cipd: Refactor client to make it more readable.

go/src/infra/tools/cipd/storage.go

Index: go/src/infra/tools/cipd/storage.go
diff --git a/go/src/infra/tools/cipd/storage.go b/go/src/infra/tools/cipd/storage.go
new file mode 100644
index 0000000000000000000000000000000000000000..787dfeff33dcbc41db0a5a16dadde4578ff26356
--- /dev/null
+++ b/go/src/infra/tools/cipd/storage.go
@@ -0,0 +1,278 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package cipd
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"time"
+)
+
+const (
+	// uploadChunkSize is the max size of a single PUT HTTP request during upload.
+	uploadChunkSize int64 = 4 * 1024 * 1024
+	// uploadMaxErrors is the number of transient errors after which upload is aborted.
+	uploadMaxErrors = 20
+	// downloadReportInterval defines frequency of "downloaded X%" log lines.
+	downloadReportInterval = 5 * time.Second
+	// downloadMaxAttempts is how many times to retry a download on errors.
+	downloadMaxAttempts = 10
+)
+
+// errTransientError is returned by getNextOffset in case of retryable error.
+var errTransientError = errors.New("Transient error in getUploadedOffset")
+
+// storageImpl implements storage via Google Storage signed URLs.
+type storageImpl struct {
+	client    *Client
+	chunkSize int64
+}
+
+// Google Storage resumable upload protocol.
+// See https://cloud.google.com/storage/docs/concepts-techniques#resumable
+
+func (s *storageImpl) upload(url string, data io.ReadSeeker) error {
+	// Grab the total length of the file.
+	length, err := data.Seek(0, os.SEEK_END)
+	if err != nil {
+		return err
+	}
+	_, err = data.Seek(0, os.SEEK_SET)
+	if err != nil {
+		return err
+	}
+
+	// Offset of data known to be persisted in the storage or -1 if needed to ask
+	// Google Storage for it.
+	offset := int64(0)
+	// Number of transient errors reported so far.
+	errors := 0
+
+	// Called when some new data is uploaded.
+	reportProgress := func(offset int64) {
+		if length != 0 {
+			s.client.Log.Infof("cipd: uploading - %d%%", offset*100/length)
+		}
+	}
+
+	// Called when transient error happens.
+	reportTransientError := func() {
+		// Need to query for latest uploaded offset to resume.
+		errors++
+		offset = -1
+		if errors < uploadMaxErrors {
+			s.client.Log.Warningf("cipd: transient upload error, retrying...")
+			s.client.clock.sleep(2 * time.Second)
+		}
+	}
+
+	reportProgress(0)
+	for errors < uploadMaxErrors {
+		// Grab latest uploaded offset if not known.
+		if offset == -1 {
+			offset, err = s.getNextOffset(url, length)
+			if err == errTransientError {
+				reportTransientError()
+				continue
+			}
+			if err != nil {
+				return err
+			}
+			reportProgress(offset)
+			if offset == length {
+				return nil
+			}
+			s.client.Log.Warningf("cipd: resuming upload from offset %d", offset)
+		}
+
+		// Length of a chunk to upload.
+		chunk := s.chunkSize
+		if chunk > length-offset {
+			chunk = length - offset
+		}
+
+		// Upload the chunk.
+		data.Seek(offset, os.SEEK_SET)
+		r, err := http.NewRequest("PUT", url, io.LimitReader(data, chunk))
+		if err != nil {
+			return err
+		}
+		rangeHeader := fmt.Sprintf("bytes %d-%d/%d", offset, offset+chunk-1, length)
+		r.Header.Set("Content-Range", rangeHeader)
+		r.Header.Set("Content-Length", fmt.Sprintf("%d", chunk))
+		r.Header.Set("User-Agent", s.client.UserAgent)
+		resp, err := s.client.doAnonymousHTTPRequest(r)
+		if err != nil {
+			if isTemporaryNetError(err) {
+				reportTransientError()
+				continue
+			}
+			return err
+		}
+		resp.Body.Close()
+
+		// Partially or fully uploaded.
+		if resp.StatusCode == 308 || resp.StatusCode == 200 {
+			offset += chunk
+			reportProgress(offset)
+			if offset == length {
+				return nil
+			}
+			continue
+		}
+
+		// Transient error.
+		if isTemporaryHTTPError(resp.StatusCode) {
+			reportTransientError()
+			continue
+		}
+
+		// Fatal error.
+		return fmt.Errorf("Unexpected response during file upload: HTTP %d", resp.StatusCode)
+	}
+
+	return ErrUploadError
+}
+
+// getNextOffset queries the storage for size of persisted data.
