Adds a new class HttpCache::Writers for multiple cache transactions reading from the network.

net/http/http_cache_writers_unittest.cc

+// Copyright (c) 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/http/http_cache_writers.h"
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "base/run_loop.h"
+#include "net/http/http_cache.h"
+#include "net/http/http_cache_transaction.h"
+#include "net/http/http_transaction.h"
+#include "net/http/http_transaction_test_util.h"
+#include "net/http/mock_http_cache.h"
+#include "net/test/gtest_util.h"
+
+using net::test::IsError;
+using net::test::IsOk;
+
+namespace net {
+
+class WritersTest : public testing::Test {
+ public:
+  WritersTest() : disk_entry_(nullptr), request_(kSimpleGET_Transaction) {}
+
+  ~WritersTest() override {
+    if (disk_entry_)
+      disk_entry_->Close();
+  }
+
+  void CreateWriters(const std::string& url) {
+    cache_.CreateBackendEntry(kSimpleGET_Transaction.url, &disk_entry_,
+                              nullptr);
+    writers_ = base::MakeUnique<HttpCache::Writers>(disk_entry_);
+  }
+
+  std::unique_ptr<HttpTransaction> CreateNetworkTransaction() {
+    std::unique_ptr<HttpTransaction> transaction;
+    MockNetworkLayer* network_layer = cache_.network_layer();
+    network_layer->CreateTransaction(DEFAULT_PRIORITY, &transaction);
+    return transaction;
+  }
+
+  void CreateWritersAddTransaction(
+      bool is_exclusive = false,
+      net::RequestPriority priority = DEFAULT_PRIORITY) {

[Randy Smith (Not in Mondays), 2017/06/29 00:53:49]

The google style guide discourages default arguments
(https://google.github.io/styleguide/cppguide.html#Default_Arguments ).  I'm not
determined to hold to the style guide for test code, but it's better to be
consistent than not, so I'd suggest instead have two functions with different
names, one that calls the other with the above arguments.   Up to you.

[shivanisha, 2017/07/05 17:44:24]

Created CreateWritersAddTransactionPriority which takes priority and passes it
to CreateWritersAddTransaction. Keeping is_exclusive as default argument since
it really is mostly false and set only in very few test cases.

+    std::unique_ptr<HttpTransaction> transaction;
+    int rv = cache_.CreateTransaction(&transaction);
+    EXPECT_EQ(rv, OK);
+    EXPECT_TRUE(transaction);
+
+    TestCompletionCallback callback;
+
+    CreateWriters(kSimpleGET_Transaction.url);
+
+    // Create and Start a mock network transaction.
+    std::unique_ptr<HttpTransaction> network_transaction;
+    network_transaction = CreateNetworkTransaction();
+    network_transaction->Start(&request_, callback.callback(),
+                               NetLogWithSource());
+    base::RunLoop().RunUntilIdle();
+
+    EXPECT_TRUE(writers_->IsEmpty());
+    writers_->AddTransaction(
+        static_cast<HttpCache::Transaction*>(transaction.get()),
+        std::move(network_transaction), is_exclusive);
+    transaction->SetPriority(priority);
+    EXPECT_TRUE(writers_->HasTransaction(
+        static_cast<HttpCache::Transaction*>(transaction.get())));
+    transactions_.push_back(std::move(transaction));
+  }
+
+  void AddTransactionToExistingWriters() {
+    std::unique_ptr<HttpTransaction> transaction;
+    int rv = cache_.CreateTransaction(&transaction);
+    EXPECT_EQ(rv, OK);
+    EXPECT_TRUE(transaction);
+
+    EXPECT_TRUE(writers_);
+    writers_->AddTransaction(
+        static_cast<HttpCache::Transaction*>(transaction.get()), nullptr,
+        false);
+    transactions_.push_back(std::move(transaction));
+  }
+
+  int Read(std::string* result) {
+    EXPECT_TRUE(transactions_.size() >= (size_t)1);
+    HttpCache::Transaction* transaction =
+        static_cast<HttpCache::Transaction*>(transactions_.begin()->get());
+    TestCompletionCallback callback;
+
+    std::string content;
+    int rv = 0;
+    do {
+      scoped_refptr<IOBuffer> buf(new IOBuffer(256));
+      rv = writers_->Read(buf.get(), 256, callback.callback(), transaction);
+      if (rv == ERR_IO_PENDING) {
+        rv = callback.WaitForResult();
+        base::RunLoop().RunUntilIdle();
+      }
+
+      if (rv > 0)
+        content.append(buf->data(), rv);
+      else if (rv < 0)
+        return rv;
+    } while (rv > 0);
+
+    result->swap(content);
+    return OK;
+  }
+
+  int ReadAll(std::vector<std::string>* results) {
+    int rv = 0;
+    do {
+      std::vector<scoped_refptr<IOBuffer>> bufs;
+      std::vector<TestCompletionCallback> callbacks(results->size());
+
+      // Multiple transactions should be able to read.
+      for (size_t i = 0; i < transactions_.size(); i++) {
+        bufs.push_back(new IOBuffer(256));
+        rv = writers_->Read(
+            bufs[i].get(), 256, callbacks[i].callback(),
+            static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+        EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+      }
+
+      if (rv == ERR_IO_PENDING) {

