GIF: Avoid copying/storing data when possible

If the input SkStream has a length and position, do not copy and store
LZW blocks or ColorMaps. Instead, mark the position and size, and read
from the stream when necessary.

This will save memory in Chromium's use case, which has already
buffered all of its data.

In the case where we *do* need to copy, store it on the SkStreamBuffer.
This allows SkGifImageReader to have simpler code.

Add tests.

Change-Id: Ic65fa766328ae2e5974b2084bc2099e19aced731
Reviewed-on: https://skia-review.googlesource.com/6157
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>

4 files changed, 223 insertions, 69 deletions

diff --git a/tests/CodecPartialTest.cpp b/tests/CodecPartialTest.cpp
index 93e5d63f22..62f9d8570e 100644
--- a/tests/CodecPartialTest.cpp
+++ b/tests/CodecPartialTest.cpp
@@ -12,6 +12,7 @@
 #include "SkRWBuffer.h"
 #include "SkString.h"
 
+#include "FakeStreams.h"
 #include "Resources.h"
 #include "Test.h"
 
@@ -50,46 +51,6 @@ static void compare_bitmaps(skiatest::Reporter* r, const SkBitmap& bm1, const Sk
     }
 }
 
-/*
- *  Represents a stream without all of its data.
- */
-class HaltingStream : public SkStream {
-public:
-    HaltingStream(sk_sp<SkData> data, size_t initialLimit)
-        : fTotalSize(data->size())
-        , fLimit(initialLimit)
-        , fStream(std::move(data))
-    {}
-
-    void addNewData(size_t extra) {
-        fLimit = SkTMin(fTotalSize, fLimit + extra);
-    }
-
-    size_t read(void* buffer, size_t size) override {
-        if (fStream.getPosition() + size > fLimit) {
-            size = fLimit - fStream.getPosition();
-        }
-
-        return fStream.read(buffer, size);
-    }
-
-    bool isAtEnd() const override {
-        return fStream.isAtEnd();
-    }
-
-    bool hasPosition() const override { return true; }
-    size_t getPosition() const override { return fStream.getPosition(); }
-    bool rewind() override { return fStream.rewind(); }
-    bool move(long offset) override { return fStream.move(offset); }
-
-    bool isAllDataReceived() const { return fLimit == fTotalSize; }
-
-private:
-    const size_t    fTotalSize;
-    size_t          fLimit;
-    SkMemoryStream  fStream;
-};
-
 static void test_partial(skiatest::Reporter* r, const char* name, size_t minBytes = 0) {
     sk_sp<SkData> file = make_from_resource(name);
     if (!file) {
diff --git a/tests/CodecTest.cpp b/tests/CodecTest.cpp
index 05859a95b3..19494b280d 100644
--- a/tests/CodecTest.cpp
+++ b/tests/CodecTest.cpp
@@ -5,6 +5,7 @@
  * found in the LICENSE file.
  */
 
+#include "FakeStreams.h"
 #include "Resources.h"
 #include "SkAndroidCodec.h"
 #include "SkBitmap.h"
@@ -891,35 +892,6 @@ private:
     const size_t   fLimit;
 };
 
