github.com/ltltlt/go-source-code@v0.0.0-20190830023027-95be009773aa/encoding/binary/binary.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package binary implements simple translation between numbers and byte
// sequences and encoding and decoding of varints.
//
// Numbers are translated by reading and writing fixed-size values.
// A fixed-size value is either a fixed-size arithmetic
// type (bool, int8, uint8, int16, float32, complex64, ...)
// or an array or struct containing only fixed-size values.
//
// The varint functions encode and decode single integer values using
// a variable-length encoding; smaller values require fewer bytes.
// For a specification, see
// https://developers.google.com/protocol-buffers/docs/encoding.
//
// This package favors simplicity over efficiency. Clients that require
// high-performance serialization, especially for large data structures,
// should look at more advanced solutions such as the encoding/gob
// package or protocol buffers.
package binary

import (
	"errors"
	"io"
	"math"
	"reflect"
)

// A ByteOrder specifies how to convert byte sequences into
// 16-, 32-, or 64-bit unsigned integers.
type ByteOrder interface {
	Uint16([]byte) uint16
	Uint32([]byte) uint32
	Uint64([]byte) uint64
	PutUint16([]byte, uint16)
	PutUint32([]byte, uint32)
	PutUint64([]byte, uint64)
	String() string
}

// LittleEndian is the little-endian implementation of ByteOrder.
var LittleEndian littleEndian

// BigEndian is the big-endian implementation of ByteOrder.
var BigEndian bigEndian

type littleEndian struct{}

func (littleEndian) Uint16(b []byte) uint16 {
	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
	return uint16(b[0]) | uint16(b[1])<<8
}

func (littleEndian) PutUint16(b []byte, v uint16) {
	_ = b[1] // early bounds check to guarantee safety of writes below
	b[0] = byte(v)
	b[1] = byte(v >> 8)
}

func (littleEndian) Uint32(b []byte) uint32 {
	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
}

func (littleEndian) PutUint32(b []byte, v uint32) {
	_ = b[3] // early bounds check to guarantee safety of writes below
	b[0] = byte(v)
	b[1] = byte(v >> 8)
	b[2] = byte(v >> 16)
	b[3] = byte(v >> 24)
}

func (littleEndian) Uint64(b []byte) uint64 {
	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
}

func (littleEndian) PutUint64(b []byte, v uint64) {
	// the assemblely this function generate will only do index check once(maybe because this is in standard library), but if you write you own PutUint64 function which acts exactly like this, it will do index check 9 times, which is inefficiently.
	// use `go tool objdump` to see assemblely code.
	_ = b[7] // early bounds check to guarantee safety of writes below
	b[0] = byte(v)
	b[1] = byte(v >> 8)
	b[2] = byte(v >> 16)
	b[3] = byte(v >> 24)
	b[4] = byte(v >> 32)
	b[5] = byte(v >> 40)
	b[6] = byte(v >> 48)
	b[7] = byte(v >> 56)
}

func (littleEndian) String() string { return "LittleEndian" }

func (littleEndian) GoString() string { return "binary.LittleEndian" }

type bigEndian struct{}

func (bigEndian) Uint16(b []byte) uint16 {
	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
	return uint16(b[1]) | uint16(b[0])<<8
}

func (bigEndian) PutUint16(b []byte, v uint16) {
	_ = b[1] // early bounds check to guarantee safety of writes below
	b[0] = byte(v >> 8)
	b[1] = byte(v)
}

func (bigEndian) Uint32(b []byte) uint32 {
	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
}

func (bigEndian) PutUint32(b []byte, v uint32) {
	_ = b[3] // early bounds check to guarantee safety of writes below
	b[0] = byte(v >> 24)
	b[1] = byte(v >> 16)
	b[2] = byte(v >> 8)
	b[3] = byte(v)
}

func (bigEndian) Uint64(b []byte) uint64 {
	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
}

func (bigEndian) PutUint64(b []byte, v uint64) {
	_ = b[7] // early bounds check to guarantee safety of writes below
	b[0] = byte(v >> 56)
	b[1] = byte(v >> 48)
	b[2] = byte(v >> 40)
	b[3] = byte(v >> 32)
	b[4] = byte(v >> 24)
	b[5] = byte(v >> 16)
	b[6] = byte(v >> 8)
	b[7] = byte(v)
}

