Golang 표준 라 이브 러 리 Buffer

type Buffer struct {
    buf       []byte            // contents are the bytes buf[off : len(buf)]
    off       int               // read at &buf[off], write at &buf[len(buf)]
    runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each WriteByte or Rune
    bootstrap [64]byte          // memory to hold first slice; helps small buffers (Printf) avoid allocation.
    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.
type readOp int
const (
    opInvalid  readOp = iota // Non-read operation.
    opReadRune               // Read rune.
    opRead                   // Any other read operation.
)

func NewBuffer(buf []byte) *Buffer { return &Buffer{buf: buf} }
func NewBufferString(s string) *Buffer {
    return &Buffer{buf: []byte(s)}
}

func (b *Buffer) Read(p []byte) (n int, err error)
func (b *Buffer) Next(n int) []byte
func (b *Buffer) ReadByte() (c byte, err error)
func (b *Buffer) ReadRune() (r rune, size int, err error)
func (b *Buffer) ReadBytes(delim byte) (line []byte, err error)
func (b *Buffer) readSlice(delim byte) (line []byte, err error)
func (b *Buffer) ReadString(delim byte) (line string, err error)
func (b *Buffer) Write(p []byte) (n int, err error)
func (b *Buffer) WriteString(s string) (n int, err error)
func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error)
func (b *Buffer) WriteTo(w io.Writer) (n int64, err error)
func (b *Buffer) WriteByte(c byte) error
func (b *Buffer) WriteRune(r rune) (n int, err error)

func (b *Buffer) Read(p []byte) (n int, err error) {
    b.lastRead = opInvalid
    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
    if n > 0 {
        b.lastRead = opRead
    }
    return
}

// 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) {
    b.lastRead = opInvalid
    if b.off >= len(b.buf) {
        // Buffer is empty, reset to recover space.
        b.Truncate(0)
        return 0, 0, io.EOF
    }
    b.lastRead = opReadRune
    c := b.buf[b.off]
    if c < utf8.RuneSelf {
        b.off++
        return rune(c), 1, nil
    }
    r, n := utf8.DecodeRune(b.buf[b.off:])
    b.off += n
    return r, n, 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 := 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
}

// 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 := b.grow(len(p))
    return copy(b.buf[m:], p), 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
    }
    n = utf8.EncodeRune(b.runeBytes[0:], r)
    b.Write(b.runeBytes[0:n])
    return n, nil
}

// 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
    // 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
}

// 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 b.off < len(b.buf) {
        nBytes := b.Len()
        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.Truncate(0)
    return
}

// 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) {
    b.lastRead = opInvalid
    switch {
    case n < 0 || n > b.Len():
        panic("bytes.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 ErrTooLarge.
func (b *Buffer) grow(n int) int {
    m := b.Len()
    //   Buffer  ，  Buffer
    if m == 0 && b.off != 0 {
        b.Truncate(0)
    }
    //    n   Buffer   
    if len(b.buf)+n > cap(b.buf) {
        //      buf
        var buf []byte
        //Buffer buf     ，      ，  n  bootstrap   ，
        //   boostrap   buf            。
        if b.buf == nil && n <= len(b.bootstrap) {
            buf = b.bootstrap[0:]
        //       ，  b.buf            slice  ，   b.buf       buf。
        } else if m+n <= cap(b.buf)/2 {
            copy(b.buf[:], b.buf[b.off:])
            buf = b.buf[:m]
        } else {
            //    ，      
            buf = makeSlice(2*cap(b.buf) + n)
            copy(buf, b.buf[b.off:])
        }
        b.buf = buf
        b.off = 0
    }
    //  n   ，           
    b.buf = b.buf[0 : b.off+m+n]
    return b.off + 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[0:m]
}