+func (s *storageImpl) getNextOffset(url string, length int64) (offset int64, err error) {
+	r, err := http.NewRequest("PUT", url, nil)
+	if err != nil {
+		return
+	}
+	r.Header.Set("Content-Range", fmt.Sprintf("bytes */%d", length))
+	r.Header.Set("Content-Length", "0")
+	r.Header.Set("User-Agent", s.client.UserAgent)
+	resp, err := s.client.doAnonymousHTTPRequest(r)
+	if err != nil {
+		if isTemporaryNetError(err) {
+			err = errTransientError
+		}
+		return
+	}
+	resp.Body.Close()
+
+	if resp.StatusCode == 200 {
+		// Fully uploaded.
+		offset = length
+	} else if resp.StatusCode == 308 {
+		// Partially uploaded, extract last uploaded offset from Range header.
+		rangeHeader := resp.Header.Get("Range")
+		if rangeHeader != "" {
+			_, err = fmt.Sscanf(rangeHeader, "bytes=0-%d", &offset)
+			if err == nil {
+				// |offset| is an *offset* of a last uploaded byte, not the data length.
+				offset++
+			}
+		}
+	} else if isTemporaryHTTPError(resp.StatusCode) {
+		err = errTransientError
+	} else {
+		err = fmt.Errorf("Unexpected response (HTTP %d) when querying for uploaded offset", resp.StatusCode)
+	}
+	return
+}
+
+// TODO(vadimsh): Use resumable download protocol.
+
+func (s *storageImpl) download(url string, output io.WriteSeeker) error {
+	// reportProgress print fetch progress, throttling the reports rate.
+	var prevProgress int64 = 1000 // >100%
+	var prevReportTs time.Time
+	reportProgress := func(read int64, total int64) {
+		now := s.client.clock.now()
+		progress := read * 100 / total
+		if progress < prevProgress || read == total || now.Sub(prevReportTs) > downloadReportInterval {
+			s.client.Log.Infof("cipd: fetching - %d%%", progress)
+			prevReportTs = now
+			prevProgress = progress
+		}
+	}
+
+	// download is a separate function to be able to use deferred close.
+	download := func(out io.WriteSeeker, src io.ReadCloser, totalLen int64) error {
+		defer src.Close()
+		s.client.Log.Infof("cipd: about to fetch %.1f Mb", float32(totalLen)/1024.0/1024.0)
+		reportProgress(0, totalLen)
+		_, err := io.Copy(out, &readerWithProgress{
+			reader:   src,
+			callback: func(read int64) { reportProgress(read, totalLen) },
+		})
+		if err == nil {
+			s.client.Log.Infof("cipd: fetch finished successfully")
+		}
+		return err
+	}
+
+	// Download the actual data (several attempts).
+	for attempt := 0; attempt < downloadMaxAttempts; attempt++ {
+		// Rewind output to zero offset.
+		_, err := output.Seek(0, os.SEEK_SET)
+		if err != nil {
+			return err
+		}
+
+		// Send the request.
+		s.client.Log.Infof("cipd: initiating the fetch")
+		var req *http.Request
+		var resp *http.Response
+		req, err = http.NewRequest("GET", url, nil)
+		if err != nil {
+			return err
+		}
+		req.Header.Set("User-Agent", s.client.UserAgent)
+		resp, err = s.client.doAnonymousHTTPRequest(req)
+		if err != nil {
+			if isTemporaryNetError(err) {
+				s.client.Log.Warningf("cipd: transient network error: %s", err)
+				continue
+			}
+			return err
+		}
+
+		// Transient error, retry.
+		if isTemporaryHTTPError(resp.StatusCode) {
+			resp.Body.Close()
+			s.client.Log.Warningf("cipd: transient HTTP error %d while fetching the file", resp.StatusCode)
+			continue
+		}
+
+		// Fatal error, abort.
+		if resp.StatusCode >= 400 {
+			resp.Body.Close()
+			return fmt.Errorf("Server replied with HTTP code %d", resp.StatusCode)
+		}
+
+		// Try to fetch (will close resp.Body when done).
+		err = download(output, resp.Body, resp.ContentLength)
+		if err != nil {
+			s.client.Log.Warningf("cipd: transient error fetching the file: %s", err)
+			continue
+		}
+
+		// Success.
+		return nil
+	}
+
+	return ErrDownloadError
+}
+
+// readerWithProgress is io.Reader that calls callback whenever something is
+// read from it.
+type readerWithProgress struct {
+	reader   io.Reader
+	total    int64
+	callback func(total int64)
+}
+
+func (r *readerWithProgress) Read(p []byte) (int, error) {
+	n, err := r.reader.Read(p)
+	r.total += int64(n)
+	r.callback(r.total)
+	return n, err
+}