ServiceWorkerWriteToCacheJob: refactor

content/browser/service_worker/service_worker_cache_writer.h

+// 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.
+
+#ifndef CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_CACHE_WRITER_H_
+#define CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_CACHE_WRITER_H_
+
+#include <map>
+#include <set>
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "content/common/content_export.h"
+#include "net/base/io_buffer.h"
+#include "net/base/net_errors.h"
+
+namespace content {
+
+struct HttpResponseInfoIOBuffer;
+class ServiceWorkerCacheWriterCore;
+class ServiceWorkerResponseReader;
+class ServiceWorkerResponseWriter;
+class ServiceWorkerStorage;
+
+// This class is responsible for possibly updating the ServiceWorker script
+// cache for an installed ServiceWorker main script. If there is no existing
+// cache entry, this class always writes supplied data back to the cache; if
+// there is an existing cache entry, this class only writes supplied data back
+// if there is a cache mismatch.
+//
+// Note that writes done by this class cannot be "short" - ie, if they succeed,
+// they always write all the supplied data back. Therefore completions are
+// signalled with net::Error without a count of bytes written.
+//
+// This class's behavior is modelled as a state machine; see the DoLoop function
+// for comments about this.
+class CONTENT_EXPORT ServiceWorkerCacheWriter {
+ public:
+  using OnWriteCompleteCallback = base::Callback<void(net::Error)>;
+
+  // The types for the factory functions passed into the constructor. These are
+  // responsible for creating readers from the existing cache entry and writers
+  // to the new cache entry when called. These are passed in as factories
+  // instead of passing readers and writers in directly to avoid creating
+  // writers to entries that won't be updated, and because this class may need
+  // multiple readers internally.
+  using ResponseReaderCreator =
+      base::Callback<scoped_ptr<ServiceWorkerResponseReader>(void)>;
+  using ResponseWriterCreator =
+      base::Callback<scoped_ptr<ServiceWorkerResponseWriter>(void)>;
+
+  // The existing reader may be null, in which case this instance will
+  // unconditionally write back data supplied to |MaybeWriteHeaders| and
+  // |MaybeWriteData|.
+  ServiceWorkerCacheWriter(const ResponseReaderCreator& reader_creator,
+                           const ResponseWriterCreator& writer_creator);
+
+  ~ServiceWorkerCacheWriter();
+
+  // Writes the supplied |headers| back to the cache. Returns ERR_IO_PENDING if
+  // the write will complete asynchronously, in which case |callback| will be
+  // called when it completes. Otherwise, returns a code other than
+  // ERR_IO_PENDING and does not invoke |callback|. Note that this method will
+  // not necessarily write data back to the cache if the incoming data is
+  // equivalent to the existing cached data. See the source of this function for
+  // details about how this function drives the state machine.
+  net::Error MaybeWriteHeaders(HttpResponseInfoIOBuffer* headers,
+                               const OnWriteCompleteCallback& callback);
+
+  // Writes the supplied body data |data| back to the cache. Returns
+  // ERR_IO_PENDING if the write will complete asynchronously, in which case
+  // |callback| will be called when it completes. Otherwise, returns a code
+  // other than ERR_IO_PENDING and does not invoke |callback|. Note that this
+  // method will not necessarily write data back to the cache if the incoming
+  // data is equivalent to the existing cached data. See the source of this
+  // function for details about how this function drives the state machine.
+  net::Error MaybeWriteData(net::IOBuffer* buf,
+                            size_t buf_size,
+                            const OnWriteCompleteCallback& callback);
+
+  // Returns a count of bytes written back to the cache.
+  size_t bytes_written() const { return bytes_written_; }
+  bool did_replace() const { return did_replace_; }
+
+ private:
+  // States for the state machine.
+  //
+  // The state machine flows roughly like this: if there is no existing cache
+  // entry, incoming headers and data are written directly back to the cache
+  // ("passthrough mode", the PASSTHROUGH states). If there is an existing cache
+  // entry, incoming headers and data are compared to the existing cache entry
+  // ("compare mode", the COMPARE states); if at any point the incoming
+  // headers/data are not equal to the cached headers/data, this class copies
+  // the cached data up to the point where the incoming data and the cached data
+  // diverged ("copy mode", the COPY states), then switches to "passthrough
+  // mode" to write the remainder of the incoming data. The overall effect is to
+  // avoid rewriting the cache entry if the incoming data is identical to the
+  // cached data.
+  //
+  // Note that after a call to MaybeWriteHeaders or MaybeWriteData completes,
+  // the machine is always in STATE_DONE, indicating that the call is finished;
+  // those methods are responsible for setting a new initial state.
+  enum State {
+    STATE_START,
+    // Control flows linearly through these four states, then loops from
+    // READ_DATA_FOR_COMPARE_DONE to READ_DATA_FOR_COMPARE, or exits to
+    // READ_HEADERS_FOR_COPY.
+    STATE_READ_HEADERS_FOR_COMPARE,
+    STATE_READ_HEADERS_FOR_COMPARE_DONE,
+    STATE_READ_DATA_FOR_COMPARE,
+    STATE_READ_DATA_FOR_COMPARE_DONE,
+
+    // Control flows linearly through these states, with each pass from
+    // READ_DATA_FOR_COPY to WRITE_DATA_FOR_COPY_DONE copying one block of data
+    // at a time. Control loops from WRITE_DATA_FOR_COPY_DONE back to
+    // READ_DATA_FOR_COPY if there is more data to copy, or exits to
+    // WRITE_DATA_FOR_PASSTHROUGH.
