fakeinetd: attempted ipv6-ization (and it's done)

but entire applet can be orders of magnitude smaller
if written as an inetd service.
So did that (#ifdef'ed out entire old version).
inetd version is less than 10% of old one!
function                                             old     new   delta
packed_usage                                       22083   22105     +22
nobodystr                                              4       -      -4
bind_ip_address                                        4       -      -4
ident_substr                                          20       -     -20
chmatch                                               22       -     -22
movefd                                                25       -     -25
skipchars                                             49       -     -49
handlexitsigs                                         51       -     -51
replyError                                            70       -     -70
.rodata                                           158120  158024     -96
deleteConn                                           102       -    -102
G                                                    524     388    -136
conns                                                560       -    -560
fakeidentd_main                                     1457     143   -1314
------------------------------------------------------------------------------
(add/remove: 0/10 grow/shrink: 1/3 up/down: 22/-2453)       Total: -2431 bytes

3 files changed, 214 insertions, 190 deletions

diff --git a/include/usage.h b/include/usage.h
index 14650e5..4e52065 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -826,6 +826,7 @@
        "\\( and \\) or null; if \\( and \\) are not used, they return the number\n" \
        "of characters matched or 0."
 
+#if 0 /* bloaty */
 #define fakeidentd_trivial_usage \
        "[-b ip] [STRING]"
 #define fakeidentd_full_usage \
@@ -833,6 +834,14 @@
        "\n\nOptions:\n" \
        "	-b	Bind to ip address\n" \
        "	STRING	The ident answer string (default is nobody)"
+#else /* inetd-only */
+#define fakeidentd_trivial_usage \
+       "[username]"
+#define fakeidentd_full_usage \
+       "Return a (faked) ident response.\n" \
+       "This applet is meant to run from inetd.\n" \
+       "Optional argument is the username to return (default is 'nobody')."
+#endif
 
 #define false_trivial_usage \
        ""
diff --git a/networking/fakeidentd.c b/networking/fakeidentd.c
index 7eac480..8c07082 100644
--- a/networking/fakeidentd.c
+++ b/networking/fakeidentd.c
@@ -9,12 +9,62 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
 
+/* Ident crash course
+ *
+ * Incoming requests are of form "6191, 23\r\n" - peer asks us
+ * "which user connected from your port 6191 to my port 23?"
+ * We should answer:
+ * "6193, 23 : USERID : UNIX : username\r\n"
+ * and close the connection.
+ * We can also reply:
+ * "6195, 23 : USERID : OTHER[,US-ASCII] : username\r\n"
+ * "6195, 23 : ERROR : INVALID-PORT/NO-USER/HIDDEN-USER/UNKNOWN-ERROR\r\n"
+ * but we probably will never want that.
+ */
+
 #include "busybox.h"
+
+#define SANE_INETD_ONLY_VERSION
+
+#ifdef SANE_INETD_ONLY_VERSION
+
+int fakeidentd_main(int argc, char **argv)
+{
+	char buf[64];
+	const char *bogouser = "nobody";
+	char *cur = buf;
+	int rem = sizeof(buf)-1;
+
+	if (argv[1])
+		bogouser = argv[1];
+
+	alarm(30);
+	while (1) {
+		char *p;
+		int sz = safe_read(0, cur, rem);
+		if (sz < 0) return 1;
+		cur[sz] = '\0';
+		p = strpbrk(cur, "\r\n");
+		if (p) {
+			*p = '\0';
+			break;
+		}
+		cur += sz;
+		rem -= sz;
+		if (!rem || !sz)
+			break;
+	}
+	printf("%s : USERID : UNIX : %s\r\n", buf, bogouser);
+	return 0;
+}
+
+#else
+
+/* Welcome to the bloaty horrors */
+
 #include <sys/syslog.h>
 #include <sys/uio.h>
 
-
-#define IDENT_PORT  113
 #define MAXCONNS    20
 #define MAXIDLETIME 45
 
@@ -43,9 +93,9 @@ enum { ident_substr_len = sizeof(ident_substr) - 1 };
  * in `conns' array + FCS
  */
 static struct {
-	char buf[20];
-	int len;
 	time_t lasttime;
+	int len;
+	char buf[20];
 } conns[MAXCONNS];
 
