media/blink/buffered_resource_loader.cc

   1 // Copyright 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/blink/buffered_resource_loader.h"
   6
   7 #include "base/bits.h"
   8 #include "base/callback_helpers.h"
   9 #include "base/metrics/histogram.h"
  10 #include "base/strings/string_number_conversions.h"
  11 #include "base/strings/string_util.h"
  12 #include "media/base/media_log.h"
  13 #include "media/blink/cache_util.h"
  14 #include "net/http/http_byte_range.h"
  15 #include "net/http/http_request_headers.h"
  16 #include "third_party/WebKit/public/platform/WebString.h"
  17 #include "third_party/WebKit/public/platform/WebURLError.h"
  18 #include "third_party/WebKit/public/platform/WebURLResponse.h"
  19 #include "third_party/WebKit/public/web/WebKit.h"
  20 #include "third_party/WebKit/public/web/WebURLLoaderOptions.h"
  21
  22 using blink::WebFrame;
  23 using blink::WebString;
  24 using blink::WebURLError;
  25 using blink::WebURLLoader;
  26 using blink::WebURLLoaderOptions;
  27 using blink::WebURLRequest;
  28 using blink::WebURLResponse;
  29
  30 namespace media {
  31
  32 static const int kHttpOK = 200;
  33 static const int kHttpPartialContent = 206;
  34
  35 // Define the number of bytes in a megabyte.
  36 static const int kMegabyte = 1024 * 1024;
  37
  38 // Minimum capacity of the buffer in forward or backward direction.
  39 //
  40 // 2MB is an arbitrary limit; it just seems to be "good enough" in practice.
  41 static const int kMinBufferCapacity = 2 * kMegabyte;
  42
  43 // Maximum capacity of the buffer in forward or backward direction. This is
  44 // effectively the largest single read the code path can handle.
  45 // 20MB is an arbitrary limit; it just seems to be "good enough" in practice.
  46 static const int kMaxBufferCapacity = 20 * kMegabyte;
  47
  48 // Maximum number of bytes outside the buffer we will wait for in order to
  49 // fulfill a read. If a read starts more than 2MB away from the data we
  50 // currently have in the buffer, we will not wait for buffer to reach the read's
  51 // location and will instead reset the request.
  52 static const int kForwardWaitThreshold = 2 * kMegabyte;
  53
  54 // Computes the suggested backward and forward capacity for the buffer
  55 // if one wants to play at |playback_rate| * the natural playback speed.
  56 // Use a value of 0 for |bitrate| if it is unknown.
  57 static void ComputeTargetBufferWindow(float playback_rate, int bitrate,
  58                                       int* out_backward_capacity,
  59                                       int* out_forward_capacity) {
  60   static const int kDefaultBitrate = 200 * 1024 * 8;  // 200 Kbps.
  61   static const int kMaxBitrate = 20 * kMegabyte * 8;  // 20 Mbps.
  62   static const float kMaxPlaybackRate = 25.0;
  63   static const int kTargetSecondsBufferedAhead = 10;
  64   static const int kTargetSecondsBufferedBehind = 2;
  65
  66   // Use a default bit rate if unknown and clamp to prevent overflow.
  67   if (bitrate <= 0)
  68     bitrate = kDefaultBitrate;
  69   bitrate = std::min(bitrate, kMaxBitrate);
  70
  71   // Only scale the buffer window for playback rates greater than 1.0 in
  72   // magnitude and clamp to prevent overflow.
  73   bool backward_playback = false;
  74   if (playback_rate < 0.0f) {
  75     backward_playback = true;
  76     playback_rate *= -1.0f;
  77   }
  78
  79   playback_rate = std::max(playback_rate, 1.0f);
  80   playback_rate = std::min(playback_rate, kMaxPlaybackRate);
  81
  82   int bytes_per_second = (bitrate / 8.0) * playback_rate;
  83
  84   // Clamp between kMinBufferCapacity and kMaxBufferCapacity.
