make hello.c a server that echos things

flake.nix

@@ -12,10 +12,8 @@
 
   outputs = { self, nixpkgs, flake-utils }:
     let
-      lastModifiedDate = self.lastModifiedDate or self.lastModified or "19700101";
-
-      # Generate a user-friendly version number (e.g. "1.2.3-20231027-DIRTY").
-      version = "${builtins.readFile ./VERSION.txt}.${builtins.substring 0 8 (self.lastModifiedDate or "19700101")}.${self.shortRev or "DIRTY"}";
+      # Generate a user-friendly version number (e.g. "1.2.3-DIRTY").
+      version = "${builtins.readFile ./VERSION.txt}${self.shortRev or "DIRTY"}";
 
       # System types to support.
       supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
@@ -50,7 +48,7 @@
           packages.container = pkgs.callPackage ./container.nix { package = packages.default; };
           apps.hello = flake-utils.lib.mkApp { drv = packages.default; };
           defaultApp = apps.hello;
-#          devShells.default = import ./shell.nix { inherit pkgs; };
+          devShells.default = import ./shell.nix { inherit pkgs; };
         }
       );
 }

hello.c

@@ -1,6 +1,69 @@
-#include "stdio.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
 
-int main(int argc, char **argv)
-{
-    printf("Hello, world!\n");
+int echo() {
+  int listen_socket, client_socket;
+  struct sockaddr_in listen_addr, client_addr;
+  socklen_t client_addr_len;
+  char buffer[1024];
+  int bytes_received;
+
+  // Create a socket
+  listen_socket = socket(AF_INET, SOCK_STREAM, 0);
+  if (listen_socket < 0) {
+    perror("socket");
+    exit(1);
+  }
+
+  // Bind the socket to port 5001
+  listen_addr.sin_family = AF_INET;
+  listen_addr.sin_port = htons(5001);
+  listen_addr.sin_addr.s_addr = INADDR_ANY;
+  if (bind(listen_socket, (struct sockaddr *)&listen_addr, sizeof(listen_addr)) < 0) {
+    perror("bind");
+    exit(1);
+  }
+
+  // Listen for connections
+  listen(listen_socket, 5);
+
+  // Accept a connection
+  client_addr_len = sizeof(client_addr);
+  client_socket = accept(listen_socket, (struct sockaddr *)&client_addr, &client_addr_len);
+  if (client_socket < 0) {
+    perror("accept");
+    exit(1);
+  }
+
+  // Echo the data back to the client
+  while (1) {
+    bytes_received = recv(client_socket, buffer, sizeof(buffer), 0);
+    if (bytes_received < 0) {
+      perror("recv");
+      exit(1);
+    }
+
+    if (bytes_received == 0) {
+      // The client has closed the connection
+      break;
+    }
+
+    send(client_socket, buffer, bytes_received, 0);
+  }
+
+  // Close the sockets
+  close(listen_socket);
+  close(client_socket);
+
+  return 0;
+}
+
+int main() {
+  while (1) {
+    echo();
+  }
+  return 0;
 }