diff options
Diffstat (limited to 'vendor/github.com/syndtr/goleveldb/leveldb/util/buffer.go')
-rw-r--r-- | vendor/github.com/syndtr/goleveldb/leveldb/util/buffer.go | 293 |
1 files changed, 293 insertions, 0 deletions
diff --git a/vendor/github.com/syndtr/goleveldb/leveldb/util/buffer.go b/vendor/github.com/syndtr/goleveldb/leveldb/util/buffer.go new file mode 100644 index 000000000..21de24255 --- /dev/null +++ b/vendor/github.com/syndtr/goleveldb/leveldb/util/buffer.go @@ -0,0 +1,293 @@ +// 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 util + +// This a copy of Go std bytes.Buffer with some modification +// and some features stripped. + +import ( + "bytes" + "io" +) + +// 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 (Printf) avoid allocation. +} + +// Bytes returns a slice of the contents of the unread portion of the buffer; +// len(b.Bytes()) == b.Len(). If the caller changes the contents of the +// returned slice, the contents of the buffer will change provided there +// are no intervening method calls on the Buffer. +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>". +func (b *Buffer) String() string { + if b == nil { + // Special case, useful in debugging. + return "<nil>" + } + return string(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 } + +// Truncate discards all but the first n unread bytes from the buffer. +// It panics if n is negative or greater than the length of the buffer. +func (b *Buffer) Truncate(n int) { + switch { + case n < 0 || n > b.Len(): + panic("leveldb/util.Buffer: truncation out of range") + case n == 0: + // Reuse buffer space. + b.off = 0 + } + b.buf = b.buf[0 : b.off+n] +} + +// Reset resets the buffer so it has no content. +// b.Reset() is the same as b.Truncate(0). +func (b *Buffer) Reset() { b.Truncate(0) } + +// 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 bytes.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.Truncate(0) + } + if len(b.buf)+n > cap(b.buf) { + var buf []byte + if b.buf == nil && n <= len(b.bootstrap) { + buf = b.bootstrap[0:] + } else if m+n <= cap(b.buf)/2 { + // We can slide things down instead of allocating a new + // slice. We only need m+n <= cap(b.buf) 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:]) + buf = b.buf[:m] + } else { + // not enough space anywhere + buf = makeSlice(2*cap(b.buf) + n) + copy(buf, b.buf[b.off:]) + } + b.buf = buf + b.off = 0 + } + b.buf = b.buf[0 : b.off+m+n] + return b.off + m +} + +// Alloc allocs n bytes of slice from the buffer, growing the buffer as +// needed. If n is negative, Alloc will panic. +// If the buffer can't grow it will panic with bytes.ErrTooLarge. +func (b *Buffer) Alloc(n int) []byte { + if n < 0 { + panic("leveldb/util.Buffer.Alloc: negative count") + } + m := b.grow(n) + return b.buf[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 bytes.ErrTooLarge. +func (b *Buffer) Grow(n int) { + if n < 0 { + panic("leveldb/util.Buffer.Grow: negative count") + } + m := b.grow(n) + b.buf = b.buf[0: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 bytes.ErrTooLarge. +func (b *Buffer) Write(p []byte) (n int, err error) { + m := b.grow(len(p)) + return copy(b.buf[m:], p), 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 bytes.ErrTooLarge. +func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) { + // If buffer is empty, reset to recover space. + if b.off >= len(b.buf) { + b.Truncate(0) + } + for { + if free := cap(b.buf) - len(b.buf); free < MinRead { + // not enough space at end + newBuf := b.buf + if b.off+free < MinRead { + // not enough space using beginning of buffer; + // double buffer capacity + newBuf = makeSlice(2*cap(b.buf) + MinRead) + } + copy(newBuf, b.buf[b.off:]) + b.buf = newBuf[:len(b.buf)-b.off] + b.off = 0 + } + m, e := r.Read(b.buf[len(b.buf):cap(b.buf)]) + b.buf = b.buf[0 : len(b.buf)+m] + n += int64(m) + if e == io.EOF { + break + } + if e != nil { + return n, e + } + } + return n, nil // err is EOF, so return nil explicitly +} + +// makeSlice allocates a slice of size n. If the allocation fails, it panics +// with bytes.ErrTooLarge. +func makeSlice(n int) []byte { + // If the make fails, give a known error. + defer func() { + if recover() != nil { + panic(bytes.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) { + if b.off < len(b.buf) { + nBytes := b.Len() + m, e := w.Write(b.buf[b.off:]) + if m > nBytes { + panic("leveldb/util.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.Truncate(0) + return +} + +// 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 +// bytes.ErrTooLarge. +func (b *Buffer) WriteByte(c byte) error { + m := b.grow(1) + b.buf[m] = c + return 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) { + if b.off >= len(b.buf) { + // Buffer is empty, reset to recover space. + b.Truncate(0) + if len(p) == 0 { + return + } + return 0, io.EOF + } + n = copy(p, b.buf[b.off:]) + b.off += n + return +} + +// 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 { + m := b.Len() + if n > m { + n = m + } + data := b.buf[b.off : b.off+n] + b.off += n + 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() (c byte, err error) { + if b.off >= len(b.buf) { + // Buffer is empty, reset to recover space. + b.Truncate(0) + return 0, io.EOF + } + c = b.buf[b.off] + b.off++ + return c, 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 +} + +// readSlice is like ReadBytes but returns a reference to internal buffer data. +func (b *Buffer) readSlice(delim byte) (line []byte, err error) { + i := bytes.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 + return line, err +} + +// NewBuffer creates and initializes a new Buffer using buf as its initial +// contents. It 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} } |