diff --git a/BUILD.gn b/BUILD.gn
index 25c805c..5657ac1 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2029,6 +2029,10 @@
     "testing/embedder_test.h",
     "testing/embedder_test_mock_delegate.h",
     "testing/embedder_test_timer_handling_delegate.h",
+    "testing/fake_file_access.cpp",
+    "testing/fake_file_access.h",
+    "testing/range_set.cpp",
+    "testing/range_set.h",
   ]
   deps = [
     ":pdfium",
diff --git a/core/fpdfapi/parser/cpdf_security_handler_embeddertest.cpp b/core/fpdfapi/parser/cpdf_security_handler_embeddertest.cpp
index 49a898f..91346da 100644
--- a/core/fpdfapi/parser/cpdf_security_handler_embeddertest.cpp
+++ b/core/fpdfapi/parser/cpdf_security_handler_embeddertest.cpp
@@ -62,6 +62,7 @@
     CompareBitmap(page_bitmap, 612, 792, md5);
     FPDFBitmap_Destroy(page_bitmap);
     EXPECT_TRUE(FPDFPage_GenerateContent(page));
+    SetWholeFileAvailable();
     EXPECT_TRUE(FPDF_SaveAsCopy(document(), this, 0));
     UnloadPage(page);
   }
diff --git a/fpdfsdk/fpdf_dataavail_embeddertest.cpp b/fpdfsdk/fpdf_dataavail_embeddertest.cpp
index c40f857..2084153 100644
--- a/fpdfsdk/fpdf_dataavail_embeddertest.cpp
+++ b/fpdfsdk/fpdf_dataavail_embeddertest.cpp
@@ -12,10 +12,25 @@
 #include "public/fpdfview.h"
 #include "testing/embedder_test.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "testing/range_set.h"
 #include "testing/test_support.h"
 #include "testing/utils/path_service.h"
 
 namespace {
+
+class MockDownloadHints : public FX_DOWNLOADHINTS {
+ public:
+  static void SAddSegment(FX_DOWNLOADHINTS* pThis, size_t offset, size_t size) {
+  }
+
+  MockDownloadHints() {
+    FX_DOWNLOADHINTS::version = 1;
+    FX_DOWNLOADHINTS::AddSegment = SAddSegment;
+  }
+
+  ~MockDownloadHints() {}
+};
+
 class TestAsyncLoader : public FX_DOWNLOADHINTS, FX_FILEAVAIL {
  public:
   explicit TestAsyncLoader(const std::string& file_name) {
@@ -60,7 +75,9 @@
   }
 
   size_t max_already_available_bound() const {
-    return available_ranges_.empty() ? 0 : available_ranges_.rbegin()->second;
+    return available_ranges_.IsEmpty()
+               ? 0
+               : available_ranges_.ranges().rbegin()->second;
   }
 
   void FlushRequestedData() {
@@ -72,45 +89,11 @@
 
  private:
   void SetDataAvailable(size_t start, size_t size) {
-    if (size == 0)
-      return;
-    const auto range = std::make_pair(start, start + size);
-    if (available_ranges_.empty()) {
-      available_ranges_.insert(range);
-      return;
-    }
-    auto start_it = available_ranges_.upper_bound(range);
-    if (start_it != available_ranges_.begin())
-      --start_it;  // start now points to the key equal or lower than offset.
-    if (start_it->second < range.first)
-      ++start_it;  // start element is entirely before current range, skip it.
-
-    auto end_it = available_ranges_.upper_bound(
-        std::make_pair(range.second, range.second));
-    if (start_it == end_it) {  // No ranges to merge.
-      available_ranges_.insert(range);
-      return;
-    }
-
-    --end_it;
-
-    size_t new_start = std::min<size_t>(start_it->first, range.first);
-    size_t new_end = std::max(end_it->second, range.second);
-
-    available_ranges_.erase(start_it, ++end_it);
-    available_ranges_.insert(std::make_pair(new_start, new_end));
+    available_ranges_.Union(RangeSet::Range(start, start + size));
   }
 
   bool CheckDataAlreadyAvailable(size_t start, size_t size) const {
-    if (size == 0)
-      return false;
-    const auto range = std::make_pair(start, start + size);
-    auto it = available_ranges_.upper_bound(range);
-    if (it == available_ranges_.begin())
-      return false;  // No ranges includes range.start().
-
-    --it;  // Now it starts equal or before range.start().
-    return it->second >= range.second;
+    return available_ranges_.Contains(RangeSet::Range(start, start + size));
   }
 
   int GetBlockImpl(unsigned long pos, unsigned char* pBuf, unsigned long size) {
@@ -165,14 +148,7 @@
   size_t max_requested_bound_ = 0;
   bool is_new_data_available_ = true;
 
