ircd::fs: Add experimental stdin::tty support.

include/ircd/fs/stdin.h

@@ -13,6 +13,23 @@
 
 namespace ircd::fs::stdin
 {
+	struct tty;
+
 	// Yields ircd::ctx to read line from stdin
 	string_view readline(const mutable_buffer &);
 }
+
+/// Directly represents the controlling tty of stdin if supported. The primary
+/// purpose here is to allow writing text to stdin to provide readline-esque
+/// history to the terminal console.
+///
+/// The member write() must be used, not fs::write(). The latter will throw
+/// an error when used on this.
+///
+struct ircd::fs::stdin::tty
+:fd
+{
+	size_t write(const string_view &);
+
+	tty();
+};

ircd/fs.cc

@@ -109,6 +109,29 @@ ircd::fs::stdin::readline(const mutable_buffer &buf)
 	};
 }
 
+//
+// tty
+//
+
+ircd::fs::stdin::tty::tty()
+:fd{[]
+{
+	thread_local char buf[256];
+	syscall(::ttyname_r, STDIN_FILENO, buf, sizeof(buf));
+	return fd
+	{
+		string_view{buf}, std::ios_base::out
+	};
+}()}
+{
+}
+
+size_t
+ircd::fs::stdin::tty::write(const string_view &buf)
+{
+	return syscall(::write, int(*this), buf.data(), buf.size());
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // fs/read.h