diff --git a/minidump/minidump_context_writer_test.cc b/minidump/minidump_context_writer_test.cc
index 43f6476..9359514 100644
--- a/minidump/minidump_context_writer_test.cc
+++ b/minidump/minidump_context_writer_test.cc
@@ -19,6 +19,7 @@
 #include "gtest/gtest.h"
 #include "minidump/minidump_context.h"
 #include "minidump/test/minidump_context_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
@@ -39,7 +40,7 @@ TEST(MinidumpContextWriter, MinidumpContextX86Writer) {
     ASSERT_EQ(sizeof(MinidumpContextX86), file_writer.string().size());
 
     const MinidumpContextX86* observed =
-        reinterpret_cast<const MinidumpContextX86*>(&file_writer.string()[0]);
+        MinidumpWritableAtRVA<MinidumpContextX86>(file_writer.string(), 0);
     ExpectMinidumpContextX86(0, observed);
   }
 
@@ -56,7 +57,7 @@ TEST(MinidumpContextWriter, MinidumpContextX86Writer) {
     ASSERT_EQ(sizeof(MinidumpContextX86), file_writer.string().size());
 
     const MinidumpContextX86* observed =
-        reinterpret_cast<const MinidumpContextX86*>(&file_writer.string()[0]);
+        MinidumpWritableAtRVA<MinidumpContextX86>(file_writer.string(), 0);
     ExpectMinidumpContextX86(kSeed, observed);
   }
 }
@@ -75,7 +76,7 @@ TEST(MinidumpContextWriter, MinidumpContextAMD64Writer) {
     ASSERT_EQ(sizeof(MinidumpContextAMD64), file_writer.string().size());
 
     const MinidumpContextAMD64* observed =
-        reinterpret_cast<const MinidumpContextAMD64*>(&file_writer.string()[0]);
+        MinidumpWritableAtRVA<MinidumpContextAMD64>(file_writer.string(), 0);
     ExpectMinidumpContextAMD64(0, observed);
   }
 
@@ -92,7 +93,7 @@ TEST(MinidumpContextWriter, MinidumpContextAMD64Writer) {
     ASSERT_EQ(sizeof(MinidumpContextAMD64), file_writer.string().size());
 
     const MinidumpContextAMD64* observed =
-        reinterpret_cast<const MinidumpContextAMD64*>(&file_writer.string()[0]);
+        MinidumpWritableAtRVA<MinidumpContextAMD64>(file_writer.string(), 0);
     ExpectMinidumpContextAMD64(kSeed, observed);
   }
 }
diff --git a/minidump/minidump_crashpad_info_writer_test.cc b/minidump/minidump_crashpad_info_writer_test.cc
index 3cbbfb6..b59301b 100644
--- a/minidump/minidump_crashpad_info_writer_test.cc
+++ b/minidump/minidump_crashpad_info_writer_test.cc
@@ -22,6 +22,7 @@
 #include "minidump/minidump_simple_string_dictionary_writer.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
 #include "minidump/test/minidump_string_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
@@ -55,20 +56,19 @@ void GetCrashpadInfoStream(
   ASSERT_TRUE(directory);
 
   ASSERT_EQ(kMinidumpStreamTypeCrashpadInfo, directory[0].StreamType);
-  ASSERT_EQ(sizeof(MinidumpCrashpadInfo), directory[0].Location.DataSize);
-  ASSERT_EQ(kCrashpadInfoStreamOffset, directory[0].Location.Rva);
+  EXPECT_EQ(kCrashpadInfoStreamOffset, directory[0].Location.Rva);
 
-  *crashpad_info = reinterpret_cast<const MinidumpCrashpadInfo*>(
-      &file_contents[kCrashpadInfoStreamOffset]);
+  *crashpad_info = MinidumpWritableAtLocationDescriptor<MinidumpCrashpadInfo>(
+      file_contents, directory[0].Location);
+  ASSERT_TRUE(*crashpad_info);
 
   if (simple_annotations) {
-    ASSERT_GE((*crashpad_info)->simple_annotations.DataSize,
-              sizeof(MinidumpSimpleStringDictionary));
-    ASSERT_EQ(kSimpleAnnotationsOffset,
+    EXPECT_EQ(kSimpleAnnotationsOffset,
               (*crashpad_info)->simple_annotations.Rva);
     *simple_annotations =
-        reinterpret_cast<const MinidumpSimpleStringDictionary*>(
-            &file_contents[kSimpleAnnotationsOffset]);
+        MinidumpWritableAtLocationDescriptor<MinidumpSimpleStringDictionary>(
+            file_contents, (*crashpad_info)->simple_annotations);
+    ASSERT_TRUE(*simple_annotations);
   } else {
     ASSERT_EQ(0u, (*crashpad_info)->simple_annotations.DataSize);
     ASSERT_EQ(0u, (*crashpad_info)->simple_annotations.Rva);
diff --git a/minidump/minidump_exception_writer_test.cc b/minidump/minidump_exception_writer_test.cc
index e1cad61..2b51327 100644
--- a/minidump/minidump_exception_writer_test.cc
+++ b/minidump/minidump_exception_writer_test.cc
@@ -27,6 +27,7 @@
 #include "minidump/minidump_file_writer.h"
 #include "minidump/test/minidump_context_test_util.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
@@ -50,11 +51,12 @@ void GetExceptionStream(const std::string& file_contents,
   ASSERT_NO_FATAL_FAILURE(VerifyMinidumpHeader(header, 1, 0));
 
   ASSERT_EQ(kMinidumpStreamTypeException, directory[0].StreamType);
-  ASSERT_GE(directory[0].Location.DataSize, sizeof(MINIDUMP_EXCEPTION_STREAM));
-  ASSERT_EQ(kExceptionStreamOffset, directory[0].Location.Rva);
+  EXPECT_EQ(kExceptionStreamOffset, directory[0].Location.Rva);
 
-  *exception_stream = reinterpret_cast<const MINIDUMP_EXCEPTION_STREAM*>(
-      &file_contents[kExceptionStreamOffset]);
+  *exception_stream =
+      MinidumpWritableAtLocationDescriptor<MINIDUMP_EXCEPTION_STREAM>(
+          file_contents, directory[0].Location);
+  ASSERT_TRUE(exception_stream);
 }
 
 // The MINIDUMP_EXCEPTION_STREAMs |expected| and |observed| are compared against
@@ -83,13 +85,9 @@ void ExpectExceptionStream(const MINIDUMP_EXCEPTION_STREAM* expected,
     EXPECT_EQ(expected->ExceptionRecord.ExceptionInformation[index],
               observed->ExceptionRecord.ExceptionInformation[index]);
   }
-  EXPECT_EQ(expected->ThreadContext.DataSize, observed->ThreadContext.DataSize);
-  ASSERT_NE(0u, observed->ThreadContext.DataSize);
-  ASSERT_NE(0u, observed->ThreadContext.Rva);
-  ASSERT_GE(file_contents.size(),
-            observed->ThreadContext.Rva + observed->ThreadContext.DataSize);
-  *context = reinterpret_cast<const MinidumpContextX86*>(
-      &file_contents[observed->ThreadContext.Rva]);
+  *context = MinidumpWritableAtLocationDescriptor<MinidumpContextX86>(
+      file_contents, observed->ThreadContext);
+  ASSERT_TRUE(context);
 }
 
