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89 lines
2.5 KiB
Go
89 lines
2.5 KiB
Go
package ioutils
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const maxCap = 1e6
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// BytesPipe is io.ReadWriter which works similarly to pipe(queue).
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// All written data could be read only once. Also BytesPipe is allocating
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// and releasing new byte slices to adjust to current needs, so there won't be
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// overgrown buffer after high load peak.
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// BytesPipe isn't goroutine-safe, caller must synchronize it if needed.
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type BytesPipe struct {
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buf [][]byte // slice of byte-slices of buffered data
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lastRead int // index in the first slice to a read point
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bufLen int // length of data buffered over the slices
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}
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// NewBytesPipe creates new BytesPipe, initialized by specified slice.
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// If buf is nil, then it will be initialized with slice which cap is 64.
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// buf will be adjusted in a way that len(buf) == 0, cap(buf) == cap(buf).
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func NewBytesPipe(buf []byte) *BytesPipe {
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if cap(buf) == 0 {
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buf = make([]byte, 0, 64)
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}
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return &BytesPipe{
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buf: [][]byte{buf[:0]},
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}
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}
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// Write writes p to BytesPipe.
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// It can allocate new []byte slices in a process of writing.
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func (bp *BytesPipe) Write(p []byte) (n int, err error) {
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for {
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// write data to the last buffer
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b := bp.buf[len(bp.buf)-1]
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// copy data to the current empty allocated area
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n := copy(b[len(b):cap(b)], p)
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// increment buffered data length
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bp.bufLen += n
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// include written data in last buffer
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bp.buf[len(bp.buf)-1] = b[:len(b)+n]
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// if there was enough room to write all then break
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if len(p) == n {
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break
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}
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// more data: write to the next slice
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p = p[n:]
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// allocate slice that has twice the size of the last unless maximum reached
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nextCap := 2 * cap(bp.buf[len(bp.buf)-1])
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if maxCap < nextCap {
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nextCap = maxCap
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}
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// add new byte slice to the buffers slice and continue writing
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bp.buf = append(bp.buf, make([]byte, 0, nextCap))
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}
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return
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}
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func (bp *BytesPipe) len() int {
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return bp.bufLen - bp.lastRead
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}
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// Read reads bytes from BytesPipe.
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// Data could be read only once.
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func (bp *BytesPipe) Read(p []byte) (n int, err error) {
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for {
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read := copy(p, bp.buf[0][bp.lastRead:])
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n += read
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bp.lastRead += read
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if bp.len() == 0 {
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// we have read everything. reset to the beginning.
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bp.lastRead = 0
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bp.bufLen -= len(bp.buf[0])
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bp.buf[0] = bp.buf[0][:0]
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break
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}
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// break if everything was read
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if len(p) == read {
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break
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}
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// more buffered data and more asked. read from next slice.
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p = p[read:]
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bp.lastRead = 0
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bp.bufLen -= len(bp.buf[0])
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bp.buf[0] = nil // throw away old slice
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bp.buf = bp.buf[1:] // switch to next
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}
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return
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}
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