  85   *out_forward_capacity = std::max(
  86       kTargetSecondsBufferedAhead * bytes_per_second, kMinBufferCapacity);
  87   *out_backward_capacity = std::max(
  88       kTargetSecondsBufferedBehind * bytes_per_second, kMinBufferCapacity);
  89
  90   *out_forward_capacity = std::min(*out_forward_capacity, kMaxBufferCapacity);
  91   *out_backward_capacity = std::min(*out_backward_capacity, kMaxBufferCapacity);
  92
  93   if (backward_playback)
  94     std::swap(*out_forward_capacity, *out_backward_capacity);
  95 }
  96
  97 BufferedResourceLoader::BufferedResourceLoader(
  98     const GURL& url,
  99     CORSMode cors_mode,
 100     int64 first_byte_position,
 101     int64 last_byte_position,
 102     DeferStrategy strategy,
 103     int bitrate,
 104     float playback_rate,
 105     MediaLog* media_log)
 106     : buffer_(kMinBufferCapacity, kMinBufferCapacity),
 107       loader_failed_(false),
 108       defer_strategy_(strategy),
 109       might_be_reused_from_cache_in_future_(true),
 110       range_supported_(false),
 111       saved_forward_capacity_(0),
 112       url_(url),
 113       cors_mode_(cors_mode),
 114       first_byte_position_(first_byte_position),
 115       last_byte_position_(last_byte_position),
 116       single_origin_(true),
 117       offset_(0),
 118       content_length_(kPositionNotSpecified),
 119       instance_size_(kPositionNotSpecified),
 120       read_position_(0),
 121       read_size_(0),
 122       read_buffer_(NULL),
 123       first_offset_(0),
 124       last_offset_(0),
 125       bitrate_(bitrate),
 126       playback_rate_(playback_rate),
 127       media_log_(media_log),
 128       cancel_upon_deferral_(false) {
 129
 130   // Set the initial capacity of |buffer_| based on |bitrate_| and
 131   // |playback_rate_|.
 132   UpdateBufferWindow();
 133 }
 134
 135 BufferedResourceLoader::~BufferedResourceLoader() {}
 136
 137 void BufferedResourceLoader::Start(
 138     const StartCB& start_cb,
 139     const LoadingStateChangedCB& loading_cb,
 140     const ProgressCB& progress_cb,
 141     WebFrame* frame) {
 142   // Make sure we have not started.
 143   DCHECK(start_cb_.is_null());
 144   DCHECK(loading_cb_.is_null());
 145   DCHECK(progress_cb_.is_null());
 146   DCHECK(!start_cb.is_null());
 147   DCHECK(!loading_cb.is_null());
 148   DCHECK(!progress_cb.is_null());
 149   CHECK(frame);
 150
 151   start_cb_ = start_cb;
 152   loading_cb_ = loading_cb;
 153   progress_cb_ = progress_cb;
 154
 155   if (first_byte_position_ != kPositionNotSpecified) {
 156     // TODO(hclam): server may not support range request so |offset_| may not
 157     // equal to |first_byte_position_|.
 158     offset_ = first_byte_position_;
 159   }
 160
 161   // Prepare the request.
 162   WebURLRequest request(url_);
 163   // TODO(mkwst): Split this into video/audio.
 164   request.setRequestContext(WebURLRequest::RequestContextVideo);
 165
 166   if (IsRangeRequest()) {
 167     request.setHTTPHeaderField(
 168         WebString::fromUTF8(net::HttpRequestHeaders::kRange),
 169         WebString::fromUTF8(net::HttpByteRange::Bounded(
 170             first_byte_position_, last_byte_position_).GetHeaderValue()));
 171   }
 172
 173   frame->setReferrerForRequest(request, blink::WebURL());
 174
 175   // Disable compression, compression for audio/video doesn't make sense...
 176   request.setHTTPHeaderField(
 177       WebString::fromUTF8(net::HttpRequestHeaders::kAcceptEncoding),
 178       WebString::fromUTF8("identity;q=1, *;q=0"));
 179
 180   // Check for our test WebURLLoader.
