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- // 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 bytes
- // Simple byte buffer for marshaling data.
- import (
- "errors"
- "io"
- "unicode/utf8"
- )
- // smallBufferSize is an initial allocation minimal capacity.
- const smallBufferSize = 64
- // A Buffer is a variable-sized buffer of bytes with Read and Write methods.
- // The zero value for Buffer is an empty buffer ready to use.
- type Buffer struct {
- buf []byte // contents are the bytes buf[off : len(buf)]
- off int // read at &buf[off], write at &buf[len(buf)]
- lastRead readOp // last read operation, so that Unread* can work correctly.
- }
- // The readOp constants describe the last action performed on
- // the buffer, so that UnreadRune and UnreadByte can check for
- // invalid usage. opReadRuneX constants are chosen such that
- // converted to int they correspond to the rune size that was read.
- type readOp int8
- // Don't use iota for these, as the values need to correspond with the
- // names and comments, which is easier to see when being explicit.
- const (
- opRead readOp = -1 // Any other read operation.
- opInvalid readOp = 0 // Non-read operation.
- opReadRune1 readOp = 1 // Read rune of size 1.
- opReadRune2 readOp = 2 // Read rune of size 2.
- opReadRune3 readOp = 3 // Read rune of size 3.
- opReadRune4 readOp = 4 // Read rune of size 4.
- )
- // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
- var ErrTooLarge = errors.New("bytes.Buffer: too large")
- var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read")
- const maxInt = int(^uint(0) >> 1)
- // Bytes returns a slice of length b.Len() holding the unread portion of the buffer.
- // The slice is valid for use only until the next buffer modification (that is,
- // only until the next call to a method like Read, Write, Reset, or Truncate).
- // The slice aliases the buffer content at least until the next buffer modification,
- // so immediate changes to the slice will affect the result of future reads.
- func (b *Buffer) Bytes() []byte { return b.buf[b.off:] }
- // String returns the contents of the unread portion of the buffer
- // as a string. If the Buffer is a nil pointer, it returns "<nil>".
- //
- // To build strings more efficiently, see the strings.Builder type.
- func (b *Buffer) String() string {
- if b == nil {
- // Special case, useful in debugging.
- return "<nil>"
- }
- return string(b.buf[b.off:])
- }
- // empty reports whether the unread portion of the buffer is empty.
- func (b *Buffer) empty() bool { return len(b.buf) <= b.off }
- // Len returns the number of bytes of the unread portion of the buffer;
- // b.Len() == len(b.Bytes()).
- func (b *Buffer) Len() int { return len(b.buf) - b.off }
- // Cap returns the capacity of the buffer's underlying byte slice, that is, the
- // total space allocated for the buffer's data.
- func (b *Buffer) Cap() int { return cap(b.buf) }
- // Truncate discards all but the first n unread bytes from the buffer
- // but continues to use the same allocated storage.
- // It panics if n is negative or greater than the length of the buffer.
- func (b *Buffer) Truncate(n int) {
- if n == 0 {
- b.Reset()
- return
- }
- b.lastRead = opInvalid
- if n < 0 || n > b.Len() {
- panic("bytes.Buffer: truncation out of range")
- }
- b.buf = b.buf[:b.off+n]
- }
- // Reset resets the buffer to be empty,
- // but it retains the underlying storage for use by future writes.
- // Reset is the same as Truncate(0).
- func (b *Buffer) Reset() {
- b.buf = b.buf[:0]
- b.off = 0
- b.lastRead = opInvalid
- }
- // tryGrowByReslice is a inlineable version of grow for the fast-case where the
- // internal buffer only needs to be resliced.
- // It returns the index where bytes should be written and whether it succeeded.
- func (b *Buffer) tryGrowByReslice(n int) (int, bool) {
- if l := len(b.buf); n <= cap(b.buf)-l {
- b.buf = b.buf[:l+n]
- return l, true
- }
- return 0, false
- }
- // grow grows the buffer to guarantee space for n more bytes.
