3 files changed, 90 insertions, 0 deletions
diff --git a/image/imgLoader.cpp b/image/imgLoader.cpp
index 3545c5be2..5e5ee7829 100644
--- a/image/imgLoader.cpp
+++ b/image/imgLoader.cpp
@@ -2558,6 +2558,11 @@ imgLoader::GetMimeTypeFromContent(const char* aContents,
                               !memcmp(aContents, "\000\000\002\000", 4))) {
     aContentType.AssignLiteral(IMAGE_ICO);
 
+  // WebPs always begin with RIFF, a 32-bit length, and WEBP.
+  } else if (aLength >= 12 && !memcmp(aContents, "RIFF", 4) &&
+                              !memcmp(aContents + 8, "WEBP", 4)) {
+    aContentType.AssignLiteral(IMAGE_WEBP);
+
   } else {
     /* none of the above?  I give up */
     return NS_ERROR_NOT_AVAILABLE;
diff --git a/image/test/gtest/TestLoader.cpp b/image/test/gtest/TestLoader.cpp
new file mode 100644
index 000000000..5551f3f05
--- /dev/null
+++ b/image/test/gtest/TestLoader.cpp
@@ -0,0 +1,84 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "gtest/gtest.h"
+
+#include "Common.h"
+#include "imgLoader.h"
+#include "nsMimeTypes.h"
+#include "nsString.h"
+
+using namespace mozilla;
+using namespace mozilla::image;
+
+static void
+CheckMimeType(const char* aContents, size_t aLength, const char* aExpected)
+{
+  nsAutoCString detected;
+  nsresult rv = imgLoader::GetMimeTypeFromContent(aContents, aLength, detected);
+  if (aExpected) {
+    ASSERT_TRUE(NS_SUCCEEDED(rv));
+    EXPECT_TRUE(detected.EqualsASCII(aExpected));
+  } else {
+    ASSERT_TRUE(NS_FAILED(rv));
+    EXPECT_TRUE(detected.IsEmpty());
+  }
+}
+
+class ImageLoader : public ::testing::Test
+{
+protected:
+  AutoInitializeImageLib mInit;
+};
+
+TEST_F(ImageLoader, DetectGIF)
+{
+  const char buffer[] = "GIF87a";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_GIF);
+}
+
+TEST_F(ImageLoader, DetectPNG)
+{
+  const char buffer[] = "\x89\x50\x4E\x47\x0D\x0A\x1A\x0A";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_PNG);
+}
+
+TEST_F(ImageLoader, DetectJPEG)
+{
+  const char buffer[] = "\xFF\xD8\xFF";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_JPEG);
+}
+
+TEST_F(ImageLoader, DetectART)
+{
+  const char buffer[] = "\x4A\x47\xFF\xFF\x00";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_ART);
+}
+
+TEST_F(ImageLoader, DetectBMP)
+{
+  const char buffer[] = "BM";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_BMP);
+}
+
+TEST_F(ImageLoader, DetectICO)
+{
+  const char buffer[] = "\x00\x00\x01\x00";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_ICO);
+}
+
+TEST_F(ImageLoader, DetectWebP)
+{
+  const char buffer[] = "RIFF\xFF\xFF\xFF\xFFWEBPVP8L";
+  CheckMimeType(buffer, sizeof(buffer), IMAGE_WEBP);
+}
+
+TEST_F(ImageLoader, DetectNone)
+{
+  const char buffer[] = "abcdefghijklmnop";
+  CheckMimeType(buffer, sizeof(buffer), nullptr);
+}
+
diff --git a/image/test/gtest/moz.build b/image/test/gtest/moz.build
index 5cf6d5116..3548eaecc 100644
--- a/image/test/gtest/moz.build
+++ b/image/test/gtest/moz.build
@@ -13,6 +13,7 @@ UNIFIED_SOURCES = [
     'TestDecoders.cpp',
     'TestDecodeToSurface.cpp',
     'TestDeinterlacingFilter.cpp',
+    'TestLoader.cpp',
     'TestMetadata.cpp',
     'TestRemoveFrameRectFilter.cpp',
     'TestSourceBuffer.cpp',