Add a buffered SkStream class.

This is used by Android to buffer an input stream which may not
otherwise be able to rewind.

Add a test for the new class.

R=bungeman@google.com, mtklein@google.com, reed@google.com

Review URL: https://codereview.chromium.org/23717055

git-svn-id: http://skia.googlecode.com/svn/trunk@11488 2bbb7eff-a529-9590-31e7-b0007b416f81

gyp/tests.gyp

@@ -62,6 +62,7 @@
         '../tests/FontHostTest.cpp',
         '../tests/FontMgrTest.cpp',
         '../tests/FontNamesTest.cpp',
+        '../tests/FrontBufferedStreamTest.cpp',
         '../tests/GeometryTest.cpp',
         '../tests/GLInterfaceValidation.cpp',
         '../tests/GLProgramsTest.cpp',

gyp/utils.gyp

@@ -34,6 +34,7 @@
         '../src/utils/SkThreadPool.cpp',
 
         '../include/utils/SkBoundaryPatch.h',
+        '../include/utils/SkFrontBufferedStream.h',
         '../include/utils/SkCamera.h',
         '../include/utils/SkCanvasStateUtils.h',
         '../include/utils/SkCubicInterval.h',
@@ -65,6 +66,7 @@
         '../src/utils/SkBitSet.cpp',
         '../src/utils/SkBitSet.h',
         '../src/utils/SkBoundaryPatch.cpp',
+        '../src/utils/SkFrontBufferedStream.cpp',
         '../src/utils/SkCamera.cpp',
         '../src/utils/SkCanvasStack.h',
         '../src/utils/SkCanvasStack.cpp',

include/utils/SkFrontBufferedStream.h

@@ -0,0 +1,77 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkStream.h"
+#include "SkTemplates.h"
+
+/**
+ *  Specialized stream that only buffers the first X bytes of a stream,
+ *  where X is passed in by the user. Note that unlike some buffered
+ *  stream APIs, once more than those bytes are read, no more buffering
+ *  is done. This stream is designed for a use case where the caller
+ *  knows that rewind will only be called from within X bytes (inclusive),
+ *  and the wrapped stream is not necessarily able to rewind at all.
+ */
+class SkFrontBufferedStream : public SkStreamRewindable {
+public:
+    /**
+     *  Creates a new stream that wraps and buffers SkStream.
+     *  @param stream SkStream to buffer. If NULL, NULL is returned. After
+     *      this call, unref stream and do not refer to it.
+     *      SkFrontBufferedStream is expected to be its only owner.
+     *  @param bufferSize Exact size of the buffer to be used.
+     *  @return An SkStream that can buffer up to bufferSize.
+     */
+    static SkStreamRewindable* Create(SkStream* stream, size_t bufferSize);
+
+    virtual size_t read(void* buffer, size_t size) SK_OVERRIDE;
+
+    virtual bool isAtEnd() const SK_OVERRIDE;
+
+    virtual bool rewind() SK_OVERRIDE;
+
+    virtual bool hasPosition() const SK_OVERRIDE { return true; }
+
+    virtual size_t getPosition() const SK_OVERRIDE { return fOffset; }
+
+    virtual bool hasLength() const SK_OVERRIDE;
+
+    virtual size_t getLength() const SK_OVERRIDE;
+
+    virtual SkStreamRewindable* duplicate() const SK_OVERRIDE { return NULL; }
+
+private:
+    SkAutoTUnref<SkStream>  fStream;
+    // Current offset into the stream. Always >= 0.
+    size_t                  fOffset;
+    // Amount that has been buffered by calls to read. Will always be less than
+    // fBufferSize.
+    size_t                  fBufferedSoFar;
+    // Total size of the buffer.
+    const size_t            fBufferSize;
+    SkAutoTMalloc<char>     fBuffer;
+
+    // Private. Use Create.
+    SkFrontBufferedStream(SkStream*, size_t bufferSize);
+
+    // Read up to size bytes from already buffered data, and copy to
+    // dst, if non-NULL. Updates fOffset. Assumes that fOffset is less
+    // than fBufferedSoFar.
+    size_t readFromBuffer(char* dst, size_t size);
+
+    // Buffer up to size bytes from the stream, and copy to dst if non-
+    // NULL. Updates fOffset and fBufferedSoFar. Assumes that fOffset is
+    // less than fBufferedSoFar, and size is greater than 0.
+    size_t bufferAndWriteTo(char* dst, size_t size);
+
+    // Read up to size bytes directly from the stream and into dst if non-
+    // NULL. Updates fOffset. Assumes fOffset is at or beyond the buffered
+    // data, and size is greater than 0.
+    size_t readDirectlyFromStream(char* dst, size_t size);
+
+    typedef SkStream INHERITED;
+};

