// 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" ) // 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)] bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation. lastRead readOp // last read operation, so that Unread* can work correctly. // FIXME: it would be advisable to align Buffer to cachelines to avoid false // sharing. } // 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 returns 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 } // Check if we can make use of bootstrap array. if b.buf == nil && n <= len(b.bootstrap) { b.buf = b.bootstrap[:n] 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) 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) { if 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 } // 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 errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read") } 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 size // 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)} }