 181   scoped_ptr<WebURLLoader> loader;
 182   if (test_loader_) {
 183     loader = test_loader_.Pass();
 184   } else {
 185     WebURLLoaderOptions options;
 186     if (cors_mode_ == kUnspecified) {
 187       options.allowCredentials = true;
 188       options.crossOriginRequestPolicy =
 189           WebURLLoaderOptions::CrossOriginRequestPolicyAllow;
 190     } else {
 191       options.exposeAllResponseHeaders = true;
 192       // The author header set is empty, no preflight should go ahead.
 193       options.preflightPolicy = WebURLLoaderOptions::PreventPreflight;
 194       options.crossOriginRequestPolicy =
 195           WebURLLoaderOptions::CrossOriginRequestPolicyUseAccessControl;
 196       if (cors_mode_ == kUseCredentials)
 197         options.allowCredentials = true;
 198     }
 199     loader.reset(frame->createAssociatedURLLoader(options));
 200   }
 201
 202   // Start the resource loading.
 203   loader->loadAsynchronously(request, this);
 204   active_loader_.reset(new ActiveLoader(loader.Pass()));
 205   loading_cb_.Run(kLoading);
 206 }
 207
 208 void BufferedResourceLoader::Stop() {
 209   // Reset callbacks.
 210   start_cb_.Reset();
 211   loading_cb_.Reset();
 212   progress_cb_.Reset();
 213   read_cb_.Reset();
 214
 215   // Cancel and reset any active loaders.
 216   active_loader_.reset();
 217 }
 218
 219 void BufferedResourceLoader::Read(
 220     int64 position,
 221     int read_size,
 222     uint8* buffer,
 223     const ReadCB& read_cb) {
 224   DCHECK(start_cb_.is_null());
 225   DCHECK(read_cb_.is_null());
 226   DCHECK(!read_cb.is_null());
 227   DCHECK(buffer);
 228   DCHECK_GT(read_size, 0);
 229
 230   // Save the parameter of reading.
 231   read_cb_ = read_cb;
 232   read_position_ = position;
 233   read_size_ = read_size;
 234   read_buffer_ = buffer;
 235
 236   // Reads should immediately fail if the loader also failed.
 237   if (loader_failed_) {
 238     DoneRead(kFailed, 0);
 239     return;
 240   }
 241
 242   // If we're attempting to read past the end of the file, return a zero
 243   // indicating EOF.
 244   //
 245   // This can happen with callees that read in fixed-sized amounts for parsing
 246   // or at the end of chunked 200 responses when we discover the actual length
 247   // of the file.
 248   if (instance_size_ != kPositionNotSpecified &&
 249       instance_size_ <= read_position_) {
 250     DVLOG(1) << "Appear to have seeked beyond EOS; returning 0.";
 251     DoneRead(kOk, 0);
 252     return;
 253   }
 254
 255   // Make sure |offset_| and |read_position_| does not differ by a large
 256   // amount.
 257   if (read_position_ > offset_ + kint32max ||
 258       read_position_ < offset_ + kint32min) {
 259     DoneRead(kCacheMiss, 0);
 260     return;
 261   }
 262
 263   // Make sure |read_size_| is not too large for the buffer to ever be able to
 264   // fulfill the read request.
 265   if (read_size_ > kMaxBufferCapacity) {
 266     DoneRead(kFailed, 0);
 267     return;
 268   }
 269
 270   // Prepare the parameters.
 271   first_offset_ = read_position_ - offset_;
 272   last_offset_ = first_offset_ + read_size_;
 273
 274   // If we can serve the request now, do the actual read.
 275   if (CanFulfillRead()) {
 276     ReadInternal();
 277     UpdateDeferBehavior();
 278     return;
 279   }
 280
 281   // If we expect the read request to be fulfilled later, expand capacity as
 282   // necessary and disable deferring.
 283   if (WillFulfillRead()) {
 284     // Advance offset as much as possible to create additional capacity.
