Http Cache: Add support for resuming downloading a

resource after the original request was interrupted.

BUG=8995
TEST=unittests


Review URL: http://codereview.chromium.org/197016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@25551 0039d316-1c4b-4281-b951-d872f2087c98

5 files changed, 282 insertions, 44 deletions

diff --git a/net/http/http_cache.cc b/net/http/http_cache.cc
index 12d0844..be9dc48 100644
--- a/net/http/http_cache.cc
+++ b/net/http/http_cache.cc
@@ -64,9 +64,11 @@ enum {
   // This bit is set if the response info has vary header data.
   RESPONSE_INFO_HAS_VARY_DATA = 1 << 11,
 
-  // TODO(darin): Add other bits to indicate alternate request methods and
-  // whether or not we are storing a partial document.  For now, we don't
-  // support storing those.
+  // This bit is set if the request was cancelled before completion.
+  RESPONSE_INFO_TRUNCATED = 1 << 12,
+
+  // TODO(darin): Add other bits to indicate alternate request methods.
+  // For now, we don't support storing those.
 };
 
 //-----------------------------------------------------------------------------
@@ -179,6 +181,7 @@ class HttpCache::Transaction
         reading_(false),
         invalid_range_(false),
         enable_range_support_(enable_range_support),
+        truncated_(false),
         read_offset_(0),
         effective_load_flags_(0),
         final_upload_progress_(0),
@@ -248,6 +251,10 @@ class HttpCache::Transaction
   // to the transaction.  Returns network error code.
   int EntryAvailable(ActiveEntry* entry);
 
+  // This transaction is being deleted and we are not done writing to the cache.
+  // We need to indicate that the response data was truncated.
+  void AddTruncatedFlag();
+
  private:
   // This is a helper function used to trigger a completion callback.  It may
   // only be called if callback_ is non-null.
@@ -327,8 +334,9 @@ class HttpCache::Transaction
   // nothing without side-effect.
   void WriteToEntry(int index, int offset, IOBuffer* data, int data_len);
 
-  // Called to write response_ to the cache entry.
-  void WriteResponseInfoToEntry();
+  // Called to write response_ to the cache entry. |truncated| indicates if the
+  // entry should be marked as incomplete.
+  void WriteResponseInfoToEntry(bool truncated);
 
   // Called to append response data to the cache entry.
   void AppendResponseDataToEntry(IOBuffer* data, int data_len);
@@ -383,6 +391,7 @@ class HttpCache::Transaction
   bool reading_;  // We are already reading.
   bool invalid_range_;  // We may bypass the cache for this request.
   bool enable_range_support_;
+  bool truncated_;  // We don't have all the response data.
   scoped_refptr<IOBuffer> read_buf_;
   int read_buf_len_;
   int read_offset_;
@@ -398,7 +407,11 @@ class HttpCache::Transaction
 HttpCache::Transaction::~Transaction() {
   if (!revoked()) {
     if (entry_) {
-      cache_->DoneWithEntry(entry_, this);
+      bool cancel_request = reading_ && !partial_.get() &&
+                            enable_range_support_ &&
+                            response_.headers->response_code() == 200;
+
+      cache_->DoneWithEntry(entry_, this, cancel_request);
     } else {
       cache_->RemovePendingTransaction(this);
     }
@@ -558,12 +571,12 @@ int HttpCache::Transaction::Read(IOBuffer* buf, int buf_len,
     mode_ = NONE;
   }
 
+  reading_ = true;
   int rv;
 
   switch (mode_) {
     case READ_WRITE:
       DCHECK(partial_.get());
-      reading_ = true;
       if (!network_trans_.get()) {
         // We are just reading from the cache, but we may be writing later.
         rv = ReadFromEntry(buf, buf_len);
@@ -697,6 +710,12 @@ int HttpCache::Transaction::EntryAvailable(ActiveEntry* entry) {
   return rv;
 }
 
+void HttpCache::Transaction::AddTruncatedFlag() {
+  DCHECK(mode_ & WRITE);
+  truncated_ = true;
+  WriteResponseInfoToEntry(true);
+}
+
 void HttpCache::Transaction::DoCallback(int rv) {
   DCHECK(rv != ERR_IO_PENDING);
   DCHECK(callback_);
@@ -877,6 +896,10 @@ int HttpCache::Transaction::BeginCacheRead() {
     return HandleResult(ERR_CACHE_MISS);
   }
 