src/utils/SkFrontBufferedStream.cpp

@@ -0,0 +1,147 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkFrontBufferedStream.h"
+
+SkStreamRewindable* SkFrontBufferedStream::Create(SkStream* stream, size_t bufferSize) {
+    if (NULL == stream) {
+        return NULL;
+    }
+    return SkNEW_ARGS(SkFrontBufferedStream, (stream, bufferSize));
+}
+
+SkFrontBufferedStream::SkFrontBufferedStream(SkStream* stream, size_t bufferSize)
+    : fStream(SkRef(stream))
+    , fOffset(0)
+    , fBufferedSoFar(0)
+    , fBufferSize(bufferSize)
+    , fBuffer(bufferSize) {}
+
+bool SkFrontBufferedStream::isAtEnd() const {
+    if (fOffset < fBufferedSoFar) {
+        // Even if the underlying stream is at the end, this stream has been
+        // rewound after buffering, so it is not at the end.
+        return false;
+    }
+
+    return fStream->isAtEnd();
+}
+
+bool SkFrontBufferedStream::rewind() {
+    // Only allow a rewind if we have not exceeded the buffer.
+    if (fOffset <= fBufferSize) {
+        fOffset = 0;
+        return true;
+    }
+    return false;
+}
+
+bool SkFrontBufferedStream::hasLength() const {
+    return fStream->hasLength();
+}
+
+size_t SkFrontBufferedStream::getLength() const {
+    return fStream->getLength();
+}
+
+size_t SkFrontBufferedStream::readFromBuffer(char* dst, size_t size) {
+    SkASSERT(fOffset < fBufferedSoFar);
+    // Some data has already been copied to fBuffer. Read up to the
+    // lesser of the size requested and the remainder of the buffered
+    // data.
+    const size_t bytesToCopy = SkTMin(size, fBufferedSoFar - fOffset);
+    if (dst != NULL) {
+        memcpy(dst, fBuffer + fOffset, bytesToCopy);
+    }
+
+    // Update fOffset to the new position. It is guaranteed to be
+    // within the buffered data.
+    fOffset += bytesToCopy;
+    SkASSERT(fOffset <= fBufferedSoFar);
+
+    return bytesToCopy;
+}
+
+size_t SkFrontBufferedStream::bufferAndWriteTo(char* dst, size_t size) {
+    SkASSERT(size > 0);
+    SkASSERT(fOffset >= fBufferedSoFar);
+    // Data needs to be buffered. Buffer up to the lesser of the size requested
+    // and the remainder of the max buffer size.
+    const size_t bytesToBuffer = SkTMin(size, fBufferSize - fBufferedSoFar);
+    char* buffer = fBuffer + fOffset;
+    const size_t buffered = fStream->read(buffer, bytesToBuffer);
+
+    fBufferedSoFar += buffered;
+    fOffset = fBufferedSoFar;
+    SkASSERT(fBufferedSoFar <= fBufferSize);
+
+    // Copy the buffer to the destination buffer and update the amount read.
+    if (dst != NULL) {
+        memcpy(dst, buffer, buffered);
+    }
+
+    return buffered;
+}
+
+size_t SkFrontBufferedStream::readDirectlyFromStream(char* dst, size_t size) {
+    SkASSERT(size > 0);
+    // If we get here, we have buffered all that can be buffered.
+    SkASSERT(fBufferSize == fBufferedSoFar && fOffset >= fBufferSize);
+
+    const size_t bytesReadDirectly = fStream->read(dst, size);
+    fOffset += bytesReadDirectly;
+
+    // If we have read past the end of the buffer, rewinding is no longer
+    // supported, so we can go ahead and free the memory.
+    if (bytesReadDirectly > 0) {
+        fBuffer.reset(0);
+    }
+
+    return bytesReadDirectly;
+}
+
+size_t SkFrontBufferedStream::read(void* voidDst, size_t size) {
+    // Cast voidDst to a char* for easy addition.
+    char* dst = reinterpret_cast<char*>(voidDst);
+    SkDEBUGCODE(const size_t totalSize = size;)
+    const size_t start = fOffset;
+
+    // First, read any data that was previously buffered.
+    if (fOffset < fBufferedSoFar) {
+        const size_t bytesCopied = this->readFromBuffer(dst, size);
+
+        // Update the remaining number of bytes needed to read
+        // and the destination buffer.
+        size -= bytesCopied;
+        SkASSERT(size + (fOffset - start) == totalSize);
+        if (dst != NULL) {
+            dst += bytesCopied;
+        }
+    }
+
+    // Buffer any more data that should be buffered, and copy it to the
+    // destination.
+    if (size > 0 && fBufferedSoFar < fBufferSize) {
+        const size_t buffered = this->bufferAndWriteTo(dst, size);
+
+        // Update the remaining number of bytes needed to read
+        // and the destination buffer.
+        size -= buffered;
+        SkASSERT(size + (fOffset - start) == totalSize);
+        if (dst != NULL) {
+            dst += buffered;
+        }
+    }
+
+    if (size > 0 && !fStream->isAtEnd()) {
+        const size_t bytesReadDirectly = this->readDirectlyFromStream(dst, size);
+        SkDEBUGCODE(size -= bytesReadDirectly;)
+        SkASSERT(size + (fOffset - start) == totalSize);
+    }
+
+    return fOffset - start;
+}

