SkPDF: detect YUV-JPEG without relying on ImageGenerator

src/pdf/SkJpegInfo.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkData.h"
+#include "SkJpegInfo.h"
+
+namespace {
+class JpegSegment {
+public:
+    JpegSegment(const SkData* skdata)
+        : fData(static_cast<const char*>(skdata->data()))
+        , fSize(skdata->size())
+        , fOffset(0)
+        , fLength(0) {}
+    bool read() {
+        if (!this->readBigendianUint16(&fMarker)) {
+            return false;
+        }
+        if (JpegSegment::StandAloneMarker(fMarker)) {
+            fLength = 0;
+            fBuffer = NULL;
+            return true;
+        }
+        if (!this->readBigendianUint16(&fLength) || fLength < 2) {
+            return false;
+        }
+        fLength -= 2;  // Length includes itself for some reason.
+        if (fOffset + fLength > fSize) {
+            return false;  // Segment too long.
+        }
+        fBuffer = &fData[fOffset];
+        fOffset += fLength;
+        return true;
+    }
+
+    bool isSOF() {
+        return (fMarker & 0xFFF0) == 0xFFC0 && fMarker != 0xFFC4 &&
+               fMarker != 0xFFC8 && fMarker != 0xFFCC;
+    }
+    uint16_t marker() { return fMarker; }
+    uint16_t length() { return fLength; }
+    const char* data() { return fBuffer; }
+
+    static uint16_t GetBigendianUint16(const char* ptr) {
+        // "the most significant byte shall come first"
+        return (static_cast<uint8_t>(ptr[0]) << 8) |
+            static_cast<uint8_t>(ptr[1]);
+    }
+
+private:
+    const char* const fData;
+    const size_t fSize;
+    size_t fOffset;
+    const char* fBuffer;
+    uint16_t fMarker;
+    uint16_t fLength;
+
+    bool readBigendianUint16(uint16_t* value) {
+        if (fOffset + 2 > fSize) {
+            return false;
+        }
+        *value = JpegSegment::GetBigendianUint16(&fData[fOffset]);
+        fOffset += 2;
+        return true;
+    }
+    static bool StandAloneMarker(uint16_t marker) {
+        // RST[m] markers or SOI, EOI, TEM
+        return (marker & 0xFFF8) == 0xFFD0 || marker == 0xFFD8 ||
+               marker == 0xFFD9 || marker == 0xFF01;
+    }
+};
+}  // namespace
+
+bool SkIsJFIF(const SkData* skdata, SkJFIFInfo* info) {
+    static const uint16_t kSOI = 0xFFD8;
+    static const uint16_t kAPP0 = 0xFFE0;
+    JpegSegment segment(skdata);
+    if (!segment.read() || segment.marker() != kSOI) {
+        return false;  // not a JPEG
+    }
+    if (!segment.read() || segment.marker() != kAPP0) {
+        return false;  // not an APP0 segment
+    }
+    static const char kJfif[] = {'J', 'F', 'I', 'F', '\0'};
+    SkASSERT(segment.data());
+    if (SkToSizeT(segment.length()) < sizeof(kJfif) ||
+        0 != memcmp(segment.data(), kJfif, sizeof(kJfif))) {
+        return false;  // Not JFIF JPEG
+    }
+    do {
+        if (!segment.read()) {
+            return false;  // malformed JPEG
+        }
+    } while (!segment.isSOF());
+    if (segment.length() < 6) {
+        return false;  // SOF segment is short
+    }
+    if (8 != segment.data()[0]) {
+        return false;  // Only support 8-bit precision
+    }
+    int numberOfComponents = segment.data()[5];
+    if (numberOfComponents != 1 && numberOfComponents != 3) {
+        return false;  // Invalid JFIF
+    }
+    if (info) {
+        info->fHeight = JpegSegment::GetBigendianUint16(&segment.data()[1]);
+        info->fWidth = JpegSegment::GetBigendianUint16(&segment.data()[3]);
+        if (numberOfComponents == 3) {
+            info->fType = SkJFIFInfo::kYCbCr;
+        } else {
+            info->fType = SkJFIFInfo::kGrayscale;
+        }
+    }
+    return true;
+}
+
+