+  // We don't have the whole resource.
+  if (truncated_)
+    return HandleResult(ERR_CACHE_MISS);
+
   return HandleResult(rv);
 }
 
@@ -908,7 +931,8 @@ int HttpCache::Transaction::BeginPartialCacheValidation() {
     return HandleResult(rv);
   }
 
-  if (response_.headers->response_code() != 206 && !partial_.get())
+  if (response_.headers->response_code() != 206 && !partial_.get() &&
+      !truncated_)
     return BeginCacheValidation();
 
   if (!enable_range_support_)
@@ -925,8 +949,8 @@ int HttpCache::Transaction::BeginPartialCacheValidation() {
     }
   }
 
-  if (!partial_->UpdateFromStoredHeaders(response_.headers,
-                                         entry_->disk_entry)) {
+  if (!partial_->UpdateFromStoredHeaders(response_.headers, entry_->disk_entry,
+                                         truncated_)) {
     // The stored data cannot be used. Get rid of it and restart this request.
     DoomPartialEntry(!byte_range_requested);
     mode_ = WRITE;
@@ -987,9 +1011,8 @@ int HttpCache::Transaction::BeginExternallyConditionalizedRequest() {
       external_validation_.type_info().related_response_header_name,
       &validator);
 
-  if (response_.headers->response_code() != 200 ||
-      validator.empty() ||
-      validator != external_validation_.value) {
+  if (response_.headers->response_code() != 200 || truncated_ ||
+      validator.empty() || validator != external_validation_.value) {
     // The externally conditionalized request is not a validation request
     // for our existing cache entry. Proceed with caching disabled.
     DoneWritingToEntry(true);
@@ -1251,7 +1274,7 @@ int HttpCache::Transaction::ReadFromEntry(IOBuffer* data, int data_len) {
 int HttpCache::Transaction::ReadResponseInfoFromEntry() {
   DCHECK(entry_);
 
-  if (!HttpCache::ReadResponseInfo(entry_->disk_entry, &response_))
+  if (!HttpCache::ReadResponseInfo(entry_->disk_entry, &response_, &truncated_))
     return ERR_CACHE_READ_FAILURE;
   return OK;
 }
@@ -1274,7 +1297,7 @@ void HttpCache::Transaction::WriteToEntry(int index, int offset,
   }
 }
 
-void HttpCache::Transaction::WriteResponseInfoToEntry() {
+void HttpCache::Transaction::WriteResponseInfoToEntry(bool truncated) {
   if (!entry_)
     return;
 
@@ -1298,8 +1321,12 @@ void HttpCache::Transaction::WriteResponseInfoToEntry() {
   // headers; when in record mode, record everything.
   bool skip_transient_headers = (cache_->mode() != RECORD);
 
+  if (truncated) {
+    DCHECK_EQ(200, response_.headers->response_code());
+  }
+
   if (!HttpCache::WriteResponseInfo(entry_->disk_entry, &response_,
-                                    skip_transient_headers)) {
+                                    skip_transient_headers, truncated)) {
     DLOG(ERROR) << "failed to write response info to cache";
     DoneWritingToEntry(false);
   }
@@ -1336,7 +1363,7 @@ void HttpCache::Transaction::DoneWritingToEntry(bool success) {
 }
 
 void HttpCache::Transaction::DoomPartialEntry(bool delete_object) {
-  cache_->DoneWithEntry(entry_, this);
+  cache_->DoneWithEntry(entry_, this, false);
   cache_->DoomEntry(cache_key_);
   entry_ = NULL;
   if (delete_object)
@@ -1429,7 +1456,7 @@ void HttpCache::Transaction::OnNetworkInfoAvailable(int result) {
       auth_response_ = *new_response;
     } else {
       bool partial_content = ValidatePartialResponse(new_response->headers);
-      if (partial_content && mode_ == READ_WRITE &&
+      if (partial_content && mode_ == READ_WRITE && !truncated_ &&
           response_.headers->response_code() == 200) {
         // We have stored the full entry, but it changed and the server is
         // sending a range. We have to delete the old entry.
@@ -1452,7 +1479,7 @@ void HttpCache::Transaction::OnNetworkInfoAvailable(int result) {
             // If we are already reading, we already updated the headers for
             // this request; doing it again will change Content-Length.
             if (!reading_)
-              WriteResponseInfoToEntry();
+              WriteResponseInfoToEntry(false);
           }
 
