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