173 lines
4.8 KiB
Go
173 lines
4.8 KiB
Go
// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package cryptobyte contains types that help with parsing and constructing
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// length-prefixed, binary messages, including ASN.1 DER. (The asn1 subpackage
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// contains useful ASN.1 constants.)
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//
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// The String type is for parsing. It wraps a []byte slice and provides helper
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// functions for consuming structures, value by value.
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//
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// The Builder type is for constructing messages. It providers helper functions
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// for appending values and also for appending length-prefixed submessages –
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// without having to worry about calculating the length prefix ahead of time.
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//
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// See the documentation and examples for the Builder and String types to get
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// started.
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package cryptobyte // import "golang.org/x/crypto/cryptobyte"
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// String represents a string of bytes. It provides methods for parsing
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// fixed-length and length-prefixed values from it.
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type String []byte
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// read advances a String by n bytes and returns them. If less than n bytes
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// remain, it returns nil.
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func (s *String) read(n int) []byte {
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if len(*s) < n || n < 0 {
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return nil
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}
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v := (*s)[:n]
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*s = (*s)[n:]
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return v
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}
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// Skip advances the String by n byte and reports whether it was successful.
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func (s *String) Skip(n int) bool {
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return s.read(n) != nil
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}
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// ReadUint8 decodes an 8-bit value into out and advances over it.
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// It reports whether the read was successful.
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func (s *String) ReadUint8(out *uint8) bool {
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v := s.read(1)
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if v == nil {
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return false
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}
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*out = uint8(v[0])
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return true
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}
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// ReadUint16 decodes a big-endian, 16-bit value into out and advances over it.
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// It reports whether the read was successful.
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func (s *String) ReadUint16(out *uint16) bool {
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v := s.read(2)
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if v == nil {
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return false
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}
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*out = uint16(v[0])<<8 | uint16(v[1])
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return true
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}
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// ReadUint24 decodes a big-endian, 24-bit value into out and advances over it.
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// It reports whether the read was successful.
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func (s *String) ReadUint24(out *uint32) bool {
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v := s.read(3)
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if v == nil {
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return false
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}
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*out = uint32(v[0])<<16 | uint32(v[1])<<8 | uint32(v[2])
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return true
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}
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// ReadUint32 decodes a big-endian, 32-bit value into out and advances over it.
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// It reports whether the read was successful.
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func (s *String) ReadUint32(out *uint32) bool {
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v := s.read(4)
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if v == nil {
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return false
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}
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*out = uint32(v[0])<<24 | uint32(v[1])<<16 | uint32(v[2])<<8 | uint32(v[3])
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return true
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}
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// ReadUint64 decodes a big-endian, 64-bit value into out and advances over it.
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// It reports whether the read was successful.
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func (s *String) ReadUint64(out *uint64) bool {
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v := s.read(8)
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if v == nil {
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return false
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}
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*out = uint64(v[0])<<56 | uint64(v[1])<<48 | uint64(v[2])<<40 | uint64(v[3])<<32 | uint64(v[4])<<24 | uint64(v[5])<<16 | uint64(v[6])<<8 | uint64(v[7])
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return true
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}
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func (s *String) readUnsigned(out *uint32, length int) bool {
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v := s.read(length)
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if v == nil {
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return false
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}
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var result uint32
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for i := 0; i < length; i++ {
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result <<= 8
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result |= uint32(v[i])
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}
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*out = result
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return true
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}
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func (s *String) readLengthPrefixed(lenLen int, outChild *String) bool {
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lenBytes := s.read(lenLen)
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if lenBytes == nil {
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return false
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}
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var length uint32
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for _, b := range lenBytes {
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length = length << 8
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length = length | uint32(b)
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}
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v := s.read(int(length))
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if v == nil {
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return false
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}
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*outChild = v
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return true
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}
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// ReadUint8LengthPrefixed reads the content of an 8-bit length-prefixed value
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// into out and advances over it. It reports whether the read was successful.
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func (s *String) ReadUint8LengthPrefixed(out *String) bool {
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return s.readLengthPrefixed(1, out)
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}
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// ReadUint16LengthPrefixed reads the content of a big-endian, 16-bit
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// length-prefixed value into out and advances over it. It reports whether the
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// read was successful.
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func (s *String) ReadUint16LengthPrefixed(out *String) bool {
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return s.readLengthPrefixed(2, out)
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}
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// ReadUint24LengthPrefixed reads the content of a big-endian, 24-bit
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// length-prefixed value into out and advances over it. It reports whether
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// the read was successful.
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func (s *String) ReadUint24LengthPrefixed(out *String) bool {
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return s.readLengthPrefixed(3, out)
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}
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// ReadBytes reads n bytes into out and advances over them. It reports
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// whether the read was successful.
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func (s *String) ReadBytes(out *[]byte, n int) bool {
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v := s.read(n)
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if v == nil {
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return false
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}
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*out = v
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return true
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}
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// CopyBytes copies len(out) bytes into out and advances over them. It reports
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// whether the copy operation was successful
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func (s *String) CopyBytes(out []byte) bool {
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n := len(out)
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v := s.read(n)
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if v == nil {
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return false
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}
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return copy(out, v) == n
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}
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// Empty reports whether the string does not contain any bytes.
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func (s String) Empty() bool {
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return len(s) == 0
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}
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