 TEST(MinidumpExceptionWriter, Minimal) {
diff --git a/minidump/minidump_file_writer_test.cc b/minidump/minidump_file_writer_test.cc
index 51369f5..cda9356 100644
--- a/minidump/minidump_file_writer_test.cc
+++ b/minidump/minidump_file_writer_test.cc
@@ -23,6 +23,7 @@
 #include "minidump/minidump_stream_writer.h"
 #include "minidump/minidump_writable.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/file_writer.h"
 #include "util/file/string_file_writer.h"
 
@@ -106,8 +107,9 @@ TEST(MinidumpFileWriter, OneStream) {
   EXPECT_EQ(kStreamSize, directory[0].Location.DataSize);
   EXPECT_EQ(kStreamOffset, directory[0].Location.Rva);
 
-  const uint8_t* stream_data =
-      reinterpret_cast<const uint8_t*>(&file_writer.string()[kStreamOffset]);
+  const uint8_t* stream_data = MinidumpWritableAtLocationDescriptor<uint8_t>(
+      file_writer.string(), directory[0].Location);
+  ASSERT_TRUE(stream_data);
 
   std::string expected_stream(kStreamSize, kStreamValue);
   EXPECT_EQ(0, memcmp(stream_data, expected_stream.c_str(), kStreamSize));
@@ -118,38 +120,38 @@ TEST(MinidumpFileWriter, ThreeStreams) {
   const time_t kTimestamp = 0x155d2fb8;
   minidump_file.SetTimestamp(kTimestamp);
 
-  const size_t kStream1Size = 5;
-  const MinidumpStreamType kStream1Type = static_cast<MinidumpStreamType>(0x6d);
-  const uint8_t kStream1Value = 0x5a;
-  TestStream stream1(kStream1Type, kStream1Size, kStream1Value);
-  minidump_file.AddStream(&stream1);
+  const size_t kStream0Size = 5;
+  const MinidumpStreamType kStream0Type = static_cast<MinidumpStreamType>(0x6d);
+  const uint8_t kStream0Value = 0x5a;
+  TestStream stream0(kStream0Type, kStream0Size, kStream0Value);
+  minidump_file.AddStream(&stream0);
 
   // Make the second stream’s type be a smaller quantity than the first stream’s
   // to test that the streams show up in the order that they were added, not in
   // numeric order.
-  const size_t kStream2Size = 3;
-  const MinidumpStreamType kStream2Type = static_cast<MinidumpStreamType>(0x4d);
-  const uint8_t kStream2Value = 0xa5;
+  const size_t kStream1Size = 3;
+  const MinidumpStreamType kStream1Type = static_cast<MinidumpStreamType>(0x4d);
+  const uint8_t kStream1Value = 0xa5;
+  TestStream stream1(kStream1Type, kStream1Size, kStream1Value);
+  minidump_file.AddStream(&stream1);
+
+  const size_t kStream2Size = 1;
+  const MinidumpStreamType kStream2Type = static_cast<MinidumpStreamType>(0x7e);
+  const uint8_t kStream2Value = 0x36;
   TestStream stream2(kStream2Type, kStream2Size, kStream2Value);
   minidump_file.AddStream(&stream2);
 
-  const size_t kStream3Size = 1;
-  const MinidumpStreamType kStream3Type = static_cast<MinidumpStreamType>(0x7e);
-  const uint8_t kStream3Value = 0x36;
-  TestStream stream3(kStream3Type, kStream3Size, kStream3Value);
-  minidump_file.AddStream(&stream3);
-
   StringFileWriter file_writer;
   ASSERT_TRUE(minidump_file.WriteEverything(&file_writer));
 
   const size_t kDirectoryOffset = sizeof(MINIDUMP_HEADER);
-  const size_t kStream1Offset =
+  const size_t kStream0Offset =
       kDirectoryOffset + 3 * sizeof(MINIDUMP_DIRECTORY);
-  const size_t kStream2Padding = 3;
+  const size_t kStream1Padding = 3;
+  const size_t kStream1Offset = kStream0Offset + kStream0Size + kStream1Padding;
+  const size_t kStream2Padding = 1;
   const size_t kStream2Offset = kStream1Offset + kStream1Size + kStream2Padding;
-  const size_t kStream3Padding = 1;
-  const size_t kStream3Offset = kStream2Offset + kStream2Size + kStream3Padding;
-  const size_t kFileSize = kStream3Offset + kStream3Size;
+  const size_t kFileSize = kStream2Offset + kStream2Size;
 
   ASSERT_EQ(kFileSize, file_writer.string().size());
 
@@ -159,40 +161,43 @@ TEST(MinidumpFileWriter, ThreeStreams) {
   ASSERT_NO_FATAL_FAILURE(VerifyMinidumpHeader(header, 3, kTimestamp));
   ASSERT_TRUE(directory);
 
-  EXPECT_EQ(kStream1Type, directory[0].StreamType);
-  EXPECT_EQ(kStream1Size, directory[0].Location.DataSize);
-  EXPECT_EQ(kStream1Offset, directory[0].Location.Rva);
-  EXPECT_EQ(kStream2Type, directory[1].StreamType);
-  EXPECT_EQ(kStream2Size, directory[1].Location.DataSize);
-  EXPECT_EQ(kStream2Offset, directory[1].Location.Rva);
-  EXPECT_EQ(kStream3Type, directory[2].StreamType);
-  EXPECT_EQ(kStream3Size, directory[2].Location.DataSize);
-  EXPECT_EQ(kStream3Offset, directory[2].Location.Rva);
+  EXPECT_EQ(kStream0Type, directory[0].StreamType);
+  EXPECT_EQ(kStream0Size, directory[0].Location.DataSize);
+  EXPECT_EQ(kStream0Offset, directory[0].Location.Rva);
+  EXPECT_EQ(kStream1Type, directory[1].StreamType);
+  EXPECT_EQ(kStream1Size, directory[1].Location.DataSize);
+  EXPECT_EQ(kStream1Offset, directory[1].Location.Rva);
+  EXPECT_EQ(kStream2Type, directory[2].StreamType);
+  EXPECT_EQ(kStream2Size, directory[2].Location.DataSize);
+  EXPECT_EQ(kStream2Offset, directory[2].Location.Rva);
 