func (bigEndian) String() string { return "BigEndian" }

func (bigEndian) GoString() string { return "binary.BigEndian" }

// Read reads structured binary data from r into data.
// Data must be a pointer to a fixed-size value or a slice
// of fixed-size values.
// Bytes read from r are decoded using the specified byte order
// and written to successive fields of the data.
// When decoding boolean values, a zero byte is decoded as false, and
// any other non-zero byte is decoded as true.
// When reading into structs, the field data for fields with
// blank (_) field names is skipped; i.e., blank field names
// may be used for padding.
// When reading into a struct, all non-blank fields must be exported
// or Read may panic.
//
// The error is EOF only if no bytes were read.
// If an EOF happens after reading some but not all the bytes,
// Read returns ErrUnexpectedEOF.
func Read(r io.Reader, order ByteOrder, data interface{}) error {
	// Fast path for basic types and slices.
	if n := intDataSize(data); n != 0 {
		var b [8]byte
		var bs []byte
		if n > len(b) {
			bs = make([]byte, n)
		} else {
			bs = b[:n]
		}
		if _, err := io.ReadFull(r, bs); err != nil {
			return err
		}
		switch data := data.(type) {
		case *bool:
			*data = b[0] != 0
		case *int8:
			*data = int8(b[0])
		case *uint8:
			*data = b[0]
		case *int16:
			*data = int16(order.Uint16(bs))
		case *uint16:
			*data = order.Uint16(bs)
		case *int32:
			*data = int32(order.Uint32(bs))
		case *uint32:
			*data = order.Uint32(bs)
		case *int64:
			*data = int64(order.Uint64(bs))
		case *uint64:
			*data = order.Uint64(bs)
		case []bool:
			for i, x := range bs { // Easier to loop over the input for 8-bit values.
				data[i] = x != 0
			}
		case []int8:
			for i, x := range bs {
				data[i] = int8(x)
			}
		case []uint8:
			copy(data, bs)
		case []int16:
			for i := range data {
				data[i] = int16(order.Uint16(bs[2*i:]))
			}
		case []uint16:
			for i := range data {
				data[i] = order.Uint16(bs[2*i:])
			}
		case []int32:
			for i := range data {
				data[i] = int32(order.Uint32(bs[4*i:]))
			}
		case []uint32:
			for i := range data {
				data[i] = order.Uint32(bs[4*i:])
			}
		case []int64:
			for i := range data {
				data[i] = int64(order.Uint64(bs[8*i:]))
			}
		case []uint64:
			for i := range data {
				data[i] = order.Uint64(bs[8*i:])
			}
		}
		return nil
	}

	// Fallback to reflect-based decoding.
	v := reflect.ValueOf(data)
	size := -1
	switch v.Kind() {
	case reflect.Ptr:
		v = v.Elem()
		size = dataSize(v)
	case reflect.Slice:
		size = dataSize(v)
	}
	if size < 0 {
		return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
	}
	d := &decoder{order: order, buf: make([]byte, size)}
	if _, err := io.ReadFull(r, d.buf); err != nil {
		return err
	}
	d.value(v)
	return nil
}

// Write writes the binary representation of data into w.
// Data must be a fixed-size value or a slice of fixed-size
// values, or a pointer to such data.
// Boolean values encode as one byte: 1 for true, and 0 for false.
// Bytes written to w are encoded using the specified byte order
// and read from successive fields of the data.
// When writing structs, zero values are written for fields
// with blank (_) field names.
func Write(w io.Writer, order ByteOrder, data interface{}) error {
	// Fast path for basic types and slices.
	if n := intDataSize(data); n != 0 {
		var b [8]byte
		var bs []byte
		if n > len(b) {
			bs = make([]byte, n)
		} else {
			bs = b[:n]
		}
		switch v := data.(type) {
		case *bool:
			if *v {
				b[0] = 1
			} else {
				b[0] = 0
			}
		case bool:
			if v {
				b[0] = 1
			} else {
				b[0] = 0
			}
		case []bool:
			for i, x := range v {
				if x {
					bs[i] = 1
				} else {
					bs[i] = 0
				}
			}
		case *int8:
			b[0] = byte(*v)
		case int8:
			b[0] = byte(v)
		case []int8:
			for i, x := range v {
				bs[i] = byte(x)
			}
		case *uint8:
			b[0] = *v
		case uint8:
			b[0] = v
		case []uint8:
			bs = v
		case *int16:
			order.PutUint16(bs, uint16(*v))
		case int16:
			order.PutUint16(bs, uint16(v))
		case []int16:
			for i, x := range v {
				order.PutUint16(bs[2*i:], uint16(x))
			}
		case *uint16:
			order.PutUint16(bs, *v)
		case uint16:
			order.PutUint16(bs, v)
		case []uint16:
			for i, x := range v {
				order.PutUint16(bs[2*i:], x)
			}
		case *int32:
			order.PutUint32(bs, uint32(*v))
		case int32:
			order.PutUint32(bs, uint32(v))
		case []int32:
			for i, x := range v {
				order.PutUint32(bs[4*i:], uint32(x))
			}
		case *uint32:
			order.PutUint32(bs, *v)
		case uint32:
			order.PutUint32(bs, v)
		case []uint32:
			for i, x := range v {
				order.PutUint32(bs[4*i:], x)
			}
		case *int64:
			order.PutUint64(bs, uint64(*v))
		case int64:
			order.PutUint64(bs, uint64(v))
		case []int64:
			for i, x := range v {
				order.PutUint64(bs[8*i:], uint64(x))
			}
		case *uint64:
			order.PutUint64(bs, *v)
		case uint64:
			order.PutUint64(bs, v)
		case []uint64:
			for i, x := range v {
				order.PutUint64(bs[8*i:], x)
			}
		}
		_, err := w.Write(bs)
		return err
	}

