src/content/renderer/media/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 "content/renderer/media/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 "content/public/common/url_constants.h"
  13 #include "content/renderer/media/cache_util.h"
  14 #include "media/base/media_log.h"
  15 #include "net/http/http_byte_range.h"
  16 #include "net/http/http_request_headers.h"
  17 #include "third_party/WebKit/public/platform/WebString.h"
  18 #include "third_party/WebKit/public/platform/WebURLError.h"
  19 #include "third_party/WebKit/public/platform/WebURLResponse.h"
  20 #include "third_party/WebKit/public/web/WebKit.h"
  21 #include "third_party/WebKit/public/web/WebURLLoaderOptions.h"
  22
  23 using blink::WebFrame;
  24 using blink::WebString;
  25 using blink::WebURLError;
  26 using blink::WebURLLoader;
  27 using blink::WebURLLoaderOptions;
  28 using blink::WebURLRequest;
  29 using blink::WebURLResponse;
  30
  31 namespace content {
  32
  33 static const int kHttpOK = 200;
  34 static const int kHttpPartialContent = 206;
  35
  36 // Define the number of bytes in a megabyte.
  37 static const int kMegabyte = 1024 * 1024;
  38
  39 // Minimum capacity of the buffer in forward or backward direction.
  40 //
  41 // 2MB is an arbitrary limit; it just seems to be "good enough" in practice.
  42 static const int kMinBufferCapacity = 2 * kMegabyte;
  43
  44 // Maximum capacity of the buffer in forward or backward direction. This is
  45 // effectively the largest single read the code path can handle.
  46 // 20MB is an arbitrary limit; it just seems to be "good enough" in practice.
  47 static const int kMaxBufferCapacity = 20 * kMegabyte;
  48
  49 // Maximum number of bytes outside the buffer we will wait for in order to
  50 // fulfill a read. If a read starts more than 2MB away from the data we
  51 // currently have in the buffer, we will not wait for buffer to reach the read's
  52 // location and will instead reset the request.
  53 static const int kForwardWaitThreshold = 2 * kMegabyte;
  54
  55 // Computes the suggested backward and forward capacity for the buffer
  56 // if one wants to play at |playback_rate| * the natural playback speed.
  57 // Use a value of 0 for |bitrate| if it is unknown.
  58 static void ComputeTargetBufferWindow(float playback_rate, int bitrate,
  59                                       int* out_backward_capacity,
  60                                       int* out_forward_capacity) {
  61   static const int kDefaultBitrate = 200 * 1024 * 8;  // 200 Kbps.
  62   static const int kMaxBitrate = 20 * kMegabyte * 8;  // 20 Mbps.
  63   static const float kMaxPlaybackRate = 25.0;
  64   static const int kTargetSecondsBufferedAhead = 10;
  65   static const int kTargetSecondsBufferedBehind = 2;
  66
  67   // Use a default bit rate if unknown and clamp to prevent overflow.
  68   if (bitrate <= 0)
  69     bitrate = kDefaultBitrate;
  70   bitrate = std::min(bitrate, kMaxBitrate);
  71
  72   // Only scale the buffer window for playback rates greater than 1.0 in
  73   // magnitude and clamp to prevent overflow.
  74   bool backward_playback = false;
  75   if (playback_rate < 0.0f) {
  76     backward_playback = true;
  77     playback_rate *= -1.0f;
  78   }
  79
  80   playback_rate = std::max(playback_rate, 1.0f);
  81   playback_rate = std::min(playback_rate, kMaxPlaybackRate);
  82
  83   int bytes_per_second = (bitrate / 8.0) * playback_rate;
  84
  85   // Clamp between kMinBufferCapacity and kMaxBufferCapacity.
