Userspace: Implement super simple DNS resolver in userspace

You connect to this service using unix domain sockets and send the
asked domain name. It will respond with ip address or 'unavailable'

There is no DNS cache implemented so all calls ask the nameserver.

userspace/nslookup/CMakeLists.txt

@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.26)
+
+project(nslookup CXX)
+
+set(SOURCES
+	main.cpp
+)
+
+add_executable(nslookup ${SOURCES})
+target_compile_options(nslookup PUBLIC -O2 -g)
+target_link_libraries(nslookup PUBLIC libc)
+
+add_custom_target(nslookup-install
+	COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_BINARY_DIR}/nslookup ${BANAN_BIN}/
+	DEPENDS nslookup
+)

userspace/nslookup/main.cpp

@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+int main(int argc, char** argv)
+{
+	if (argc != 2)
+	{
+		fprintf(stderr, "usage: %s DOMAIN\n", argv[0]);
+		return 1;
+	}
+
+	int socket = ::socket(AF_UNIX, SOCK_SEQPACKET, 0);
+	if (socket == -1)
+	{
+		perror("socket");
+		return 1;
+	}
+
+	sockaddr_un addr;
+	addr.sun_family = AF_UNIX;
+	strcpy(addr.sun_path, "/tmp/resolver.sock");
+	if (connect(socket, (sockaddr*)&addr, sizeof(addr)) == -1)
+	{
+		perror("connect");
+		return 1;
+	}
+
+	if (send(socket, argv[1], strlen(argv[1]), 0) == -1)
+	{
+		perror("send");
+		return 1;
+	}
+
+	char buffer[128];
+	ssize_t nrecv = recv(socket, buffer, sizeof(buffer), 0);
+	if (nrecv == -1)
+	{
+		perror("recv");
+		return 1;
+	}
+	buffer[nrecv] = '\0';
+
+	printf("%s\n", buffer);
+	return 0;
+}