	// Fallback to reflect-based encoding.
	v := reflect.Indirect(reflect.ValueOf(data))
	size := dataSize(v)
	if size < 0 {
		return errors.New("binary.Write: invalid type " + reflect.TypeOf(data).String())
	}
	buf := make([]byte, size)
	e := &encoder{order: order, buf: buf}
	e.value(v)
	_, err := w.Write(buf)
	return err
}

// Size returns how many bytes Write would generate to encode the value v, which
// must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
// If v is neither of these, Size returns -1.
func Size(v interface{}) int {
	return dataSize(reflect.Indirect(reflect.ValueOf(v)))
}

// dataSize returns the number of bytes the actual data represented by v occupies in memory.
// For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
// it returns the length of the slice times the element size and does not count the memory
// occupied by the header. If the type of v is not acceptable, dataSize returns -1.
func dataSize(v reflect.Value) int {
	if v.Kind() == reflect.Slice {
		if s := sizeof(v.Type().Elem()); s >= 0 {
			return s * v.Len()
		}
		return -1
	}
	return sizeof(v.Type())
}

// sizeof returns the size >= 0 of variables for the given type or -1 if the type is not acceptable.
func sizeof(t reflect.Type) int {
	switch t.Kind() {
	case reflect.Array:
		if s := sizeof(t.Elem()); s >= 0 {
			return s * t.Len()
		}

	case reflect.Struct:
		sum := 0
		for i, n := 0, t.NumField(); i < n; i++ {
			s := sizeof(t.Field(i).Type)
			if s < 0 {
				return -1
			}
			sum += s
		}
		return sum

	case reflect.Bool,
		reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
		reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
		reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
		return int(t.Size())
	}

	return -1
}

type coder struct {
	order ByteOrder
	buf   []byte
}

type decoder coder
type encoder coder

func (d *decoder) bool() bool {
	x := d.buf[0]
	d.buf = d.buf[1:]
	return x != 0
}

func (e *encoder) bool(x bool) {
	if x {
		e.buf[0] = 1
	} else {
		e.buf[0] = 0
	}
	e.buf = e.buf[1:]
}

func (d *decoder) uint8() uint8 {
	x := d.buf[0]
	d.buf = d.buf[1:]
	return x
}

func (e *encoder) uint8(x uint8) {
	e.buf[0] = x
	e.buf = e.buf[1:]
}

func (d *decoder) uint16() uint16 {
	x := d.order.Uint16(d.buf[0:2])
	d.buf = d.buf[2:]
	return x
}

func (e *encoder) uint16(x uint16) {
	e.order.PutUint16(e.buf[0:2], x)
	e.buf = e.buf[2:]
}

func (d *decoder) uint32() uint32 {
	x := d.order.Uint32(d.buf[0:4])
	d.buf = d.buf[4:]
	return x
}

func (e *encoder) uint32(x uint32) {
	e.order.PutUint32(e.buf[0:4], x)
	e.buf = e.buf[4:]
}

func (d *decoder) uint64() uint64 {
	x := d.order.Uint64(d.buf[0:8])
	d.buf = d.buf[8:]
	return x
}

func (e *encoder) uint64(x uint64) {
	e.order.PutUint64(e.buf[0:8], x)
	e.buf = e.buf[8:]
}

func (d *decoder) int8() int8 { return int8(d.uint8()) }

func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }

func (d *decoder) int16() int16 { return int16(d.uint16()) }

func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }

func (d *decoder) int32() int32 { return int32(d.uint32()) }

func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }

func (d *decoder) int64() int64 { return int64(d.uint64()) }

func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }

func (d *decoder) value(v reflect.Value) {
	switch v.Kind() {
	case reflect.Array:
		l := v.Len()
		for i := 0; i < l; i++ {
			d.value(v.Index(i))
		}