 285     int advance = std::min(first_offset_, buffer_.forward_bytes());
 286     bool ret = buffer_.Seek(advance);
 287     DCHECK(ret);
 288
 289     offset_ += advance;
 290     first_offset_ -= advance;
 291     last_offset_ -= advance;
 292
 293     // Expand capacity to accomodate a read that extends past the normal
 294     // capacity.
 295     //
 296     // This can happen when reading in a large seek index or when the
 297     // first byte of a read request falls within kForwardWaitThreshold.
 298     if (last_offset_ > buffer_.forward_capacity()) {
 299       saved_forward_capacity_ = buffer_.forward_capacity();
 300       buffer_.set_forward_capacity(last_offset_);
 301     }
 302
 303     // Make sure we stop deferring now that there's additional capacity.
 304     DCHECK(!ShouldDefer())
 305         << "Capacity was not adjusted properly to prevent deferring.";
 306     UpdateDeferBehavior();
 307
 308     return;
 309   }
 310
 311   // Make a callback to report failure.
 312   DoneRead(kCacheMiss, 0);
 313 }
 314
 315 int64 BufferedResourceLoader::content_length() {
 316   return content_length_;
 317 }
 318
 319 int64 BufferedResourceLoader::instance_size() {
 320   return instance_size_;
 321 }
 322
 323 bool BufferedResourceLoader::range_supported() {
 324   return range_supported_;
 325 }
 326
 327 /////////////////////////////////////////////////////////////////////////////
 328 // blink::WebURLLoaderClient implementation.
 329 void BufferedResourceLoader::willSendRequest(
 330     WebURLLoader* loader,
 331     WebURLRequest& newRequest,
 332     const WebURLResponse& redirectResponse) {
 333
 334   // The load may have been stopped and |start_cb| is destroyed.
 335   // In this case we shouldn't do anything.
 336   if (start_cb_.is_null()) {
 337     // Set the url in the request to an invalid value (empty url).
 338     newRequest.setURL(blink::WebURL());
 339     return;
 340   }
 341
 342   // Only allow |single_origin_| if we haven't seen a different origin yet.
 343   if (single_origin_)
 344     single_origin_ = url_.GetOrigin() == GURL(newRequest.url()).GetOrigin();
 345
 346   url_ = newRequest.url();
 347 }
 348
 349 void BufferedResourceLoader::didSendData(
 350     WebURLLoader* loader,
 351     unsigned long long bytes_sent,
 352     unsigned long long total_bytes_to_be_sent) {
 353   NOTIMPLEMENTED();
 354 }
 355
 356 void BufferedResourceLoader::didReceiveResponse(
 357     WebURLLoader* loader,
 358     const WebURLResponse& response) {
 359   DVLOG(1) << "didReceiveResponse: HTTP/"
 360            << (response.httpVersion() == WebURLResponse::HTTP_0_9 ? "0.9" :
 361                response.httpVersion() == WebURLResponse::HTTP_1_0 ? "1.0" :
 362                response.httpVersion() == WebURLResponse::HTTP_1_1 ? "1.1" :
 363                "Unknown")
 364            << " " << response.httpStatusCode();
 365   DCHECK(active_loader_.get());
 366
 367   // The loader may have been stopped and |start_cb| is destroyed.
 368   // In this case we shouldn't do anything.
 369   if (start_cb_.is_null())
 370     return;
 371
 372   uint32 reasons = GetReasonsForUncacheability(response);
 373   might_be_reused_from_cache_in_future_ = reasons == 0;
 374   UMA_HISTOGRAM_BOOLEAN("Media.CacheUseful", reasons == 0);
 375   int shift = 0;
 376   int max_enum = base::bits::Log2Ceiling(kMaxReason);
 377   while (reasons) {
 378     DCHECK_LT(shift, max_enum);  // Sanity check.
 379     if (reasons & 0x1) {
 380       UMA_HISTOGRAM_ENUMERATION("Media.UncacheableReason",
 381                                 shift,
 382                                 max_enum); // PRESUBMIT_IGNORE_UMA_MAX
 383     }
 384
 385     reasons >>= 1;
 386     ++shift;
 387   }
 388
 389   // Expected content length can be |kPositionNotSpecified|, in that case
 390   // |content_length_| is not specified and this is a streaming response.
