Use a short timeout, rather than immediate mode, for text output.

That means that we do some buffering of packets.  It also means we don't
depend on the immediate-mode APIs being available.

While we're at it, use the short timeout if we're doing text output in
"line-buffered mode" as well as if we're doing it to a terminal.

diff --git a/tcpdump.c b/tcpdump.c
index dfa340b6113777cdbd99810c4f2527df7f2de223..64aad1603d2a2cc771eb8ec3d77f5a5549375de9 100644 (file)
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -203,6 +203,7 @@ static int Iflag;                   /* rfmon (monitor) mode */
 static int Jflag;                      /* list available time stamp types */
 static int jflag = -1;                 /* packet time stamp source */
 #endif
+static int lflag;                      /* line-buffered output */
 static int pflag;                      /* don't go promiscuous */
 #ifdef HAVE_PCAP_SETDIRECTION
 static int Qflag = -1;                 /* restrict captured packet by send/receive direction */
@@ -213,6 +214,7 @@ static int Uflag;                   /* "unbuffered" output of dump files */
 static int Wflag;                      /* recycle output files after this number of files */
 static int WflagChars;
 static char *zflag = NULL;             /* compress each savefile using a specified command (like gzip or bzip2) */
+static int timeout = 1000;             /* default timeout = 1000 ms = 1 s */
 #ifdef HAVE_PCAP_SET_IMMEDIATE_MODE
 static int immediate_mode;
 #endif
@@ -1229,7 +1231,7 @@ open_interface(const char *device, netdissect_options *ndo, char *ebuf)
                 */
                *ebuf = '\0';
                pc = pcap_open(device, ndo->ndo_snaplen,
-                   pflag ? 0 : PCAP_OPENFLAG_PROMISCUOUS, 1000, NULL,
+                   pflag ? 0 : PCAP_OPENFLAG_PROMISCUOUS, timeout, NULL,
                    ebuf);
                if (pc == NULL) {
                        /*
@@ -1311,7 +1313,7 @@ open_interface(const char *device, netdissect_options *ndo, char *ebuf)
                        error("%s: Can't set monitor mode: %s",
                            device, pcap_statustostr(status));
        }
-       status = pcap_set_timeout(pc, 1000);
+       status = pcap_set_timeout(pc, timeout);
        if (status != 0)
                error("%s: pcap_set_timeout failed: %s",
                    device, pcap_statustostr(status));
@@ -1411,7 +1413,7 @@ open_interface(const char *device, netdissect_options *ndo, char *ebuf)
         */
        if (ndo->ndo_snaplen == 0)
                ndo->ndo_snaplen = MAXIMUM_SNAPLEN;
-       pc = pcap_open_live(device, ndo->ndo_snaplen, !pflag, 1000, ebuf);
+       pc = pcap_open_live(device, ndo->ndo_snaplen, !pflag, timeout, ebuf);
        if (pc == NULL) {
                /*
                 * If this failed with "No such device", that means
@@ -1668,6 +1670,7 @@ main(int argc, char **argv)
                        setvbuf(stdout, NULL, _IOLBF, 0);
 #endif
 #endif /* _WIN32 */
+                       lflag = 1;
                        break;
 
                case 'K':
@@ -1924,19 +1927,18 @@ main(int argc, char **argv)
        if (VFileName != NULL && RFileName != NULL)
                error("-V and -r are mutually exclusive.");
 
-#ifdef HAVE_PCAP_SET_IMMEDIATE_MODE
        /*
-        * If we're printing dissected packets to the standard output
-        * and the standard output is a terminal, use immediate mode,
-        * as the user's probably expecting to see packets pop up
-        * immediately.
+        * If we're printing dissected packets to the standard output,
+        * and either the standard output is a terminal or we're doing
+        * "line" buffering, set the capture timeout to .1 second rather
+        * than 1 second, as the user's probably expecting to see packets
+        * pop up immediately shortly after they arrive.
         *
-        * XXX - set the timeout to a lower value, instead?  If so,
-        * what value would be appropriate?
+        * XXX - would there be some value appropriate for all cases,
+        * based on, say, the buffer size and packet input rate?
         */
-       if ((WFileName == NULL || print) && isatty(1))
-               immediate_mode = 1;
-#endif
+       if ((WFileName == NULL || print) && (isatty(1) || lflag))
+               timeout = 100;
 
 #ifdef WITH_CHROOT
        /* if run as root, prepare for chrooting */