By popular request reinstate fakeidentd's standalone mode.

Since this is also needed for other applets like telnetd,
introduce generic driver for such things.
It even supports inetd-wait ('linger') mode, when inetd
hands out listen socket to child and waits to it to die,
instead of handing out accepted socket and continuing
listening itself (nowait mode).
Code growth ~200 bytes.
NB: our inetd doesn't support wait mode yet (or mabe it is buggy).

1 files changed, 144 insertions, 0 deletions

diff --git a/networking/isrv_identd.c b/networking/isrv_identd.c
new file mode 100644
index 0000000..b9481f8
--- /dev/null
+++ b/networking/isrv_identd.c
@@ -0,0 +1,144 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Fake identd server.
+ *
+ * Copyright (C) 2007 Denis Vlasenko
+ *
+ * Licensed under GPL version 2, see file LICENSE in this tarball for details.
+ */
+
+#include <syslog.h>
+#include "busybox.h"
+#include "isrv.h"
+
+enum { TIMEOUT = 20 };
+
+/* Why use alarm(TIMEOUT-1)?
+ * isrv's internal select() will run with timeout=TIMEOUT.
+ * If nothing happens during TIMEOUT-1 seconds (no accept/read),
+ * then ALL sessions timed out by now. Instead of closing them one-by-one
+ * (isrv calls do_timeout for each 'stale' session),
+ * SIGALRM triggered by alarm(TIMEOUT-1) will kill us, terminating them all.
+ */
+
+typedef struct identd_buf_t {
+	int pos;
+	int fd_flag;
+	char buf[64 - 2*sizeof(int)];
+} identd_buf_t;
+
+static const char *bogouser = "nobody";
+
+static int new_peer(isrv_state_t *state, int fd)
+{
+	int peer;
+	identd_buf_t *buf = xzalloc(sizeof(*buf));
+
+	alarm(TIMEOUT - 1);
+
+	peer = isrv_register_peer(state, buf);
+	if (peer < 0)
+		return 0; /* failure */
+	if (isrv_register_fd(state, peer, fd) < 0)
+		return peer; /* failure, unregister peer */
+
+	buf->fd_flag = fcntl(fd, F_GETFL, 0) | O_NONBLOCK;
+	isrv_want_rd(state, fd);
+	return 0;
+}
+
+static int do_rd(int fd, void **paramp)
+{
+	identd_buf_t *buf = *paramp;
+	char *cur, *p;
+	int sz;
+
+	alarm(TIMEOUT - 1);
+
+	cur = buf->buf + buf->pos;
+
+	fcntl(fd, F_SETFL, buf->fd_flag | O_NONBLOCK);
+	sz = safe_read(fd, cur, sizeof(buf->buf) - buf->pos);
+
+	if (sz < 0) {
+		if (errno != EAGAIN)
+			goto term; /* terminate this session if !EAGAIN */
+		goto ok;
+	}
+
+	buf->pos += sz;
+	buf->buf[buf->pos] = '\0';
+	p = strpbrk(cur, "\r\n");
+	if (p)
+		*p = '\0';
+	if (p || !sz || buf->pos == sizeof(buf->buf)) {
+		/* fd is still in nonblocking mode - we never block here */
+		fdprintf(fd, "%s : USERID : UNIX : %s\r\n", buf->buf, bogouser);
+		goto term;
+	}
+ ok:
+	fcntl(fd, F_SETFL, buf->fd_flag & ~O_NONBLOCK);
+	return 0;
+ term:
+	fcntl(fd, F_SETFL, buf->fd_flag & ~O_NONBLOCK);
+	free(buf);
+	return 1;
+}
+
+static int do_timeout(void **paramp)
+{
+	return 1; /* terminate session */
+}
+
+static void inetd_mode(void)
+{
+	identd_buf_t *buf = xzalloc(sizeof(*buf));
+	/* We do NOT want nonblocking I/O here! */
+	buf->fd_flag = fcntl(0, F_GETFL, 0);
+	while (do_rd(0, (void*)&buf) == 0) /* repeat */;
+}
+
+int fakeidentd_main(int argc, char **argv)
+{
+	enum {
+		OPT_foreground = 0x1,
+		OPT_inetd      = 0x2,
+		OPT_inetdwait  = 0x4,
+		OPT_nodeamon   = 0x7,
+		OPT_bindaddr   = 0x8,
+	};
+
+	const char *bind_address = NULL;
+	unsigned opt;
+	int fd;
+
+	opt = getopt32(argc, argv, "fiwb:", &bind_address);
+	if (optind < argc)
+		bogouser = argv[optind];
+
+	/* Daemonize if no -f or -i or -w */
+	bb_sanitize_stdio(!(opt & OPT_nodeamon));
+	if (!(opt & OPT_nodeamon)) {
+		openlog(applet_name, 0, LOG_DAEMON);
+		logmode = LOGMODE_SYSLOG;
+	}
+
+	if (opt & OPT_inetd) {
+		inetd_mode();
+		return 0;
+	}
+
+	/* Ignore closed connections when writing */
+	signal(SIGPIPE, SIG_IGN);
+
+	if (opt & OPT_inetdwait) {
+		fd = 0;
+	} else {
+		fd = create_and_bind_stream_or_die(bind_address,
+				bb_lookup_port("identd", "tcp", 113));
+		xlisten(fd, 5);
+	}
+
+	isrv_run(fd, new_peer, do_rd, NULL, do_timeout, TIMEOUT, 1);
+	return 0;
+}