From e671fe0c3efc497397af3362a4b79c895fbd8bfc Mon Sep 17 00:00:00 2001 From: Joe Tsai Date: Mon, 6 Feb 2023 11:37:39 -0800 Subject: bytes: add Buffer.Available and Buffer.AvailableBuffer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This adds a new Buffer.AvailableBuffer method that returns an empty buffer with a possibly non-empty capacity for use with append-like APIs. The typical usage pattern is something like: b := bb.AvailableBuffer() b = appendValue(b, v) bb.Write(b) It allows logic combining append-like APIs with Buffer to avoid needing to allocate and manage buffers themselves and allows the append-like APIs to directly write into the Buffer. The Buffer.Write method uses the builtin copy function, which avoids copying bytes if the source and destination are identical. Thus, Buffer.Write is a constant-time call for this pattern. Performance: BenchmarkBufferAppendNoCopy 2.909 ns/op 5766942167.24 MB/s This benchmark should only be testing the cost of bookkeeping and never the copying of the input slice. Thus, the MB/s should be orders of magnitude faster than RAM. Fixes #53685 Change-Id: I0b41e54361339df309db8d03527689b123f99085 Reviewed-on: https://go-review.googlesource.com/c/go/+/474635 Run-TryBot: Joseph Tsai Reviewed-by: Daniel Martí Reviewed-by: Cherry Mui TryBot-Result: Gopher Robot Auto-Submit: Joseph Tsai Reviewed-by: Ian Lance Taylor --- src/bytes/buffer.go | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'src/bytes/buffer.go') diff --git a/src/bytes/buffer.go b/src/bytes/buffer.go index ee83fd8b36..5ab58c78bb 100644 --- a/src/bytes/buffer.go +++ b/src/bytes/buffer.go @@ -53,6 +53,12 @@ const maxInt = int(^uint(0) >> 1) // so immediate changes to the slice will affect the result of future reads. func (b *Buffer) Bytes() []byte { return b.buf[b.off:] } +// AvailableBuffer returns an empty buffer with b.Available() capacity. +// This buffer is intended to be appended to and +// passed to an immediately succeeding Write call. +// The buffer is only valid until the next write operation on b. +func (b *Buffer) AvailableBuffer() []byte { return b.buf[len(b.buf):] } + // String returns the contents of the unread portion of the buffer // as a string. If the Buffer is a nil pointer, it returns "". // @@ -76,6 +82,9 @@ func (b *Buffer) Len() int { return len(b.buf) - b.off } // total space allocated for the buffer's data. func (b *Buffer) Cap() int { return cap(b.buf) } +// Available returns how many bytes are unused in the buffer. +func (b *Buffer) Available() int { return cap(b.buf) - len(b.buf) } + // Truncate discards all but the first n unread bytes from the buffer // but continues to use the same allocated storage. // It panics if n is negative or greater than the length of the buffer. -- cgit v1.3