-  using Range = std::pair<size_t, size_t>;
-  struct range_compare {
-    bool operator()(const Range& lval, const Range& rval) const {
-      return lval.first < rval.first;
-    }
-  };
-  using RangesContainer = std::set<Range, range_compare>;
-  RangesContainer available_ranges_;
+  RangeSet available_ranges_;
 };
 
 }  // namespace
@@ -182,13 +158,15 @@
 TEST_F(FPDFDataAvailEmbeddertest, TrailerUnterminated) {
   // Document must load without crashing but is too malformed to be available.
   EXPECT_FALSE(OpenDocument("trailer_unterminated.pdf"));
-  EXPECT_FALSE(FPDFAvail_IsDocAvail(avail_, &hints_));
+  MockDownloadHints hints;
+  EXPECT_FALSE(FPDFAvail_IsDocAvail(avail_, &hints));
 }
 
 TEST_F(FPDFDataAvailEmbeddertest, TrailerAsHexstring) {
   // Document must load without crashing but is too malformed to be available.
   EXPECT_FALSE(OpenDocument("trailer_as_hexstring.pdf"));
-  EXPECT_FALSE(FPDFAvail_IsDocAvail(avail_, &hints_));
+  MockDownloadHints hints;
+  EXPECT_FALSE(FPDFAvail_IsDocAvail(avail_, &hints));
 }
 
 TEST_F(FPDFDataAvailEmbeddertest, LoadUsingHintTables) {
diff --git a/fpdfsdk/fpdfdoc_embeddertest.cpp b/fpdfsdk/fpdfdoc_embeddertest.cpp
index 5db610e..19147d4 100644
--- a/fpdfsdk/fpdfdoc_embeddertest.cpp
+++ b/fpdfsdk/fpdfdoc_embeddertest.cpp
@@ -248,6 +248,10 @@
   EXPECT_TRUE(OpenDocument("page_labels.pdf"));
   EXPECT_EQ(7, FPDF_GetPageCount(document()));
 
+  // We do not request labels, when use FPDFAvail_IsXXXAvail.
+  // Flush all data, to allow read labels.
+  SetWholeFileAvailable();
+
   unsigned short buf[128];
   EXPECT_EQ(0u, FPDF_GetPageLabel(document(), -2, buf, sizeof(buf)));
   EXPECT_EQ(0u, FPDF_GetPageLabel(document(), -1, buf, sizeof(buf)));
diff --git a/fpdfsdk/fpdfview_embeddertest.cpp b/fpdfsdk/fpdfview_embeddertest.cpp
index 97ba9d7..699fc8a 100644
--- a/fpdfsdk/fpdfview_embeddertest.cpp
+++ b/fpdfsdk/fpdfview_embeddertest.cpp
@@ -12,6 +12,23 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/utils/path_service.h"
 
+namespace {
+
+class MockDownloadHints : public FX_DOWNLOADHINTS {
+ public:
+  static void SAddSegment(FX_DOWNLOADHINTS* pThis, size_t offset, size_t size) {
+  }
+
+  MockDownloadHints() {
+    FX_DOWNLOADHINTS::version = 1;
+    FX_DOWNLOADHINTS::AddSegment = SAddSegment;
+  }
+
+  ~MockDownloadHints() {}
+};
+
+}  // namespace
+
 TEST(fpdf, CApiTest) {
   EXPECT_TRUE(CheckPDFiumCApi());
 }
@@ -319,12 +336,13 @@
 // reference loop. Cross references will be rebuilt successfully.
 TEST_F(FPDFViewEmbeddertest, CrossRefV4Loop) {
   EXPECT_TRUE(OpenDocument("bug_xrefv4_loop.pdf"));
+  MockDownloadHints hints;
 