           if (mode_ == UPDATE) {
@@ -1485,7 +1512,7 @@ void HttpCache::Transaction::OnNetworkInfoAvailable(int result) {
           partial_->FixContentLength(new_response->headers);
 
         response_ = *new_response;
-        WriteResponseInfoToEntry();
+        WriteResponseInfoToEntry(truncated_);
 
         // Truncate response data.
         TruncateResponseData();
@@ -1495,8 +1522,7 @@ void HttpCache::Transaction::OnNetworkInfoAvailable(int result) {
         if (response_.headers->IsRedirect(NULL))
           DoneWritingToEntry(true);
       }
-      if (reading_) {
-        DCHECK(partial_.get());
+      if (reading_ && partial_.get()) {
         if (network_trans_.get()) {
           result = ReadFromNetwork(read_buf_, read_buf_len_);
         } else {
@@ -1636,7 +1662,8 @@ void HttpCache::Suspend(bool suspend) {
 
 // static
 bool HttpCache::ParseResponseInfo(const char* data, int len,
-                                  HttpResponseInfo* response_info) {
+                                  HttpResponseInfo* response_info,
+                                  bool* response_truncated) {
   Pickle pickle(data, len);
   void* iter = NULL;
 
@@ -1690,12 +1717,15 @@ bool HttpCache::ParseResponseInfo(const char* data, int len,
       return false;
   }
 
+  *response_truncated = (flags & RESPONSE_INFO_TRUNCATED) ? true : false;
+
   return true;
 }
 
 // static
 bool HttpCache::ReadResponseInfo(disk_cache::Entry* disk_entry,
-                                 HttpResponseInfo* response_info) {
+                                 HttpResponseInfo* response_info,
+                                 bool* response_truncated) {
   int size = disk_entry->GetDataSize(kResponseInfoIndex);
 
   scoped_refptr<IOBuffer> buffer = new IOBuffer(size);
@@ -1705,13 +1735,15 @@ bool HttpCache::ReadResponseInfo(disk_cache::Entry* disk_entry,
     return false;
   }
 
-  return ParseResponseInfo(buffer->data(), size, response_info);
+  return ParseResponseInfo(buffer->data(), size, response_info,
+                           response_truncated);
 }
 
 // static
 bool HttpCache::WriteResponseInfo(disk_cache::Entry* disk_entry,
                                   const HttpResponseInfo* response_info,
-                                  bool skip_transient_headers) {
+                                  bool skip_transient_headers,
+                                  bool response_truncated) {
   int flags = RESPONSE_INFO_VERSION;
   if (response_info->ssl_info.cert) {
     flags |= RESPONSE_INFO_HAS_CERT;
@@ -1721,6 +1753,8 @@ bool HttpCache::WriteResponseInfo(disk_cache::Entry* disk_entry,
     flags |= RESPONSE_INFO_HAS_SECURITY_BITS;
   if (response_info->vary_data.is_valid())
     flags |= RESPONSE_INFO_HAS_VARY_DATA;
+  if (response_truncated)
+    flags |= RESPONSE_INFO_TRUNCATED;
 
   Pickle pickle;
   pickle.WriteInt(flags);
@@ -1942,7 +1976,8 @@ int HttpCache::AddTransactionToEntry(ActiveEntry* entry, Transaction* trans) {
   return trans->EntryAvailable(entry);
 }
 
-void HttpCache::DoneWithEntry(ActiveEntry* entry, Transaction* trans) {
+void HttpCache::DoneWithEntry(ActiveEntry* entry, Transaction* trans,
+                              bool cancel) {
   // If we already posted a task to move on to the next transaction and this was
   // the writer, there is nothing to cancel.
   if (entry->will_process_pending_queue && entry->readers.empty())
@@ -1951,8 +1986,19 @@ void HttpCache::DoneWithEntry(ActiveEntry* entry, Transaction* trans) {
   if (entry->writer) {
     DCHECK(trans == entry->writer);
 
