The Buffer type has two new methods: Available and AvailableBuffer. T…

…hese may be used along with the Write method to append directly to the Buffer.

types/buffer-ext.go

@@ -18,10 +18,12 @@ type BufferInterface interface {
 	io.StringWriter
 	WriteRune(rune) (int, error)
 	Bytes() []byte
+	AvailableBuffer() []byte
 	fmt.Stringer
 	Len() int
 	Size() int64
 	Cap() int
+	Available() int
 	Truncate(int)
 	Reset()
 	Grow(int)

types/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 "<nil>".
 //
@@ -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.
@@ -100,7 +109,7 @@ func (b *Buffer) Reset() {
 	b.lastRead = opInvalid
 }
 
-// tryGrowByReslice is a inlineable version of grow for the fast-case where the
+// tryGrowByReslice is an inlineable version of grow for the fast-case where the
 // internal buffer only needs to be resliced.
 // It returns the index where bytes should be written and whether it succeeded.
 func (b *Buffer) tryGrowByReslice(n int) (int, bool) {