Clean-up buffer implementation.

This also adds substantial test cases.

The Read/Write interfaces are dropped as they are not necessary.

PiperOrigin-RevId: 300461547

1 files changed, 111 insertions, 103 deletions

diff --git a/pkg/buffer/view.go b/pkg/buffer/view.go
index 00fc11e9c..e6901eadb 100644
--- a/pkg/buffer/view.go
+++ b/pkg/buffer/view.go
@@ -38,14 +38,6 @@ func (v *View) TrimFront(count int64) {
 	}
 }
 
-// Read implements io.Reader.Read.
-//
-// Note that reading does not advance the read index. This must be done
-// manually using TrimFront or other methods.
-func (v *View) Read(p []byte) (int, error) {
-	return v.ReadAt(p, 0)
-}
-
 // ReadAt implements io.ReaderAt.ReadAt.
 func (v *View) ReadAt(p []byte, offset int64) (int, error) {
 	var (
@@ -54,54 +46,46 @@ func (v *View) ReadAt(p []byte, offset int64) (int, error) {
 	)
 	for buf := v.data.Front(); buf != nil && done < int64(len(p)); buf = buf.Next() {
 		needToSkip := int(offset - skipped)
-		if l := buf.write - buf.read; l <= needToSkip {
-			skipped += int64(l)
+		if sz := buf.ReadSize(); sz <= needToSkip {
+			skipped += int64(sz)
 			continue
 		}
 
 		// Actually read data.
-		n := copy(p[done:], buf.data[buf.read+needToSkip:buf.write])
+		n := copy(p[done:], buf.ReadSlice()[needToSkip:])
 		skipped += int64(needToSkip)
 		done += int64(n)
 	}
-	if int(done) < len(p) {
+	if int(done) < len(p) || offset+done == v.size {
 		return int(done), io.EOF
 	}
 	return int(done), nil
 }
 
-// Write implements io.Writer.Write.
-func (v *View) Write(p []byte) (int, error) {
-	v.Append(p) // Does not fail.
-	return len(p), nil
-}
-
 // advanceRead advances the view's read index.
 //
 // Precondition: there must be sufficient bytes in the buffer.
 func (v *View) advanceRead(count int64) {
 	for buf := v.data.Front(); buf != nil && count > 0; {
-		l := int64(buf.write - buf.read)
-		if l > count {
+		sz := int64(buf.ReadSize())
+		if sz > count {
 			// There is still data for reading.
-			buf.read += int(count)
+			buf.ReadMove(int(count))
 			v.size -= count
 			count = 0
 			break
 		}
 
-		// Read from this buffer.
-		buf.read += int(l)
-		count -= l
-		v.size -= l
-
-		// When all data has been read from a buffer, we push
-		// it into the empty buffer pool for reuse.
+		// Consume the whole buffer.
 		oldBuf := buf
 		buf = buf.Next() // Iterate.
 		v.data.Remove(oldBuf)
 		oldBuf.Reset()
 		bufferPool.Put(oldBuf)
+
+		// Update counts.
+		count -= sz
+		v.size -= sz
 	}
 	if count > 0 {
 		panic(fmt.Sprintf("advanceRead still has %d bytes remaining", count))
@@ -109,37 +93,39 @@ func (v *View) advanceRead(count int64) {
 }
 
