Vendor dependencies for GCS

vendor/google.golang.org/appengine/blobstore/read.go

@@ -0,0 +1,160 @@
+// Copyright 2012 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package blobstore
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"sync"
+
+	"github.com/golang/protobuf/proto"
+	"golang.org/x/net/context"
+
+	"google.golang.org/appengine"
+	"google.golang.org/appengine/internal"
+
+	blobpb "google.golang.org/appengine/internal/blobstore"
+)
+
+// openBlob returns a reader for a blob. It always succeeds; if the blob does
+// not exist then an error will be reported upon first read.
+func openBlob(c context.Context, blobKey appengine.BlobKey) Reader {
+	return &reader{
+		c:       c,
+		blobKey: blobKey,
+	}
+}
+
+const readBufferSize = 256 * 1024
+
+// reader is a blob reader. It implements the Reader interface.
+type reader struct {
+	c context.Context
+
+	// Either blobKey or filename is set:
+	blobKey  appengine.BlobKey
+	filename string
+
+	closeFunc func() // is nil if unavailable or already closed.
+
+	// buf is the read buffer. r is how much of buf has been read.
+	// off is the offset of buf[0] relative to the start of the blob.
+	// An invariant is 0 <= r && r <= len(buf).
+	// Reads that don't require an RPC call will increment r but not off.
+	// Seeks may modify r without discarding the buffer, but only if the
+	// invariant can be maintained.
+	mu  sync.Mutex
+	buf []byte
+	r   int
+	off int64
+}
+
+func (r *reader) Close() error {
+	if f := r.closeFunc; f != nil {
+		f()
+	}
+	r.closeFunc = nil
+	return nil
+}
+
+func (r *reader) Read(p []byte) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.r == len(r.buf) {
+		if err := r.fetch(r.off + int64(r.r)); err != nil {
+			return 0, err
+		}
+	}
+	n := copy(p, r.buf[r.r:])
+	r.r += n
+	return n, nil
+}
+
+func (r *reader) ReadAt(p []byte, off int64) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	// Convert relative offsets to absolute offsets.
+	ab0 := r.off + int64(r.r)
+	ab1 := r.off + int64(len(r.buf))
+	ap0 := off
+	ap1 := off + int64(len(p))
+	// Check if we can satisfy the read entirely out of the existing buffer.
+	if r.off <= ap0 && ap1 <= ab1 {
+		// Convert off from an absolute offset to a relative offset.
+		rp0 := int(ap0 - r.off)
+		return copy(p, r.buf[rp0:]), nil
+	}
+	// Restore the original Read/Seek offset after ReadAt completes.
+	defer r.seek(ab0)
+	// Repeatedly fetch and copy until we have filled p.
+	n := 0
+	for len(p) > 0 {
+		if err := r.fetch(off + int64(n)); err != nil {
+			return n, err
+		}
+		r.r = copy(p, r.buf)
+		n += r.r
+		p = p[r.r:]
+	}
+	return n, nil
+}
+
+func (r *reader) Seek(offset int64, whence int) (ret int64, err error) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	switch whence {
+	case os.SEEK_SET:
+		ret = offset
+	case os.SEEK_CUR:
+		ret = r.off + int64(r.r) + offset
+	case os.SEEK_END:
+		return 0, errors.New("seeking relative to the end of a blob isn't supported")
+	default:
+		return 0, fmt.Errorf("invalid Seek whence value: %d", whence)
+	}
+	if ret < 0 {
+		return 0, errors.New("negative Seek offset")
+	}
+	return r.seek(ret)
+}
+
+// fetch fetches readBufferSize bytes starting at the given offset. On success,
+// the data is saved as r.buf.
+func (r *reader) fetch(off int64) error {
+	req := &blobpb.FetchDataRequest{
+		BlobKey:    proto.String(string(r.blobKey)),
+		StartIndex: proto.Int64(off),
+		EndIndex:   proto.Int64(off + readBufferSize - 1), // EndIndex is inclusive.
+	}
+	res := &blobpb.FetchDataResponse{}
+	if err := internal.Call(r.c, "blobstore", "FetchData", req, res); err != nil {
+		return err
+	}
+	if len(res.Data) == 0 {
+		return io.EOF
+	}
+	r.buf, r.r, r.off = res.Data, 0, off
+	return nil
+}
+
+// seek seeks to the given offset with an effective whence equal to SEEK_SET.
+// It discards the read buffer if the invariant cannot be maintained.
+func (r *reader) seek(off int64) (int64, error) {
+	delta := off - r.off
+	if delta >= 0 && delta < int64(len(r.buf)) {
+		r.r = int(delta)
+		return off, nil
+	}
+	r.buf, r.r, r.off = nil, 0, off
+	return off, nil
+}