-  const uint8_t* stream1_data =
-      reinterpret_cast<const uint8_t*>(&file_writer.string()[kStream1Offset]);
+  const uint8_t* stream0_data = MinidumpWritableAtLocationDescriptor<uint8_t>(
+      file_writer.string(), directory[0].Location);
+  ASSERT_TRUE(stream0_data);
+
+  std::string expected_stream0(kStream0Size, kStream0Value);
+  EXPECT_EQ(0, memcmp(stream0_data, expected_stream0.c_str(), kStream0Size));
+
+  const int kZeroes[16] = {};
+  ASSERT_GE(sizeof(kZeroes), kStream1Padding);
+  EXPECT_EQ(0, memcmp(stream0_data + kStream0Size, kZeroes, kStream1Padding));
+
+  const uint8_t* stream1_data = MinidumpWritableAtLocationDescriptor<uint8_t>(
+      file_writer.string(), directory[1].Location);
+  ASSERT_TRUE(stream1_data);
 
   std::string expected_stream1(kStream1Size, kStream1Value);
   EXPECT_EQ(0, memcmp(stream1_data, expected_stream1.c_str(), kStream1Size));
 
-  const int kZeroes[16] = {};
   ASSERT_GE(sizeof(kZeroes), kStream2Padding);
   EXPECT_EQ(0, memcmp(stream1_data + kStream1Size, kZeroes, kStream2Padding));
 
-  const uint8_t* stream2_data =
-      reinterpret_cast<const uint8_t*>(&file_writer.string()[kStream2Offset]);
+  const uint8_t* stream2_data = MinidumpWritableAtLocationDescriptor<uint8_t>(
+      file_writer.string(), directory[2].Location);
+  ASSERT_TRUE(stream2_data);
 
   std::string expected_stream2(kStream2Size, kStream2Value);
   EXPECT_EQ(0, memcmp(stream2_data, expected_stream2.c_str(), kStream2Size));
-
-  ASSERT_GE(sizeof(kZeroes), kStream3Padding);
-  EXPECT_EQ(0, memcmp(stream2_data + kStream2Size, kZeroes, kStream3Padding));
-
-  const uint8_t* stream3_data =
-      reinterpret_cast<const uint8_t*>(&file_writer.string()[kStream3Offset]);
-
-  std::string expected_stream3(kStream3Size, kStream3Value);
-  EXPECT_EQ(0, memcmp(stream3_data, expected_stream3.c_str(), kStream3Size));
 }
 
 TEST(MinidumpFileWriter, ZeroLengthStream) {
@@ -226,18 +231,18 @@ TEST(MinidumpFileWriter, ZeroLengthStream) {
 TEST(MinidumpFileWriterDeathTest, SameStreamType) {
   MinidumpFileWriter minidump_file;
 
-  const size_t kStream1Size = 5;
-  const MinidumpStreamType kStream1Type = static_cast<MinidumpStreamType>(0x4d);
-  const uint8_t kStream1Value = 0x5a;
-  TestStream stream1(kStream1Type, kStream1Size, kStream1Value);
-  minidump_file.AddStream(&stream1);
+  const size_t kStream0Size = 5;
+  const MinidumpStreamType kStream0Type = static_cast<MinidumpStreamType>(0x4d);
+  const uint8_t kStream0Value = 0x5a;
+  TestStream stream0(kStream0Type, kStream0Size, kStream0Value);
+  minidump_file.AddStream(&stream0);
 
   // It is an error to add a second stream of the same type.
-  const size_t kStream2Size = 3;
-  const MinidumpStreamType kStream2Type = static_cast<MinidumpStreamType>(0x4d);
-  const uint8_t kStream2Value = 0xa5;
-  TestStream stream2(kStream2Type, kStream2Size, kStream2Value);
-  ASSERT_DEATH(minidump_file.AddStream(&stream2), "already present");
+  const size_t kStream1Size = 3;
+  const MinidumpStreamType kStream1Type = static_cast<MinidumpStreamType>(0x4d);
+  const uint8_t kStream1Value = 0xa5;
+  TestStream stream1(kStream1Type, kStream1Size, kStream1Value);
+  ASSERT_DEATH(minidump_file.AddStream(&stream1), "already present");
 }
 
 }  // namespace
diff --git a/minidump/minidump_memory_writer_test.cc b/minidump/minidump_memory_writer_test.cc
index 66a3fc6..8060db7 100644
--- a/minidump/minidump_memory_writer_test.cc
+++ b/minidump/minidump_memory_writer_test.cc
@@ -24,6 +24,7 @@
 #include "minidump/minidump_stream_writer.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
 #include "minidump/test/minidump_memory_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
@@ -63,17 +64,11 @@ void GetMemoryListStream(const std::string& file_contents,
 
   ASSERT_EQ(kMinidumpStreamTypeMemoryList,
             directory[directory_index].StreamType);
-  ASSERT_GE(directory[directory_index].Location.DataSize,
-            sizeof(MINIDUMP_MEMORY_LIST));
-  ASSERT_EQ(kMemoryListStreamOffset, directory[directory_index].Location.Rva);
+  EXPECT_EQ(kMemoryListStreamOffset, directory[directory_index].Location.Rva);
 
-  *memory_list = reinterpret_cast<const MINIDUMP_MEMORY_LIST*>(
-      &file_contents[kMemoryListStreamOffset]);
-
-  ASSERT_EQ(sizeof(MINIDUMP_MEMORY_LIST) +
-                (*memory_list)->NumberOfMemoryRanges *
-                    sizeof(MINIDUMP_MEMORY_DESCRIPTOR),
-            directory[directory_index].Location.DataSize);
+  *memory_list = MinidumpWritableAtLocationDescriptor<MINIDUMP_MEMORY_LIST>(
+      file_contents, directory[directory_index].Location);
+  ASSERT_TRUE(memory_list);
 }
 
 TEST(MinidumpMemoryWriter, EmptyMemoryList) {
diff --git a/minidump/minidump_misc_info_writer_test.cc b/minidump/minidump_misc_info_writer_test.cc
index 5960685..a342f27 100644
--- a/minidump/minidump_misc_info_writer_test.cc
+++ b/minidump/minidump_misc_info_writer_test.cc
@@ -25,6 +25,7 @@
 #include "gtest/gtest.h"
 #include "minidump/minidump_file_writer.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 #include "util/stdlib/strlcpy.h"
 
@@ -49,13 +50,11 @@ void GetMiscInfoStream(const std::string& file_contents, const T** misc_info) {
   ASSERT_TRUE(directory);
 
   ASSERT_EQ(kMinidumpStreamTypeMiscInfo, directory[0].StreamType);
-  ASSERT_EQ(kMiscInfoStreamSize, directory[0].Location.DataSize);
-  ASSERT_EQ(kMiscInfoStreamOffset, directory[0].Location.Rva);
+  EXPECT_EQ(kMiscInfoStreamOffset, directory[0].Location.Rva);
 
-  *misc_info =
-      reinterpret_cast<const T*>(&file_contents[kMiscInfoStreamOffset]);
-
-  ASSERT_EQ(kMiscInfoStreamSize, (*misc_info)->SizeOfInfo);
+  *misc_info = MinidumpWritableAtLocationDescriptor<T>(file_contents,
+                                                       directory[0].Location);
+  ASSERT_TRUE(misc_info);
 }
 
 void ExpectNULPaddedString16Equal(const char16* expected,
diff --git a/minidump/minidump_module_writer_test.cc b/minidump/minidump_module_writer_test.cc
index 6aba549..1aef0f1 100644
--- a/minidump/minidump_module_writer_test.cc
+++ b/minidump/minidump_module_writer_test.cc
@@ -24,6 +24,7 @@
 #include "minidump/minidump_file_writer.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
 #include "minidump/test/minidump_string_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 #include "util/misc/uuid.h"
 