+    STATE_READ_HEADERS_FOR_COPY,
+    STATE_READ_HEADERS_FOR_COPY_DONE,
+    STATE_WRITE_HEADERS_FOR_COPY,
+    STATE_WRITE_HEADERS_FOR_COPY_DONE,
+    STATE_READ_DATA_FOR_COPY,
+    STATE_READ_DATA_FOR_COPY_DONE,
+    STATE_WRITE_DATA_FOR_COPY,
+    STATE_WRITE_DATA_FOR_COPY_DONE,
+
+    // Control flows linearly through these states, with a loop between
+    // WRITE_DATA_FOR_PASSTHROUGH and WRITE_DATA_FOR_PASSTHROUGH_DONE.
+    STATE_WRITE_HEADERS_FOR_PASSTHROUGH,
+    STATE_WRITE_HEADERS_FOR_PASSTHROUGH_DONE,
+    STATE_WRITE_DATA_FOR_PASSTHROUGH,
+    STATE_WRITE_DATA_FOR_PASSTHROUGH_DONE,
+
+    // This state means "done with the current call; ready for another one."
+    STATE_DONE,
+  };
+
+  // Drives this class's state machine. This function steps the state machine
+  // until one of:
+  //   a) One of the state functions returns an error
+  //   b) The state machine reaches STATE_DONE
+  // A successful value (net::OK or greater) indicates that the requested
+  // operation completed synchronously. A return value of ERR_IO_PENDING
+  // indicates that some step had to submit asynchronous IO for later
+  // completion, and the state machine will resume running (via AsyncDoLoop)
+  // when that asynchronous IO completes. Any other return value indicates that
+  // the requested operation failed synchronously.
+  int DoLoop(int result);
+
+  // State handlers. See function comments in the corresponding source file for
+  // details on these.
+  int DoStart(int result);
+  int DoReadHeadersForCompare(int result);
+  int DoReadHeadersForCompareDone(int result);
+  int DoReadDataForCompare(int result);
+  int DoReadDataForCompareDone(int result);
+  int DoReadHeadersForCopy(int result);
+  int DoReadHeadersForCopyDone(int result);
+  int DoWriteHeadersForCopy(int result);
+  int DoWriteHeadersForCopyDone(int result);
+  int DoReadDataForCopy(int result);
+  int DoReadDataForCopyDone(int result);
+  int DoWriteDataForCopy(int result);
+  int DoWriteDataForCopyDone(int result);
+  int DoWriteHeadersForPassthrough(int result);
+  int DoWriteHeadersForPassthroughDone(int result);
+  int DoWriteDataForPassthrough(int result);
+  int DoWriteDataForPassthroughDone(int result);
+  int DoDone(int result);
+
+  // Wrappers for asynchronous calls. These are responsible for scheduling a
+  // callback to drive the state machine if needed. These either:
+  //   a) Return ERR_IO_PENDING, and schedule a callback to run the state
+  //      machine's Run() later, or
+  //   b) Return some other value and do not schedule a callback.
+  int ReadInfoHelper(const scoped_ptr<ServiceWorkerResponseReader>& reader,
+                     HttpResponseInfoIOBuffer* buf);
+  int ReadDataHelper(const scoped_ptr<ServiceWorkerResponseReader>& reader,
+                     net::IOBuffer* buf,
+                     int buf_len);
+  int WriteInfoHelper(const scoped_ptr<ServiceWorkerResponseWriter>& writer,
+                      HttpResponseInfoIOBuffer* buf);
+  int WriteDataHelper(const scoped_ptr<ServiceWorkerResponseWriter>& writer,
+                      net::IOBuffer* buf,
+                      int buf_len);
+
+  // Callback used by the above helpers for their IO operations. This is only
+  // run when those IO operations complete asynchronously, in which case it
+  // invokes the synchronous DoLoop function and runs the client callback (the
+  // one passed into MaybeWriteData/MaybeWriteHeaders) if that invocation
+  // of DoLoop completes synchronously.
+  void AsyncDoLoop(int result);
+
+  State state_;
+  // Note that this variable is only used for assertions; it reflects "state !=
+  // DONE && not in synchronous DoLoop".
+  bool io_pending_;
+  bool comparing_;
+
+  scoped_refptr<HttpResponseInfoIOBuffer> headers_to_read_;
+  scoped_refptr<HttpResponseInfoIOBuffer> headers_to_write_;
+  scoped_refptr<net::IOBuffer> data_to_read_;
+  int len_to_read_;
+  scoped_refptr<net::IOBuffer> data_to_copy_;
+  scoped_refptr<net::IOBuffer> data_to_write_;
+  int len_to_write_;
+  OnWriteCompleteCallback pending_callback_;
+
+  size_t cached_length_;
+
+  size_t bytes_compared_;
+  size_t bytes_copied_;
+  size_t bytes_written_;
+
+  bool did_replace_;
+
+  size_t compare_offset_;
+
+  ResponseReaderCreator reader_creator_;
+  ResponseWriterCreator writer_creator_;
+  scoped_ptr<ServiceWorkerResponseReader> compare_reader_;
+  scoped_ptr<ServiceWorkerResponseReader> copy_reader_;
+  scoped_ptr<ServiceWorkerResponseWriter> writer_;
+  base::WeakPtrFactory<ServiceWorkerCacheWriter> weak_factory_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_SERVICE_WORKER_SERVICE_WORKER_CACHE_WRITER_H_