 /* When using global variables, bind those at least to a structure. */
@@ -55,111 +105,92 @@ static struct {
 	int conncnt;
 } G;
 
-/*
- * Prototypes
- */
-static void reply(int s, char *buf);
-static void replyError(int s, char *buf);
+static char *bind_ip_address;
 
-static const char *nobodystr = "nobody"; /* this needs to be declared like this */
-static char *bind_ip_address = "0.0.0.0";
+static int chmatch(char c, char *chars)
+{
+	for (; *chars; chars++)
+		if (c == *chars)
+			return 1;
+	return 0;
+}
 
-static void movefd(int from, int to)
+static int skipchars(char **p, char *chars)
 {
-	if (from != to) {
-		dup2(from, to);
-		close(from);
-	}
+	while (chmatch(**p, chars))
+		(*p)++;
+	if (**p == '\r' || **p == '\n')
+		return 0;
+	return 1;
 }
 
-static void inetbind(void)
+static int parseAddrs(char *ptr, char **myaddr, char **heraddr)
 {
-	int s, port;
-	struct sockaddr_in addr;
-	int len = sizeof(addr);
-	struct servent *se;
+	/* parse <port-on-server> , <port-on-client> */
 
-	se = getservbyname("identd", "tcp");
-	port = IDENT_PORT;
-	if (se)
-		port = se->s_port;
+	if (!skipchars(&ptr, " \t"))
+		return -1;
 
-	s = xsocket(AF_INET, SOCK_STREAM, 0);
+	*myaddr = ptr;
 
-	setsockopt_reuseaddr(s);
+	if (!skipchars(&ptr, "1234567890"))
+		return -1;
 
-	memset(&addr, 0, sizeof(addr));
-	addr.sin_addr.s_addr = inet_addr(bind_ip_address);
-	addr.sin_family = AF_INET;
-	addr.sin_port = htons(port);
+	if (!chmatch(*ptr, " \t,"))
+		return -1;
 
-	xbind(s, (struct sockaddr *)&addr, len);
-	xlisten(s, 5);
+	*ptr++ = '\0';
 
-	movefd(s, 0);
-}
+	if (!skipchars(&ptr, " \t,") )
+		return -1;
 
-static void handlexitsigs(int signum)
-{
-	if (unlink(PIDFILE) < 0)
-		close(open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0644));
-	exit(0);
-}
+	*heraddr = ptr;
 
-/* May succeed. If not, won't care. */
-static void writepid(uid_t nobody, uid_t nogrp)
-{
-	char buf[sizeof(int)*3 + 2];
-	int fd = open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0664);
+	skipchars(&ptr, "1234567890");
 
-	if (fd < 0)
-		return;
+	if (!chmatch(*ptr, " \n\r"))
+		return -1;
 
-	sprintf(buf, "%d\n", getpid());
-	write(fd, buf, strlen(buf));
-	fchown(fd, nobody, nogrp);
-	close(fd);
+	*ptr = '\0';
 
-	/* should this handle ILL, ... (see signal(7)) */
-	signal(SIGTERM, handlexitsigs);
-	signal(SIGINT,  handlexitsigs);
-	signal(SIGQUIT, handlexitsigs);
+	return 0;
 }
 
-/* return 0 as parent, 1 as child */
-static int godaemon(void)
+static void replyError(int s, char *buf)
 {
-	uid_t nobody, nogrp;
-	struct passwd *pw;
-
-	switch (fork()) {
-	case -1:
-		bb_perror_msg_and_die("fork");
-
-	case 0:
-		pw = getpwnam(nobodystr);
-		if (pw == NULL)
-			bb_error_msg_and_die("cannot find uid/gid of user '%s'", nobodystr);
-		nobody = pw->pw_uid;
-		nogrp = pw->pw_gid;
-		writepid(nobody, nogrp);
-
-		close(0);
-		inetbind();
-		xsetgid(nogrp);
-		xsetuid(nobody);
-		close(1);
-		close(2);
+	struct iovec iv[3];
+	iv[0].iov_base = "0, 0 : ERROR : ";   iv[0].iov_len = 15;
+	iv[1].iov_base = buf;                 iv[1].iov_len = strlen(buf);
+	iv[2].iov_base = "\r\n";              iv[2].iov_len = 2;
+	writev(s, iv, 3);
+}
 
