Add a buffered SkStream class.

tests/FrontBufferedStreamTest.cpp

+/*
+ * 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)