-// Stream that is not an asset stream (!hasPosition() or !hasLength())
-class NotAssetMemStream : public SkStream {
-public:
-    NotAssetMemStream(sk_sp<SkData> data) : fStream(std::move(data)) {}
-
-    bool hasPosition() const override {
-        return false;
-    }
-
-    bool hasLength() const override {
-        return false;
-    }
-
-    size_t peek(void* buf, size_t bytes) const override {
-        return fStream.peek(buf, bytes);
-    }
-    size_t read(void* buf, size_t bytes) override {
-        return fStream.read(buf, bytes);
-    }
-    bool rewind() override {
-        return fStream.rewind();
-    }
-    bool isAtEnd() const override {
-        return fStream.isAtEnd();
-    }
-private:
-    SkMemoryStream fStream;
-};
-
 // Disable RAW tests for Win32.
 #if defined(SK_CODEC_DECODES_RAW) && (!defined(_WIN32))
 // Test that the RawCodec works also for not asset stream. This will test the code path using
diff --git a/tests/FakeStreams.h b/tests/FakeStreams.h
new file mode 100644
index 0000000000..6b510b8970
--- /dev/null
+++ b/tests/FakeStreams.h
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2016 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 "SkStream.h"
+
+#ifndef FakeStreams_DEFINED
+#define FakeStreams_DEFINED
+
+// Stream that is not an asset stream (!hasPosition() or !hasLength())
+class NotAssetMemStream : public SkStream {
+public:
+    NotAssetMemStream(sk_sp<SkData> data) : fStream(std::move(data)) {}
+
+    bool hasPosition() const override {
+        return false;
+    }
+
+    bool hasLength() const override {
+        return false;
+    }
+
+    size_t peek(void* buf, size_t bytes) const override {
+        return fStream.peek(buf, bytes);
+    }
+    size_t read(void* buf, size_t bytes) override {
+        return fStream.read(buf, bytes);
+    }
+    bool rewind() override {
+        return fStream.rewind();
+    }
+    bool isAtEnd() const override {
+        return fStream.isAtEnd();
+    }
+private:
+    SkMemoryStream fStream;
+};
+
+/*
+ *  Represents a stream without all of its data.
+ */
+class HaltingStream : public SkStream {
+public:
+    HaltingStream(sk_sp<SkData> data, size_t initialLimit)
+        : fTotalSize(data->size())
+        , fLimit(initialLimit)
+        , fStream(std::move(data))
+    {}
+
+    void addNewData(size_t extra) {
+        fLimit = SkTMin(fTotalSize, fLimit + extra);
+    }
+
+    size_t read(void* buffer, size_t size) override {
+        if (fStream.getPosition() + size > fLimit) {
+            size = fLimit - fStream.getPosition();
+        }
+
+        return fStream.read(buffer, size);
+    }
+
+    bool isAtEnd() const override {
+        return fStream.isAtEnd();
+    }
+
+    bool hasLength() const override { return true; }
+    size_t getLength() const override { return fLimit; }
+
+    bool hasPosition() const override { return true; }
+    size_t getPosition() const override { return fStream.getPosition(); }
+    bool rewind() override { return fStream.rewind(); }
+    bool move(long offset) override { return fStream.move(offset); }
+    bool seek(size_t position) override { return fStream.seek(position); }
+
+    bool isAllDataReceived() const { return fLimit == fTotalSize; }
+
+private:
+    const size_t    fTotalSize;
+    size_t          fLimit;
+    SkMemoryStream  fStream;
+};
+#endif // FakeStreams_DEFINED
diff --git a/tests/StreamBufferTest.cpp b/tests/StreamBufferTest.cpp
new file mode 100644
index 0000000000..96bca35c92
--- /dev/null
+++ b/tests/StreamBufferTest.cpp
@@ -0,0 +1,135 @@
+/*
+ * Copyright 2016 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 "SkOSPath.h"
+#include "SkStream.h"
+#include "SkStreamBuffer.h"
+
+#include "FakeStreams.h"
+#include "Test.h"
+
+static const char* gText = "Four score and seven years ago";
+
+static void test_get_data_at_position(skiatest::Reporter* r, SkStreamBuffer* buffer, size_t position,
+                                    size_t length) {
+    sk_sp<SkData> data = buffer->getDataAtPosition(position, length);