   // Make sure calling FPDFAvail_IsDocAvail() on this file does not infinite
   // loop either. See bug 875.
   int ret = PDF_DATA_NOTAVAIL;
   while (ret == PDF_DATA_NOTAVAIL)
-    ret = FPDFAvail_IsDocAvail(avail_, &hints_);
+    ret = FPDFAvail_IsDocAvail(avail_, &hints);
   EXPECT_EQ(PDF_DATA_AVAIL, ret);
 }
 
diff --git a/testing/embedder_test.cpp b/testing/embedder_test.cpp
index 82ffb3b..dab06af 100644
--- a/testing/embedder_test.cpp
+++ b/testing/embedder_test.cpp
@@ -19,6 +19,7 @@
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/test_support.h"
 #include "testing/utils/path_service.h"
+#include "third_party/base/ptr_util.h"
 
 #ifdef PDF_ENABLE_V8
 #include "v8/include/v8-platform.h"
@@ -36,12 +37,6 @@
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 #endif  // PDF_ENABLE_V8
 
-FPDF_BOOL Is_Data_Avail(FX_FILEAVAIL* pThis, size_t offset, size_t size) {
-  return true;
-}
-
-void Add_Segment(FX_DOWNLOADHINTS* pThis, size_t offset, size_t size) {}
-
 int GetBitmapBytesPerPixel(FPDF_BITMAP bitmap) {
   const int format = FPDFBitmap_GetFormat(bitmap);
   switch (format) {
@@ -69,9 +64,7 @@
       loader_(nullptr),
       file_length_(0),
       file_contents_(nullptr) {
-  memset(&hints_, 0, sizeof(hints_));
   memset(&file_access_, 0, sizeof(file_access_));
-  memset(&file_avail_, 0, sizeof(file_avail_));
   delegate_ = default_delegate_.get();
 
 #ifdef PDF_ENABLE_V8
@@ -151,46 +144,52 @@
   file_access_.m_FileLen = static_cast<unsigned long>(file_length_);
   file_access_.m_GetBlock = TestLoader::GetBlock;
   file_access_.m_Param = loader_;
-  return OpenDocumentHelper(password, must_linearize, &file_avail_, &hints_,
-                            &file_access_, &document_, &avail_, &form_handle_);
+  fake_file_access_ = pdfium::MakeUnique<FakeFileAccess>(&file_access_);
+  return OpenDocumentHelper(password, must_linearize, fake_file_access_.get(),
+                            &document_, &avail_, &form_handle_);
 }
 
 bool EmbedderTest::OpenDocumentHelper(const char* password,
                                       bool must_linearize,
-                                      FX_FILEAVAIL* file_avail,
-                                      FX_DOWNLOADHINTS* hints,
-                                      FPDF_FILEACCESS* file_access,
+                                      FakeFileAccess* network_simulator,
                                       FPDF_DOCUMENT* document,
                                       FPDF_AVAIL* avail,
                                       FPDF_FORMHANDLE* form_handle) {
-  file_avail->version = 1;
-  file_avail->IsDataAvail = Is_Data_Avail;
-
-  hints->version = 1;
-  hints->AddSegment = Add_Segment;
-
-  *avail = FPDFAvail_Create(file_avail, file_access);
-
+  network_simulator->AddSegment(0, 1024);
+  network_simulator->SetRequestedDataAvailable();
+  *avail = FPDFAvail_Create(network_simulator->GetFileAvail(),
+                            network_simulator->GetFileAccess());
   if (FPDFAvail_IsLinearized(*avail) == PDF_LINEARIZED) {
+    int32_t nRet = PDF_DATA_NOTAVAIL;
+    while (nRet == PDF_DATA_NOTAVAIL) {
+      network_simulator->SetRequestedDataAvailable();
+      nRet =
+          FPDFAvail_IsDocAvail(*avail, network_simulator->GetDownloadHints());
+    }
+    if (nRet == PDF_DATA_ERROR)
+      return false;
+
     *document = FPDFAvail_GetDocument(*avail, password);
     if (!*document)
       return false;
 
