API and test for retrieving image filters from image objects

Added FPDFImageObj_GetImageFilterCount() and
FPDFImageObj_GetImageFilters() for retrieving image filters of image
objects.
    * Added a corresponding embedder test.
    * Changed the filter of an image object in embedded_image.pdf from
      DCTDecode to ASCIIHexDecode + DCTDecode, so we have a test case
      for images with more than one filter.

Bug=pdfium:677

Change-Id: I398790a2cad33fea4ca16a0eb0889c04caa6b962
Reviewed-on: https://pdfium-review.googlesource.com/10130
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: Jane Liu <janeliulwq@google.com>

5 files changed, 118 insertions, 0 deletions

diff --git a/fpdfsdk/fpdfedit_embeddertest.cpp b/fpdfsdk/fpdfedit_embeddertest.cpp
index c381b25efa..e62ef2149b 100644
--- a/fpdfsdk/fpdfedit_embeddertest.cpp
+++ b/fpdfsdk/fpdfedit_embeddertest.cpp
@@ -1038,3 +1038,49 @@ TEST_F(FPDFEditEmbeddertest, DestroyPageObject) {
   // There should be no memory leaks with a call to FPDFPageObj_Destroy().
   FPDFPageObj_Destroy(rect);
 }
+
+TEST_F(FPDFEditEmbeddertest, GetImageFilters) {
+  EXPECT_TRUE(OpenDocument("embedded_images.pdf"));
+  FPDF_PAGE page = LoadPage(0);
+  ASSERT_TRUE(page);
+
+  // Verify that retrieving the filter of a non-image object would fail.
+  FPDF_PAGEOBJECT obj = FPDFPage_GetObject(page, 32);
+  ASSERT_NE(FPDF_PAGEOBJ_IMAGE, FPDFPageObj_GetType(obj));
+  ASSERT_EQ(0, FPDFImageObj_GetImageFilterCount(obj));
+  EXPECT_EQ(0u, FPDFImageObj_GetImageFilter(obj, 0, nullptr, 0));
+
+  // Verify the returned filter string for an image object with a single filter.
+  obj = FPDFPage_GetObject(page, 33);
+  ASSERT_EQ(FPDF_PAGEOBJ_IMAGE, FPDFPageObj_GetType(obj));
+  ASSERT_EQ(1, FPDFImageObj_GetImageFilterCount(obj));
+  unsigned long len = FPDFImageObj_GetImageFilter(obj, 0, nullptr, 0);
+  std::vector<char> buf(len);
+  EXPECT_EQ(24u, FPDFImageObj_GetImageFilter(obj, 0, buf.data(), len));
+  EXPECT_STREQ(L"FlateDecode",
+               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
+                   .c_str());
+  EXPECT_EQ(0u, FPDFImageObj_GetImageFilter(obj, 1, nullptr, 0));
+
+  // Verify all the filters for an image object with a list of filters.
+  obj = FPDFPage_GetObject(page, 38);
+  ASSERT_EQ(FPDF_PAGEOBJ_IMAGE, FPDFPageObj_GetType(obj));
+  ASSERT_EQ(2, FPDFImageObj_GetImageFilterCount(obj));
+  len = FPDFImageObj_GetImageFilter(obj, 0, nullptr, 0);
+  buf.clear();
+  buf.resize(len);
+  EXPECT_EQ(30u, FPDFImageObj_GetImageFilter(obj, 0, buf.data(), len));
+  EXPECT_STREQ(L"ASCIIHexDecode",
+               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
+                   .c_str());
+
+  len = FPDFImageObj_GetImageFilter(obj, 1, nullptr, 0);
+  buf.clear();
+  buf.resize(len);
+  EXPECT_EQ(20u, FPDFImageObj_GetImageFilter(obj, 1, buf.data(), len));
+  EXPECT_STREQ(L"DCTDecode",
+               GetPlatformWString(reinterpret_cast<unsigned short*>(buf.data()))
+                   .c_str());
+
+  UnloadPage(page);
+}
diff --git a/fpdfsdk/fpdfeditimg.cpp b/fpdfsdk/fpdfeditimg.cpp
index 0d0c54604b..b4254e97c6 100644
--- a/fpdfsdk/fpdfeditimg.cpp
+++ b/fpdfsdk/fpdfeditimg.cpp
@@ -10,6 +10,8 @@
 #include "core/fpdfapi/page/cpdf_image.h"
 #include "core/fpdfapi/page/cpdf_imageobject.h"
 #include "core/fpdfapi/page/cpdf_pageobject.h"
+#include "core/fpdfapi/parser/cpdf_array.h"
+#include "core/fpdfapi/parser/cpdf_name.h"
 #include "fpdfsdk/fsdk_define.h"
 #include "third_party/base/ptr_util.h"
 