- // It returns the index where bytes should be written.
- // If the buffer can't grow it will panic with ErrTooLarge.
- func (b *Buffer) grow(n int) int {
- m := b.Len()
- // If buffer is empty, reset to recover space.
- if m == 0 && b.off != 0 {
- b.Reset()
- }
- // Try to grow by means of a reslice.
- if i, ok := b.tryGrowByReslice(n); ok {
- return i
- }
- if b.buf == nil && n <= smallBufferSize {
- b.buf = make([]byte, n, smallBufferSize)
- return 0
- }
- c := cap(b.buf)
- if n <= c/2-m {
- // We can slide things down instead of allocating a new
- // slice. We only need m+n <= c to slide, but
- // we instead let capacity get twice as large so we
- // don't spend all our time copying.
- copy(b.buf, b.buf[b.off:])
- } else if c > maxInt-c-n {
- panic(ErrTooLarge)
- } else {
- // Not enough space anywhere, we need to allocate.
- buf := makeSlice(2*c + n)
- copy(buf, b.buf[b.off:])
- b.buf = buf
- }
- // Restore b.off and len(b.buf).
- b.off = 0
- b.buf = b.buf[:m+n]
- return m
- }
- // Grow grows the buffer's capacity, if necessary, to guarantee space for
- // another n bytes. After Grow(n), at least n bytes can be written to the
- // buffer without another allocation.
- // If n is negative, Grow will panic.
- // If the buffer can't grow it will panic with ErrTooLarge.
- func (b *Buffer) Grow(n int) {
- if n < 0 {
- panic("bytes.Buffer.Grow: negative count")
- }
- m := b.grow(n)
- b.buf = b.buf[:m]
- }
- // Write appends the contents of p to the buffer, growing the buffer as
- // needed. The return value n is the length of p; err is always nil. If the
- // buffer becomes too large, Write will panic with ErrTooLarge.
- func (b *Buffer) Write(p []byte) (n int, err error) {
- b.lastRead = opInvalid
- m, ok := b.tryGrowByReslice(len(p))
- if !ok {
- m = b.grow(len(p))
- }
- return copy(b.buf[m:], p), nil
- }
- // WriteString appends the contents of s to the buffer, growing the buffer as
- // needed. The return value n is the length of s; err is always nil. If the
- // buffer becomes too large, WriteString will panic with ErrTooLarge.
- func (b *Buffer) WriteString(s string) (n int, err error) {
- b.lastRead = opInvalid
- m, ok := b.tryGrowByReslice(len(s))
- if !ok {
- m = b.grow(len(s))
- }
- return copy(b.buf[m:], s), nil
- }
- // MinRead is the minimum slice size passed to a Read call by
- // Buffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond
- // what is required to hold the contents of r, ReadFrom will not grow the
- // underlying buffer.
- const MinRead = 512
- // ReadFrom reads data from r until EOF and appends it to the buffer, growing
- // the buffer as needed. The return value n is the number of bytes read. Any
- // error except io.EOF encountered during the read is also returned. If the
- // buffer becomes too large, ReadFrom will panic with ErrTooLarge.
- func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
- b.lastRead = opInvalid
- for {
- i := b.grow(MinRead)
- b.buf = b.buf[:i]
- m, e := r.Read(b.buf[i:cap(b.buf)])
- if m < 0 {
- panic(errNegativeRead)
- }
- b.buf = b.buf[:i+m]
- n += int64(m)
- if e == io.EOF {
- return n, nil // e is EOF, so return nil explicitly
- }
- if e != nil {
- return n, e
- }
- }
- }
- // makeSlice allocates a slice of size n. If the allocation fails, it panics
- // with ErrTooLarge.
- func makeSlice(n int) []byte {
- // If the make fails, give a known error.
- defer func() {
- if recover() != nil {
- panic(ErrTooLarge)
- }
- }()
- return make([]byte, n)
- }
- // WriteTo writes data to w until the buffer is drained or an error occurs.