-    // Assume that this is not a successful write.
-    DoneWritingToEntry(entry, false);
+    // Assume there was a failure.
+    bool success = false;
+    if (cancel) {
+      DCHECK(entry->disk_entry);
+      // This is a successful operation in the sense that we want to keep the
+      // entry.
+      success = true;
+      // Double check that there is something worth keeping.
+      if (!entry->disk_entry->GetDataSize(kResponseContentIndex))
+        success = false;
+      trans->AddTruncatedFlag();
+    }
+    DoneWritingToEntry(entry, success);
   } else {
     DoneReadingFromEntry(entry, trans);
   }
diff --git a/net/http/http_cache.h b/net/http/http_cache.h
index f1807b7..b6599b2 100644
--- a/net/http/http_cache.h
+++ b/net/http/http_cache.h
@@ -97,18 +97,23 @@ class HttpCache : public HttpTransactionFactory {
   virtual HttpCache* GetCache();
   virtual void Suspend(bool suspend);
 
-  // Helper function for reading response info from the disk cache.
+  // Helper function for reading response info from the disk cache.  If the
+  // cache doesn't have the whole resource *|request_truncated| is set to true.
   static bool ReadResponseInfo(disk_cache::Entry* disk_entry,
-                               HttpResponseInfo* response_info);
+                               HttpResponseInfo* response_info,
+                               bool* response_truncated);
 
-  // Helper function for writing response info into the disk cache.
+  // Helper function for writing response info into the disk cache.  If the
+  // cache doesn't have the whole resource |request_truncated| should be true.
   static bool WriteResponseInfo(disk_cache::Entry* disk_entry,
                                 const HttpResponseInfo* response_info,
-                                bool skip_transient_headers);
+                                bool skip_transient_headers,
+                                bool response_truncated);
 
   // Given a header data blob, convert it to a response info object.
   static bool ParseResponseInfo(const char* data, int len,
-                                HttpResponseInfo* response_info);
+                                HttpResponseInfo* response_info,
+                                bool* response_truncated);
 
   // Get/Set the cache's mode.
   void set_mode(Mode value) { mode_ = value; }
@@ -162,7 +167,7 @@ class HttpCache : public HttpTransactionFactory {
   ActiveEntry* CreateEntry(const std::string& cache_key);
   void DestroyEntry(ActiveEntry* entry);
   int AddTransactionToEntry(ActiveEntry* entry, Transaction* trans);
-  void DoneWithEntry(ActiveEntry* entry, Transaction* trans);
+  void DoneWithEntry(ActiveEntry* entry, Transaction* trans, bool cancel);
   void DoneWritingToEntry(ActiveEntry* entry, bool success);
   void DoneReadingFromEntry(ActiveEntry* entry, Transaction* trans);
   void ConvertWriterToReader(ActiveEntry* entry);
diff --git a/net/http/http_cache_unittest.cc b/net/http/http_cache_unittest.cc
index 8d01b6a..a72c36d 100644
--- a/net/http/http_cache_unittest.cc
+++ b/net/http/http_cache_unittest.cc
@@ -2013,7 +2013,7 @@ TEST(HttpCache, GET_Previous206_NotSparse) {
 
   net::HttpResponseInfo response;
   response.headers = new net::HttpResponseHeaders(raw_headers);
-  net::HttpCache::WriteResponseInfo(entry, &response, true);
+  EXPECT_TRUE(net::HttpCache::WriteResponseInfo(entry, &response, true, false));
 
   scoped_refptr<net::IOBuffer> buf(new net::IOBuffer(500));
   int len = static_cast<int>(base::strlcpy(buf->data(),
@@ -2056,7 +2056,7 @@ TEST(HttpCache, RangeGET_Previous206_NotSparse_2) {
 
   net::HttpResponseInfo response;
   response.headers = new net::HttpResponseHeaders(raw_headers);
-  net::HttpCache::WriteResponseInfo(entry, &response, true);
+  EXPECT_TRUE(net::HttpCache::WriteResponseInfo(entry, &response, true, false));
 
   scoped_refptr<net::IOBuffer> buf(new net::IOBuffer(500));
   int len = static_cast<int>(base::strlcpy(buf->data(),
@@ -2238,6 +2238,159 @@ TEST(HttpCache, RangeGET_OK_LoadOnlyFromCache) {
 }
 #endif
 
