
// Encode all the fields of a struct to a bytestring.
func encode(i interface{}) (ret []byte, err error) {
var buf bytes.Buffer
var res error
reflected := reflect.ValueOf(i).Elem()
fields := reflected.NumField()
for j := 0; j < fields; j += 1 {
field := reflected.Field(j)
tipe := reflected.Type().Field(j)
if ignoreField(tipe.Name) {
continue
}
logf(logTypeCodec, "Type name %s Kind=%v", tipe.Name, field.Kind())
switch field.Kind() {
case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
// Call the length overrider to tell us if we shoud be using a shorter
// encoding.
encodingSize := uintptr(codecDefaultSize)
lFunc, getLength := reflected.Type().MethodByName(tipe.Name + "__length")
logf(logTypeCodec, "Looking for length overrider for type %v", tipe.Name)
if getLength {
lengthResult := lFunc.Func.Call([]reflect.Value{reflect.ValueOf(i).Elem()})
encodingSize = uintptr(lengthResult[0].Uint())
logf(logTypeCodec, "Overriden length to %v", encodingSize)
}
if isVarint(tipe) {
if encodingSize != 0 {
varintEncode(&buf, field.Uint())
}
res = nil
break
}
res = uintEncode(&buf, field, encodingSize)
case reflect.Array, reflect.Slice:
res = arrayEncode(&buf, field)
default:
return nil, fmt.Errorf("Unknown type")
}
if res != nil {
return nil, res
}
}
ret = buf.Bytes()
logf(logTypeCodec, "Total encoded length = %v", len(ret))
return ret, nil
}
func uintDecodeIntBuf(val []byte) uint64 {
tmp := uint64(0)
for b := 0; b < len(val); b++ {
tmp = (tmp << 8) + uint64(val[b])
}
return tmp
}
func uintDecodeInt(r io.Reader, size uintptr) (uint64, error) {
val := make([]byte, size)
_, err := io.ReadFull(r, val)
if err != nil {
return 0, err
}
return uintDecodeIntBuf(val), nil
}
func uintDecode(r io.Reader, v reflect.Value, encodingSize uintptr) (uintptr, error) {
size := v.Type().Size()
if encodingSize != codecDefaultSize {
if encodingSize > size {
return 0, fmt.Errorf("Requested a length longer than the native type")
}
size = encodingSize
}
tmp, err := uintDecodeInt(r, size)
if err != nil {
return 0, err
}
v.SetUint(tmp)
return size, nil
}
func varintDecode(r io.Reader, v reflect.Value) (uintptr, error) {
p := make([]byte, 8)
_, err := r.Read(p[:1])
if err != nil {
return 0, err
}
value := uint64(p[0] & 0x3f)
extra := uintptr(1<<(p[0]>>6)) - 1
if extra > 0 {
tail, err := uintDecodeInt(r, extra)
if err != nil {
return 0, err
}
value = (value << (8 * extra)) | tail
}
v.SetUint(value)
return 1 + extra, nil
}
func encodeArgs(args ...interface{}) []byte {
var buf bytes.Buffer
var res error
for _, arg := range args {
reflected := reflect.ValueOf(arg)
switch reflected.Kind() {
case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
res = uintEncode(&buf, reflected, codecDefaultSize)
case reflect.Array, reflect.Slice:
res = arrayEncode(&buf, reflected)
default:
panic(fmt.Sprintf("Unknown type"))
}
if res != nil {
panic(fmt.Sprintf("Encoding error"))
}
}
return buf.Bytes()
}
func arrayDecode(r io.Reader, v reflect.Value, encodingSize uintptr) (uintptr, error) {
logf(logTypeCodec, "encodingSize = %v", encodingSize)
val := make([]byte, encodingSize)
logf(logTypeCodec, "Reading array of size %v", encodingSize)
// Go will return EOF if you try to read 0 bytes off a closed stream.
if encodingSize == 0 {
return 0, nil
}
_, err := io.ReadFull(r, val)
if err != nil {
return 0, err
}
v.SetBytes(val)
return encodingSize, nil
}
// Decode all the fields of a struct from a bytestring. Takes
// a pointer to the struct to fill in
func decode(i interface{}, data []byte) (uintptr, error) {
buf := bytes.NewReader(data)
var res error
reflected := reflect.ValueOf(i).Elem()
fields := reflected.NumField()
bytesread := uintptr(0)
for j := 0; j < fields; j++ {
br := uintptr(0)
field := reflected.Field(j)
tipe := reflected.Type().Field(j)
if ignoreField(tipe.Name) {
continue
}
// Call the length overrider to tell us if we should be using a shorter
// encoding.
encodingSize := uintptr(codecDefaultSize)
lFunc, getLength := reflected.Type().MethodByName(tipe.Name + "__length")
if getLength {
lengthResult := lFunc.Func.Call([]reflect.Value{reflect.ValueOf(i).Elem()})
encodingSize = uintptr(lengthResult[0].Uint())
logf(logTypeCodec, "Length overrider for %s returns %v", tipe.Name, encodingSize)
}
switch field.Kind() {
case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
if isVarint(tipe) && encodingSize != 0 {
br, res = varintDecode(buf, field)
} else {
br, res = uintDecode(buf, field, encodingSize)
}
case reflect.Array, reflect.Slice:
if encodingSize == codecDefaultSize {
encodingSize = uintptr(buf.Len())
}
br, res = arrayDecode(buf, field, encodingSize)
default:
return 0, fmt.Errorf("Unknown type")
}
if res != nil {
logf(logTypeCodec, "Error while reading field %v: %v", tipe.Name, res)
return bytesread, res
}
bytesread += br
}
return bytesread, nil
}
func backtrace() string {
bt := string("")
for i := 1; ; i++ {
_, file, line, ok := runtime.Caller(i)
if !ok {
break
}
bt = fmt.Sprintf("%v: %d\n", file, line) + bt
}
return bt
}