[Randy Smith (Not in Mondays), 2017/06/29 00:53:50]

I don't think this test makes sense.  If any of the rvs aren't ERR_IO_PENDING,
the code below will hang since the callbacks won't be called, and this just
tests the last one.  I'd suggest tracking if any rv isn't ERR_IO_PENDING,
returning that rv if so, and removing this conditional.

[shivanisha, 2017/07/05 17:44:25]

Since the EXPECT_EQ above asserts all rvs to be ERR_IO_PENDING, removing this
if. Here and in all similar functions.

+        int prev_rv = callbacks[0].WaitForResult();
+        for (size_t i = 1; i < callbacks.size(); i++) {

[Randy Smith (Not in Mondays), 2017/06/29 00:53:49]

nit: I think this fails if *results is of length 1 (rv isn't set properly below
in that case).   Could you either DCHECK that that's not true or change the
logic here so it does work?

[shivanisha, 2017/07/05 17:44:24]

Changed the logic to have rv = prev_rv before the loop starts. Here and in all
similar functions.

+          rv = callbacks[i].WaitForResult();
+          EXPECT_EQ(rv, prev_rv);
+          prev_rv = rv;
+        }
+      }
+
+      if (rv > 0) {
+        for (size_t i = 0; i < results->size(); i++)
+          results->at(i).append(bufs[i]->data(), rv);
+      } else if (rv <= 0) {
+        return rv;
+      }
+    } while (rv > 0);
+
+    return OK;
+  }
+
+  void ReadVerifyTwoDifferentBufferSizes(std::vector<std::string>* results) {
+    EXPECT_EQ(2u, results->size());
+
+    // Check only the 1st Read and not the complete response because the smaller
+    // buffer transaction will need to read the remaining response from the
+    // cache which will be tested when integrated with HttpCache::Transaction
+    // layer.
+
+    int rv = 0;
+
+    std::vector<scoped_refptr<IOBuffer>> bufs;
+    std::vector<TestCompletionCallback> callbacks(results->size());
+
+    int larger_buffer_size = 20;
+    int smaller_buffer_size = 10;

[Randy Smith (Not in Mondays), 2017/06/29 00:53:49]

Reasonable to also test the case where the smaller buffer size is first?  In
that case I'd expect the larger buffer to return with only the smaller buffer
size read.

[shivanisha, 2017/07/05 17:44:24]

Added, also changed this function to work in both tests.