+// Tests the handling of the "truncation" flag.
+TEST(HttpCache, WriteResponseInfo_Truncated) {
+  MockHttpCache cache;
+  disk_cache::Entry* entry;
+  ASSERT_TRUE(cache.disk_cache()->CreateEntry("http://www.google.com", &entry));
+
+  std::string headers("HTTP/1.1 200 OK");
+  headers = net::HttpUtil::AssembleRawHeaders(headers.data(), headers.size());
+  net::HttpResponseInfo response;
+  response.headers = new net::HttpResponseHeaders(headers);
+
+  // Set the last argument for this to be an incomplete request.
+  EXPECT_TRUE(net::HttpCache::WriteResponseInfo(entry, &response, true, true));
+  bool truncated = false;
+  EXPECT_TRUE(net::HttpCache::ReadResponseInfo(entry, &response, &truncated));
+  EXPECT_TRUE(truncated);
+
+  // And now test the opposite case.
+  EXPECT_TRUE(net::HttpCache::WriteResponseInfo(entry, &response, true, false));
+  truncated = true;
+  EXPECT_TRUE(net::HttpCache::ReadResponseInfo(entry, &response, &truncated));
+  EXPECT_FALSE(truncated);
+  entry->Close();
+}
+
+// Tests that we delete an entry when the request is cancelled before starting
+// to read from the network.
+TEST(HttpCache, DoomOnDestruction) {
+  MockHttpCache cache;
+  cache.http_cache()->set_enable_range_support(true);
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  Context* c =  new Context(cache.http_cache()->CreateTransaction());
+
+  int rv = c->trans->Start(&request, &c->callback, NULL);
+  if (rv == net::ERR_IO_PENDING)
+    c->result = c->callback.WaitForResult();
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Destroy the transaction. We only have the headers so we should delete this
+  // entry.
+  delete c;
+
+  RunTransactionTest(cache.http_cache(), kSimpleGET_Transaction);
+
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(2, cache.disk_cache()->create_count());
+}
+
+// Tests that we mark an entry as incomplete when the request is cancelled.
+TEST(HttpCache, Set_Truncated_Flag) {
+  MockHttpCache cache;
+  cache.http_cache()->set_enable_range_support(true);
+
+  MockHttpRequest request(kSimpleGET_Transaction);
+
+  Context* c =  new Context(cache.http_cache()->CreateTransaction());
+
+  int rv = c->trans->Start(&request, &c->callback, NULL);
+  if (rv == net::ERR_IO_PENDING)
+    rv = c->callback.WaitForResult();
+
+  EXPECT_EQ(1, cache.network_layer()->transaction_count());
+  EXPECT_EQ(0, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  // Make sure that the entry has some data stored.
+  scoped_refptr<net::IOBufferWithSize> buf = new net::IOBufferWithSize(10);
+  rv = c->trans->Read(buf, buf->size(), &c->callback);
+  if (rv == net::ERR_IO_PENDING)
+    rv = c->callback.WaitForResult();
+  EXPECT_EQ(buf->size(), rv);
+
+  // Destroy the transaction.
+  delete c;
+
+  // Verify that the entry is marked as incomplete.
+  disk_cache::Entry* entry;
+  ASSERT_TRUE(cache.disk_cache()->OpenEntry(kSimpleGET_Transaction.url,
+                                            &entry));
+  net::HttpResponseInfo response;
+  bool truncated = false;
+  EXPECT_TRUE(net::HttpCache::ReadResponseInfo(entry, &response, &truncated));
+  EXPECT_TRUE(truncated);
+  entry->Close();
+}
+
+// Tests that we can continue with a request that was interrupted.
+TEST(HttpCache, GET_IncompleteResource) {
+  MockHttpCache cache;
+  cache.http_cache()->set_enable_range_support(true);
+  AddMockTransaction(&kRangeGET_TransactionOK);
+
+  // Create a disk cache entry that stores an incomplete resource.
+  disk_cache::Entry* entry;
+  ASSERT_TRUE(cache.disk_cache()->CreateEntry(kRangeGET_TransactionOK.url,
+                                              &entry));
+
+  // Content-length will be intentionally bogus.
+  std::string raw_headers("HTTP/1.1 200 OK\n"
+                          "Last-Modified: something\n"
+                          "ETag: \"foo\"\n"
+                          "Accept-Ranges: bytes\n"
+                          "Content-Length: 10\n");
+  raw_headers = net::HttpUtil::AssembleRawHeaders(raw_headers.data(),
+                                                  raw_headers.size());
+
+  net::HttpResponseInfo response;
+  response.headers = new net::HttpResponseHeaders(raw_headers);
+  // Set the last argument for this to be an incomplete request.
+  EXPECT_TRUE(net::HttpCache::WriteResponseInfo(entry, &response, true, true));
+
+  scoped_refptr<net::IOBuffer> buf(new net::IOBuffer(100));
+  int len = static_cast<int>(base::strlcpy(buf->data(),
+                                           "rg: 00-09 rg: 10-19 ", 100));
+  EXPECT_EQ(len, entry->WriteData(1, 0, buf, len, NULL, true));
+
+  // Now make a regular request.
+  std::string headers;
+  MockTransaction transaction(kRangeGET_TransactionOK);
+  transaction.request_headers = "";
+  transaction.data = "rg: 00-09 rg: 10-19 rg: 20-29 rg: 30-39 rg: 40-49 "
+                     "rg: 50-59 rg: 60-69 rg: 70-79 ";
+  RunTransactionTestWithResponse(cache.http_cache(), transaction, &headers);
+
+  // We update the headers with the ones received while revalidating.
+  std::string expected_headers(
+      "HTTP/1.1 200 OK\n"
+      "Last-Modified: Sat, 18 Apr 2009 01:10:43 GMT\n"
+      "Accept-Ranges: bytes\n"
+      "ETag: \"foo\"\n"
+      "Content-Length: 10\n");
+
+  EXPECT_EQ(expected_headers, headers);
+  EXPECT_EQ(2, cache.network_layer()->transaction_count());
+  EXPECT_EQ(1, cache.disk_cache()->open_count());
+  EXPECT_EQ(1, cache.disk_cache()->create_count());
+
+  RemoveMockTransaction(&kRangeGET_TransactionOK);
+
+  // Verify that the disk entry was updated.
+  EXPECT_EQ(80, entry->GetDataSize(1));
+  bool truncated = true;
+  EXPECT_TRUE(net::HttpCache::ReadResponseInfo(entry, &response, &truncated));
+  EXPECT_FALSE(truncated);
+  entry->Close();
+}
+
 TEST(HttpCache, SyncRead) {
   MockHttpCache cache;
 