-    int32_t nRet = PDF_DATA_NOTAVAIL;
-    while (nRet == PDF_DATA_NOTAVAIL)
-      nRet = FPDFAvail_IsDocAvail(*avail, hints);
-    if (nRet == PDF_DATA_ERROR)
-      return false;
-
-    nRet = FPDFAvail_IsFormAvail(*avail, hints);
-    if (nRet == PDF_FORM_ERROR || nRet == PDF_FORM_NOTAVAIL)
+    nRet = PDF_DATA_NOTAVAIL;
+    while (nRet == PDF_DATA_NOTAVAIL) {
+      network_simulator->SetRequestedDataAvailable();
+      nRet =
+          FPDFAvail_IsFormAvail(*avail, network_simulator->GetDownloadHints());
+    }
+    if (nRet == PDF_FORM_ERROR)
       return false;
 
     int page_count = FPDF_GetPageCount(*document);
     for (int i = 0; i < page_count; ++i) {
       nRet = PDF_DATA_NOTAVAIL;
-      while (nRet == PDF_DATA_NOTAVAIL)
-        nRet = FPDFAvail_IsPageAvail(*avail, i, hints);
+      while (nRet == PDF_DATA_NOTAVAIL) {
+        network_simulator->SetRequestedDataAvailable();
+        nRet = FPDFAvail_IsPageAvail(*avail, i,
+                                     network_simulator->GetDownloadHints());
+      }
 
       if (nRet == PDF_DATA_ERROR)
         return false;
@@ -198,8 +197,9 @@
   } else {
     if (must_linearize)
       return false;
-
-    *document = FPDF_LoadCustomDocument(file_access, password);
+    network_simulator->SetWholeFileAvailable();
+    *document =
+        FPDF_LoadCustomDocument(network_simulator->GetFileAccess(), password);
     if (!*document)
       return false;
   }
@@ -248,14 +248,16 @@
 
 int EmbedderTest::GetFirstPageNum() {
   int first_page = FPDFAvail_GetFirstPageNum(document_);
-  (void)FPDFAvail_IsPageAvail(avail_, first_page, &hints_);
+  (void)FPDFAvail_IsPageAvail(avail_, first_page,
+                              fake_file_access_->GetDownloadHints());
   return first_page;
 }
 
 int EmbedderTest::GetPageCount() {
   int page_count = FPDF_GetPageCount(document_);
   for (int i = 0; i < page_count; ++i)
-    (void)FPDFAvail_IsPageAvail(avail_, i, &hints_);
+    (void)FPDFAvail_IsPageAvail(avail_, i,
+                                fake_file_access_->GetDownloadHints());
   return page_count;
 }
 
@@ -314,16 +316,16 @@
                              int height,
                              const char* md5,
                              const char* password) {
-  FPDF_FILEACCESS file_access;
-  memset(&file_access, 0, sizeof(file_access));
-  file_access.m_FileLen = m_String.size();
-  file_access.m_GetBlock = GetBlockFromString;
-  file_access.m_Param = &m_String;
-  FX_FILEAVAIL file_avail;
-  FX_DOWNLOADHINTS hints;
+  memset(&saved_file_access_, 0, sizeof(saved_file_access_));
+  saved_file_access_.m_FileLen = m_String.size();
+  saved_file_access_.m_GetBlock = GetBlockFromString;
+  saved_file_access_.m_Param = &m_String;
 
-  ASSERT_TRUE(OpenDocumentHelper(password, false, &file_avail, &hints,
-                                 &file_access, &m_SavedDocument, &m_SavedAvail,
+  saved_fake_file_access_ =
+      pdfium::MakeUnique<FakeFileAccess>(&saved_file_access_);
+
+  ASSERT_TRUE(OpenDocumentHelper(password, false, saved_fake_file_access_.get(),
+                                 &m_SavedDocument, &m_SavedAvail,
                                  &m_SavedForm));
   EXPECT_EQ(1, FPDF_GetPageCount(m_SavedDocument));
   m_SavedPage = FPDF_LoadPage(m_SavedDocument, 0);
@@ -346,6 +348,11 @@
   CloseSaved();
 }
 