+    bufs.push_back(new IOBuffer(larger_buffer_size));
+    bufs.push_back(new IOBuffer(smaller_buffer_size));
+
+    // Multiple transactions should be able to read with different sized
+    // buffers.
+    for (size_t i = 0; i < transactions_.size(); i++) {
+      int buffer_size = i == 0 ? larger_buffer_size : smaller_buffer_size;
+      rv = writers_->Read(
+          bufs[i].get(), buffer_size, callbacks[i].callback(),
+          static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+      EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+    }
+
+    for (size_t i = 0; i < callbacks.size(); i++) {
+      int buffer_size = i == 0 ? larger_buffer_size : smaller_buffer_size;
+      rv = callbacks[i].WaitForResult();
+      EXPECT_EQ(rv, buffer_size);
+    }
+
+    for (size_t i = 0; i < results->size(); i++) {
+      int buffer_size = i == 0 ? larger_buffer_size : smaller_buffer_size;
+      results->at(i).append(bufs[i]->data(), buffer_size);
+    }
+
+    EXPECT_EQ(results->at(0).substr(0, smaller_buffer_size), results->at(1));
+  }
+
+  int ReadAllDeleteActiveTransaction(std::vector<std::string>* results) {
+    int rv = 0;
+    bool first_iter = true;
+    do {
+      std::vector<scoped_refptr<IOBuffer>> bufs;
+      std::vector<TestCompletionCallback> callbacks(results->size());
+
+      // Multiple transactions should be able to read.
+      for (size_t i = 0; i < transactions_.size(); i++) {
+        bufs.push_back(new IOBuffer(256));
+        if (!first_iter && i == 0)
+          continue;
+
+        rv = writers_->Read(
+            bufs[i].get(), 256, callbacks[i].callback(),
+            static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+        EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+      }
+
+      if (rv == ERR_IO_PENDING) {

[Randy Smith (Not in Mondays), 2017/06/29 00:53:49]

Same comment as above--I don't think this makes sense, because the test is in
trouble if any rv wasn't ERR_IO_PENDING, and this only tests the last one.

(Applies at all other relevant locations in file.)

[shivanisha, 2017/07/05 17:44:24]

Changed.

+        if (first_iter) {
+          // Delete active transaction.
+          RemoveFirstTransaction();
+        }
+        int prev_rv = callbacks[1].WaitForResult();
+        for (size_t i = 2; i < callbacks.size(); i++) {

[Randy Smith (Not in Mondays), 2017/06/29 00:53:49]

Same comment as above--I think this fails (doesn't set rv properly) if
callbacks.size() == 2.

(Applies at all other relevant locations in file.)

[shivanisha, 2017/07/05 17:44:24]