 // Truncate truncates the view to the given bytes.
+//
+// This will not grow the view, only shrink it. If a length is passed that is
+// greater than the current size of the view, then nothing will happen.
+//
+// Precondition: length must be >= 0.
 func (v *View) Truncate(length int64) {
-	if length < 0 || length >= v.size {
+	if length < 0 {
+		panic("negative length provided")
+	}
+	if length >= v.size {
 		return // Nothing to do.
 	}
 	for buf := v.data.Back(); buf != nil && v.size > length; buf = v.data.Back() {
-		l := int64(buf.write - buf.read) // Local bytes.
-		switch {
-		case v.size-l >= length:
-			// Drop the buffer completely; see above.
-			v.data.Remove(buf)
-			v.size -= l
-			buf.Reset()
-			bufferPool.Put(buf)
-
-		case v.size > length && v.size-l < length:
-			// Just truncate the buffer locally.
-			delta := (length - (v.size - l))
-			buf.write = buf.read + int(delta)
+		sz := int64(buf.ReadSize())
+		if after := v.size - sz; after < length {
+			// Truncate the buffer locally.
+			left := (length - after)
+			buf.write = buf.read + int(left)
 			v.size = length
-
-		default:
-			// Should never happen.
-			panic("invalid buffer during truncation")
+			break
 		}
+
+		// Drop the buffer completely; see above.
+		v.data.Remove(buf)
+		buf.Reset()
+		bufferPool.Put(buf)
+		v.size -= sz
 	}
-	v.size = length // Save the new size.
 }
 
-// Grow grows the given view to the number of bytes. If zero
-// is true, all these bytes will be zero. If zero is false,
-// then this is the caller's responsibility.
+// Grow grows the given view to the number of bytes, which will be appended. If
+// zero is true, all these bytes will be zero. If zero is false, then this is
+// the caller's responsibility.
 //
 // Precondition: length must be >= 0.
 func (v *View) Grow(length int64, zero bool) {
@@ -149,29 +135,29 @@ func (v *View) Grow(length int64, zero bool) {
 	for v.size < length {
 		buf := v.data.Back()
 
-		// Is there at least one buffer?
+		// Is there some space in the last buffer?
 		if buf == nil || buf.Full() {
-			buf = bufferPool.Get().(*Buffer)
+			buf = bufferPool.Get().(*buffer)
 			v.data.PushBack(buf)
 		}
 
 		// Write up to length bytes.
-		l := len(buf.data) - buf.write
-		if int64(l) > length-v.size {
-			l = int(length - v.size)
+		sz := buf.WriteSize()
+		if int64(sz) > length-v.size {
+			sz = int(length - v.size)
 		}
 
 		// Zero the written section; note that this pattern is
 		// specifically recognized and optimized by the compiler.
 		if zero {
-			for i := buf.write; i < buf.write+l; i++ {
+			for i := buf.write; i < buf.write+sz; i++ {
 				buf.data[i] = 0
 			}
 		}
 
 		// Advance the index.
-		buf.write += l
-		v.size += int64(l)
+		buf.WriteMove(sz)
+		v.size += int64(sz)
 	}
 }
 
@@ -181,31 +167,40 @@ func (v *View) Prepend(data []byte) {
 	if buf := v.data.Front(); buf != nil && buf.read > 0 {
 		// Fill up before the first write.
 		avail := buf.read
-		copy(buf.data[0:], data[len(data)-avail:])
-		data = data[:len(data)-avail]
-		v.size += int64(avail)
+		bStart := 0
+		dStart := len(data) - avail
+		if avail > len(data) {
+			bStart = avail - len(data)
+			dStart = 0
+		}
+		n := copy(buf.data[bStart:], data[dStart:])
+		data = data[:dStart]
+		v.size += int64(n)
+		buf.read -= n
 	}
 
 	for len(data) > 0 {
 		// Do we need an empty buffer?
-		buf := bufferPool.Get().(*Buffer)
+		buf := bufferPool.Get().(*buffer)
 		v.data.PushFront(buf)
 
 		// The buffer is empty; copy last chunk.
-		start := len(data) - len(buf.data)
-		if start < 0 {
-			start = 0 // Everything.
+		avail := len(buf.data)
+		bStart := 0
+		dStart := len(data) - avail
+		if avail > len(data) {
+			bStart = avail - len(data)
+			dStart = 0
 		}
 