-		signal(SIGHUP, SIG_IGN);
-		signal(SIGPIPE, SIG_IGN); /* connection closed when writing (raises ???) */
+static void reply(int s, char *buf)
+{
+	char *myaddr, *heraddr;
 
-		setsid();
+	myaddr = heraddr = NULL;
 
-		return 1;
+	if (parseAddrs(buf, &myaddr, &heraddr))
+		replyError(s, "X-INVALID-REQUEST");
+	else {
+		struct iovec iv[6];
+		iv[0].iov_base = myaddr;               iv[0].iov_len = strlen(myaddr);
+		iv[1].iov_base = ", ";                 iv[1].iov_len = 2;
+		iv[2].iov_base = heraddr;              iv[2].iov_len = strlen(heraddr);
+		iv[3].iov_base = (void *)ident_substr; iv[3].iov_len = ident_substr_len;
+		iv[4].iov_base = (void *)G.identuser;  iv[4].iov_len = strlen(G.identuser);
+		iv[5].iov_base = "\r\n";               iv[5].iov_len = 2;
+		writev(s, iv, 6);
 	}
+}
 
-	return 0;
+static void movefd(int from, int to)
+{
+	if (from != to) {
+		dup2(from, to);
+		close(from);
+	}
 }
 
 static void deleteConn(int s)
@@ -215,15 +246,32 @@ static int checkInput(char *buf, int len, int l)
 	return 0;
 }
 
+/* May succeed. If not, won't care. */
+static const char *to_unlink;
+static void writepid(void)
+{
+	int fd = open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0664);
+	if (fd < 0)
+		return;
+	to_unlink = PIDFILE;
+	fdprintf(fd, "%d\n", getpid());
+	close(fd);
+}
+
+static void handlexitsigs(int signum)
+{
+	if (to_unlink)
+		if (unlink(to_unlink) < 0)
+			close(open(to_unlink, O_WRONLY|O_CREAT|O_TRUNC, 0644));
+	exit(0);
+}
+
 int fakeidentd_main(int argc, char **argv)
 {
-	/* This applet is an inetd-style daemon */
-	openlog(applet_name, 0, LOG_DAEMON);
-	logmode = LOGMODE_SYSLOG;
+	int fd;
+	pid_t pid;
 
-	memset(conns, 0, sizeof(conns));
-	memset(&G, 0, sizeof(G));
-	FD_ZERO(&G.readfds);
+	/* FD_ZERO(&G.readfds); - in bss, already zeroed */
 	FD_SET(0, &G.readfds);
 
 	/* handle -b <ip> parameter */
@@ -232,11 +280,30 @@ int fakeidentd_main(int argc, char **argv)
 	if (optind < argc)
 		G.identuser = argv[optind];
 	else
-		G.identuser = nobodystr;
+		G.identuser = "nobody";
 
-	/* daemonize and have the parent return */
-	if (godaemon() == 0)
-		return 0;
+	writepid();
+	signal(SIGTERM, handlexitsigs);
+	signal(SIGINT,  handlexitsigs);
+	signal(SIGQUIT, handlexitsigs);
+	signal(SIGHUP, SIG_IGN);
+	signal(SIGPIPE, SIG_IGN); /* ignore closed connections when writing */
+
+	fd = create_and_bind_stream_or_die(bind_ip_address, bb_lookup_port("identd", "tcp", 113));
+	xlisten(fd, 5);
+
+	pid = fork();
+	if (pid < 0)
+		bb_perror_msg_and_die("fork");
+	if (pid != 0) /* parent */
+		exit(0);
+	/* child */
+	setsid();
+	movefd(fd, 0);
+	while (fd)
+		close(fd--);
+	openlog(applet_name, 0, LOG_DAEMON);
+	logmode = LOGMODE_SYSLOG;
 