+    REPORTER_ASSERT(r, data);
+    if (data) {
+        REPORTER_ASSERT(r, !memcmp(data->data(), gText + position, length));
+    }
+}
+
+// Test buffering from the beginning, by different amounts.
+static void test_buffer_from_beginning(skiatest::Reporter* r, SkStream* stream, size_t length) {
+    SkStreamBuffer buffer(stream);
+
+    // Buffer an arbitrary amount:
+    size_t buffered = length / 2;
+    REPORTER_ASSERT(r, buffer.buffer(buffered));
+    REPORTER_ASSERT(r, !memcmp(buffer.get(), gText, buffered));
+
+    // Buffering less is free:
+    REPORTER_ASSERT(r, buffer.buffer(buffered / 2));
+
+    // Buffer more should succeed:
+    REPORTER_ASSERT(r, buffer.buffer(length));
+    REPORTER_ASSERT(r, !memcmp(buffer.get(), gText, length));
+}
+
+// Test flushing the stream as we read.
+static void test_flushing(skiatest::Reporter* r, SkStream* stream, size_t length,
+                          bool getDataAtPosition) {
+    SkStreamBuffer buffer(stream);
+    const size_t step = 5;
+    for (size_t position = 0; position + step <= length; position += step) {
+        REPORTER_ASSERT(r, buffer.buffer(step));
+        REPORTER_ASSERT(r, buffer.markPosition() == position);
+
+        if (!getDataAtPosition) {
+            REPORTER_ASSERT(r, !memcmp(buffer.get(), gText + position, step));
+        }
+        buffer.flush();
+    }
+
+    REPORTER_ASSERT(r, !buffer.buffer(step));
+
+    if (getDataAtPosition) {
+        for (size_t position = 0; position + step <= length; position += step) {
+            test_get_data_at_position(r, &buffer, position, step);
+        }
+    }
+}
+
+DEF_TEST(StreamBuffer, r) {
+    const size_t size = strlen(gText);
+    sk_sp<SkData> data(SkData::MakeWithoutCopy(gText, size));
+
+    SkString tmpDir = skiatest::GetTmpDir();
+    const char* subdir = "streamBuffer.txt";
+    SkString path;
+
+    if (!tmpDir.isEmpty()) {
+        path = SkOSPath::Join(tmpDir.c_str(), subdir);
+        SkFILEWStream writer(path.c_str());
+        writer.write(gText, size);
+    }
+
+    struct {
+        std::function<SkStream*()> createStream;
+        bool                       skipIfNoTmpDir;
+    } factories[] = {
+        { [&data]() { return new SkMemoryStream(data); },       false },
+        { [&data]() { return new NotAssetMemStream(data); },    false },
+        { [&path]() { return new SkFILEStream(path.c_str()); }, true  },
+    };
+
+    for (auto f : factories) {
+        if (tmpDir.isEmpty() && f.skipIfNoTmpDir) {
+            continue;
+        }
+        test_buffer_from_beginning(r, f.createStream(), size);
+        test_flushing(r, f.createStream(), size, false);
+        test_flushing(r, f.createStream(), size, true);
+    }
+
+    // Stream that will receive more data. Will be owned by the SkStreamBuffer.
+    HaltingStream* stream = new HaltingStream(data, 6);
+    SkStreamBuffer buffer(stream);
+
+    // Can only buffer less than what's available (6).
+    REPORTER_ASSERT(r, !buffer.buffer(7));
+    REPORTER_ASSERT(r, buffer.buffer(5));
+    REPORTER_ASSERT(r, !memcmp(buffer.get(), gText, 5));
+
+    // Add some more data. We can buffer and read all of it.
+    stream->addNewData(8);
+    REPORTER_ASSERT(r, buffer.buffer(14));
+    REPORTER_ASSERT(r, !memcmp(buffer.get(), gText, 14));
+
+    // Flush the buffer, which moves the position.
+    buffer.flush();
+
+    // Add some data, and try to read more. Can only read what is
+    // available.
+    stream->addNewData(9);
+    REPORTER_ASSERT(r, !buffer.buffer(13));
+    stream->addNewData(4);
+    REPORTER_ASSERT(r, buffer.buffer(13));
+
+    // Do not call get on this data. We'll come back to this data after adding
+    // more.
+    buffer.flush();
+    const size_t remaining = size - 27;
+    REPORTER_ASSERT(r, remaining > 0);
+    stream->addNewData(remaining);
+    REPORTER_ASSERT(r, buffer.buffer(remaining));
+    REPORTER_ASSERT(r, !memcmp(buffer.get(), gText + 27, remaining));
+
+    // Now go back to the data we skipped.
+    test_get_data_at_position(r, &buffer, 14, 13);
+}