Add custom RWops for use with constant containers

SDL2pp/ExtraRWops.hh

@@ -88,6 +88,61 @@ public:
 	}
 };
 
+template<typename C>
+class ConstContainerRWops : public CustomRWops {
+protected:
+	const C& container_;
+	size_t position_;
+
+public:
+	ConstContainerRWops(const C& container) : container_(container), position_(0) {
+	}
+
+	ConstContainerRWops(const ConstContainerRWops&) = default;
+	ConstContainerRWops& operator=(const ConstContainerRWops&) = default;
+	ConstContainerRWops(ConstContainerRWops&&) = default;
+	ConstContainerRWops& operator=(ConstContainerRWops&&) = default;
+
+	virtual Sint64 Seek(Sint64 offset, int whence) override {
+		switch (whence) {
+		case RW_SEEK_SET:
+			position_ = offset;
+			break;
+		case RW_SEEK_CUR:
+			position_ = position_ + offset;
+			break;
+		case RW_SEEK_END:
+			position_ = container_.size() + offset;
+			break;
+		default:
+			throw Exception("Unexpected whence value for WritableMemRWops::Seek");
+		}
+		return position_;
+	}
+
+	virtual size_t Read(void* ptr, size_t size, size_t maxnum) override {
+		if (position_ + size > container_.size())
+			return 0;
+
+		int toread = std::min((container_.size() - position_), maxnum * size);
+
+		std::copy(container_.begin() + position_, container_.begin() + position_ + toread, reinterpret_cast<unsigned char*>(ptr));
+
+		position_ += toread;
+
+		return toread / size;
+	}
+
+	virtual size_t Write(const void*, size_t, size_t) override {
+		SDL_SetError("Can't write to read-only container");
+		return 0;
+	}
+
+	virtual int Close() override {
+		return 0;
+	}
+};
+
 }
 
 #endif

tests/test_rwops.cc

@@ -114,6 +114,33 @@ BEGIN_TEST()
 		}
 	}
 
+	// Short test for ContainerRWops
+	{
+		const std::vector<char> buffer = { 'a', 'b', 'c', 'd' };
+
+		RWops rw((ConstContainerRWops<std::vector<char>>(buffer)));
+
+		{
+			// Read via C++
+			EXPECT_TRUE(rw.Seek(0, SEEK_SET) == 0);
+
+			char buf[4] = {0};
+			EXPECT_TRUE(rw.Read(buf, 1, 4) == 4);
+			EXPECT_TRUE(buf[0] == 'a' && buf[3] == 'd');
+
+			// Position after read
+			EXPECT_TRUE(rw.Tell() == 4);
+		}
+
+		{
+			// Write
+			char buf[4] = {0};
+
+			EXPECT_TRUE(rw.Write(buf, 1, 4) == 0);
+			EXPECT_TRUE(rw.Write(buf, 4, 1) == 0);
+		}
+	}
+
 	// SDL file read test
 	{
 		RWops rw = RWops::FromFile(TESTDATA_DIR "/test.txt");