 	/* main loop where we process all events and never exit */
 	while (1) {
@@ -252,10 +319,11 @@ int fakeidentd_main(int argc, char **argv)
 
 			if (FD_ISSET(s, &rfds)) {
 				char *buf = conns[i].buf;
-				unsigned int len = conns[i].len;
-				unsigned int l;
+				unsigned len = conns[i].len;
+				unsigned l;
 
-				if ((l = read(s, buf + len, sizeof(conns[0].buf) - len)) > 0) {
+				l = read(s, buf + len, sizeof(conns[0].buf) - len);
+				if (l > 0) {
 					if (checkInput(buf, len, l)) {
 						reply(s, buf);
 						goto deleteconn;
@@ -268,10 +336,8 @@ int fakeidentd_main(int argc, char **argv)
 				} else {
 					goto deleteconn;
 				}
-
 				conns[i].lasttime = tim;
 				continue;
-
 deleteconn:
 				deleteConn(s);
 			} else {
@@ -287,7 +353,7 @@ deleteconn:
 			int s = accept(0, NULL, 0);
 
 			if (s < 0) {
-				if (errno != EINTR) /* EINTR */
+				if (errno != EINTR)
 					bb_perror_msg("accept");
 			} else {
 				if (G.conncnt == MAXCONNS)
@@ -297,7 +363,6 @@ deleteconn:
 
 				movefd(s, i + FCS); /* move if not already there */
 				FD_SET(i + FCS, &G.readfds);
-
 				conns[i].len = 0;
 				conns[i].lasttime = time(NULL);
 			}
@@ -307,81 +372,4 @@ deleteconn:
 	return 0;
 }
 
-static int parseAddrs(char *ptr, char **myaddr, char **heraddr);
-static void reply(int s, char *buf)
-{
-	char *myaddr, *heraddr;
-
-	myaddr = heraddr = NULL;
-
-	if (parseAddrs(buf, &myaddr, &heraddr))
-		replyError(s, "X-INVALID-REQUEST");
-	else {
-		struct iovec iv[6];
-		iv[0].iov_base = myaddr;               iv[0].iov_len = strlen(myaddr);
-		iv[1].iov_base = ", ";                 iv[1].iov_len = 2;
-		iv[2].iov_base = heraddr;              iv[2].iov_len = strlen(heraddr);
-		iv[3].iov_base = (void *)ident_substr; iv[3].iov_len = ident_substr_len;
-		iv[4].iov_base = (void *)G.identuser;  iv[4].iov_len = strlen(G.identuser);
-		iv[5].iov_base = "\r\n";               iv[5].iov_len = 2;
-		writev(s, iv, 6);
-	}
-}
-
-static void replyError(int s, char *buf)
-{
-	struct iovec iv[3];
-	iv[0].iov_base = "0, 0 : ERROR : ";   iv[0].iov_len = 15;
-	iv[1].iov_base = buf;                 iv[1].iov_len = strlen(buf);
-	iv[2].iov_base = "\r\n";              iv[2].iov_len = 2;
-	writev(s, iv, 3);
-}
-
-static int chmatch(char c, char *chars)
-{
-	for (; *chars; chars++)
-		if (c == *chars)
-			return 1;
-	return 0;
-}
-
-static int skipchars(char **p, char *chars)
-{
-	while (chmatch(**p, chars))
-		(*p)++;
-	if (**p == '\r' || **p == '\n')
-		return 0;
-	return 1;
-}
-
-static int parseAddrs(char *ptr, char **myaddr, char **heraddr)
-{
-	/* parse <port-on-server> , <port-on-client> */
-
-	if (!skipchars(&ptr, " \t"))
-		return -1;
-
-	*myaddr = ptr;
-
-	if (!skipchars(&ptr, "1234567890"))
-		return -1;
-
-	if (!chmatch(*ptr, " \t,"))
-		return -1;
-
-	*ptr++ = '\0';
-
-	if (!skipchars(&ptr, " \t,") )
-		return -1;
-
-	*heraddr = ptr;
-
-	skipchars(&ptr, "1234567890");
-
-	if (!chmatch(*ptr, " \n\r"))
-		return -1;
-
-	*ptr = '\0';
-
-	return 0;
-}
+#endif /* !SANE_INETD_ONLY_VERSION */
diff --git a/networking/inetd.c b/networking/inetd.c
index 75665ba..93c16bf 100644
--- a/networking/inetd.c
+++ b/networking/inetd.c
@@ -23,7 +23,7 @@
  *    may be used to endorse or promote products derived from this software
  *    without specific prior written permission.
  *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS "AS IS" AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
@@ -36,8 +36,7 @@
  * SUCH DAMAGE.
  */
 
