From 4f937f540734e6f5977b9c279f8f24035a259310 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sat, 15 Apr 2017 18:40:07 +0100
Subject: [PATCH] ipif: Introduce eat_optionalstr (and make protocol optional)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 ipif/service.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/ipif/service.c b/ipif/service.c
index df03926..b401a5c 100644
--- a/ipif/service.c
+++ b/ipif/service.c
@@ -30,7 +30,7 @@
  *
  *  The remaining arguments are supplied by the (untrusted) caller:
  *
- *  <local-addr>,<peer-addr>,<mtu>,<proto>
+ *  <local-addr>,<peer-addr>,<mtu>[,[<proto>]]
  *
  *      As for slattach.  The only supported protocol is slip.
  *      Alternatively, set to `debug' to print debugging info and
@@ -125,6 +125,7 @@
 #include <unistd.h>
 #include <stdint.h>
 #include <poll.h>
+#include <stddef.h>
 
 #include <sys/types.h>
 #include <sys/wait.h>
@@ -323,6 +324,30 @@ static void eat_prefixmask(const char **argp, const char *what,
   if (len_r) *len_r= len;
 }
 
+static char *eat_optionalstr(const char **argp,
+			     const char *what,
+			     const char *def) {
+  ptrdiff_t len;
+  const char *start= *argp;
+  const char *comma= strchr(start, ',');
+  if (comma) {
+    len= comma - start;
+    *argp= comma + 1;
+  } else {
+    len= strlen(start);
+    *argp= start + len;
+  }
+  if (!len) {
+    start= def;
+    len= strlen(def);
+  }
+  char *r = malloc(len+1);
+  if (!r) sysfatal("malloc for command line string");
+  memcpy(r,start,len);
+  r[len]= 0;
+  return r;
+}
+
 static int addrnet_isin(unsigned long prefix, unsigned long mask,
 			unsigned long mprefix, unsigned long mmask) {
   return  !(~mask & mmask)  &&  (prefix & mmask) == mprefix;
@@ -545,12 +570,13 @@ static void parseargs(int argc, const char *const *argv) {
   peeraddr= eat_addr(&carg,"peer-addr", ",",0);
   mtu= eat_number(&carg,"mtu", 576,65536, ",",0);
   localallow= peerallow= 0;
-  
-  if (!strcmp(carg,"debug")) {
+
+  char *protostr = eat_optionalstr(&carg,"protocol","slip");
+  if (!strcmp(protostr,"debug")) {
     proto= 0;
   } else {
     for (cprotop= protos_ok;
-	 (proto= *cprotop) && strcmp(proto,carg);
+	 (proto= *cprotop) && strcmp(proto,protostr);
 	 cprotop++);
     if (!proto) fatal("invalid protocol");
   }
-- 
2.30.2