@@ -48,15 +49,11 @@ void GetModuleListStream(const std::string& file_contents,
   ASSERT_TRUE(directory);
 
   ASSERT_EQ(kMinidumpStreamTypeModuleList, directory[0].StreamType);
-  ASSERT_GE(directory[0].Location.DataSize, sizeof(MINIDUMP_MODULE_LIST));
-  ASSERT_EQ(kModuleListStreamOffset, directory[0].Location.Rva);
+  EXPECT_EQ(kModuleListStreamOffset, directory[0].Location.Rva);
 
-  *module_list = reinterpret_cast<const MINIDUMP_MODULE_LIST*>(
-      &file_contents[kModuleListStreamOffset]);
-
-  ASSERT_EQ(sizeof(MINIDUMP_MODULE_LIST) +
-                (*module_list)->NumberOfModules * sizeof(MINIDUMP_MODULE),
-            directory[0].Location.DataSize);
+  *module_list = MinidumpWritableAtLocationDescriptor<MINIDUMP_MODULE_LIST>(
+      file_contents, directory[0].Location);
+  ASSERT_TRUE(module_list);
 }
 
 TEST(MinidumpModuleWriter, EmptyModuleList) {
@@ -92,19 +89,15 @@ void ExpectCodeViewRecord(const MINIDUMP_LOCATION_DESCRIPTOR* codeview_record,
                           uint32_t expected_pdb_age) {
   if (expected_pdb_name) {
     EXPECT_NE(0u, codeview_record->Rva);
-    ASSERT_LE(codeview_record->Rva + codeview_record->DataSize,
-              file_contents.size());
 
     std::string observed_pdb_name;
     if (expected_pdb_uuid) {
       // The CodeView record should be a PDB 7.0 link.
-      EXPECT_GE(codeview_record->DataSize,
-                sizeof(MinidumpModuleCodeViewRecordPDB70));
       const MinidumpModuleCodeViewRecordPDB70* codeview_pdb70_record =
-          reinterpret_cast<const MinidumpModuleCodeViewRecordPDB70*>(
-              &file_contents[codeview_record->Rva]);
-      EXPECT_EQ(MinidumpModuleCodeViewRecordPDB70::kSignature,
-                codeview_pdb70_record->signature);
+          MinidumpWritableAtLocationDescriptor<
+              MinidumpModuleCodeViewRecordPDB70>(file_contents,
+                                                 *codeview_record);
+      ASSERT_TRUE(codeview_pdb70_record);
       EXPECT_EQ(0,
                 memcmp(expected_pdb_uuid,
                        &codeview_pdb70_record->uuid,
@@ -117,13 +110,11 @@ void ExpectCodeViewRecord(const MINIDUMP_LOCATION_DESCRIPTOR* codeview_record,
               offsetof(MinidumpModuleCodeViewRecordPDB70, pdb_name));
     } else {
       // The CodeView record should be a PDB 2.0 link.
-      EXPECT_GE(codeview_record->DataSize,
-                sizeof(MinidumpModuleCodeViewRecordPDB20));
       const MinidumpModuleCodeViewRecordPDB20* codeview_pdb20_record =
-          reinterpret_cast<const MinidumpModuleCodeViewRecordPDB20*>(
-              &file_contents[codeview_record->Rva]);
-      EXPECT_EQ(MinidumpModuleCodeViewRecordPDB20::kSignature,
-                codeview_pdb20_record->signature);
+          MinidumpWritableAtLocationDescriptor<
+              MinidumpModuleCodeViewRecordPDB20>(file_contents,
+                                                 *codeview_record);
+      ASSERT_TRUE(codeview_pdb20_record);
       EXPECT_EQ(static_cast<uint32_t>(expected_pdb_timestamp),
                 codeview_pdb20_record->timestamp);
       EXPECT_EQ(expected_pdb_age, codeview_pdb20_record->age);
@@ -157,14 +148,12 @@ void ExpectMiscellaneousDebugRecord(
     uint32_t expected_debug_type,
     bool expected_debug_utf16) {
   if (expected_debug_name) {
-    EXPECT_GE(misc_record->DataSize, sizeof(IMAGE_DEBUG_MISC));
     EXPECT_NE(0u, misc_record->Rva);
-    ASSERT_LE(misc_record->Rva + misc_record->DataSize, file_contents.size());
     const IMAGE_DEBUG_MISC* misc_debug_record =
-        reinterpret_cast<const IMAGE_DEBUG_MISC*>(
-            &file_contents[misc_record->Rva]);
+        MinidumpWritableAtLocationDescriptor<IMAGE_DEBUG_MISC>(file_contents,
+                                                               *misc_record);
+    ASSERT_TRUE(misc_debug_record);
     EXPECT_EQ(expected_debug_type, misc_debug_record->DataType);
-    EXPECT_EQ(misc_record->DataSize, misc_debug_record->Length);
     EXPECT_EQ(expected_debug_utf16, misc_debug_record->Unicode);
     EXPECT_EQ(0u, misc_debug_record->Reserved[0]);
     EXPECT_EQ(0u, misc_debug_record->Reserved[1]);
diff --git a/minidump/minidump_simple_string_dictionary_writer_test.cc b/minidump/minidump_simple_string_dictionary_writer_test.cc
index bbe2476..7ab62a8 100644
--- a/minidump/minidump_simple_string_dictionary_writer_test.cc
+++ b/minidump/minidump_simple_string_dictionary_writer_test.cc
@@ -19,16 +19,23 @@
 #include "gtest/gtest.h"
 #include "minidump/minidump_extensions.h"
 #include "minidump/test/minidump_string_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
 namespace test {
 namespace {
 
-const MinidumpSimpleStringDictionary* MinidumpSimpleStringDictionaryCast(
-    const StringFileWriter& file_writer) {
-  return reinterpret_cast<const MinidumpSimpleStringDictionary*>(
-      &file_writer.string()[0]);
+const MinidumpSimpleStringDictionary* MinidumpSimpleStringDictionaryAtStart(
+    const std::string& file_contents,
+    size_t count) {
+  MINIDUMP_LOCATION_DESCRIPTOR location_descriptor;
+  location_descriptor.DataSize =
+      sizeof(MinidumpSimpleStringDictionary) +
+      count * sizeof(MinidumpSimpleStringDictionaryEntry);
+  location_descriptor.Rva = 0;
+  return MinidumpWritableAtLocationDescriptor<MinidumpSimpleStringDictionary>(
+      file_contents, location_descriptor);
 }
 
 TEST(MinidumpSimpleStringDictionaryWriter, EmptySimpleStringDictionary) {
@@ -41,7 +48,8 @@ TEST(MinidumpSimpleStringDictionaryWriter, EmptySimpleStringDictionary) {
             file_writer.string().size());
 
   const MinidumpSimpleStringDictionary* dictionary =
-      MinidumpSimpleStringDictionaryCast(file_writer);
+      MinidumpSimpleStringDictionaryAtStart(file_writer.string(), 0);
+  ASSERT_TRUE(dictionary);
   EXPECT_EQ(0u, dictionary->count);
 }
 