tests/FrontBufferedStreamTest.cpp

@@ -0,0 +1,160 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkFrontBufferedStream.h"
+#include "SkRefCnt.h"
+#include "SkTypes.h"
+#include "Test.h"
+
+static void test_read(skiatest::Reporter* reporter, SkStream* bufferedStream,
+                      const void* expectations, size_t bytesToRead) {
+    // output for reading bufferedStream.
+    SkAutoMalloc storage(bytesToRead);
+
+    size_t bytesRead = bufferedStream->read(storage.get(), bytesToRead);
+    REPORTER_ASSERT(reporter, bytesRead == bytesToRead || bufferedStream->isAtEnd());
+    REPORTER_ASSERT(reporter, memcmp(storage.get(), expectations, bytesRead) == 0);
+}
+
+static void test_rewind(skiatest::Reporter* reporter,
+                        SkStream* bufferedStream, bool shouldSucceed) {
+    const bool success = bufferedStream->rewind();
+    REPORTER_ASSERT(reporter, success == shouldSucceed);
+}
+
+// All tests will buffer this string, and compare output to the original.
+// The string is long to ensure that all of our lengths being tested are
+// smaller than the string length.
+const char gAbcs[] = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwx";
+
+// Tests reading the stream across boundaries of what has been buffered so far and what
+// the total buffer size is.
+static void test_incremental_buffering(skiatest::Reporter* reporter, size_t bufferSize) {
+    SkMemoryStream memStream(gAbcs, strlen(gAbcs), false);
+
+    SkAutoTUnref<SkStream> bufferedStream(SkFrontBufferedStream::Create(&memStream, bufferSize));
+
+    // First, test reading less than the max buffer size.
+    test_read(reporter, bufferedStream, gAbcs, bufferSize / 2);
+
+    // Now test rewinding back to the beginning and reading less than what was
+    // already buffered.
+    test_rewind(reporter, bufferedStream, true);
+    test_read(reporter, bufferedStream, gAbcs, bufferSize / 4);
+
+    // Now test reading part of what was buffered, and buffering new data.
+    test_read(reporter, bufferedStream, gAbcs + bufferedStream->getPosition(), bufferSize / 2);
+
+    // Now test reading what was buffered, buffering new data, and
+    // reading directly from the stream.
+    test_rewind(reporter, bufferedStream, true);
+    test_read(reporter, bufferedStream, gAbcs, bufferSize << 1);
+
+    // We have reached the end of the buffer, so rewinding will fail.
+    // This test assumes that the stream is larger than the buffer; otherwise the
+    // result of rewind should be true.
+    test_rewind(reporter, bufferedStream, false);
+}
+
+static void test_perfectly_sized_buffer(skiatest::Reporter* reporter, size_t bufferSize) {
+    SkMemoryStream memStream(gAbcs, strlen(gAbcs), false);
+    SkAutoTUnref<SkStream> bufferedStream(SkFrontBufferedStream::Create(&memStream, bufferSize));
+
+    // Read exactly the amount that fits in the buffer.
+    test_read(reporter, bufferedStream, gAbcs, bufferSize);
+
+    // Rewinding should succeed.
+    test_rewind(reporter, bufferedStream, true);
+
+    // Once again reading buffered info should succeed
+    test_read(reporter, bufferedStream, gAbcs, bufferSize);
+
+    // Read past the size of the buffer. At this point, we cannot return.
+    test_read(reporter, bufferedStream, gAbcs + bufferedStream->getPosition(), 1);
