AK: Move memory streams from LibCore

Tests/AK/TestMemoryStream.cpp

@@ -0,0 +1,94 @@
+/*
+ * Copyright (c) 2021, sin-ack <sin-ack@protonmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/MemoryStream.h>
+#include <AK/String.h>
+#include <LibCore/Stream.h>
+#include <LibTest/TestCase.h>
+
+TEST_CASE(allocating_memory_stream_empty)
+{
+    AllocatingMemoryStream stream;
+
+    EXPECT_EQ(stream.used_buffer_size(), 0ul);
+
+    {
+        Array<u8, 32> array;
+        auto read_bytes = MUST(stream.read(array));
+        EXPECT_EQ(read_bytes.size(), 0ul);
+    }
+
+    {
+        auto offset = MUST(stream.offset_of("test"sv.bytes()));
+        EXPECT(!offset.has_value());
+    }
+}
+
+TEST_CASE(allocating_memory_stream_offset_of)
+{
+    AllocatingMemoryStream stream;
+    MUST(stream.write_entire_buffer("Well Hello Friends! :^)"sv.bytes()));
+
+    {
+        auto offset = MUST(stream.offset_of(" "sv.bytes()));
+        EXPECT(offset.has_value());
+        EXPECT_EQ(offset.value(), 4ul);
+    }
+
+    {
+        auto offset = MUST(stream.offset_of("W"sv.bytes()));
+        EXPECT(offset.has_value());
+        EXPECT_EQ(offset.value(), 0ul);
+    }
+
+    {
+        auto offset = MUST(stream.offset_of(")"sv.bytes()));
+        EXPECT(offset.has_value());
+        EXPECT_EQ(offset.value(), 22ul);
+    }
+
+    {
+        auto offset = MUST(stream.offset_of("-"sv.bytes()));
+        EXPECT(!offset.has_value());
+    }
+
+    MUST(stream.discard(1));
+
+    {
+        auto offset = MUST(stream.offset_of("W"sv.bytes()));
+        EXPECT(!offset.has_value());
+    }
+
+    {
+        auto offset = MUST(stream.offset_of("e"sv.bytes()));
+        EXPECT(offset.has_value());
+        EXPECT_EQ(offset.value(), 0ul);
+    }
+}
+
+TEST_CASE(allocating_memory_stream_offset_of_oob)
+{
+    AllocatingMemoryStream stream;
+    // NOTE: This test is to make sure that offset_of() doesn't read past the end of the "initialized" data.
+    //       So we have to assume some things about the behaviour of this class:
+    //       - The chunk size is 4096 bytes.
+    //       - A chunk is moved to the end when it's fully read from
+    //       - A free chunk is used as-is, no new ones are allocated if one exists.
+
+    // First, fill exactly one chunk.
+    for (size_t i = 0; i < 256; ++i)
+        MUST(stream.write_entire_buffer("AAAAAAAAAAAAAAAA"sv.bytes()));
+
+    // Then discard it all.
+    MUST(stream.discard(4096));
+    // Now we can write into this chunk again, knowing that it's initialized to all 'A's.
+    MUST(stream.write_entire_buffer("Well Hello Friends! :^)"sv.bytes()));
+
+    {
+        auto offset = MUST(stream.offset_of("A"sv.bytes()));
+        EXPECT(!offset.has_value());
+    }
+}