@@ -59,7 +67,8 @@ TEST(MinidumpSimpleStringDictionaryWriter, EmptyKeyValue) {
             file_writer.string().size());
 
   const MinidumpSimpleStringDictionary* dictionary =
-      MinidumpSimpleStringDictionaryCast(file_writer);
+      MinidumpSimpleStringDictionaryAtStart(file_writer.string(), 1);
+  ASSERT_TRUE(dictionary);
   EXPECT_EQ(1u, dictionary->count);
   EXPECT_EQ(12u, dictionary->entries[0].key);
   EXPECT_EQ(20u, dictionary->entries[0].value);
@@ -89,7 +98,8 @@ TEST(MinidumpSimpleStringDictionaryWriter, OneKeyValue) {
             file_writer.string().size());
 
   const MinidumpSimpleStringDictionary* dictionary =
-      MinidumpSimpleStringDictionaryCast(file_writer);
+      MinidumpSimpleStringDictionaryAtStart(file_writer.string(), 1);
+  ASSERT_TRUE(dictionary);
   EXPECT_EQ(1u, dictionary->count);
   EXPECT_EQ(12u, dictionary->entries[0].key);
   EXPECT_EQ(20u, dictionary->entries[0].value);
@@ -131,7 +141,8 @@ TEST(MinidumpSimpleStringDictionaryWriter, ThreeKeysValues) {
             file_writer.string().size());
 
   const MinidumpSimpleStringDictionary* dictionary =
-      MinidumpSimpleStringDictionaryCast(file_writer);
+      MinidumpSimpleStringDictionaryAtStart(file_writer.string(), 3);
+  ASSERT_TRUE(dictionary);
   EXPECT_EQ(3u, dictionary->count);
   EXPECT_EQ(28u, dictionary->entries[0].key);
   EXPECT_EQ(36u, dictionary->entries[0].value);
@@ -188,7 +199,8 @@ TEST(MinidumpSimpleStringDictionaryWriter, DuplicateKeyValue) {
             file_writer.string().size());
 
   const MinidumpSimpleStringDictionary* dictionary =
-      MinidumpSimpleStringDictionaryCast(file_writer);
+      MinidumpSimpleStringDictionaryAtStart(file_writer.string(), 1);
+  ASSERT_TRUE(dictionary);
   EXPECT_EQ(1u, dictionary->count);
   EXPECT_EQ(12u, dictionary->entries[0].key);
   EXPECT_EQ(20u, dictionary->entries[0].value);
diff --git a/minidump/minidump_system_info_writer_test.cc b/minidump/minidump_system_info_writer_test.cc
index 28c91df..da7895b 100644
--- a/minidump/minidump_system_info_writer_test.cc
+++ b/minidump/minidump_system_info_writer_test.cc
@@ -23,6 +23,7 @@
 #include "minidump/minidump_file_writer.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
 #include "minidump/test/minidump_string_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
@@ -56,17 +57,17 @@ void GetSystemInfoStream(const std::string& file_contents,
   ASSERT_TRUE(directory);
 
   ASSERT_EQ(kMinidumpStreamTypeSystemInfo, directory[0].StreamType);
-  ASSERT_EQ(sizeof(MINIDUMP_SYSTEM_INFO), directory[0].Location.DataSize);
-  ASSERT_EQ(kSystemInfoStreamOffset, directory[0].Location.Rva);
+  EXPECT_EQ(kSystemInfoStreamOffset, directory[0].Location.Rva);
 
-  *system_info = reinterpret_cast<const MINIDUMP_SYSTEM_INFO*>(
-      &file_contents[kSystemInfoStreamOffset]);
+  *system_info = MinidumpWritableAtLocationDescriptor<MINIDUMP_SYSTEM_INFO>(
+      file_contents, directory[0].Location);
+  ASSERT_TRUE(system_info);
 
-  ASSERT_EQ(kCSDVersionOffset, (*system_info)->CSDVersionRva);
+  EXPECT_EQ(kCSDVersionOffset, (*system_info)->CSDVersionRva);
 
   *csd_version =
       MinidumpStringAtRVA(file_contents, (*system_info)->CSDVersionRva);
-  ASSERT_EQ(kCSDVersionBytes, (*csd_version)->Length);
+  EXPECT_EQ(kCSDVersionBytes, (*csd_version)->Length);
 }
 
 TEST(MinidumpSystemInfoWriter, Empty) {
diff --git a/minidump/minidump_thread_writer_test.cc b/minidump/minidump_thread_writer_test.cc
index fb2baff..74fc7fe 100644
--- a/minidump/minidump_thread_writer_test.cc
+++ b/minidump/minidump_thread_writer_test.cc
@@ -23,6 +23,7 @@
 #include "minidump/test/minidump_context_test_util.h"
 #include "minidump/test/minidump_memory_writer_test_util.h"
 #include "minidump/test/minidump_file_writer_test_util.h"
+#include "minidump/test/minidump_writable_test_util.h"
 #include "util/file/string_file_writer.h"
 
 namespace crashpad {
@@ -51,19 +52,18 @@ void GetThreadListStream(const std::string& file_contents,
   ASSERT_TRUE(directory);
 
   ASSERT_EQ(kMinidumpStreamTypeThreadList, directory[0].StreamType);
-  ASSERT_GE(directory[0].Location.DataSize, sizeof(MINIDUMP_THREAD_LIST));
-  ASSERT_EQ(kThreadListStreamOffset, directory[0].Location.Rva);
+  EXPECT_EQ(kThreadListStreamOffset, directory[0].Location.Rva);
 
-  *thread_list = reinterpret_cast<const MINIDUMP_THREAD_LIST*>(
-      &file_contents[kThreadListStreamOffset]);
-
-  ASSERT_EQ(sizeof(MINIDUMP_THREAD_LIST) +
-                (*thread_list)->NumberOfThreads * sizeof(MINIDUMP_THREAD),
-            directory[0].Location.DataSize);
+  *thread_list = MinidumpWritableAtLocationDescriptor<MINIDUMP_THREAD_LIST>(
+      file_contents, directory[0].Location);
+  ASSERT_TRUE(thread_list);
 
   if (memory_list) {
-    *memory_list = reinterpret_cast<const MINIDUMP_MEMORY_LIST*>(
-        &file_contents[directory[1].Location.Rva]);
+    ASSERT_EQ(kMinidumpStreamTypeMemoryList, directory[1].StreamType);
+
+    *memory_list = MinidumpWritableAtLocationDescriptor<MINIDUMP_MEMORY_LIST>(
+        file_contents, directory[1].Location);
+    ASSERT_TRUE(*memory_list);
   }
 }
 
diff --git a/minidump/test/minidump_file_writer_test_util.cc b/minidump/test/minidump_file_writer_test_util.cc
index e87c099..723e97d 100644
--- a/minidump/test/minidump_file_writer_test_util.cc
+++ b/minidump/test/minidump_file_writer_test_util.cc
@@ -32,15 +32,6 @@ const MINIDUMP_HEADER* MinidumpHeaderAtStart(
           file_contents, location_descriptor);
 