+    test_rewind(reporter, bufferedStream, false);
+}
+
+static void test_skipping(skiatest::Reporter* reporter, size_t bufferSize) {
+    SkMemoryStream memStream(gAbcs, strlen(gAbcs), false);
+    SkAutoTUnref<SkStream> bufferedStream(SkFrontBufferedStream::Create(&memStream, bufferSize));
+
+    // Skip half the buffer.
+    bufferedStream->skip(bufferSize / 2);
+
+    // Rewind, then read part of the buffer, which should have been read.
+    test_rewind(reporter, bufferedStream, true);
+    test_read(reporter, bufferedStream, gAbcs, bufferSize / 4);
+
+    // Now skip beyond the buffered piece, but still within the total buffer.
+    bufferedStream->skip(bufferSize / 2);
+
+    // Test that reading will still work.
+    test_read(reporter, bufferedStream, gAbcs + bufferedStream->getPosition(), bufferSize / 4);
+
+    test_rewind(reporter, bufferedStream, true);
+    test_read(reporter, bufferedStream, gAbcs, bufferSize);
+}
+
+// A custom class whose isAtEnd behaves the way Android's stream does - since it is an adaptor to a
+// Java InputStream, it does not know that it is at the end until it has attempted to read beyond
+// the end and failed. Used by test_read_beyond_buffer.
+class AndroidLikeMemoryStream : public SkMemoryStream {
+public:
+    AndroidLikeMemoryStream(void* data, size_t size, bool ownMemory)
+        : INHERITED(data, size, ownMemory)
+        , fIsAtEnd(false) {}
+
+    size_t read(void* dst, size_t requested) SK_OVERRIDE {
+        size_t bytesRead = this->INHERITED::read(dst, requested);
+        if (bytesRead < requested) {
+            fIsAtEnd = true;
+        }
+        return bytesRead;
+    }
+
+    bool isAtEnd() const SK_OVERRIDE {
+        return fIsAtEnd;
+    }
+
+private:
+    bool fIsAtEnd;
+    typedef SkMemoryStream INHERITED;
+};
+
+// This test ensures that buffering the exact length of the stream and attempting to read beyond it
+// does not invalidate the buffer.
+static void test_read_beyond_buffer(skiatest::Reporter* reporter, size_t bufferSize) {
+    // Use a stream that behaves like Android's stream.
+    AndroidLikeMemoryStream memStream((void*)gAbcs, bufferSize, false);
+
+    // Create a buffer that matches the length of the stream.
+    SkAutoTUnref<SkStream> bufferedStream(SkFrontBufferedStream::Create(&memStream, bufferSize));
+
+    // Attempt to read one more than the bufferSize
+    test_read(reporter, bufferedStream.get(), gAbcs, bufferSize + 1);
+    test_rewind(reporter, bufferedStream.get(), true);
+
+    // Ensure that the initial read did not invalidate the buffer.
+    test_read(reporter, bufferedStream, gAbcs, bufferSize);
+}
+
+static void test_buffers(skiatest::Reporter* reporter, size_t bufferSize) {
+    test_incremental_buffering(reporter, bufferSize);
+    test_perfectly_sized_buffer(reporter, bufferSize);
+    test_skipping(reporter, bufferSize);
+    test_read_beyond_buffer(reporter, bufferSize);
+}
+
+static void TestStreams(skiatest::Reporter* reporter) {
+    // Test 6 and 64, which are used by Android, as well as another arbitrary length.
+    test_buffers(reporter, 6);
+    test_buffers(reporter, 15);
+    test_buffers(reporter, 64);
+}
+
+#include "TestClassDef.h"
+DEFINE_TESTCLASS("FrontBufferedStream", FrontBufferedStreamTestClass, TestStreams)