diff --git a/net/http/partial_data.cc b/net/http/partial_data.cc
index 70d7d18..fcd7808 100644
--- a/net/http/partial_data.cc
+++ b/net/http/partial_data.cc
@@ -65,6 +65,12 @@ int PartialData::PrepareCacheValidation(disk_cache::Entry* entry,
   if (sparse_entry_) {
     cached_min_len_ = entry->GetAvailableRange(current_range_start_, len,
                                                &cached_start_);
+  } else if (truncated_) {
+    if (!current_range_start_) {
+      // Update the cached range only the first time.
+      cached_min_len_ = static_cast<int32>(byte_range_.first_byte_position());
+      cached_start_ = 0;
+    }
   } else {
     cached_min_len_ = len;
     cached_start_ = current_range_start_;
@@ -80,7 +86,8 @@ int PartialData::PrepareCacheValidation(disk_cache::Entry* entry,
   if (!cached_min_len_) {
     // We don't have anything else stored.
     final_range_ = true;
-    cached_start_ = current_range_start_ + len;
+    cached_start_ =
+        byte_range_.HasLastBytePosition() ? current_range_start_  + len : 0;
   }
 
   if (current_range_start_ == cached_start_) {
@@ -108,9 +115,24 @@ bool PartialData::IsLastRange() const {
 }
 