   if (header) {
-    if (header->Signature != MINIDUMP_SIGNATURE) {
-      EXPECT_EQ(static_cast<uint32_t>(MINIDUMP_SIGNATURE), header->Signature);
-      return nullptr;
-    }
-    if (header->Version != MINIDUMP_VERSION) {
-      EXPECT_EQ(static_cast<uint32_t>(MINIDUMP_VERSION), header->Version);
-      return nullptr;
-    }
-
     location_descriptor.DataSize =
         header->NumberOfStreams * sizeof(MINIDUMP_DIRECTORY);
     location_descriptor.Rva = header->StreamDirectoryRva;
@@ -57,8 +48,6 @@ void VerifyMinidumpHeader(const MINIDUMP_HEADER* header,
                           uint32_t streams,
                           uint32_t timestamp) {
   ASSERT_TRUE(header);
-  EXPECT_EQ(static_cast<uint32_t>(MINIDUMP_SIGNATURE), header->Signature);
-  EXPECT_EQ(static_cast<uint32_t>(MINIDUMP_VERSION), header->Version);
   ASSERT_EQ(streams, header->NumberOfStreams);
   ASSERT_EQ(streams ? sizeof(MINIDUMP_HEADER) : 0u, header->StreamDirectoryRva);
   EXPECT_EQ(0u, header->CheckSum);
diff --git a/minidump/test/minidump_file_writer_test_util.h b/minidump/test/minidump_file_writer_test_util.h
index 846fa12..9b561e0 100644
--- a/minidump/test/minidump_file_writer_test_util.h
+++ b/minidump/test/minidump_file_writer_test_util.h
@@ -45,13 +45,15 @@ const MINIDUMP_HEADER* MinidumpHeaderAtStart(
 //! \brief Verifies, via gtest assertions, that a MINIDUMP_HEADER contains
 //!     expected values.
 //!
-//! All fields in the MINIDUMP_HEADER will be evaluated. Most are compared to
-//! their correct default values. MINIDUMP_HEADER::NumberOfStreams is compared
-//! to \a streams, and MINIDUMP_HEADER::TimeDateStamp is compared to \a
-//! timestamp. Most fields are checked with nonfatal EXPECT-style assertions,
-//! but MINIDUMP_HEADER::NumberOfStreams and MINIDUMP_HEADER::StreamDirectoryRva
-//! are checked with fatal ASSERT-style assertions, because they must be
-//! correct in order for processing of the minidump to continue.
+//! All fields in the MINIDUMP_HEADER will be evaluated except for the Signature
+//! and Version fields, because those are checked by MinidumpHeaderAtStart().
+//! Most other fields are are compared to their correct default values.
+//! MINIDUMP_HEADER::NumberOfStreams is compared to \a streams, and
+//! MINIDUMP_HEADER::TimeDateStamp is compared to \a timestamp. Most fields are
+//! checked with nonfatal EXPECT-style assertions, but
+//! MINIDUMP_HEADER::NumberOfStreams and MINIDUMP_HEADER::StreamDirectoryRva are
+//! checked with fatal ASSERT-style assertions, because they must be correct in
+//! order for processing of the minidump to continue.
 void VerifyMinidumpHeader(const MINIDUMP_HEADER* header,
                           uint32_t streams,
                           uint32_t timestamp);
diff --git a/minidump/test/minidump_writable_test_util.cc b/minidump/test/minidump_writable_test_util.cc
index 7466d7c..3e98a03 100644
--- a/minidump/test/minidump_writable_test_util.cc
+++ b/minidump/test/minidump_writable_test_util.cc
@@ -16,6 +16,7 @@
 
 #include <string>
 
+#include "base/strings/string16.h"
 #include "gtest/gtest.h"
 
 namespace crashpad {
@@ -34,12 +35,20 @@ const void* MinidumpWritableAtRVAInternal(const std::string& file_contents,
 const void* MinidumpWritableAtLocationDescriptorInternal(
     const std::string& file_contents,
     const MINIDUMP_LOCATION_DESCRIPTOR& location,
-    size_t expected_minimum_size) {
+    size_t expected_size,
+    bool allow_oversized_data) {
   if (location.DataSize == 0) {
     EXPECT_EQ(0u, location.Rva);
     return nullptr;
-  } else if (location.DataSize < expected_minimum_size) {
-    EXPECT_GE(location.DataSize, expected_minimum_size);
+  }
+
+  if (allow_oversized_data) {
+    if (location.DataSize < expected_size) {
+      EXPECT_GE(location.DataSize, expected_size);
+      return nullptr;
+    }
+  } else if (location.DataSize != expected_size) {
+    EXPECT_EQ(expected_size, location.DataSize);
     return nullptr;
   }
 
@@ -54,5 +63,213 @@ const void* MinidumpWritableAtLocationDescriptorInternal(
   return rv;
 }
 