 		// We have to put the data at the end of the current
 		// buffer in order to ensure that the next prepend will
 		// correctly fill up the beginning of this buffer.
-		bStart := len(buf.data) - len(data[start:])
-		n := copy(buf.data[bStart:], data[start:])
-		buf.read = bStart
-		buf.write = len(buf.data)
-		data = data[:start]
+		n := copy(buf.data[bStart:], data[dStart:])
+		data = data[:dStart]
 		v.size += int64(n)
+		buf.read = len(buf.data) - n
+		buf.write = len(buf.data)
 	}
 }
 
@@ -214,16 +209,16 @@ func (v *View) Append(data []byte) {
 	for done := 0; done < len(data); {
 		buf := v.data.Back()
 
-		// Find the first empty buffer.
+		// Ensure there's a buffer with space.
 		if buf == nil || buf.Full() {
-			buf = bufferPool.Get().(*Buffer)
+			buf = bufferPool.Get().(*buffer)
 			v.data.PushBack(buf)
 		}
 
 		// Copy in to the given buffer.
-		n := copy(buf.data[buf.write:], data[done:])
+		n := copy(buf.WriteSlice(), data[done:])
 		done += n
-		buf.write += n
+		buf.WriteMove(n)
 		v.size += int64(n)
 	}
 }
@@ -232,52 +227,52 @@ func (v *View) Append(data []byte) {
 //
 // This method should not be used in any performance-sensitive paths. It may
 // allocate a fresh byte slice sufficiently large to contain all the data in
-// the buffer.
+// the buffer. This is principally for debugging.
 //
 // N.B. Tee data still belongs to this view, as if there is a single buffer
 // present, then it will be returned directly. This should be used for
 // temporary use only, and a reference to the given slice should not be held.
 func (v *View) Flatten() []byte {
-	if buf := v.data.Front(); buf.Next() == nil {
-		return buf.data[buf.read:buf.write] // Only one buffer.
+	if buf := v.data.Front(); buf == nil {
+		return nil // No data at all.
+	} else if buf.Next() == nil {
+		return buf.ReadSlice() // Only one buffer.
 	}
 	data := make([]byte, 0, v.size) // Need to flatten.
 	for buf := v.data.Front(); buf != nil; buf = buf.Next() {
 		// Copy to the allocated slice.
-		data = append(data, buf.data[buf.read:buf.write]...)
+		data = append(data, buf.ReadSlice()...)
 	}
 	return data
 }
 
 // Size indicates the total amount of data available in this view.
-func (v *View) Size() (sz int64) {
-	sz = v.size // Pre-calculated.
-	return sz
+func (v *View) Size() int64 {
+	return v.size
 }
 
 // Copy makes a strict copy of this view.
 func (v *View) Copy() (other View) {
 	for buf := v.data.Front(); buf != nil; buf = buf.Next() {
-		other.Append(buf.data[buf.read:buf.write])
+		other.Append(buf.ReadSlice())
 	}
-	return other
+	return
 }
 
 // Apply applies the given function across all valid data.
 func (v *View) Apply(fn func([]byte)) {
 	for buf := v.data.Front(); buf != nil; buf = buf.Next() {
-		if l := int64(buf.write - buf.read); l > 0 {
-			fn(buf.data[buf.read:buf.write])
-		}
+		fn(buf.ReadSlice())
 	}
 }
 
 // Merge merges the provided View with this one.
 //
-// The other view will be empty after this operation.
+// The other view will be appended to v, and other will be empty after this
+// operation completes.
 func (v *View) Merge(other *View) {
 	// Copy over all buffers.
-	for buf := other.data.Front(); buf != nil && !buf.Empty(); buf = other.data.Front() {
+	for buf := other.data.Front(); buf != nil; buf = other.data.Front() {
 		other.data.Remove(buf)
 		v.data.PushBack(buf)
 	}
@@ -288,6 +283,9 @@ func (v *View) Merge(other *View) {
 }
 
