package circbuf
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import (
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"fmt"
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)
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// Buffer implements a circular buffer. It is a fixed size,
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// and new writes overwrite older data, such that for a buffer
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// of size N, for any amount of writes, only the last N bytes
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// are retained.
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type Buffer struct {
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data []byte
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size int64
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writeCursor int64
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written int64
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}
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// NewBuffer creates a new buffer of a given size. The size
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// must be greater than 0.
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func NewBuffer(size int64) (*Buffer, error) {
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if size <= 0 {
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return nil, fmt.Errorf("Size must be positive")
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}
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b := &Buffer{
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size: size,
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data: make([]byte, size),
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}
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return b, nil
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}
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// Write writes up to len(buf) bytes to the internal ring,
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// overriding older data if necessary.
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func (b *Buffer) Write(buf []byte) (int, error) {
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// Account for total bytes written
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n := len(buf)
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b.written += int64(n)
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// If the buffer is larger than ours, then we only care
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// about the last size bytes anyways
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if int64(n) > b.size {
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buf = buf[int64(n)-b.size:]
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}
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// Copy in place
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remain := b.size - b.writeCursor
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copy(b.data[b.writeCursor:], buf)
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if int64(len(buf)) > remain {
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copy(b.data, buf[remain:])
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}
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// Update location of the cursor
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b.writeCursor = ((b.writeCursor + int64(len(buf))) % b.size)
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return n, nil
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}
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// Size returns the size of the buffer
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func (b *Buffer) Size() int64 {
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return b.size
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}
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// TotalWritten provides the total number of bytes written
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func (b *Buffer) TotalWritten() int64 {
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return b.written
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}
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// Bytes provides a slice of the bytes written. This
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// slice should not be written to.
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func (b *Buffer) Bytes() []byte {
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switch {
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case b.written >= b.size && b.writeCursor == 0:
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return b.data
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case b.written > b.size:
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out := make([]byte, b.size)
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copy(out, b.data[b.writeCursor:])
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copy(out[b.size-b.writeCursor:], b.data[:b.writeCursor])
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return out
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default:
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return b.data[:b.writeCursor]
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}
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}
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// Reset resets the buffer so it has no content.
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func (b *Buffer) Reset() {
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b.writeCursor = 0
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b.written = 0
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}
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// String returns the contents of the buffer as a string
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func (b *Buffer) String() string {
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return string(b.Bytes())
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}
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