make it so.

.gitignore

@@ -0,0 +1 @@
+bin/

Makefile

@@ -0,0 +1,15 @@
+TARGET=867
+BUILDDIR=bin/
+PREFIX=/usr/local/bin/
+MAIN=main.c
+override CFLAGS+=-Werror -Wall -g -fPIC -O2 -DNDEBUG -ftrapv -Wfloat-equal -Wundef -Wwrite-strings -Wuninitialized -pedantic -std=gnu11
+
+all: main.c
+	mkdir -p $(BUILDDIR)
+	$(CC) $(MAIN) -o $(BUILDDIR)$(TARGET) $(CFLAGS)
+
+install: all
+	install $(BUILDDIR)$(TARGET) $(PREFIX)$(TARGET)
+
+uninstall:
+	rm -rf $(PREFIX)$(TARGET)

README.md

@@ -0,0 +1,4 @@
+# 867
+
+An implementation of [RFC 867](https://tools.ietf.org/html/rfc867), the “time
+of the day” service, for the heck of it.

main.c

@@ -0,0 +1,63 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <time.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+
+void die(const char *msg) {
+    perror(msg);
+    exit(1);
+}
+
+char* get_tod() {
+    time_t t = time(NULL);
+    struct tm *tm = localtime(&t);
+    char* res = malloc(64);
+
+    int len = strftime(res, 64, "%c\n", tm);
+
+    res[len] = '\0';
+
+    return res;
+}
+
+int main(int argc, char *argv[]) {
+  int sockfd;
+  int newsockfd;
+  int port = 13;
+  socklen_t clilen;
+  struct sockaddr_in serv_addr, cli_addr;
+  int n;
+  char* tod;
+
+  sockfd = socket(AF_INET, SOCK_STREAM, 0);
+  if (sockfd < 0) die("error opening socket.");
+
+  bzero((char *) &serv_addr, sizeof(serv_addr));
+  serv_addr.sin_family = AF_INET;
+  serv_addr.sin_addr.s_addr = INADDR_ANY;
+  serv_addr.sin_port = htons(port);
+  if (bind(sockfd, (struct sockaddr *) &serv_addr,
+     sizeof(serv_addr)) < 0) die("error binding socket.");
+
+  clilen = sizeof(cli_addr);
+
+  while (1) {
+    listen(sockfd, 5);
+
+    newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr, &clilen);
+    if (newsockfd < 0) die("error accepting");
+
+    tod = get_tod();
+    n = write(newsockfd, tod, 64);
+    if (n < 0) die("error writing to socket");
+    free(tod);
+    close(newsockfd);
+  }
+
+  close(sockfd);
+  return 0;
+}