github.com/elfadel/cilium@v1.6.12/pkg/bpf/binary/binary.go

// Copyright 2019 Authors of Cilium
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Copyright (c) 2009 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//   * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//   * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//   * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package binary

import (
	"encoding/binary"
	"math"
	"reflect"
)

type coder struct {
	order  binary.ByteOrder
	buf    []byte
	offset int
}

type decoder coder

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

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

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

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

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

func (d *decoder) skip(v reflect.Value) {
	d.offset += dataSize(v)
}

// 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
}

// 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())
}

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

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

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

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

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()),
		))
	}
}

// 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.
// This Read function differs from the upstream encoding/binary.Read as it does
// not requires the caller to setup a reader as well as this function does
// not allocate any memory to read from the given slice of bytes.
func Read(r []byte, order binary.ByteOrder, data interface{}) error {
	// Fallback to reflect-based decoding.
	v := reflect.ValueOf(data)
	switch v.Kind() {
	case reflect.Ptr:
		v = v.Elem()
	}
	d := &decoder{order: order, buf: r}
	d.value(v)
	return nil
}