+template <>
+const IMAGE_DEBUG_MISC* MinidumpWritableAtLocationDescriptor<IMAGE_DEBUG_MISC>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  const IMAGE_DEBUG_MISC* misc =
+      TMinidumpWritableAtLocationDescriptor<IMAGE_DEBUG_MISC>(file_contents,
+                                                              location);
+  if (!misc) {
+    return nullptr;
+  }
+
+  if (misc->DataType != IMAGE_DEBUG_MISC_EXENAME) {
+    EXPECT_EQ(static_cast<uint32_t>(IMAGE_DEBUG_MISC_EXENAME), misc->DataType);
+    return nullptr;
+  }
+
+  if (misc->Length != location.DataSize) {
+    EXPECT_EQ(location.DataSize, misc->Length);
+    return nullptr;
+  }
+
+  if (misc->Unicode == 0) {
+    size_t string_length = misc->Length - offsetof(IMAGE_DEBUG_MISC, Data) - 1;
+    if (misc->Data[string_length] != '\0') {
+      EXPECT_EQ('\0', misc->Data[string_length]);
+      return nullptr;
+    }
+  } else if (misc->Unicode == 1) {
+    if (misc->Length % sizeof(char16) != 0) {
+      EXPECT_EQ(0u, misc->Length % sizeof(char16));
+      return nullptr;
+    }
+
+    size_t string_length =
+        (misc->Length - offsetof(IMAGE_DEBUG_MISC, Data)) / sizeof(char16) - 1;
+    const char16* data16 = reinterpret_cast<const char16*>(misc->Data);
+    if (data16[string_length] != '\0') {
+      EXPECT_EQ('\0', data16[string_length]);
+      return nullptr;
+    }
+  } else {
+    ADD_FAILURE() << "misc->Unicode " << misc->Unicode;
+    return nullptr;
+  }
+
+  return misc;
+}
+
+template <>
+const MINIDUMP_HEADER* MinidumpWritableAtLocationDescriptor<MINIDUMP_HEADER>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  const MINIDUMP_HEADER* header =
+      TMinidumpWritableAtLocationDescriptor<MINIDUMP_HEADER>(file_contents,
+                                                             location);
+  if (!header) {
+    return nullptr;
+  }
+
+  if (header->Signature != MINIDUMP_SIGNATURE) {
+    EXPECT_EQ(static_cast<uint32_t>(MINIDUMP_SIGNATURE), header->Signature);
+    return nullptr;
+  }
+  if (header->Version != MINIDUMP_VERSION) {
+    EXPECT_EQ(static_cast<uint32_t>(MINIDUMP_VERSION), header->Version);
+    return nullptr;
+  }
+
+  return header;
+}
+
+namespace {
+
+struct MinidumpMemoryListTraits {
+  typedef MINIDUMP_MEMORY_LIST ListType;
+  static constexpr size_t kElementSize = sizeof(MINIDUMP_MEMORY_DESCRIPTOR);
+  static size_t ElementCount(const ListType* list) {
+    return list->NumberOfMemoryRanges;
+  }
+};
+
+struct MinidumpModuleListTraits {
+  typedef MINIDUMP_MODULE_LIST ListType;
+  static constexpr size_t kElementSize = sizeof(MINIDUMP_MODULE);
+  static size_t ElementCount(const ListType* list) {
+    return list->NumberOfModules;
+  }
+};
+
+struct MinidumpThreadListTraits {
+  typedef MINIDUMP_THREAD_LIST ListType;
+  static constexpr size_t kElementSize = sizeof(MINIDUMP_THREAD);
+  static size_t ElementCount(const ListType* list) {
+    return list->NumberOfThreads;
+  }
+};
+
+struct MinidumpSimpleStringDictionaryListTraits {
+  typedef MinidumpSimpleStringDictionary ListType;
+  static constexpr size_t kElementSize =
+      sizeof(MinidumpSimpleStringDictionaryEntry);
+  static size_t ElementCount(const ListType* list) {
+    return list->count;
+  }
+};
+
+template <typename T>
+const typename T::ListType* MinidumpListAtLocationDescriptor(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  const typename T::ListType* list =
+      TMinidumpWritableAtLocationDescriptor<typename T::ListType>(file_contents,
+                                                                  location);
+  if (!list) {
+    return nullptr;
+  }
+
+  size_t expected_size =
+      sizeof(typename T::ListType) + T::ElementCount(list) * T::kElementSize;
+  if (location.DataSize != expected_size) {
+    EXPECT_EQ(expected_size, location.DataSize);
+    return nullptr;
+  }
+
+  return list;
+}
+
+}  // namespace
+
+template <>
+const MINIDUMP_MEMORY_LIST* MinidumpWritableAtLocationDescriptor<
+    MINIDUMP_MEMORY_LIST>(const std::string& file_contents,
+                          const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return MinidumpListAtLocationDescriptor<MinidumpMemoryListTraits>(
+      file_contents, location);
+}
+
+template <>
+const MINIDUMP_MODULE_LIST* MinidumpWritableAtLocationDescriptor<
+    MINIDUMP_MODULE_LIST>(const std::string& file_contents,
+                          const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return MinidumpListAtLocationDescriptor<MinidumpModuleListTraits>(
+      file_contents, location);
+}
+
+template <>
+const MINIDUMP_THREAD_LIST* MinidumpWritableAtLocationDescriptor<
+    MINIDUMP_THREAD_LIST>(const std::string& file_contents,
+                          const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return MinidumpListAtLocationDescriptor<MinidumpThreadListTraits>(
+      file_contents, location);
+}
+
+template <>
+const MinidumpSimpleStringDictionary*
+MinidumpWritableAtLocationDescriptor<MinidumpSimpleStringDictionary>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return MinidumpListAtLocationDescriptor<
+      MinidumpSimpleStringDictionaryListTraits>(file_contents, location);
+}
+
+namespace {
+
+template <typename T>
+const T* MinidumpCVPDBAtLocationDescriptor(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  const T* cv_pdb =
+      TMinidumpWritableAtLocationDescriptor<T>(file_contents, location);
+  if (!cv_pdb) {
+    return nullptr;
+  }
+
+  if (cv_pdb->signature != T::kSignature) {
+    EXPECT_EQ(T::kSignature, cv_pdb->signature);
+    return nullptr;
+  }
+
+  size_t string_length = location.DataSize - offsetof(T, pdb_name) - 1;
+  if (cv_pdb->pdb_name[string_length] != '\0') {
+    EXPECT_EQ('\0', cv_pdb->pdb_name[string_length]);
+    return nullptr;
+  }
+
+  return cv_pdb;
+}
+
+}  // namespace
+
+template <>
+const MinidumpModuleCodeViewRecordPDB20*
+MinidumpWritableAtLocationDescriptor<MinidumpModuleCodeViewRecordPDB20>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return MinidumpCVPDBAtLocationDescriptor<MinidumpModuleCodeViewRecordPDB20>(
+      file_contents, location);
+}
+
+template <>
+const MinidumpModuleCodeViewRecordPDB70*
+MinidumpWritableAtLocationDescriptor<MinidumpModuleCodeViewRecordPDB70>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return MinidumpCVPDBAtLocationDescriptor<MinidumpModuleCodeViewRecordPDB70>(
+      file_contents, location);
+}
+
 }  // namespace test
 }  // namespace crashpad
diff --git a/minidump/test/minidump_writable_test_util.h b/minidump/test/minidump_writable_test_util.h
index a637f19..8b5ddba 100644
--- a/minidump/test/minidump_writable_test_util.h
+++ b/minidump/test/minidump_writable_test_util.h
@@ -16,10 +16,12 @@
 #define CRASHPAD_MINIDUMP_TEST_MINIDUMP_WRITABLE_TEST_UTIL_H_
 
 #include <dbghelp.h>
+#include <stdint.h>
 
 #include <string>
 
 #include "gtest/gtest.h"
+#include "minidump/minidump_extensions.h"
 