 391   content_length_ = response.expectedContentLength();
 392
 393   // We make a strong assumption that when we reach here we have either
 394   // received a response from HTTP/HTTPS protocol or the request was
 395   // successful (in particular range request). So we only verify the partial
 396   // response for HTTP and HTTPS protocol.
 397   if (url_.SchemeIsHTTPOrHTTPS()) {
 398     bool partial_response = (response.httpStatusCode() == kHttpPartialContent);
 399     bool ok_response = (response.httpStatusCode() == kHttpOK);
 400
 401     if (IsRangeRequest()) {
 402       // Check to see whether the server supports byte ranges.
 403       std::string accept_ranges =
 404           response.httpHeaderField("Accept-Ranges").utf8();
 405       range_supported_ = (accept_ranges.find("bytes") != std::string::npos);
 406
 407       // If we have verified the partial response and it is correct, we will
 408       // return kOk. It's also possible for a server to support range requests
 409       // without advertising "Accept-Ranges: bytes".
 410       if (partial_response && VerifyPartialResponse(response)) {
 411         range_supported_ = true;
 412       } else if (ok_response && first_byte_position_ == 0 &&
 413                  last_byte_position_ == kPositionNotSpecified) {
 414         // We accept a 200 response for a Range:0- request, trusting the
 415         // Accept-Ranges header, because Apache thinks that's a reasonable thing
 416         // to return.
 417         instance_size_ = content_length_;
 418       } else {
 419         DoneStart(kFailed);
 420         return;
 421       }
 422     } else {
 423       instance_size_ = content_length_;
 424       if (response.httpStatusCode() != kHttpOK) {
 425         // We didn't request a range but server didn't reply with "200 OK".
 426         DoneStart(kFailed);
 427         return;
 428       }
 429     }
 430
 431   } else {
 432     CHECK_EQ(instance_size_, kPositionNotSpecified);
 433     if (content_length_ != kPositionNotSpecified) {
 434       if (first_byte_position_ == kPositionNotSpecified)
 435         instance_size_ = content_length_;
 436       else if (last_byte_position_ == kPositionNotSpecified)
 437         instance_size_ = content_length_ + first_byte_position_;
 438     }
 439   }
 440
 441   // Calls with a successful response.
 442   DoneStart(kOk);
 443 }
 444
 445 void BufferedResourceLoader::didReceiveData(
 446     WebURLLoader* loader,
 447     const char* data,
 448     int data_length,
 449     int encoded_data_length) {
 450   DVLOG(1) << "didReceiveData: " << data_length << " bytes";
 451   DCHECK(active_loader_.get());
 452   DCHECK_GT(data_length, 0);
 453
 454   buffer_.Append(reinterpret_cast<const uint8*>(data), data_length);
 455
 456   // If there is an active read request, try to fulfill the request.
 457   if (HasPendingRead() && CanFulfillRead())
 458     ReadInternal();
 459
 460   // At last see if the buffer is full and we need to defer the downloading.
 461   UpdateDeferBehavior();
 462
 463   // Consume excess bytes from our in-memory buffer if necessary.
 464   if (buffer_.forward_bytes() > buffer_.forward_capacity()) {
 465     int excess = buffer_.forward_bytes() - buffer_.forward_capacity();
 466     bool success = buffer_.Seek(excess);
 467     DCHECK(success);
 468     offset_ += first_offset_ + excess;
 469   }
 470
 471   // Notify latest progress and buffered offset.