 bool PartialData::UpdateFromStoredHeaders(const HttpResponseHeaders* headers,
-                                          disk_cache::Entry* entry) {
-  std::string length_value;
+                                          disk_cache::Entry* entry,
+                                          bool truncated) {
   resource_size_ = 0;
+  if (truncated) {
+    DCHECK_EQ(headers->response_code(), 200);
+    truncated_ = true;
+    sparse_entry_ = false;
+
+    // We don't have the real length and the user may be trying to create a
+    // sparse entry so let's not write to this entry.
+    if (byte_range_.IsValid())
+      return false;
+
+    byte_range_.set_first_byte_position(entry->GetDataSize(kDataStream));
+    current_range_start_ = 0;
+    return true;
+  }
+
   if (headers->response_code() == 200) {
     DCHECK(byte_range_.IsValid());
     sparse_entry_ = false;
@@ -118,6 +140,7 @@ bool PartialData::UpdateFromStoredHeaders(const HttpResponseHeaders* headers,
     return true;
   }
 
+  std::string length_value;
   if (!headers->GetNormalizedHeader(kLengthHeader, &length_value))
     return false;  // We must have stored the resource length.
 
@@ -134,6 +157,8 @@ bool PartialData::UpdateFromStoredHeaders(const HttpResponseHeaders* headers,
 
 bool PartialData::IsRequestedRangeOK() {
   if (byte_range_.IsValid()) {
+    if (truncated_)
+      return true;
     if (!byte_range_.ComputeBounds(resource_size_))
       return false;
 
@@ -154,6 +179,9 @@ bool PartialData::IsRequestedRangeOK() {
 
 bool PartialData::ResponseHeadersOK(const HttpResponseHeaders* headers) {
   if (headers->response_code() == 304) {
+    if (truncated_)
+      return true;
+
     // We must have a complete range here.
     return byte_range_.HasFirstBytePosition() &&
            byte_range_.HasLastBytePosition();
@@ -191,6 +219,9 @@ bool PartialData::ResponseHeadersOK(const HttpResponseHeaders* headers) {
 // Just assume that everything is fine and say that we are returning what was
 // requested.
 void PartialData::FixResponseHeaders(HttpResponseHeaders* headers) {
+  if (truncated_)
+    return;
+
   headers->RemoveHeader(kLengthHeader);
   headers->RemoveHeader(kRangeHeader);
 
@@ -249,7 +280,7 @@ int PartialData::CacheWrite(disk_cache::Entry* entry, IOBuffer* data,
       return ERR_INVALID_ARGUMENT;
 
     return entry->WriteData(kDataStream, static_cast<int>(current_range_start_),
-                            data, data_len, callback, false);
+                            data, data_len, callback, true);
   }
 }
 
diff --git a/net/http/partial_data.h b/net/http/partial_data.h
index 460ff21..fcbec57 100644
--- a/net/http/partial_data.h
+++ b/net/http/partial_data.h
@@ -32,7 +32,8 @@ class IOBuffer;
 class PartialData {
  public:
   PartialData()
-      : range_present_(false), final_range_(false), sparse_entry_(true) {}
+      : range_present_(false), final_range_(false), sparse_entry_(true),
+        truncated_(false) {}
   ~PartialData() {}
 
   // Performs initialization of the object by parsing the request |headers|
@@ -62,9 +63,10 @@ class PartialData {
   bool IsLastRange() const;
 
   // Extracts info from headers already stored in the cache. Returns false if
-  // there is any problem with the headers.
+  // there is any problem with the headers. |truncated| should be true if we
+  // have an incomplete 200 entry.
   bool UpdateFromStoredHeaders(const HttpResponseHeaders* headers,
-                               disk_cache::Entry* entry);
+                               disk_cache::Entry* entry, bool truncated);
 
   // Returns true if the requested range is valid given the stored data.
   bool IsRequestedRangeOK();
@@ -111,6 +113,7 @@ class PartialData {
   bool range_present_;  // True if next range entry is already stored.
   bool final_range_;
   bool sparse_entry_;
+  bool truncated_;  // We have an incomplete 200 stored.
 
   DISALLOW_COPY_AND_ASSIGN(PartialData);
 };