	case reflect.Struct:
		t := v.Type()
		l := v.NumField()
		for i := 0; i < l; i++ {
			// Note: Calling v.CanSet() below is an optimization.
			// It would be sufficient to check the field name,
			// but creating the StructField info for each field is
			// costly (run "go test -bench=ReadStruct" and compare
			// results when making changes to this code).
			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
				d.value(v)
			} else {
				d.skip(v)
			}
		}

	case reflect.Slice:
		l := v.Len()
		for i := 0; i < l; i++ {
			d.value(v.Index(i))
		}

	case reflect.Bool:
		v.SetBool(d.bool())

	case reflect.Int8:
		v.SetInt(int64(d.int8()))
	case reflect.Int16:
		v.SetInt(int64(d.int16()))
	case reflect.Int32:
		v.SetInt(int64(d.int32()))
	case reflect.Int64:
		v.SetInt(d.int64())

	case reflect.Uint8:
		v.SetUint(uint64(d.uint8()))
	case reflect.Uint16:
		v.SetUint(uint64(d.uint16()))
	case reflect.Uint32:
		v.SetUint(uint64(d.uint32()))
	case reflect.Uint64:
		v.SetUint(d.uint64())

	case reflect.Float32:
		v.SetFloat(float64(math.Float32frombits(d.uint32())))
	case reflect.Float64:
		v.SetFloat(math.Float64frombits(d.uint64()))

	case reflect.Complex64:
		v.SetComplex(complex(
			float64(math.Float32frombits(d.uint32())),
			float64(math.Float32frombits(d.uint32())),
		))
	case reflect.Complex128:
		v.SetComplex(complex(
			math.Float64frombits(d.uint64()),
			math.Float64frombits(d.uint64()),
		))
	}
}

func (e *encoder) value(v reflect.Value) {
	switch v.Kind() {
	case reflect.Array:
		l := v.Len()
		for i := 0; i < l; i++ {
			e.value(v.Index(i))
		}

	case reflect.Struct:
		t := v.Type()
		l := v.NumField()
		for i := 0; i < l; i++ {
			// see comment for corresponding code in decoder.value()
			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
				e.value(v)
			} else {
				e.skip(v)
			}
		}

	case reflect.Slice:
		l := v.Len()
		for i := 0; i < l; i++ {
			e.value(v.Index(i))
		}

	case reflect.Bool:
		e.bool(v.Bool())

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		switch v.Type().Kind() {
		case reflect.Int8:
			e.int8(int8(v.Int()))
		case reflect.Int16:
			e.int16(int16(v.Int()))
		case reflect.Int32:
			e.int32(int32(v.Int()))
		case reflect.Int64:
			e.int64(v.Int())
		}

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		switch v.Type().Kind() {
		case reflect.Uint8:
			e.uint8(uint8(v.Uint()))
		case reflect.Uint16:
			e.uint16(uint16(v.Uint()))
		case reflect.Uint32:
			e.uint32(uint32(v.Uint()))
		case reflect.Uint64:
			e.uint64(v.Uint())
		}

	case reflect.Float32, reflect.Float64:
		switch v.Type().Kind() {
		case reflect.Float32:
			e.uint32(math.Float32bits(float32(v.Float())))
		case reflect.Float64:
			e.uint64(math.Float64bits(v.Float()))
		}

	case reflect.Complex64, reflect.Complex128:
		switch v.Type().Kind() {
		case reflect.Complex64:
			x := v.Complex()
			e.uint32(math.Float32bits(float32(real(x))))
			e.uint32(math.Float32bits(float32(imag(x))))
		case reflect.Complex128:
			x := v.Complex()
			e.uint64(math.Float64bits(real(x)))
			e.uint64(math.Float64bits(imag(x)))
		}
	}
}

func (d *decoder) skip(v reflect.Value) {
	d.buf = d.buf[dataSize(v):]
}

func (e *encoder) skip(v reflect.Value) {
	n := dataSize(v)
	for i := range e.buf[0:n] {
		e.buf[i] = 0
	}
	e.buf = e.buf[n:]
}

// intDataSize returns the size of the data required to represent the data when encoded.
// It returns zero if the type cannot be implemented by the fast path in Read or Write.
func intDataSize(data interface{}) int {
	switch data := data.(type) {
	case bool, int8, uint8, *bool, *int8, *uint8:
		return 1
	case []int8:
		return len(data)
	case []uint8:
		return len(data)
	case int16, uint16, *int16, *uint16:
		return 2
	case []int16:
		return 2 * len(data)
	case []uint16:
		return 2 * len(data)
	case int32, uint32, *int32, *uint32:
		return 4
	case []int32:
		return 4 * len(data)
	case []uint32:
		return 4 * len(data)
	case int64, uint64, *int64, *uint64:
		return 8
	case []int64:
		return 8 * len(data)
	case []uint64:
		return 8 * len(data)
	}
	return 0
}