- // The return value n is the number of bytes written; it always fits into an
- // int, but it is int64 to match the io.WriterTo interface. Any error
- // encountered during the write is also returned.
- func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
- b.lastRead = opInvalid
- if nBytes := b.Len(); nBytes > 0 {
- m, e := w.Write(b.buf[b.off:])
- if m > nBytes {
- panic("bytes.Buffer.WriteTo: invalid Write count")
- }
- b.off += m
- n = int64(m)
- if e != nil {
- return n, e
- }
- // all bytes should have been written, by definition of
- // Write method in io.Writer
- if m != nBytes {
- return n, io.ErrShortWrite
- }
- }
- // Buffer is now empty; reset.
- b.Reset()
- return n, nil
- }
- // WriteByte appends the byte c to the buffer, growing the buffer as needed.
- // The returned error is always nil, but is included to match bufio.Writer's
- // WriteByte. If the buffer becomes too large, WriteByte will panic with
- // ErrTooLarge.
- func (b *Buffer) WriteByte(c byte) error {
- b.lastRead = opInvalid
- m, ok := b.tryGrowByReslice(1)
- if !ok {
- m = b.grow(1)
- }
- b.buf[m] = c
- return nil
- }
- // WriteRune appends the UTF-8 encoding of Unicode code point r to the
- // buffer, returning its length and an error, which is always nil but is
- // included to match bufio.Writer's WriteRune. The buffer is grown as needed;
- // if it becomes too large, WriteRune will panic with ErrTooLarge.
- func (b *Buffer) WriteRune(r rune) (n int, err error) {
- // Compare as uint32 to correctly handle negative runes.
- if uint32(r) < utf8.RuneSelf {
- b.WriteByte(byte(r))
- return 1, nil
- }
- b.lastRead = opInvalid
- m, ok := b.tryGrowByReslice(utf8.UTFMax)
- if !ok {
- m = b.grow(utf8.UTFMax)
- }
- n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r)
- b.buf = b.buf[:m+n]
- return n, nil
- }
- // Read reads the next len(p) bytes from the buffer or until the buffer
- // is drained. The return value n is the number of bytes read. If the
- // buffer has no data to return, err is io.EOF (unless len(p) is zero);
- // otherwise it is nil.
- func (b *Buffer) Read(p []byte) (n int, err error) {
- b.lastRead = opInvalid
- if b.empty() {
- // Buffer is empty, reset to recover space.
- b.Reset()
- if len(p) == 0 {
- return 0, nil
- }
- return 0, io.EOF
- }
- n = copy(p, b.buf[b.off:])
- b.off += n
- if n > 0 {
- b.lastRead = opRead
- }
- return n, nil
- }
- // Next returns a slice containing the next n bytes from the buffer,
- // advancing the buffer as if the bytes had been returned by Read.
- // If there are fewer than n bytes in the buffer, Next returns the entire buffer.
- // The slice is only valid until the next call to a read or write method.
- func (b *Buffer) Next(n int) []byte {
- b.lastRead = opInvalid
- m := b.Len()
- if n > m {
- n = m
- }
- data := b.buf[b.off : b.off+n]
- b.off += n
- if n > 0 {
- b.lastRead = opRead
- }
- return data
- }
- // ReadByte reads and returns the next byte from the buffer.
- // If no byte is available, it returns error io.EOF.
- func (b *Buffer) ReadByte() (byte, error) {
- if b.empty() {
- // Buffer is empty, reset to recover space.
- b.Reset()
- return 0, io.EOF
- }
- c := b.buf[b.off]
- b.off++
- b.lastRead = opRead
- return c, nil
- }
- // ReadRune reads and returns the next UTF-8-encoded
- // Unicode code point from the buffer.
- // If no bytes are available, the error returned is io.EOF.
- // If the bytes are an erroneous UTF-8 encoding, it
- // consumes one byte and returns U+FFFD, 1.
