SkPDF: Make magic make sense

src/pdf/SkPDFDocument.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPDFCanon.h"
 #include "SkPDFCanvas.h"
 #include "SkPDFDevice.h"
@@ skipping 10 matching lines @@
 SkPDFObjectSerializer::~SkPDFObjectSerializer() {
     for (int i = 0; i < fObjNumMap.objects().count(); ++i) {
         fObjNumMap.objects()[i]->drop();
     }
 }
 
 void SkPDFObjectSerializer::addObjectRecursively(const sk_sp<SkPDFObject>& object) {
     fObjNumMap.addObjectRecursively(object.get(), fSubstituteMap);
 }
 
+#define SKPDF_MAGIC "\xD3\xEB\xE9\xE1"
+#ifndef SK_BUILD_FOR_WIN32
+static_assert((SKPDF_MAGIC[0] & 0x7F) == "Skia"[0], "");
+static_assert((SKPDF_MAGIC[1] & 0x7F) == "Skia"[1], "");
+static_assert((SKPDF_MAGIC[2] & 0x7F) == "Skia"[2], "");
+static_assert((SKPDF_MAGIC[3] & 0x7F) == "Skia"[3], "");
+#endif
 void SkPDFObjectSerializer::serializeHeader(SkWStream* wStream, const SkPDFMetadata& md) {
     fBaseOffset = wStream->bytesWritten();
-    static const char kHeader[] = "%PDF-1.4\n%\xE1\xE9\xEB\xD3\n";
+    static const char kHeader[] = "%PDF-1.4\n%" SKPDF_MAGIC "\n";
     wStream->write(kHeader, strlen(kHeader));
     // The PDF spec recommends including a comment with four
     // bytes, all with their high bits set.  "\xD3\xEB\xE9\xE1" is
     // "Skia" with the high bits set.
     fInfoDict.reset(md.createDocumentInformationDict());
     this->addObjectRecursively(fInfoDict);
     this->serializeObjects(wStream);
 }
+#undef SKPDF_MAGIC
 
 // Serialize all objects in the fObjNumMap that have not yet been serialized;
 void SkPDFObjectSerializer::serializeObjects(SkWStream* wStream) {
     const SkTArray<sk_sp<SkPDFObject>>& objects = fObjNumMap.objects();
     while (fNextToBeSerialized < objects.count()) {
         SkPDFObject* object = objects[fNextToBeSerialized].get();
         int32_t index = fNextToBeSerialized + 1;  // Skip object 0.
         // "The first entry in the [XREF] table (object number 0) is
         // always free and has a generation number of 65,535; it is
         // the head of the linked list of free objects."
@@ skipping 308 matching lines @@
     return SkPDFMakeDocument(stream, nullptr, dpi, jpegEncoder).release();
 }
 
 SkDocument* SkDocument::CreatePDF(const char path[], SkScalar dpi) {
     auto delete_wstream = [](SkWStream* stream, bool) { delete stream; };
     std::unique_ptr<SkFILEWStream> stream(new SkFILEWStream(path));
     return stream->isValid()
         ? SkPDFMakeDocument(stream.release(), delete_wstream, dpi, nullptr).release()
         : nullptr;
 }