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