finger

commit faa4cbb0fdae435112893c37c78156e1f65504f3
Author: Naveen Narayanan <zerous@nocebo.space>
Date:   Fri, 24 Sep 2021 21:28:30 +0200

Implement finger client

Diffstat:
A
finger.c
 | 
124
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 124 insertions(+), 0 deletions(-)
diff --git a/finger.c b/finger.c
@@ -0,0 +1,124 @@
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/param.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <errno.h>
+#include <netdb.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define BUFSZ 128
+
+void
+usage(void)
+{
+	printf("usage: finger user@host\n");
+	exit(1);
+}
+
+int
+cred(char *u, char *h, char *s)
+{
+	char *a;
+
+	if (!(a = strchr(s, '@'))) {
+		fprintf(stderr, "hostname not found\n");
+		return 0;
+	}
+
+	if (a - s >= 32) {
+		fprintf(stderr, "username too long\n");
+		return 1;
+	}
+	memcpy(u, s, a - s);
+
+	if (strlen(a+1) > MAXHOSTNAMELEN) {
+		fprintf(stderr, "hostname too long\n");
+		return 0;
+	}
+	strcpy(h, a+1);
+
+	return 1;
+}
+
+int
+main(int argc, char **argv)
+{
+	struct addrinfo hints, *res, *p;
+	char user[32], hostname[MAXHOSTNAMELEN+1];
+	char *msg;
+	int status, sockfd, byt, len, err;
+
+	err = 0;
+
+	if (argc != 2)
+		usage();
+
+	if (!cred(user, hostname, argv[argc-1]))
+		usage();
+
+	memset(&hints, 0, sizeof(hints));
+	hints.ai_family = AF_UNSPEC;
+	hints.ai_socktype = SOCK_STREAM;
+
+	if ((status = getaddrinfo(hostname, "79", &hints, &res)) != 0) {
+		fprintf(stderr, "getaddrinfo failed: %s\n", gai_strerror(status));
+		err = 1;
+		goto err1;
+	}
+
+	for (p = res; p != NULL; p = p->ai_next) {
+		sockfd = socket(res->ai_family, res->ai_socktype,
+				res->ai_protocol);
+		if (sockfd == -1) {
+			fprintf(stderr, "socket failed: %s\n",
+				strerror(errno));
+			err = 1;
+			goto err2;
+		}
+
+		if (connect(sockfd, res->ai_addr, res->ai_addrlen) == -1) {
+			fprintf(stderr, "connect failed: %s\n",
+				strerror(errno));
+			err = 1;
+			goto err3;
+		}
+
+		len = strlen(user);
+		msg = malloc(BUFSZ);
+		if (!msg) {
+			err = 1;
+			goto err3;
+		}
+		memset(msg, 0, BUFSZ);
+		memcpy(msg, user, len);
+		msg[len] = '\r';
+		msg[len+1] = '\n';
+
+		byt = send(sockfd, msg, len+2, 0);
+		if (byt == -1) {
+			fprintf(stderr, "send failed: %s\n", strerror(errno));
+			err = 1;
+			goto err4;
+		}
+
+		do {
+			byt = recv(sockfd, msg, BUFSZ, 0);
+			for (int i = 0; i < byt; ++i)
+				putchar(msg[i]);
+		} while (byt > 0);
+	}
+
+err4:
+	free(msg);
+err3:
+	close(sockfd);
+err2:
+	freeaddrinfo(res);
+err1:
+	return err == 1 ? 2 : 0;
+}