-/*
- * Inetd - Internet super-server
+/* Inetd - Internet super-server
  *
  * This program invokes all internet services as needed.
  * connection-oriented services are invoked each time a
@@ -50,14 +49,14 @@
  * arrives; a process is created and passed a pending message
  * on file descriptor 0.  Datagram servers may either connect
  * to their peer, freeing up the original socket for inetd
- * to receive further messages on, or ``take over the socket'',
+ * to receive further messages on, or "take over the socket",
  * processing all arriving datagrams and, eventually, timing
- * out.  The first type of server is said to be ``multi-threaded'';
- * the second type of server ``single-threaded''.
+ * out.  The first type of server is said to be "multi-threaded";
+ * the second type of server "single-threaded".
  *
  * Inetd uses a configuration file which is read at startup
  * and, possibly, at some later time in response to a hangup signal.
- * The configuration file is ``free format'' with fields given in the
+ * The configuration file is "free format" with fields given in the
  * order shown below.  Continuation lines for an entry must begin with
  * a space or tab.  All fields must be present in each entry.
  *
@@ -105,8 +104,37 @@
  * Comment lines are indicated by a `#' in column 1.
  */
 
-/*
- * Here's the scoop concerning the user[.:]group feature:
+/* inetd rules for passing file descriptors to children
+ * (http://www.freebsd.org/cgi/man.cgi?query=inetd):
+ *
+ * The wait/nowait entry specifies whether the server that is invoked by
+ * inetd will take over the socket associated with the service access point,
+ * and thus whether inetd should wait for the server to exit before listen-
+ * ing for new service requests.  Datagram servers must use "wait", as
+ * they are always invoked with the original datagram socket bound to the
+ * specified service address.  These servers must read at least one datagram
+ * from the socket before exiting.  If a datagram server connects to its
+ * peer, freeing the socket so inetd can receive further messages on the
+ * socket, it is said to be a "multi-threaded" server; it should read one
+ * datagram from the socket and create a new socket connected to the peer.
+ * It should fork, and the parent should then exit to allow inetd to check
+ * for new service requests to spawn new servers.  Datagram servers which
+ * process all incoming datagrams on a socket and eventually time out are
+ * said to be "single-threaded".  The comsat(8), (biff(1)) and talkd(8)
+ * utilities are both examples of the latter type of datagram server.  The
+ * tftpd(8) utility is an example of a multi-threaded datagram server.
+ *
+ * Servers using stream sockets generally are multi-threaded and use the
+ * "nowait" entry. Connection requests for these services are accepted by
+ * inetd, and the server is given only the newly-accepted socket connected
+ * to a client of the service.  Most stream-based services operate in this
+ * manner.  Stream-based servers that use "wait" are started with the lis-
+ * tening service socket, and must accept at least one connection request
+ * before exiting.  Such a server would normally accept and process incoming
+ * connection requests until a timeout.
+ */
+
+/* Here's the scoop concerning the user[.:]group feature:
  *
  * 1) set-group-option off.
  *
@@ -125,7 +153,6 @@
  *      b) other:       setgid(specified group)
  *                      initgroups(name, specified group)
  *                      setuid()
- *
  */
 
 #include "busybox.h"
@@ -161,7 +188,7 @@
 #endif
 
 /* Reserve some descriptors, 3 stdio + at least: 1 log, 1 conf. file */
-#define FD_MARGIN       (8)
+#define FD_MARGIN       8
 static rlim_t rlim_ofile_cur = OPEN_MAX;
 static struct rlimit rlim_ofile;