1 files changed, 390 insertions, 0 deletions
diff --git a/pkg/buffer/view.go b/pkg/buffer/view.go
new file mode 100644
index 000000000..e6901eadb
--- /dev/null
+++ b/pkg/buffer/view.go
@@ -0,0 +1,390 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buffer
+
+import (
+	"fmt"
+	"io"
+)
+
+// View is a non-linear buffer.
+//
+// All methods are thread compatible.
+//
+// +stateify savable
+type View struct {
+	data bufferList
+	size int64
+}
+
+// TrimFront removes the first count bytes from the buffer.
+func (v *View) TrimFront(count int64) {
+	if count >= v.size {
+		v.advanceRead(v.size)
+	} else {
+		v.advanceRead(count)
+	}
+}
+
+// ReadAt implements io.ReaderAt.ReadAt.
+func (v *View) ReadAt(p []byte, offset int64) (int, error) {
+	var (
+		skipped int64
+		done    int64
+	)
+	for buf := v.data.Front(); buf != nil && done < int64(len(p)); buf = buf.Next() {
+		needToSkip := int(offset - skipped)
+		if sz := buf.ReadSize(); sz <= needToSkip {
+			skipped += int64(sz)
+			continue
+		}
+
+		// Actually read data.
+		n := copy(p[done:], buf.ReadSlice()[needToSkip:])
+		skipped += int64(needToSkip)
+		done += int64(n)
+	}
+	if int(done) < len(p) || offset+done == v.size {
+		return int(done), io.EOF
+	}
+	return int(done), 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; {
+		sz := int64(buf.ReadSize())
+		if sz > count {
+			// There is still data for reading.
+			buf.ReadMove(int(count))
+			v.size -= count
+			count = 0
+			break
+		}
+
+		// 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))
+	}
+}
+
+// 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 {
+		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() {
+		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
+			break
+		}
+
+		// Drop the buffer completely; see above.
+		v.data.Remove(buf)
+		buf.Reset()
+		bufferPool.Put(buf)
+		v.size -= sz
+	}
+}
+
+// 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) {
+	if length < 0 {
+		panic("negative length provided")
+	}
+	for v.size < length {
+		buf := v.data.Back()
+
+		// Is there some space in the last buffer?
+		if buf == nil || buf.Full() {
+			buf = bufferPool.Get().(*buffer)
+			v.data.PushBack(buf)
+		}
+
+		// Write up to length bytes.
+		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+sz; i++ {
+				buf.data[i] = 0
+			}
+		}
+
+		// Advance the index.
+		buf.WriteMove(sz)
+		v.size += int64(sz)
+	}
+}
+
+// Prepend prepends the given data.
+func (v *View) Prepend(data []byte) {
+	// Is there any space in the first buffer?
+	if buf := v.data.Front(); buf != nil && buf.read > 0 {
+		// Fill up before the first write.
+		avail := buf.read
+		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)
+		v.data.PushFront(buf)
+
+		// The buffer is empty; copy last chunk.
+		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.
+		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)
+	}
+}
+
+// Append appends the given data.
+func (v *View) Append(data []byte) {
+	for done := 0; done < len(data); {
+		buf := v.data.Back()
+
+		// Ensure there's a buffer with space.
+		if buf == nil || buf.Full() {
+			buf = bufferPool.Get().(*buffer)
+			v.data.PushBack(buf)
+		}
+
+		// Copy in to the given buffer.
+		n := copy(buf.WriteSlice(), data[done:])
+		done += n
+		buf.WriteMove(n)
+		v.size += int64(n)
+	}
+}
+
+// Flatten returns a flattened copy of this data.
+//
+// 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. 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 == 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.ReadSlice()...)
+	}
+	return data
+}
+
+// Size indicates the total amount of data available in this view.
+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.ReadSlice())
+	}
+	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() {
+		fn(buf.ReadSlice())
+	}
+}
+
+// Merge merges the provided View with this one.
+//
+// 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 = other.data.Front() {
+		other.data.Remove(buf)
+		v.data.PushBack(buf)
+	}
+
+	// Adjust sizes.
+	v.size += other.size
+	other.size = 0
+}
+
+// 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
+		n    int
+		err  error
+	)
+	for done < count {
+		buf := v.data.Back()
+
+		// Ensure we have an empty buffer.
+		if buf == nil || buf.Full() {
+			buf = bufferPool.Get().(*buffer)
+			v.data.PushBack(buf)
+		}
+
+		// Is this less than the minimum batch?
+		if buf.WriteSize() < minBatch && (count-done) >= int64(minBatch) {
+			tmp := make([]byte, minBatch)
+			n, err = r.Read(tmp)
+			v.Append(tmp[:n])
+			done += int64(n)
+			if err != nil {
+				break
+			}
+			continue
+		}
+
+		// Limit the read, if necessary.
+		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.WriteSlice()[:sz])
+		buf.WriteMove(n)
+		done += int64(n)
+		v.size += int64(n)
+		if err == io.EOF {
+			err = nil // Short write allowed.
+			break
+		} else if err != nil {
+			break
+		}
+	}
+	return done, err
+}
+
+// ReadToWriter reads from the buffer into an io.Writer.
+//
+// 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
+		n    int
+		err  error
+	)
+	offset := 0 // Spill-over for batching.
+	for buf := v.data.Front(); buf != nil && done < count; buf = buf.Next() {
+		// Has this been consumed? Skip it.
+		sz := buf.ReadSize()
+		if sz <= offset {
+			offset -= sz
+			continue
+		}
+		sz -= offset
+
+		// Is this less than the minimum batch?
+		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 - sz // Reset below.
+			if err != nil {
+				break
+			}
+			continue
+		}
+
+		// Limit the write if necessary.
+		if int64(sz) >= left {
+			sz = int(left)
+		}
+
+		// Perform the actual write.
+		n, err = w.Write(buf.ReadSlice()[offset : offset+sz])
+		done += int64(n)
+		if err != nil {
+			break
+		}
+
+		// Reset spill-over.
+		offset = 0
+	}
+	return done, err
+}