 472   progress_cb_.Run(offset_ + buffer_.forward_bytes() - 1);
 473   Log();
 474 }
 475
 476 void BufferedResourceLoader::didDownloadData(
 477     blink::WebURLLoader* loader,
 478     int dataLength,
 479     int encoded_data_length) {
 480   NOTIMPLEMENTED();
 481 }
 482
 483 void BufferedResourceLoader::didReceiveCachedMetadata(
 484     WebURLLoader* loader,
 485     const char* data,
 486     int data_length) {
 487   NOTIMPLEMENTED();
 488 }
 489
 490 void BufferedResourceLoader::didFinishLoading(
 491     WebURLLoader* loader,
 492     double finishTime,
 493     int64_t total_encoded_data_length) {
 494   DVLOG(1) << "didFinishLoading";
 495   DCHECK(active_loader_.get());
 496
 497   // We're done with the loader.
 498   active_loader_.reset();
 499   loading_cb_.Run(kLoadingFinished);
 500
 501   // If we didn't know the |instance_size_| we do now.
 502   if (instance_size_ == kPositionNotSpecified) {
 503     instance_size_ = offset_ + buffer_.forward_bytes();
 504   }
 505
 506   // If there is a start callback, run it.
 507   if (!start_cb_.is_null()) {
 508     DCHECK(read_cb_.is_null())
 509         << "Shouldn't have a read callback during start";
 510     DoneStart(kOk);
 511     return;
 512   }
 513
 514   // Don't leave read callbacks hanging around.
 515   if (HasPendingRead()) {
 516     // Try to fulfill with what is in the buffer.
 517     if (CanFulfillRead())
 518       ReadInternal();
 519     else
 520       DoneRead(kCacheMiss, 0);
 521   }
 522 }
 523
 524 void BufferedResourceLoader::didFail(
 525     WebURLLoader* loader,
 526     const WebURLError& error) {
 527   DVLOG(1) << "didFail: reason=" << error.reason
 528            << ", isCancellation=" << error.isCancellation
 529            << ", domain=" << error.domain.utf8().data()
 530            << ", localizedDescription="
 531            << error.localizedDescription.utf8().data();
 532   DCHECK(active_loader_.get());
 533
 534   // We don't need to continue loading after failure.
 535   //
 536   // Keep it alive until we exit this method so that |error| remains valid.
 537   scoped_ptr<ActiveLoader> active_loader = active_loader_.Pass();
 538   loader_failed_ = true;
 539   loading_cb_.Run(kLoadingFailed);
 540
 541   // Don't leave start callbacks hanging around.
 542   if (!start_cb_.is_null()) {
 543     DCHECK(read_cb_.is_null())
 544         << "Shouldn't have a read callback during start";
 545     DoneStart(kFailed);
 546     return;
 547   }
 548
 549   // Don't leave read callbacks hanging around.
 550   if (HasPendingRead()) {
 551     DoneRead(kFailed, 0);
 552   }
 553 }
 554
 555 bool BufferedResourceLoader::HasSingleOrigin() const {
 556   DCHECK(start_cb_.is_null())
 557       << "Start() must complete before calling HasSingleOrigin()";
 558   return single_origin_;
 559 }
 560
 561 bool BufferedResourceLoader::DidPassCORSAccessCheck() const {
 562   DCHECK(start_cb_.is_null())
 563       << "Start() must complete before calling DidPassCORSAccessCheck()";
 564   return !loader_failed_ && cors_mode_ != kUnspecified;
 565 }
 566
 567 void BufferedResourceLoader::UpdateDeferStrategy(DeferStrategy strategy) {
 568   if (!might_be_reused_from_cache_in_future_ && strategy == kNeverDefer)
 569     strategy = kCapacityDefer;
 570   defer_strategy_ = strategy;
 571   UpdateDeferBehavior();
 572 }
 573
 574 void BufferedResourceLoader::SetPlaybackRate(float playback_rate) {
 575   playback_rate_ = playback_rate;
 576
 577   // This is a pause so don't bother updating the buffer window as we'll likely
 578   // get unpaused in the future.
 579   if (playback_rate_ == 0.0)
 580     return;
 581
 582   // Abort any cancellations in progress if playback starts.
