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[] = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz";

[mtklein, 2013/09/19 18:56:53]

line wraps

[scroggo, 2013/09/25 17:36:01]

Done.

+
+// 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 >> 1);

[mtklein, 2013/09/19 18:56:53]

Just a nit: bufferSize / 2 here may be a little more intuitive for future
readers.  Similarly below.

[scroggo, 2013/09/25 17:36:01]

Done.

+
+    // 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 >> 2);
+
+    // Now test reading part of what was buffered, and buffering new data.
+    test_read(reporter, bufferedStream, gAbcs + bufferedStream->getPosition(), bufferSize >> 1);
+
+    // 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 >> 1);
+
+    // Rewind, then read part of the buffer, which should have been read.
+    test_rewind(reporter, bufferedStream, true);
+    test_read(reporter, bufferedStream, gAbcs, bufferSize >> 2);
+
+    // Now skip beyond the buffered piece, but still within the total buffer.
+    bufferedStream->skip(bufferSize >> 1);
+
+    // Test that reading will still work.
+    test_read(reporter, bufferedStream, gAbcs + bufferedStream->getPosition(), bufferSize >> 2);
+
+    test_rewind(reporter, bufferedStream, true);
+    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);
+}
+
+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)