 namespace crashpad {
 namespace test {
@@ -47,12 +49,18 @@ const void* MinidumpWritableAtRVAInternal(const std::string& file_contents,
 //! \param[in] file_contents The contents of the minidump file.
 //! \param[in] location A MINIDUMP_LOCATION_DESCRIPTOR giving the offset within
 //!     the minidump file of the desired object, as well as its size.
-//! \param[in] expected_minimum_size The minimum size allowable for the object.
+//! \param[in] expected_size The expected size of the object. If \a
+//!     allow_oversized_data is `true`, \a expected_size is treated as the
+//!     minimum size of \a location, but it is permitted to be larger. If \a
+//!     allow_oversized_data is `false`, the size of \a location must match
+//!     \a expected_size exactly.
+//! \param[in] allow_oversized_data Controls whether \a expected_size is a
+//!     minimum limit (`true`) or an exact match is required (`false`).
 //!
-//! \return If the size of \a location is at least as big as \a
-//!     expected_minimum_size, and if \a location is within the range of \a
-//!     file_contents, returns a pointer into \a file_contents at offset \a rva.
-//!     Otherwise, raises a gtest assertion failure and returns `nullptr`.
+//! \return If the size of \a location is agrees with \a expected_size, and if
+//!     \a location is within the range of \a file_contents, returns a pointer
+//!     into \a file_contents at offset \a rva. Otherwise, raises a gtest
+//!     assertion failure and returns `nullptr`.
 //!
 //! Do not call this function. Use the typed version,
 //! MinidumpWritableAtLocationDescriptor<>(), or another type-specific function.
@@ -61,7 +69,54 @@ const void* MinidumpWritableAtRVAInternal(const std::string& file_contents,
 const void* MinidumpWritableAtLocationDescriptorInternal(
     const std::string& file_contents,
     const MINIDUMP_LOCATION_DESCRIPTOR& location,
-    size_t expected_minimum_size);
+    size_t expected_size,
+    bool allow_oversized_data);
+
+//! \brief A traits class defining whether a minidump object type is required to
+//!     appear only as a fixed-size object or if it is variable-sized.
+//!
+//! Variable-sized data is data referenced by a MINIDUMP_LOCATION_DESCRIPTOR
+//! whose DataSize field may be larger than the size of the basic object type’s
+//! structure. This can happen for types that appear only as variable-sized
+//! lists, or types whose final fields are variable-sized lists or other
+//! variable-sized data.
+template <typename T>
+struct MinidumpWritableTraits {
+  //! \brief `true` if \a T should be treated as a variable-sized data type,
+  //!     where its base size is used solely as a minimum bound. `false` if \a
+  //!     T is a fixed-sized type, which should only appear at its base size.
+  static const bool kAllowOversizedData = false;
+};
+
+#define MINIDUMP_ALLOW_OVERSIZED_DATA(x)          \
+  template <>                                     \
+  struct MinidumpWritableTraits<x> {              \
+    static const bool kAllowOversizedData = true; \
+  }
+
+// This type appears only as a variable-sized list.
+MINIDUMP_ALLOW_OVERSIZED_DATA(MINIDUMP_DIRECTORY);
+
+// These types are permitted to be oversized because their final fields are
+// variable-sized lists.
+MINIDUMP_ALLOW_OVERSIZED_DATA(MINIDUMP_MEMORY_LIST);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MINIDUMP_MODULE_LIST);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MINIDUMP_THREAD_LIST);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MinidumpSimpleStringDictionary);
+
+// These types have final fields carrying variable-sized data (typically string
+// data).
+MINIDUMP_ALLOW_OVERSIZED_DATA(IMAGE_DEBUG_MISC);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MINIDUMP_STRING);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MinidumpModuleCodeViewRecordPDB20);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MinidumpModuleCodeViewRecordPDB70);
+MINIDUMP_ALLOW_OVERSIZED_DATA(MinidumpUTF8String);
+
+// minidump_file_writer_test accesses its variable-sized test streams via a
+// uint8_t*.
+MINIDUMP_ALLOW_OVERSIZED_DATA(uint8_t);
+
+#undef MINIDUMP_ALLOW_OVERSIZED_DATA
 
 //! \brief Returns a typed minidump object located within a minidump file’s
 //!     contents, where the offset of the object is known.
@@ -83,6 +138,42 @@ const T* MinidumpWritableAtRVA(const std::string& file_contents, RVA rva) {
 //! \brief Returns a typed minidump object located within a minidump file’s
 //!     contents, where the offset and size of the object are known.
 //!
+//! This function is similar to MinidumpWritableAtLocationDescriptor<>() and is
+//! used to implement that function. It exists independently so that template
+//! specializations are able to call this function, which provides the default
+//! implementation.
+//!
+//! Do not call this function directly. Use
+//! MinidumpWritableAtLocationDescriptor<>() instead.
+template <typename T>
+const T* TMinidumpWritableAtLocationDescriptor(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location) {
+  return reinterpret_cast<const T*>(
+      MinidumpWritableAtLocationDescriptorInternal(
+          file_contents,
+          location,
+          sizeof(T),
+          MinidumpWritableTraits<T>::kAllowOversizedData));
+}
+
+//! \brief Returns a typed minidump object located within a minidump file’s
+//!     contents, where the offset and size of the object are known.
+//!
+//! This function has template specializations that perform more stringent
+//! checking than the default implementation:
+//!  - With a MINIDUMP_HEADER template parameter, a template specialization
+//!    ensures that the structure’s magic number and version fields are correct.
+//!  - With a MINIDUMP_MEMORY_LIST, MINIDUMP_THREAD_LIST, MINIDUMP_MODULE_LIST,
+//!    or MinidumpSimpleStringDictionary template parameter, template
+//!    specializations ensure that the size given by \a location matches the
+//!    size expected of a stream containing the number of elements it claims to
+//!    have.
+//!  - With an IMAGE_DEBUG_MISC, MinidumpModuleCodeViewRecordPDB20, or
+//!    MinidumpModuleCodeViewRecordPDB70 template parameter, template
+//!    specializations ensure that the structure has the expected format
+//!    including any magic number and the `NUL`-terminated string.
+//!
 //! \param[in] file_contents The contents of the minidump file.
 //! \param[in] location A MINIDUMP_LOCATION_DESCRIPTOR giving the offset within
 //!     the minidump file of the desired object, as well as its size.
@@ -97,11 +188,52 @@ template <typename T>
 const T* MinidumpWritableAtLocationDescriptor(
     const std::string& file_contents,
     const MINIDUMP_LOCATION_DESCRIPTOR& location) {
-  return reinterpret_cast<const T*>(
-      MinidumpWritableAtLocationDescriptorInternal(
-          file_contents, location, sizeof(T)));
+  return TMinidumpWritableAtLocationDescriptor<T>(file_contents, location);
 }
 
+template <>
+const IMAGE_DEBUG_MISC* MinidumpWritableAtLocationDescriptor<IMAGE_DEBUG_MISC>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MINIDUMP_HEADER* MinidumpWritableAtLocationDescriptor<MINIDUMP_HEADER>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MINIDUMP_MEMORY_LIST* MinidumpWritableAtLocationDescriptor<
+    MINIDUMP_MEMORY_LIST>(const std::string& file_contents,
+                          const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MINIDUMP_MODULE_LIST* MinidumpWritableAtLocationDescriptor<
+    MINIDUMP_MODULE_LIST>(const std::string& file_contents,
+                          const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MINIDUMP_THREAD_LIST* MinidumpWritableAtLocationDescriptor<
+    MINIDUMP_THREAD_LIST>(const std::string& file_contents,
+                          const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MinidumpModuleCodeViewRecordPDB20*
+MinidumpWritableAtLocationDescriptor<MinidumpModuleCodeViewRecordPDB20>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MinidumpModuleCodeViewRecordPDB70*
+MinidumpWritableAtLocationDescriptor<MinidumpModuleCodeViewRecordPDB70>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
+template <>
+const MinidumpSimpleStringDictionary*
+MinidumpWritableAtLocationDescriptor<MinidumpSimpleStringDictionary>(
+    const std::string& file_contents,
+    const MINIDUMP_LOCATION_DESCRIPTOR& location);
+
 }  // namespace test
 }  // namespace crashpad