- func (b *Buffer) ReadRune() (r rune, size int, err error) {
- if b.empty() {
- // Buffer is empty, reset to recover space.
- b.Reset()
- return 0, 0, io.EOF
- }
- c := b.buf[b.off]
- if c < utf8.RuneSelf {
- b.off++
- b.lastRead = opReadRune1
- return rune(c), 1, nil
- }
- r, n := utf8.DecodeRune(b.buf[b.off:])
- b.off += n
- b.lastRead = readOp(n)
- return r, n, nil
- }
- // UnreadRune unreads the last rune returned by ReadRune.
- // If the most recent read or write operation on the buffer was
- // not a successful ReadRune, UnreadRune returns an error. (In this regard
- // it is stricter than UnreadByte, which will unread the last byte
- // from any read operation.)
- func (b *Buffer) UnreadRune() error {
- if b.lastRead <= opInvalid {
- return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
- }
- if b.off >= int(b.lastRead) {
- b.off -= int(b.lastRead)
- }
- b.lastRead = opInvalid
- return nil
- }
- var errUnreadByte = errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")
- // UnreadByte unreads the last byte returned by the most recent successful
- // read operation that read at least one byte. If a write has happened since
- // the last read, if the last read returned an error, or if the read read zero
- // bytes, UnreadByte returns an error.
- func (b *Buffer) UnreadByte() error {
- if b.lastRead == opInvalid {
- return errUnreadByte
- }
- b.lastRead = opInvalid
- if b.off > 0 {
- b.off--
- }
- return nil
- }
- // ReadBytes reads until the first occurrence of delim in the input,
- // returning a slice containing the data up to and including the delimiter.
- // If ReadBytes encounters an error before finding a delimiter,
- // it returns the data read before the error and the error itself (often io.EOF).
- // ReadBytes returns err != nil if and only if the returned data does not end in
- // delim.
- func (b *Buffer) ReadBytes(delim byte) (line []byte, err error) {
- slice, err := b.readSlice(delim)
- // return a copy of slice. The buffer's backing array may
- // be overwritten by later calls.
- line = append(line, slice...)
- return line, err
- }
- // readSlice is like ReadBytes but returns a reference to internal buffer data.
- func (b *Buffer) readSlice(delim byte) (line []byte, err error) {
- i := IndexByte(b.buf[b.off:], delim)
- end := b.off + i + 1
- if i < 0 {
- end = len(b.buf)
- err = io.EOF
- }
- line = b.buf[b.off:end]
- b.off = end
- b.lastRead = opRead
- return line, err
- }
- // ReadString reads until the first occurrence of delim in the input,
- // returning a string containing the data up to and including the delimiter.
- // If ReadString encounters an error before finding a delimiter,
- // it returns the data read before the error and the error itself (often io.EOF).
- // ReadString returns err != nil if and only if the returned data does not end
- // in delim.
- func (b *Buffer) ReadString(delim byte) (line string, err error) {
- slice, err := b.readSlice(delim)
- return string(slice), err
- }
- // NewBuffer creates and initializes a new Buffer using buf as its
- // initial contents. The new Buffer takes ownership of buf, and the
- // caller should not use buf after this call. NewBuffer is intended to
- // prepare a Buffer to read existing data. It can also be used to set
- // the initial size of the internal buffer for writing. To do that,
- // buf should have the desired capacity but a length of zero.
- //
- // In most cases, new(Buffer) (or just declaring a Buffer variable) is
- // sufficient to initialize a Buffer.
- func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }
- // NewBufferString creates and initializes a new Buffer using string s as its
- // initial contents. It is intended to prepare a buffer to read an existing
- // string.
- //
- // In most cases, new(Buffer) (or just declaring a Buffer variable) is
- // sufficient to initialize a Buffer.
- func NewBufferString(s string) *Buffer {
- return &Buffer{buf: []byte(s)}
- }
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