Changed

+          rv = callbacks[i].WaitForResult();
+          EXPECT_EQ(rv, prev_rv);
+          prev_rv = rv;
+        }
+      }
+
+      if (rv > 0) {
+        for (size_t i = 0; i < results->size(); i++)
+          results->at(i).append(bufs[i]->data(), rv);
+      }
+      first_iter = false;
+    } while (rv > 0);
+
+    return rv;
+  }
+
+  int ReadAllDeleteWaitingTransaction(size_t waiting_index,
+                                      std::vector<std::string>* results) {
+    int rv = 0;
+    bool first_iter = true;
+    do {
+      std::vector<scoped_refptr<IOBuffer>> bufs;
+      std::vector<TestCompletionCallback> callbacks(results->size());
+
+      // Multiple transactions should be able to read.
+      for (size_t i = 0; i < transactions_.size(); i++) {
+        bufs.push_back(new IOBuffer(256));
+        if (!first_iter && i == waiting_index)
+          continue;
+
+        rv = writers_->Read(
+            bufs[i].get(), 256, callbacks[i].callback(),
+            static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+        EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+      }
+
+      if (rv == ERR_IO_PENDING) {
+        if (first_iter) {
+          // Delete waiting transaction.
+          writers_->RemoveTransaction(static_cast<HttpCache::Transaction*>(
+              transactions_.at(waiting_index).get()));
+        }
+        int prev_rv = callbacks[0].WaitForResult();
+        for (size_t i = 1; i < callbacks.size(); i++) {
+          if (i == waiting_index)
+            continue;
+          rv = callbacks[i].WaitForResult();
+          EXPECT_EQ(rv, prev_rv);
+          prev_rv = rv;
+        }
+      }
+
+      if (rv > 0) {
+        for (size_t i = 0; i < results->size(); i++) {
+          if (i == waiting_index)
+            continue;
+          results->at(i).append(bufs[i]->data(), rv);
+        }
+      }
+      first_iter = false;
+    } while (rv > 0);
+
+    return rv;
+  }
+
+  int ReadAllDeleteIdleTransaction(size_t idle_index,
+                                   std::vector<std::string>* results) {
+    int rv = 0;
+    bool first_iter = true;
+    do {
+      std::vector<scoped_refptr<IOBuffer>> bufs;
+      std::vector<TestCompletionCallback> callbacks(results->size());
+
+      // Multiple transactions should be able to read.
+      for (size_t i = 0; i < transactions_.size(); i++) {
+        bufs.push_back(new IOBuffer(256));
+        if (i == idle_index)
+          continue;
+
+        rv = writers_->Read(
+            bufs[i].get(), 256, callbacks[i].callback(),
+            static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+        EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+      }
+
+      if (rv == ERR_IO_PENDING) {
+        if (first_iter) {
+          // Delete idle transaction.
+          writers_->RemoveTransaction(static_cast<HttpCache::Transaction*>(
+              transactions_.at(idle_index).get()));
+        }
+        int prev_rv = callbacks[0].WaitForResult();
+        for (size_t i = 1; i < callbacks.size(); i++) {
+          if (i == idle_index)
+            continue;
+          rv = callbacks[i].WaitForResult();
+          EXPECT_EQ(rv, prev_rv);
+          prev_rv = rv;
+        }
+      }
+
+      if (rv > 0) {
+        for (size_t i = 0; i < results->size(); i++) {
+          if (i == idle_index)
+            continue;
+          results->at(i).append(bufs[i]->data(), rv);
+        }
+      }
+      first_iter = false;
+    } while (rv > 0);
+
+    return rv;
+  }
+
+  int ReadCacheWriteFailure(std::vector<std::string>* results) {
+    int rv = 0;
+    int active_transaction_rv = 0;
+    bool first_iter = true;
+    do {
+      std::vector<scoped_refptr<IOBuffer>> bufs;
+      std::vector<TestCompletionCallback> callbacks(results->size());
+
+      // Fail the request.
+      cache_.disk_cache()->set_soft_failures(true);
+
+      // We have to open the entry again to propagate the failure flag.
+      disk_cache::Entry* en;
+      cache_.OpenBackendEntry(kSimpleGET_Transaction.url, &en);
+      en->Close();
+
+      for (size_t i = 0; i < transactions_.size(); i++) {
+        bufs.push_back(new IOBuffer(30));
+
+        if (!first_iter && i > 0)
+          break;
+        rv = writers_->Read(
