libbb: new option FEATURE_ETC_SERVICES: if off, /etc/services reads often avoided

In practice, "wget http://host.com/" always uses port 80.
People explicitly set non-standard ports via options or parameters
("telnet 1.2.3.4 567" or "telnet 1.2.3.4 ftp") instead of modifying
/etc/services.

function                                             old     new   delta
telnet_main                                         1466    1464      -2
rdate_main                                           215     198     -17
fakeidentd_main                                      269     252     -17
parse_url                                            459     392     -67
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-103)           Total: -103 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 25 insertions, 7 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 646c58bf2..a605c7f03 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -640,6 +640,11 @@ int setsockopt_bindtodevice(int fd, const char *iface) FAST_FUNC;
 int bb_getsockname(int sockfd, void *addr, socklen_t addrlen) FAST_FUNC;
 /* NB: returns port in host byte order */
 unsigned bb_lookup_port(const char *port, const char *protocol, unsigned default_port) FAST_FUNC;
+#if ENABLE_FEATURE_ETC_SERVICES
+# define bb_lookup_std_port(portstr, protocol, portnum) bb_lookup_port(portstr, protocol, portnum)
+#else
+# define bb_lookup_std_port(portstr, protocol, portnum) (portnum)
+#endif
 typedef struct len_and_sockaddr {
         socklen_t len;
         union {
diff --git a/libbb/Config.src b/libbb/Config.src
index fdf8bbb28..16e16480b 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -76,6 +76,18 @@ config FEATURE_ETC_NETWORKS
         a rarely used feature which allows you to use names
         instead of IP/mask pairs in route command.
 
+config FEATURE_ETC_SERVICES
+        bool "Consult /etc/services even for well-known ports"
+        default n
+        help
+        Look up e.g. "telnet" and "http" in /etc/services file
+        instead of assuming ports 23 and 80.
+        This is almost never necessary (everybody uses standard ports),
+        and it makes sense to avoid reading this file.
+        If you disable this option, in the cases where port is explicitly
+        specified as a service name (e.g. "telnet HOST PORTNAME"),
+        it will still be looked up in /etc/services.
+
 config FEATURE_EDITING
         bool "Command line editing"
         default y
diff --git a/networking/isrv_identd.c b/networking/isrv_identd.c
index 133d62a65..0c33dde4f 100644
--- a/networking/isrv_identd.c
+++ b/networking/isrv_identd.c
@@ -159,7 +159,7 @@ int fakeidentd_main(int argc UNUSED_PARAM, char **argv)
         fd = 0;
         if (!(opt & OPT_inetdwait)) {
                 fd = create_and_bind_stream_or_die(bind_address,
-                                bb_lookup_port("identd", "tcp", 113));
+                                bb_lookup_std_port("identd", "tcp", 113));
                 xlisten(fd, 5);
         }
 
diff --git a/networking/telnet.c b/networking/telnet.c
index 15d6a08d8..1e6be85bd 100644
--- a/networking/telnet.c
+++ b/networking/telnet.c
@@ -643,7 +643,8 @@ int telnet_main(int argc UNUSED_PARAM, char **argv)
         if (!*argv)
                 bb_show_usage();
         host = *argv++;
-        port = bb_lookup_port(*argv ? *argv++ : "telnet", "tcp", 23);
+        port = *argv ? bb_lookup_port(*argv++, "tcp", 23)
+                : bb_lookup_std_port("telnet", "tcp", 23);
         if (*argv) /* extra params?? */
                 bb_show_usage();
 
diff --git a/networking/wget.c b/networking/wget.c
index 2650b5384..b6c76e9dc 100644
--- a/networking/wget.c
+++ b/networking/wget.c
@@ -505,23 +505,23 @@ static void parse_url(const char *src_url, struct host_info *h)
                 *p = '\0';
                 h->host = p + 3;
                 if (strcmp(url, P_FTP) == 0) {
-                        h->port = bb_lookup_port(P_FTP, "tcp", 21);
+                        h->port = bb_lookup_std_port(P_FTP, "tcp", 21);
                 } else
 #if SSL_SUPPORTED
 # if ENABLE_FEATURE_WGET_HTTPS
                 if (strcmp(url, P_FTPS) == 0) {
-                        h->port = bb_lookup_port(P_FTPS, "tcp", 990);
+                        h->port = bb_lookup_std_port(P_FTPS, "tcp", 990);
                         h->protocol = P_FTPS;
                 } else
 # endif
                 if (strcmp(url, P_HTTPS) == 0) {
-                        h->port = bb_lookup_port(P_HTTPS, "tcp", 443);
+                        h->port = bb_lookup_std_port(P_HTTPS, "tcp", 443);
                         h->protocol = P_HTTPS;
                 } else
 #endif
                 if (strcmp(url, P_HTTP) == 0) {
  http:
-                        h->port = bb_lookup_port(P_HTTP, "tcp", 80);
+                        h->port = bb_lookup_std_port(P_HTTP, "tcp", 80);
                         h->protocol = P_HTTP;
                 } else {
                         *p = ':';
diff --git a/util-linux/rdate.c b/util-linux/rdate.c
index f27294e25..5ec795208 100644
--- a/util-linux/rdate.c
+++ b/util-linux/rdate.c
@@ -45,7 +45,7 @@ static time_t askremotedate(const char *host)
         alarm(10);
         signal(SIGALRM, socket_timeout);
 
-        fd = create_and_connect_stream_or_die(host, bb_lookup_port("time", "tcp", 37));
+        fd = create_and_connect_stream_or_die(host, bb_lookup_std_port("time", "tcp", 37));
 
         if (safe_read(fd, &nett, 4) != 4)    /* read time from server */
                 bb_error_msg_and_die("%s: %s", host, "short read");