  86   *out_forward_capacity = std::max(
  87       kTargetSecondsBufferedAhead * bytes_per_second, kMinBufferCapacity);
  88   *out_backward_capacity = std::max(
  89       kTargetSecondsBufferedBehind * bytes_per_second, kMinBufferCapacity);
  90
  91   *out_forward_capacity = std::min(*out_forward_capacity, kMaxBufferCapacity);
  92   *out_backward_capacity = std::min(*out_backward_capacity, kMaxBufferCapacity);
  93
  94   if (backward_playback)
  95     std::swap(*out_forward_capacity, *out_backward_capacity);
  96 }
  97
  98 BufferedResourceLoader::BufferedResourceLoader(
  99     const GURL& url,
 100     CORSMode cors_mode,
 101     int64 first_byte_position,
 102     int64 last_byte_position,
 103     DeferStrategy strategy,
 104     int bitrate,
 105     float playback_rate,
 106     media::MediaLog* media_log)
 107     : buffer_(kMinBufferCapacity, kMinBufferCapacity),
 108       loader_failed_(false),
 109       defer_strategy_(strategy),
 110       might_be_reused_from_cache_in_future_(true),
 111       range_supported_(false),
 112       saved_forward_capacity_(0),
 113       url_(url),
 114       cors_mode_(cors_mode),
 115       first_byte_position_(first_byte_position),
 116       last_byte_position_(last_byte_position),
 117       single_origin_(true),
 118       offset_(0),
 119       content_length_(kPositionNotSpecified),
 120       instance_size_(kPositionNotSpecified),
 121       read_position_(0),
 122       read_size_(0),
 123       read_buffer_(NULL),
 124       first_offset_(0),
 125       last_offset_(0),
 126       bitrate_(bitrate),
 127       playback_rate_(playback_rate),
 128       media_log_(media_log) {
 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", shift, max_enum);
 381     reasons >>= 1;
 382     ++shift;
 383   }
 384
 385   // Expected content length can be |kPositionNotSpecified|, in that case
 386   // |content_length_| is not specified and this is a streaming response.
 387   content_length_ = response.expectedContentLength();
 388
 389   // We make a strong assumption that when we reach here we have either
 390   // received a response from HTTP/HTTPS protocol or the request was
 391   // successful (in particular range request). So we only verify the partial
 392   // response for HTTP and HTTPS protocol.
 393   if (url_.SchemeIsHTTPOrHTTPS()) {
 394     bool partial_response = (response.httpStatusCode() == kHttpPartialContent);
 395     bool ok_response = (response.httpStatusCode() == kHttpOK);
 396
 397     if (IsRangeRequest()) {
 398       // Check to see whether the server supports byte ranges.
 399       std::string accept_ranges =
 400           response.httpHeaderField("Accept-Ranges").utf8();
 401       range_supported_ = (accept_ranges.find("bytes") != std::string::npos);
 402
 403       // If we have verified the partial response and it is correct, we will
 404       // return kOk. It's also possible for a server to support range requests
 405       // without advertising "Accept-Ranges: bytes".
 406       if (partial_response && VerifyPartialResponse(response)) {
 407         range_supported_ = true;
 408       } else if (ok_response && first_byte_position_ == 0 &&
 409                  last_byte_position_ == kPositionNotSpecified) {
 410         // We accept a 200 response for a Range:0- request, trusting the
 411         // Accept-Ranges header, because Apache thinks that's a reasonable thing
 412         // to return.
 413         instance_size_ = content_length_;
 414       } else {
 415         DoneStart(kFailed);
 416         return;
 417       }
 418     } else {
 419       instance_size_ = content_length_;
 420       if (response.httpStatusCode() != kHttpOK) {
 421         // We didn't request a range but server didn't reply with "200 OK".
 422         DoneStart(kFailed);
 423         return;
 424       }
 425     }
 426
 427   } else {
 428     CHECK_EQ(instance_size_, kPositionNotSpecified);
 429     if (content_length_ != kPositionNotSpecified) {
 430       if (first_byte_position_ == kPositionNotSpecified)
 431         instance_size_ = content_length_;
 432       else if (last_byte_position_ == kPositionNotSpecified)
 433         instance_size_ = content_length_ + first_byte_position_;
 434     }
 435   }
 436
 437   // Calls with a successful response.
 438   DoneStart(kOk);
 439 }
 440
 441 void BufferedResourceLoader::didReceiveData(
 442     WebURLLoader* loader,
 443     const char* data,
 444     int data_length,
 445     int encoded_data_length) {
 446   DVLOG(1) << "didReceiveData: " << data_length << " bytes";
 447   DCHECK(active_loader_.get());
 448   DCHECK_GT(data_length, 0);
 449
 450   buffer_.Append(reinterpret_cast<const uint8*>(data), data_length);
 451
 452   // If there is an active read request, try to fulfill the request.