+            bufs[i].get(), 30, callbacks[i].callback(),
+            static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+        EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+      }
+
+      if (rv == ERR_IO_PENDING) {
+        for (size_t i = 0; i < callbacks.size(); i++) {
+          // Only active transaction should succeed.
+          if (i == 0) {
+            active_transaction_rv = callbacks[i].WaitForResult();
+            EXPECT_TRUE(active_transaction_rv >= 0);
+            results->at(0).append(bufs[i]->data(), active_transaction_rv);
+          } else if (first_iter) {
+            rv = callbacks[i].WaitForResult();
+            EXPECT_EQ(ERR_CACHE_WRITE_FAILURE, rv);
+          }
+        }
+      }
+
+      first_iter = false;
+    } while (active_transaction_rv > 0);
+
+    return active_transaction_rv;
+  }
+
+  int ReadNetworkFailure(std::vector<std::string>* results, Error error) {
+    int rv = 0;
+    std::vector<scoped_refptr<IOBuffer>> bufs;
+    std::vector<TestCompletionCallback> callbacks(results->size());
+
+    for (size_t i = 0; i < transactions_.size(); i++) {
+      bufs.push_back(new IOBuffer(30));
+
+      rv = writers_->Read(
+          bufs[i].get(), 30, callbacks[i].callback(),
+          static_cast<HttpCache::Transaction*>(transactions_[i].get()));
+      EXPECT_EQ(rv, ERR_IO_PENDING);  // Since the default is asynchronous.
+    }
+
+    if (rv == ERR_IO_PENDING) {
+      for (auto& callback : callbacks) {
+        rv = callback.WaitForResult();
+        EXPECT_EQ(error, rv);
+      }
+    }
+
+    return error;
+  }
+
+  bool StopCaching() {
+    HttpCache::Transaction* transaction =
+        static_cast<HttpCache::Transaction*>(transactions_.begin()->get());
+    EXPECT_TRUE(transaction);
+    return writers_->StopCaching(transaction);
+  }
+
+  void RemoveFirstTransaction() {
+    HttpCache::Transaction* transaction =
+        static_cast<HttpCache::Transaction*>(transactions_.begin()->get());
+    EXPECT_TRUE(transaction);
+    writers_->RemoveTransaction(transaction);
+  }
+
+  void UpdateAndVerifyPriority(RequestPriority priority) {
+    writers_->UpdatePriority();
+    EXPECT_EQ(writers_->priority_, priority);
+  }
+
+  MockHttpCache cache_;
+  std::unique_ptr<HttpCache::Writers> writers_;
+  disk_cache::Entry* disk_entry_;
+
+  // Should be before transactions_ since it is accessed in the network
+  // transaction's destructor.
+  MockHttpRequest request_;
+
+  std::vector<std::unique_ptr<HttpTransaction>> transactions_;
+};
+
+// Tests successful addition of a transaction.
+TEST_F(WritersTest, AddTransaction) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+}
+
+// Tests successful addition of multiple transaction.
+TEST_F(WritersTest, AddManyTransactions) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  for (int i = 0; i < 5; i++)
+    AddTransactionToExistingWriters();
+
+  EXPECT_EQ(writers_->CountTransactionsForTesting(), 6);
+}
+
+// Tests that CanAddWriters should return false if it is exclusive writing.
+TEST_F(WritersTest, AddTransactionsExclusive) {
+  CreateWritersAddTransaction(true /* is_exclusive */);
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_FALSE(writers_->CanAddWriters());
+}
+
+// Tests StopCaching should not stop caching if there are multiple writers.
+TEST_F(WritersTest, StopCachingMultipleWriters) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+
+  EXPECT_FALSE(StopCaching());
+  EXPECT_TRUE(writers_->CanAddWriters());
+}
+
+// Tests StopCaching should stop caching if there is a single writer.
+TEST_F(WritersTest, StopCaching) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(StopCaching());
+  EXPECT_FALSE(writers_->CanAddWriters());
+}
+
+// Tests removing of an idle transaction and change in priority.
+TEST_F(WritersTest, RemoveIdleTransaction) {
+  CreateWritersAddTransaction(false, HIGHEST);
+  UpdateAndVerifyPriority(HIGHEST);
+
+  AddTransactionToExistingWriters();
+  UpdateAndVerifyPriority(HIGHEST);
+
+  EXPECT_FALSE(writers_->IsEmpty());
+  EXPECT_EQ(2, writers_->CountTransactionsForTesting());
+
+  RemoveFirstTransaction();
+  EXPECT_EQ(1, writers_->CountTransactionsForTesting());
+
+  UpdateAndVerifyPriority(DEFAULT_PRIORITY);
+}
+
+// Tests that Read is successful.