 // WriteFromReader writes to the buffer from an io.Reader.
+//
+// A minimum read size equal to unsafe.Sizeof(unintptr) is enforced,
+// provided that count is greater than or equal to unsafe.Sizeof(uintptr).
 func (v *View) WriteFromReader(r io.Reader, count int64) (int64, error) {
 	var (
 		done int64
@@ -297,17 +295,17 @@ func (v *View) WriteFromReader(r io.Reader, count int64) (int64, error) {
 	for done < count {
 		buf := v.data.Back()
 
-		// Find the first empty buffer.
+		// Ensure we have an empty buffer.
 		if buf == nil || buf.Full() {
-			buf = bufferPool.Get().(*Buffer)
+			buf = bufferPool.Get().(*buffer)
 			v.data.PushBack(buf)
 		}
 
 		// Is this less than the minimum batch?
-		if len(buf.data[buf.write:]) < minBatch && (count-done) >= int64(minBatch) {
+		if buf.WriteSize() < minBatch && (count-done) >= int64(minBatch) {
 			tmp := make([]byte, minBatch)
 			n, err = r.Read(tmp)
-			v.Write(tmp[:n])
+			v.Append(tmp[:n])
 			done += int64(n)
 			if err != nil {
 				break
@@ -316,14 +314,14 @@ func (v *View) WriteFromReader(r io.Reader, count int64) (int64, error) {
 		}
 
 		// Limit the read, if necessary.
-		end := len(buf.data)
-		if int64(end-buf.write) > (count - done) {
-			end = buf.write + int(count-done)
+		sz := buf.WriteSize()
+		if left := count - done; int64(sz) > left {
+			sz = int(left)
 		}
 
 		// Pass the relevant portion of the buffer.
-		n, err = r.Read(buf.data[buf.write:end])
-		buf.write += n
+		n, err = r.Read(buf.WriteSlice()[:sz])
+		buf.WriteMove(n)
 		done += int64(n)
 		v.size += int64(n)
 		if err == io.EOF {
@@ -340,6 +338,9 @@ func (v *View) WriteFromReader(r io.Reader, count int64) (int64, error) {
 //
 // N.B. This does not consume the bytes read. TrimFront should
 // be called appropriately after this call in order to do so.
+//
+// A minimum write size equal to unsafe.Sizeof(unintptr) is enforced,
+// provided that count is greater than or equal to unsafe.Sizeof(uintptr).
 func (v *View) ReadToWriter(w io.Writer, count int64) (int64, error) {
 	var (
 		done int64
@@ -348,15 +349,22 @@ func (v *View) ReadToWriter(w io.Writer, count int64) (int64, error) {
 	)
 	offset := 0 // Spill-over for batching.
 	for buf := v.data.Front(); buf != nil && done < count; buf = buf.Next() {
-		l := buf.write - buf.read - offset
+		// Has this been consumed? Skip it.
+		sz := buf.ReadSize()
+		if sz <= offset {
+			offset -= sz
+			continue
+		}
+		sz -= offset
 
 		// Is this less than the minimum batch?
-		if l < minBatch && (count-done) >= int64(minBatch) && (v.size-done) >= int64(minBatch) {
+		left := count - done
+		if sz < minBatch && left >= int64(minBatch) && (v.size-done) >= int64(minBatch) {
 			tmp := make([]byte, minBatch)
 			n, err = v.ReadAt(tmp, done)
 			w.Write(tmp[:n])
 			done += int64(n)
-			offset = n - l // Reset below.
+			offset = n - sz // Reset below.
 			if err != nil {
 				break
 			}
@@ -364,12 +372,12 @@ func (v *View) ReadToWriter(w io.Writer, count int64) (int64, error) {
 		}
 
 		// Limit the write if necessary.
-		if int64(l) >= (count - done) {
-			l = int(count - done)
+		if int64(sz) >= left {
+			sz = int(left)
 		}
 
 		// Perform the actual write.
-		n, err = w.Write(buf.data[buf.read+offset : buf.read+offset+l])
+		n, err = w.Write(buf.ReadSlice()[offset : offset+sz])
 		done += int64(n)
 		if err != nil {
 			break