 453   if (HasPendingRead() && CanFulfillRead())
 454     ReadInternal();
 455
 456   // At last see if the buffer is full and we need to defer the downloading.
 457   UpdateDeferBehavior();
 458
 459   // Consume excess bytes from our in-memory buffer if necessary.
 460   if (buffer_.forward_bytes() > buffer_.forward_capacity()) {
 461     int excess = buffer_.forward_bytes() - buffer_.forward_capacity();
 462     bool success = buffer_.Seek(excess);
 463     DCHECK(success);
 464     offset_ += first_offset_ + excess;
 465   }
 466
 467   // Notify latest progress and buffered offset.
 468   progress_cb_.Run(offset_ + buffer_.forward_bytes() - 1);
 469   Log();
 470 }
 471
 472 void BufferedResourceLoader::didDownloadData(
 473     blink::WebURLLoader* loader,
 474     int dataLength,
 475     int encoded_data_length) {
 476   NOTIMPLEMENTED();
 477 }
 478
 479 void BufferedResourceLoader::didReceiveCachedMetadata(
 480     WebURLLoader* loader,
 481     const char* data,
 482     int data_length) {
 483   NOTIMPLEMENTED();
 484 }
 485
 486 void BufferedResourceLoader::didFinishLoading(
 487     WebURLLoader* loader,
 488     double finishTime,
 489     int64_t total_encoded_data_length) {
 490   DVLOG(1) << "didFinishLoading";
 491   DCHECK(active_loader_.get());
 492
 493   // We're done with the loader.
 494   active_loader_.reset();
 495   loading_cb_.Run(kLoadingFinished);
 496
 497   // If we didn't know the |instance_size_| we do now.
 498   if (instance_size_ == kPositionNotSpecified) {
 499     instance_size_ = offset_ + buffer_.forward_bytes();
 500   }
 501
 502   // If there is a start callback, run it.
 503   if (!start_cb_.is_null()) {
 504     DCHECK(read_cb_.is_null())
 505         << "Shouldn't have a read callback during start";
 506     DoneStart(kOk);
 507     return;
 508   }
 509
 510   // Don't leave read callbacks hanging around.
 511   if (HasPendingRead()) {
 512     // Try to fulfill with what is in the buffer.
 513     if (CanFulfillRead())
 514       ReadInternal();
 515     else
 516       DoneRead(kCacheMiss, 0);
 517   }
 518 }
 519
 520 void BufferedResourceLoader::didFail(
 521     WebURLLoader* loader,
 522     const WebURLError& error) {
 523   DVLOG(1) << "didFail: reason=" << error.reason
 524            << ", isCancellation=" << error.isCancellation
 525            << ", domain=" << error.domain.utf8().data()
 526            << ", localizedDescription="
 527            << error.localizedDescription.utf8().data();
 528   DCHECK(active_loader_.get());
 529
 530   // We don't need to continue loading after failure.
 531   //
 532   // Keep it alive until we exit this method so that |error| remains valid.
 533   scoped_ptr<ActiveLoader> active_loader = active_loader_.Pass();
 534   loader_failed_ = true;
 535   loading_cb_.Run(kLoadingFailed);
 536
 537   // Don't leave start callbacks hanging around.
 538   if (!start_cb_.is_null()) {
 539     DCHECK(read_cb_.is_null())
 540         << "Shouldn't have a read callback during start";
 541     DoneStart(kFailed);
 542     return;
 543   }
 544
 545   // Don't leave read callbacks hanging around.