 583   if (playback_rate_ > 0 && cancel_upon_deferral_)
 584     cancel_upon_deferral_ = false;
 585
 586   UpdateBufferWindow();
 587 }
 588
 589 void BufferedResourceLoader::SetBitrate(int bitrate) {
 590   DCHECK(bitrate >= 0);
 591   bitrate_ = bitrate;
 592   UpdateBufferWindow();
 593 }
 594
 595 /////////////////////////////////////////////////////////////////////////////
 596 // Helper methods.
 597
 598 void BufferedResourceLoader::UpdateBufferWindow() {
 599   int backward_capacity;
 600   int forward_capacity;
 601   ComputeTargetBufferWindow(
 602       playback_rate_, bitrate_, &backward_capacity, &forward_capacity);
 603
 604   // This does not evict data from the buffer if the new capacities are less
 605   // than the current capacities; the new limits will be enforced after the
 606   // existing excess buffered data is consumed.
 607   buffer_.set_backward_capacity(backward_capacity);
 608   buffer_.set_forward_capacity(forward_capacity);
 609 }
 610
 611 void BufferedResourceLoader::UpdateDeferBehavior() {
 612   if (!active_loader_)
 613     return;
 614
 615   SetDeferred(ShouldDefer());
 616 }
 617
 618 void BufferedResourceLoader::SetDeferred(bool deferred) {
 619   if (active_loader_->deferred() == deferred)
 620     return;
 621
 622   active_loader_->SetDeferred(deferred);
 623   loading_cb_.Run(deferred ? kLoadingDeferred : kLoading);
 624
 625   if (deferred && cancel_upon_deferral_)
 626     CancelUponDeferral();
 627 }
 628
 629 bool BufferedResourceLoader::ShouldDefer() const {
 630   switch(defer_strategy_) {
 631     case kNeverDefer:
 632       return false;
 633
 634     case kReadThenDefer:
 635       DCHECK(read_cb_.is_null() || last_offset_ > buffer_.forward_bytes())
 636           << "We shouldn't stop deferring if we can fulfill the read";
 637       return read_cb_.is_null();
 638
 639     case kCapacityDefer:
 640       return buffer_.forward_bytes() >= buffer_.forward_capacity();
 641   }
 642   NOTREACHED();
 643   return false;
 644 }
 645
 646 bool BufferedResourceLoader::CanFulfillRead() const {
 647   // If we are reading too far in the backward direction.
 648   if (first_offset_ < 0 && (first_offset_ + buffer_.backward_bytes()) < 0)
 649     return false;
 650
 651   // If the start offset is too far ahead.
 652   if (first_offset_ >= buffer_.forward_bytes())
 653     return false;
 654
 655   // At the point, we verified that first byte requested is within the buffer.
 656   // If the request has completed, then just returns with what we have now.
 657   if (!active_loader_)
 658     return true;
 659
 660   // If the resource request is still active, make sure the whole requested
 661   // range is covered.
 662   if (last_offset_ > buffer_.forward_bytes())
 663     return false;
 664
 665   return true;
 666 }
 667
 668 bool BufferedResourceLoader::WillFulfillRead() const {
 669   // Trying to read too far behind.
 670   if (first_offset_ < 0 && (first_offset_ + buffer_.backward_bytes()) < 0)
 671     return false;
 672
 673   // Trying to read too far ahead.
 674   if ((first_offset_ - buffer_.forward_bytes()) >= kForwardWaitThreshold)
 675     return false;
 676
 677   // The resource request has completed, there's no way we can fulfill the
 678   // read request.
 679   if (!active_loader_)
 680     return false;
 681
 682   return true;
 683 }
 684
 685 void BufferedResourceLoader::ReadInternal() {
 686   // Seek to the first byte requested.
 687   bool ret = buffer_.Seek(first_offset_);
 688   DCHECK(ret);
 689
 690   // Then do the read.
 691   int read = buffer_.Read(read_buffer_, read_size_);
 692   offset_ += first_offset_ + read;
 693
 694   // And report with what we have read.
