135 lines
2.8 KiB
Go
135 lines
2.8 KiB
Go
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package fastcopy
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import (
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"io"
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"sync"
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_ "unsafe" // link to io.errInvalidWrite.
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)
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var (
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// global pool instance.
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pool = CopyPool{size: 4096}
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//go:linkname errInvalidWrite io.errInvalidWrite
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errInvalidWrite error
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)
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// CopyPool provides a memory pool of byte
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// buffers for io copies from readers to writers.
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type CopyPool struct {
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size int
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pool sync.Pool
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}
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// See CopyPool.Buffer().
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func Buffer(sz int) int {
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return pool.Buffer(sz)
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}
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// See CopyPool.CopyN().
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func CopyN(dst io.Writer, src io.Reader, n int64) (int64, error) {
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return pool.CopyN(dst, src, n)
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}
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// See CopyPool.Copy().
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func Copy(dst io.Writer, src io.Reader) (int64, error) {
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return pool.Copy(dst, src)
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}
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// Buffer sets the pool buffer size to allocate. Returns current size.
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// Note this is NOT atomically safe, please call BEFORE other calls to CopyPool.
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func (cp *CopyPool) Buffer(sz int) int {
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if sz > 0 {
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// update size
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cp.size = sz
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} else if cp.size < 1 {
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// default size
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return 4096
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}
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return cp.size
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}
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// CopyN performs the same logic as io.CopyN(), with the difference
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// being that the byte buffer is acquired from a memory pool.
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func (cp *CopyPool) CopyN(dst io.Writer, src io.Reader, n int64) (int64, error) {
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written, err := cp.Copy(dst, io.LimitReader(src, n))
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if written == n {
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return n, nil
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}
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if written < n && err == nil {
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// src stopped early; must have been EOF.
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err = io.EOF
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}
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return written, err
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}
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// Copy performs the same logic as io.Copy(), with the difference
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// being that the byte buffer is acquired from a memory pool.
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func (cp *CopyPool) Copy(dst io.Writer, src io.Reader) (int64, error) {
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// Prefer using io.WriterTo to do the copy (avoids alloc + copy)
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if wt, ok := src.(io.WriterTo); ok {
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return wt.WriteTo(dst)
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}
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// Prefer using io.ReaderFrom to do the copy.
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if rt, ok := dst.(io.ReaderFrom); ok {
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return rt.ReadFrom(src)
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}
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var buf []byte
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if b, ok := cp.pool.Get().([]byte); ok {
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// Acquired buf from pool
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buf = b
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} else {
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// Allocate new buffer of size
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buf = make([]byte, cp.Buffer(0))
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}
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// Defer release to pool
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defer cp.pool.Put(buf)
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var n int64
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for {
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// Perform next read into buf
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nr, err := src.Read(buf)
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if nr > 0 {
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// We error check AFTER checking
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// no. read bytes so incomplete
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// read still gets written up to nr.
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// Perform next write from buf
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nw, ew := dst.Write(buf[0:nr])
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// Check for valid write
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if nw < 0 || nr < nw {
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if ew == nil {
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ew = errInvalidWrite
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}
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return n, ew
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}
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// Incr total count
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n += int64(nw)
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// Check write error
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if ew != nil {
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return n, ew
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}
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// Check unequal read/writes
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if nr != nw {
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return n, io.ErrShortWrite
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}
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}
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// Return on err
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if err != nil {
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if err == io.EOF {
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err = nil // expected
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}
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return n, err
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}
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}
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}
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