+void EmbedderTest::SetWholeFileAvailable() {
+  ASSERT(fake_file_access_);
+  fake_file_access_->SetWholeFileAvailable();
+}
+
 FPDF_PAGE EmbedderTest::Delegate::GetPage(FPDF_FORMFILLINFO* info,
                                           FPDF_DOCUMENT document,
                                           int page_index) {
diff --git a/testing/embedder_test.h b/testing/embedder_test.h
index 878e50b..be89c2a 100644
--- a/testing/embedder_test.h
+++ b/testing/embedder_test.h
@@ -14,6 +14,7 @@
 #include "public/fpdf_formfill.h"
 #include "public/fpdf_save.h"
 #include "public/fpdfview.h"
+#include "testing/fake_file_access.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/test_support.h"
 
@@ -116,9 +117,7 @@
  protected:
   bool OpenDocumentHelper(const char* password,
                           bool must_linearize,
-                          FX_FILEAVAIL* file_avail,
-                          FX_DOWNLOADHINTS* hints,
-                          FPDF_FILEACCESS* file_access,
+                          FakeFileAccess* network_simulator,
                           FPDF_DOCUMENT* document,
                           FPDF_AVAIL* avail,
                           FPDF_FORMHANDLE* form_handle);
@@ -151,14 +150,14 @@
   void CloseSaved();
   void TestAndCloseSaved(int width, int height, const char* md5);
 
+  void SetWholeFileAvailable();
+
   Delegate* delegate_;
   std::unique_ptr<Delegate> default_delegate_;
   FPDF_DOCUMENT document_;
   FPDF_FORMHANDLE form_handle_;
   FPDF_AVAIL avail_;
-  FX_DOWNLOADHINTS hints_;
-  FPDF_FILEACCESS file_access_;
-  FX_FILEAVAIL file_avail_;
+  FPDF_FILEACCESS file_access_;  // must outlive avail_.
 #ifdef PDF_ENABLE_V8
   v8::Platform* platform_;
 #endif  // PDF_ENABLE_V8
@@ -172,6 +171,10 @@
   FPDF_PAGE m_SavedPage;
   FPDF_FORMHANDLE m_SavedForm;
   FPDF_AVAIL m_SavedAvail;
+  FPDF_FILEACCESS saved_file_access_;  // must outlive m_SavedAvail.
+  std::unique_ptr<FakeFileAccess> fake_file_access_;  // must outlive avail_.
+  std::unique_ptr<FakeFileAccess>
+      saved_fake_file_access_;  // must outlive m_SavedAvail.
 