 695   DoneRead(kOk, read);
 696 }
 697
 698 int64 BufferedResourceLoader::first_byte_position() const {
 699   return first_byte_position_;
 700 }
 701
 702 // static
 703 bool BufferedResourceLoader::ParseContentRange(
 704     const std::string& content_range_str, int64* first_byte_position,
 705     int64* last_byte_position, int64* instance_size) {
 706   const std::string kUpThroughBytesUnit = "bytes ";
 707   if (content_range_str.find(kUpThroughBytesUnit) != 0)
 708     return false;
 709   std::string range_spec =
 710       content_range_str.substr(kUpThroughBytesUnit.length());
 711   size_t dash_offset = range_spec.find("-");
 712   size_t slash_offset = range_spec.find("/");
 713
 714   if (dash_offset == std::string::npos || slash_offset == std::string::npos ||
 715       slash_offset < dash_offset || slash_offset + 1 == range_spec.length()) {
 716     return false;
 717   }
 718   if (!base::StringToInt64(range_spec.substr(0, dash_offset),
 719                            first_byte_position) ||
 720       !base::StringToInt64(range_spec.substr(dash_offset + 1,
 721                                              slash_offset - dash_offset - 1),
 722                            last_byte_position)) {
 723     return false;
 724   }
 725   if (slash_offset == range_spec.length() - 2 &&
 726       range_spec[slash_offset + 1] == '*') {
 727     *instance_size = kPositionNotSpecified;
 728   } else {
 729     if (!base::StringToInt64(range_spec.substr(slash_offset + 1),
 730                              instance_size)) {
 731       return false;
 732     }
 733   }
 734   if (*last_byte_position < *first_byte_position ||
 735       (*instance_size != kPositionNotSpecified &&
 736        *last_byte_position >= *instance_size)) {
 737     return false;
 738   }
 739
 740   return true;
 741 }
 742
 743 void BufferedResourceLoader::CancelUponDeferral() {
 744   cancel_upon_deferral_ = true;
 745   if (active_loader_ && active_loader_->deferred())
 746     active_loader_.reset();
 747 }
 748
 749 bool BufferedResourceLoader::VerifyPartialResponse(
 750     const WebURLResponse& response) {
 751   int64 first_byte_position, last_byte_position, instance_size;
 752   if (!ParseContentRange(response.httpHeaderField("Content-Range").utf8(),
 753                          &first_byte_position, &last_byte_position,
 754                          &instance_size)) {
 755     return false;
 756   }
 757
 758   if (instance_size != kPositionNotSpecified) {
 759     instance_size_ = instance_size;
 760   }
 761
 762   if (first_byte_position_ != kPositionNotSpecified &&
 763       first_byte_position_ != first_byte_position) {
 764     return false;
 765   }
 766
 767   // TODO(hclam): I should also check |last_byte_position|, but since
 768   // we will never make such a request that it is ok to leave it unimplemented.
 769   return true;
 770 }
 771
 772 void BufferedResourceLoader::DoneRead(Status status, int bytes_read) {
 773   if (saved_forward_capacity_) {
 774     buffer_.set_forward_capacity(saved_forward_capacity_);
 775     saved_forward_capacity_ = 0;
 776   }
 777   read_position_ = 0;
 778   read_size_ = 0;
 779   read_buffer_ = NULL;
 780   first_offset_ = 0;
 781   last_offset_ = 0;
 782   Log();
 783
 784   base::ResetAndReturn(&read_cb_).Run(status, bytes_read);
 785 }
 786
 787
 788 void BufferedResourceLoader::DoneStart(Status status) {
 789   base::ResetAndReturn(&start_cb_).Run(status);
 790 }
 791
 792 bool BufferedResourceLoader::IsRangeRequest() const {
 793   return first_byte_position_ != kPositionNotSpecified;
 794 }
 795
 796 void BufferedResourceLoader::Log() {
 797   media_log_->AddEvent(
 798       media_log_->CreateBufferedExtentsChangedEvent(
 799           offset_ - buffer_.backward_bytes(),
 800           offset_,
 801           offset_ + buffer_.forward_bytes()));
 802 }
 803
 804 }  // namespace media