initial

build.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+CC=${CC:-cc}
+CFLAGS="-Wall -Wextra -std=c99 -pedantic -lm -g"
+
+$CC $CFLAGS serve.c -o serve

ex-server.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+printf "what's your name? "
+read name
+echo "hello $name!"

readme.txt

@@ -0,0 +1,10 @@
+# serve
+
+`serve` is a super simple server. It takes as input a port to run the server on,
+and the path to a program. The program's stdin and stdout will work on the
+client which is connected to it.
+
+An example server is found in `ex-server.sh` and can be tried out with
+`serve 1234 ./ex-server.sh`.
+
+You can connect to the server with `nc -vn 127.0.0.1 1234`.

serve.c

@@ -0,0 +1,79 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include <errno.h>
+
+void
+die(const char *s, ...)
+{
+    va_list argp;
+    va_start(argp, s);
+    vfprintf(stderr, s, argp);
+    fputc('\n', stderr);
+    va_end(argp);
+    exit(1);
+}
+
+int
+main(int argc, char *argv[], char *envp[])
+{
+    if (argc < 3)
+        die("usage: serve port program args ...");
+
+    short port = atoi(argv[1]);
+    if (port == 0) {
+        die("invalid port number");
+    }
+
+    /* now skip the two first args so that we can pass argv to execve later */
+    argv += 2;
+
+    int sfd = socket(AF_INET, SOCK_STREAM, 0);
+    struct sockaddr_in server, client;
+
+    if (sfd < 0)
+        die("error encountered while initializing socket");
+    if (setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &(int){1}, sizeof(int)) < 0)
+        die("setsockopt(SO_REUSEADDR) failed");
+
+    server.sin_family = AF_INET;
+    server.sin_addr.s_addr = INADDR_ANY;
+    server.sin_port = htons(port);
+
+    /* assigning an address to the socket */
+    if (bind(sfd, (struct sockaddr *)&server, sizeof(server)) < 0) {
+        perror("bind");
+        exit(1);
+    }
+
+    /* start accepting connections */
+    if (listen(sfd, 10) < 0)
+        die("error encountered while trying to listen for connections");
+
+    /* handling connections */
+    for (;;) {
+        socklen_t client_len = sizeof(client);
+        int cfd = accept(sfd, (struct sockaddr *)&client, &client_len);
+        if (cfd < 0)
+            die("error encountered while accepting connection");
+
+        /* start new process and change stdout/stdin so that the process can
+         * read/write to the client */
+        pid_t p = fork();
+
+        if (!p) {
+            /* in the new process */
+            dup2(cfd, STDIN_FILENO);
+            dup2(cfd, STDOUT_FILENO);
+
+            int err = execve(argv[0], argv, envp);
+            die("execve() error: %d\n", err);
+        }
+        else {
+            /* in the old process */
+            close(cfd);
+        }
+    }
+}