@@ -179,3 +181,46 @@ FPDFImageObj_GetImageDataRaw(FPDF_PAGEOBJECT image_object,
 
   return len;
 }
+
+DLLEXPORT int STDCALL
+FPDFImageObj_GetImageFilterCount(FPDF_PAGEOBJECT image_object) {
+  CPDF_PageObject* pObj = CPDFPageObjectFromFPDFPageObject(image_object);
+  if (!pObj || !pObj->IsImage())
+    return 0;
+
+  CFX_RetainPtr<CPDF_Image> pImg = pObj->AsImage()->GetImage();
+  if (!pImg)
+    return 0;
+
+  CPDF_Dictionary* pDict = pImg->GetDict();
+  CPDF_Object* pFilter = pDict ? pDict->GetDirectObjectFor("Filter") : nullptr;
+  if (!pFilter)
+    return 0;
+
+  if (pFilter->IsArray())
+    return pFilter->AsArray()->GetCount();
+  if (pFilter->IsName())
+    return 1;
+
+  return 0;
+}
+
+DLLEXPORT unsigned long STDCALL
+FPDFImageObj_GetImageFilter(FPDF_PAGEOBJECT image_object,
+                            int index,
+                            void* buffer,
+                            unsigned long buflen) {
+  if (index < 0 || index >= FPDFImageObj_GetImageFilterCount(image_object))
+    return 0;
+
+  CPDF_PageObject* pObj = CPDFPageObjectFromFPDFPageObject(image_object);
+  CPDF_Object* pFilter =
+      pObj->AsImage()->GetImage()->GetDict()->GetDirectObjectFor("Filter");
+  CFX_WideString wsFilters;
+  if (pFilter->IsName())
+    wsFilters = pFilter->AsName()->GetUnicodeText();
+  else
+    wsFilters = pFilter->AsArray()->GetUnicodeTextAt(index);
+
+  return Utf16EncodeMaybeCopyAndReturnLength(wsFilters, buffer, buflen);
+}
diff --git a/fpdfsdk/fpdfview_c_api_test.c b/fpdfsdk/fpdfview_c_api_test.c
index ef5b804baa..8276eb64b7 100644
--- a/fpdfsdk/fpdfview_c_api_test.c
+++ b/fpdfsdk/fpdfview_c_api_test.c
@@ -136,6 +136,8 @@ int CheckPDFiumCApi() {
     CHK(FPDFImageObj_GetBitmap);
     CHK(FPDFImageObj_GetImageDataDecoded);
     CHK(FPDFImageObj_GetImageDataRaw);
+    CHK(FPDFImageObj_GetImageFilterCount);
+    CHK(FPDFImageObj_GetImageFilter);
     CHK(FPDFPageObj_CreateNewPath);
     CHK(FPDFPageObj_CreateNewRect);
     CHK(FPDFPath_SetStrokeColor);
diff --git a/public/fpdf_edit.h b/public/fpdf_edit.h
index aab48af3f1..54127d80ea 100644
--- a/public/fpdf_edit.h
+++ b/public/fpdf_edit.h
@@ -336,6 +336,31 @@ FPDFImageObj_GetImageDataRaw(FPDF_PAGEOBJECT image_object,
                              void* buffer,
                              unsigned long buflen);
 
+// Get the number of filters (i.e. decoders) of the image in |image_object|.
+//
+//   image_object - handle to an image object.
+//
+// Returns the number of |image_object|'s filters.
+DLLEXPORT int STDCALL
+FPDFImageObj_GetImageFilterCount(FPDF_PAGEOBJECT image_object);
+
+// Get the filter at |index| of |image_object|'s list of filters. Note that the
+// filters need to be applied in order, i.e. the first filter should be applied
+// first, then the second, etc. |buffer| is only modified if |buflen| is longer
+// than the length of the filter string.
+//
+//   image_object - handle to an image object.
+//   index        - the index of the filter requested.
+//   buffer       - buffer for holding filter string, encoded in UTF16-LE.
+//   buflen       - length of the buffer.
+//
+// Returns the length of the filter string.
+DLLEXPORT unsigned long STDCALL
+FPDFImageObj_GetImageFilter(FPDF_PAGEOBJECT image_object,
+                            int index,
+                            void* buffer,
+                            unsigned long buflen);
+
 // Create a new path object at an initial position.
 //
 //   x - initial horizontal position.
diff --git a/testing/resources/embedded_images.pdf b/testing/resources/embedded_images.pdf
index 81845822a4..82adbeaa4c 100644
--- a/testing/resources/embedded_images.pdf
+++ b/testing/resources/embedded_images.pdf