 546   if (HasPendingRead()) {
 547     DoneRead(kFailed, 0);
 548   }
 549 }
 550
 551 bool BufferedResourceLoader::HasSingleOrigin() const {
 552   DCHECK(start_cb_.is_null())
 553       << "Start() must complete before calling HasSingleOrigin()";
 554   return single_origin_;
 555 }
 556
 557 bool BufferedResourceLoader::DidPassCORSAccessCheck() const {
 558   DCHECK(start_cb_.is_null())
 559       << "Start() must complete before calling DidPassCORSAccessCheck()";
 560   return !loader_failed_ && cors_mode_ != kUnspecified;
 561 }
 562
 563 void BufferedResourceLoader::UpdateDeferStrategy(DeferStrategy strategy) {
 564   if (!might_be_reused_from_cache_in_future_ && strategy == kNeverDefer)
 565     strategy = kCapacityDefer;
 566   defer_strategy_ = strategy;
 567   UpdateDeferBehavior();
 568 }
 569
 570 void BufferedResourceLoader::SetPlaybackRate(float playback_rate) {
 571   playback_rate_ = playback_rate;
 572
 573   // This is a pause so don't bother updating the buffer window as we'll likely
 574   // get unpaused in the future.
 575   if (playback_rate_ == 0.0)
 576     return;
 577
 578   UpdateBufferWindow();
 579 }
 580
 581 void BufferedResourceLoader::SetBitrate(int bitrate) {
 582   DCHECK(bitrate >= 0);
 583   bitrate_ = bitrate;
 584   UpdateBufferWindow();
 585 }
 586
 587 /////////////////////////////////////////////////////////////////////////////
 588 // Helper methods.
 589
 590 void BufferedResourceLoader::UpdateBufferWindow() {
 591   int backward_capacity;
 592   int forward_capacity;
 593   ComputeTargetBufferWindow(
 594       playback_rate_, bitrate_, &backward_capacity, &forward_capacity);
 595
 596   // This does not evict data from the buffer if the new capacities are less
 597   // than the current capacities; the new limits will be enforced after the
 598   // existing excess buffered data is consumed.
 599   buffer_.set_backward_capacity(backward_capacity);
 600   buffer_.set_forward_capacity(forward_capacity);
 601 }
 602
 603 void BufferedResourceLoader::UpdateDeferBehavior() {
 604   if (!active_loader_)
 605     return;
 606
 607   SetDeferred(ShouldDefer());
 608 }
 609
 610 void BufferedResourceLoader::SetDeferred(bool deferred) {
 611   if (active_loader_->deferred() == deferred)
 612     return;
 613
 614   active_loader_->SetDeferred(deferred);
 615   loading_cb_.Run(deferred ? kLoadingDeferred : kLoading);
 616 }
 617
 618 bool BufferedResourceLoader::ShouldDefer() const {
 619   switch(defer_strategy_) {
 620     case kNeverDefer:
 621       return false;
 622
 623     case kReadThenDefer:
 624       DCHECK(read_cb_.is_null() || last_offset_ > buffer_.forward_bytes())
 625           << "We shouldn't stop deferring if we can fulfill the read";
 626       return read_cb_.is_null();
 627
 628     case kCapacityDefer:
 629       return buffer_.forward_bytes() >= buffer_.forward_capacity();
 630   }
 631   NOTREACHED();
 632   return false;
 633 }
 634
 635 bool BufferedResourceLoader::CanFulfillRead() const {
 636   // If we are reading too far in the backward direction.
 637   if (first_offset_ < 0 && (first_offset_ + buffer_.backward_bytes()) < 0)
 638     return false;
 639
 640   // If the start offset is too far ahead.
 641   if (first_offset_ >= buffer_.forward_bytes())
 642     return false;
 643
 644   // At the point, we verified that first byte requested is within the buffer.
 645   // If the request has completed, then just returns with what we have now.
 646   if (!active_loader_)
 647     return true;
 648
 649   // If the resource request is still active, make sure the whole requested
 650   // range is covered.
 651   if (last_offset_ > buffer_.forward_bytes())
 652     return false;
 653
 654   return true;
 655 }
 656
 657 bool BufferedResourceLoader::WillFulfillRead() const {
 658   // Trying to read too far behind.
 659   if (first_offset_ < 0 && (first_offset_ + buffer_.backward_bytes()) < 0)
 660     return false;
 661
 662   // Trying to read too far ahead.
 663   if ((first_offset_ - buffer_.forward_bytes()) >= kForwardWaitThreshold)
 664     return false;
 665
 666   // The resource request has completed, there's no way we can fulfill the
 667   // read request.
 668   if (!active_loader_)
 669     return false;
 670
 671   return true;
 672 }
 673
 674 void BufferedResourceLoader::ReadInternal() {
 675   // Seek to the first byte requested.
