io/Reader: add method ReadFull()

src/io/Reader.cxx

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: BSD-2-Clause
+// author: Max Kellermann <max.kellermann@gmail.com>
+
+#include "Reader.hxx"
+
+#include <stdexcept>
+
+void
+Reader::ReadFull(std::span<std::byte> dest)
+{
+	const auto nbytes = Read(dest);
+	if (nbytes < dest.size())
+		throw std::runtime_error{"Unexpected end of file"};
+}

src/io/Reader.hxx

@@ -28,11 +28,16 @@ public:
 	 */
 	virtual std::size_t Read(std::span<std::byte> dest) = 0;
 
+	/**
+	 * Like Read(), but throws an exception when there is not
+	 * enough data to fill the destination buffer.
+	 */
+	void ReadFull(std::span<std::byte> dest);
+
 	template<typename T>
 	requires std::is_standard_layout_v<T> && std::is_trivially_copyable_v<T>
 	void ReadT(T &dest) {
-		// TODO check return value
-		Read(std::as_writable_bytes(std::span{&dest, 1}));
+		ReadFull(std::as_writable_bytes(std::span{&dest, 1}));
 	}
 };
 

src/io/meson.build

@@ -2,6 +2,7 @@ io = static_library(
   'io',
   'FileDescriptor.cxx',
   'Open.cxx',
+  'Reader.cxx',
   'PeekReader.cxx',
   'BufferedReader.cxx',
   'BufferedOutputStream.cxx',