+TEST_F(WritersTest, Read) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  std::string content;
+  int rv = Read(&content);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+  EXPECT_EQ(expected, content);
+}
+
+// Tests that multiple transactions can read the same data simultaneously.
+TEST_F(WritersTest, ReadMultiple) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(2);
+  int rv = ReadAll(&contents);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+
+  for (auto content : contents)
+    EXPECT_EQ(expected, content);
+}
+
+// Tests that multiple transactions can read the same data simultaneously.
+TEST_F(WritersTest, ReadMultipleDifferentBufferSizes) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(2);
+  ReadVerifyTwoDifferentBufferSizes(&contents);
+}
+
+// Tests that ongoing Read completes even when active transaction is deleted
+// mid-read. Any transactions waiting should be able to get the read buffer.
+TEST_F(WritersTest, ReadMultipleDeleteActiveTransaction) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(3);
+  int rv = ReadAllDeleteActiveTransaction(&contents);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+
+  for (auto content : contents)
+    EXPECT_EQ(expected, content);
+}
+
+// Tests that removing a waiting for read transaction does not impact other
+// transactions.
+TEST_F(WritersTest, ReadMultipleDeleteWaitingTransaction) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(4);
+  size_t waiting_index = 1;
+  int rv = ReadAllDeleteWaitingTransaction(waiting_index, &contents);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+
+  size_t i = 0;
+  for (auto content : contents) {
+    if (i == waiting_index)
+      EXPECT_EQ("", content);
+    else
+      EXPECT_EQ(expected, content);
+    i++;
+  }
+}
+
+// Tests that removing an idle transaction does not impact other transactions.
+TEST_F(WritersTest, ReadMultipleDeleteIdleTransaction) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(3);
+  size_t idle_index = 1;
+  int rv = ReadAllDeleteIdleTransaction(idle_index, &contents);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+
+  size_t i = 0;
+  for (auto content : contents) {
+    if (i == idle_index) {
+      i++;
+      continue;
+    }
+    EXPECT_EQ(expected, content);
+    i++;
+  }
+}
+
+// Tests cache write failure.
+TEST_F(WritersTest, ReadMultipleCacheWriteFailed) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(3);
+  int rv = ReadCacheWriteFailure(&contents);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+
+  // Only active_transaction_ should succeed.
+  EXPECT_EQ(expected, contents.at(0));
+
+  // No new transactions should now be added.
+  EXPECT_FALSE(writers_->CanAddWriters());
+}
+
+// Tests that network read failure fails all transactions: active, waiting and
+// idle.
+TEST_F(WritersTest, ReadMultipleNetworkReadFailed) {
+  ScopedMockTransaction transaction(kSimpleGET_Transaction);
+  transaction.read_return_code = ERR_INTERNET_DISCONNECTED;
+  MockHttpRequest request(transaction);
+  request_ = request;
+
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+
+  std::vector<std::string> contents(3);
+  int rv = ReadNetworkFailure(&contents, ERR_INTERNET_DISCONNECTED);
+
+  EXPECT_EQ(rv, ERR_INTERNET_DISCONNECTED);
+}
+
+// Tests moving idle writers to readers.
+TEST_F(WritersTest, MoveIdleWritersToReaders) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_TRUE(writers_->CanAddWriters());
+  AddTransactionToExistingWriters();
+  AddTransactionToExistingWriters();
+
+  EXPECT_FALSE(writers_->IsEmpty());
+  writers_->RemoveAllIdleWriters();
+  EXPECT_TRUE(writers_->IsEmpty());
+}
+
+// Tests GetWriterLoadState.
+TEST_F(WritersTest, GetWriterLoadState) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  EXPECT_EQ(LOAD_STATE_IDLE, writers_->GetWriterLoadState());
+}
+
+// Tests truncating the entry via Writers.
+TEST_F(WritersTest, TruncateEntry) {
+  CreateWritersAddTransaction();
+  EXPECT_FALSE(writers_->IsEmpty());
+
+  std::string content;
+  int rv = Read(&content);
+
+  EXPECT_THAT(rv, IsOk());
+  std::string expected(kSimpleGET_Transaction.data);
+  EXPECT_EQ(expected, content);
+
+  writers_->TruncateEntry();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_TRUE(writers_->IsTruncatedForTesting());
+}
+
+}  // namespace net