 676   bool ret = buffer_.Seek(first_offset_);
 677   DCHECK(ret);
 678
 679   // Then do the read.
 680   int read = buffer_.Read(read_buffer_, read_size_);
 681   offset_ += first_offset_ + read;
 682
 683   // And report with what we have read.
 684   DoneRead(kOk, read);
 685 }
 686
 687 int64 BufferedResourceLoader::first_byte_position() const {
 688   return first_byte_position_;
 689 }
 690
 691 // static
 692 bool BufferedResourceLoader::ParseContentRange(
 693     const std::string& content_range_str, int64* first_byte_position,
 694     int64* last_byte_position, int64* instance_size) {
 695   const std::string kUpThroughBytesUnit = "bytes ";
 696   if (content_range_str.find(kUpThroughBytesUnit) != 0)
 697     return false;
 698   std::string range_spec =
 699       content_range_str.substr(kUpThroughBytesUnit.length());
 700   size_t dash_offset = range_spec.find("-");
 701   size_t slash_offset = range_spec.find("/");
 702
 703   if (dash_offset == std::string::npos || slash_offset == std::string::npos ||
 704       slash_offset < dash_offset || slash_offset + 1 == range_spec.length()) {
 705     return false;
 706   }
 707   if (!base::StringToInt64(range_spec.substr(0, dash_offset),
 708                            first_byte_position) ||
 709       !base::StringToInt64(range_spec.substr(dash_offset + 1,
 710                                              slash_offset - dash_offset - 1),
 711                            last_byte_position)) {
 712     return false;
 713   }
 714   if (slash_offset == range_spec.length() - 2 &&
 715       range_spec[slash_offset + 1] == '*') {
 716     *instance_size = kPositionNotSpecified;
 717   } else {
 718     if (!base::StringToInt64(range_spec.substr(slash_offset + 1),
 719                              instance_size)) {
 720       return false;
 721     }
 722   }
 723   if (*last_byte_position < *first_byte_position ||
 724       (*instance_size != kPositionNotSpecified &&
 725        *last_byte_position >= *instance_size)) {
 726     return false;
 727   }
 728
 729   return true;
 730 }
 731
 732 bool BufferedResourceLoader::VerifyPartialResponse(
 733     const WebURLResponse& response) {
 734   int64 first_byte_position, last_byte_position, instance_size;
 735   if (!ParseContentRange(response.httpHeaderField("Content-Range").utf8(),
 736                          &first_byte_position, &last_byte_position,
 737                          &instance_size)) {
 738     return false;
 739   }
 740
 741   if (instance_size != kPositionNotSpecified) {
 742     instance_size_ = instance_size;
 743   }
 744
 745   if (first_byte_position_ != kPositionNotSpecified &&
 746       first_byte_position_ != first_byte_position) {
 747     return false;
 748   }
 749
 750   // TODO(hclam): I should also check |last_byte_position|, but since
 751   // we will never make such a request that it is ok to leave it unimplemented.
 752   return true;
 753 }
 754
 755 void BufferedResourceLoader::DoneRead(Status status, int bytes_read) {
 756   if (saved_forward_capacity_) {
 757     buffer_.set_forward_capacity(saved_forward_capacity_);
 758     saved_forward_capacity_ = 0;
 759   }
 760   read_position_ = 0;
 761   read_size_ = 0;
 762   read_buffer_ = NULL;
 763   first_offset_ = 0;
 764   last_offset_ = 0;
 765   Log();
 766
 767   base::ResetAndReturn(&read_cb_).Run(status, bytes_read);
 768 }
 769
 770
 771 void BufferedResourceLoader::DoneStart(Status status) {
 772   base::ResetAndReturn(&start_cb_).Run(status);
 773 }
 774
 775 bool BufferedResourceLoader::IsRangeRequest() const {
 776   return first_byte_position_ != kPositionNotSpecified;
 777 }
 778
 779 void BufferedResourceLoader::Log() {
 780   media_log_->AddEvent(
 781       media_log_->CreateBufferedExtentsChangedEvent(
 782           offset_ - buffer_.backward_bytes(),
 783           offset_,
 784           offset_ + buffer_.forward_bytes()));
 785 }
 786
 787 }  // namespace content