  private:
   static void UnsupportedHandlerTrampoline(UNSUPPORT_INFO*, int type);
diff --git a/testing/fake_file_access.cpp b/testing/fake_file_access.cpp
new file mode 100644
index 0000000..c69f278
--- /dev/null
+++ b/testing/fake_file_access.cpp
@@ -0,0 +1,115 @@
+// Copyright 2017 PDFium 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 "testing/fake_file_access.h"
+
+#include <algorithm>
+#include <set>
+#include <utility>
+#include <vector>
+
+#include "core/fxcrt/fx_system.h"
+#include "third_party/base/ptr_util.h"
+
+namespace {
+
+class FileAccessWrapper : public FPDF_FILEACCESS {
+ public:
+  explicit FileAccessWrapper(FakeFileAccess* simulator)
+      : simulator_(simulator) {
+    m_FileLen = simulator_->GetFileSize();
+    m_GetBlock = &GetBlockImpl;
+    m_Param = this;
+  }
+
+  static int GetBlockImpl(void* param,
+                          unsigned long position,
+                          unsigned char* pBuf,
+                          unsigned long size) {
+    return static_cast<FileAccessWrapper*>(param)->simulator_->GetBlock(
+        position, pBuf, size);
+  }
+
+ private:
+  fxcrt::UnownedPtr<FakeFileAccess> simulator_;
+};
+
+class FileAvailImpl : public FX_FILEAVAIL {
+ public:
+  explicit FileAvailImpl(FakeFileAccess* simulator) : simulator_(simulator) {
+    version = 1;
+    IsDataAvail = &IsDataAvailImpl;
+  }
+
+  static FPDF_BOOL IsDataAvailImpl(FX_FILEAVAIL* pThis,
+                                   size_t offset,
+                                   size_t size) {
+    return static_cast<FileAvailImpl*>(pThis)->simulator_->IsDataAvail(offset,
+                                                                       size);
+  }
+
+ private:
+  fxcrt::UnownedPtr<FakeFileAccess> simulator_;
+};
+
+class DownloadHintsImpl : public FX_DOWNLOADHINTS {
+ public:
+  explicit DownloadHintsImpl(FakeFileAccess* simulator)
+      : simulator_(simulator) {
+    version = 1;
+    AddSegment = &AddSegmentImpl;
+  }
+
+  static void AddSegmentImpl(FX_DOWNLOADHINTS* pThis,
+                             size_t offset,
+                             size_t size) {
+    return static_cast<DownloadHintsImpl*>(pThis)->simulator_->AddSegment(
+        offset, size);
+  }
+
+ private:
+  fxcrt::UnownedPtr<FakeFileAccess> simulator_;
+};
+
+}  // namespace
+
+FakeFileAccess::FakeFileAccess(FPDF_FILEACCESS* file_access)
+    : file_access_(file_access),
+      file_access_wrapper_(pdfium::MakeUnique<FileAccessWrapper>(this)),
+      file_avail_(pdfium::MakeUnique<FileAvailImpl>(this)),
+      download_hints_(pdfium::MakeUnique<DownloadHintsImpl>(this)) {
+  ASSERT(file_access_);
+}
+
+FakeFileAccess::~FakeFileAccess() {}
+
+FPDF_BOOL FakeFileAccess::IsDataAvail(size_t offset, size_t size) const {
+  return available_data_.Contains(RangeSet::Range(offset, offset + size));
+}
+
+void FakeFileAccess::AddSegment(size_t offset, size_t size) {
+  requested_data_.Union(RangeSet::Range(offset, offset + size));
+}
+
+unsigned long FakeFileAccess::GetFileSize() {
+  return file_access_->m_FileLen;
+}
+
+int FakeFileAccess::GetBlock(unsigned long position,
+                             unsigned char* pBuf,
+                             unsigned long size) {
+  if (!IsDataAvail(static_cast<size_t>(position), static_cast<size_t>(size)))
+    return false;
+  return file_access_->m_GetBlock(file_access_->m_Param, position, pBuf, size);
+}
+
+void FakeFileAccess::SetRequestedDataAvailable() {
+  available_data_.Union(requested_data_);
+  requested_data_.Clear();
+}
+
+void FakeFileAccess::SetWholeFileAvailable() {
+  available_data_.Union(RangeSet::Range(0, static_cast<size_t>(GetFileSize())));
+  requested_data_.Clear();
+}
diff --git a/testing/fake_file_access.h b/testing/fake_file_access.h
new file mode 100644
index 0000000..1328b16
--- /dev/null
+++ b/testing/fake_file_access.h
@@ -0,0 +1,42 @@
+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TESTING_FAKE_FILE_ACCESS_H_
+#define TESTING_FAKE_FILE_ACCESS_H_
+
+#include <memory>
+
+#include "core/fxcrt/unowned_ptr.h"
+#include "public/fpdf_dataavail.h"
+#include "public/fpdfview.h"
+#include "testing/range_set.h"
+
+class FakeFileAccess {
+ public:
+  explicit FakeFileAccess(FPDF_FILEACCESS* file_access);
+  ~FakeFileAccess();
+
+  FPDF_FILEACCESS* GetFileAccess() const { return file_access_wrapper_.get(); }
+  FX_FILEAVAIL* GetFileAvail() const { return file_avail_.get(); }
+  FX_DOWNLOADHINTS* GetDownloadHints() const { return download_hints_.get(); }
+
+  FPDF_BOOL IsDataAvail(size_t offset, size_t size) const;
+  void AddSegment(size_t offset, size_t size);
+
+  unsigned long GetFileSize();
+
+  int GetBlock(unsigned long position, unsigned char* pBuf, unsigned long size);
+  void SetRequestedDataAvailable();
+  void SetWholeFileAvailable();
+
+ private:
+  fxcrt::UnownedPtr<FPDF_FILEACCESS> file_access_;
+  std::unique_ptr<FPDF_FILEACCESS> file_access_wrapper_;
+  std::unique_ptr<FX_FILEAVAIL> file_avail_;
+  std::unique_ptr<FX_DOWNLOADHINTS> download_hints_;
+  RangeSet available_data_;
+  RangeSet requested_data_;
+};
+
+#endif  // TESTING_FAKE_FILE_ACCESS_H_
diff --git a/testing/range_set.cpp b/testing/range_set.cpp
new file mode 100644
index 0000000..2fc540f
--- /dev/null
+++ b/testing/range_set.cpp
@@ -0,0 +1,74 @@
+// Copyright 2017 PDFium 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 "testing/range_set.h"
+
+#include <algorithm>
+
+#include "core/fxcrt/fx_system.h"
+
+RangeSet::RangeSet() {}
+RangeSet::~RangeSet() {}
+
+bool RangeSet::Contains(const Range& range) const {
+  if (IsEmptyRange(range))
+    return false;
+
+  const Range fixed_range = FixDirection(range);
+  auto it = ranges().upper_bound(fixed_range);
+
+  if (it == ranges().begin())
+    return false;  // No ranges includes range.first.
+
+  --it;  // Now it starts equal or before range.first.
+  return it->second >= fixed_range.second;
+}
+
+void RangeSet::Union(const Range& range) {
+  if (IsEmptyRange(range))
+    return;
+
+  Range fixed_range = FixDirection(range);
+  if (IsEmpty()) {
+    ranges_.insert(fixed_range);
+    return;
+  }
+
+  auto start = ranges_.upper_bound(fixed_range);
+  if (start != ranges_.begin())
+    --start;  // start now points to the key equal or lower than offset.
+
+  if (start->second < fixed_range.first)
+    ++start;  // start element is entirely before current range, skip it.
+
+  auto end = ranges_.upper_bound(Range(fixed_range.second, fixed_range.second));
+
+  if (start == end) {  // No ranges to merge.
+    ranges_.insert(fixed_range);
+    return;
+  }
+
+  --end;
+
+  const int new_start = std::min<size_t>(start->first, fixed_range.first);
+  const int new_end = std::max(end->second, fixed_range.second);
+
+  ranges_.erase(start, ++end);
+  ranges_.insert(Range(new_start, new_end));
+}
+
+void RangeSet::Union(const RangeSet& range_set) {
+  ASSERT(&range_set != this);
+  for (const auto& it : range_set.ranges())
+    Union(it);
+}
+
+RangeSet::Range RangeSet::FixDirection(const Range& range) const {
+  return range.first <= range.second ? range
+                                     : Range(range.second + 1, range.first + 1);
+}
+
+bool RangeSet::IsEmptyRange(const Range& range) const {
+  return range.first == range.second;
+}
diff --git a/testing/range_set.h b/testing/range_set.h
new file mode 100644
index 0000000..87cbee9
--- /dev/null
+++ b/testing/range_set.h
@@ -0,0 +1,45 @@
+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TESTING_RANGE_SET_H_
+#define TESTING_RANGE_SET_H_
+
+#include <set>
+#include <utility>
+
+class RangeSet {
+ public:
+  using Range = std::pair<size_t, size_t>;
+
+  RangeSet();
+  ~RangeSet();
+
+  bool Contains(const Range& range) const;
+
+  void Union(const Range& range);
+
+  void Union(const RangeSet& range_set);
+
+  bool IsEmpty() const { return ranges().empty(); }
+
+  void Clear() { ranges_.clear(); }
+
+  struct range_compare {
+    bool operator()(const Range& lval, const Range& rval) const {
+      return lval.first < rval.first;
+    }
+  };
+
+  using RangesContainer = std::set<Range, range_compare>;
+  const RangesContainer& ranges() const { return ranges_; }
+
+ private:
+  Range FixDirection(const Range& range) const;
+
+  bool IsEmptyRange(const Range& range) const;
+
+  RangesContainer ranges_;
+};
+
+#endif  // TESTING_RANGE_SET_H_