Implement ICP per RFC 165.

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{matrix.os}}
     strategy:
       matrix:
-        os: [ubuntu-18.04, ubuntu-20.04, macos-10.15]
+        os: [ubuntu-22.04, ubuntu-24.04, macos-14, macos-15]
     steps:
       - uses: actions/checkout@v2
       - name: Install dependencies

.gitignore

@@ -5,4 +5,5 @@ src/libncp.a
 src/ping
 src/finger
 src/finser
+src/telnet
 test/*.log

src/Makefile

@@ -2,7 +2,7 @@ CFLAGS=-g -Wall
 
 NCP=-L. -lncp
 
-all: ncp ping finger finser
+all: ncp ping finger finser telnet
 
 ncp: ncp.o imp.o
 
@@ -18,3 +18,6 @@ finger: finger.o libncp.a
 
 finser: finser.o libncp.a
 	$(CC) -o $@ $< $(NCP)
+
+telnet: telnet.o libncp.a
+	$(CC) -o $@ $< $(NCP)

src/imp.c

@@ -81,11 +81,16 @@ static void args (int argc, char **argv)
 static void make_socket (void)
 {
   struct sockaddr_in source;
+  int enable = 1;
 
   imp_sock = socket (AF_INET, SOCK_DGRAM, 0);
   if (imp_sock == -1)
     fatal ("socket");
 
+  if (setsockopt(imp_sock, SOL_SOCKET, SO_REUSEADDR,
+                 &enable, sizeof enable) != 0)
+    fatal ("setsockopt(SO_REUSEADDR)");
+
   source.sin_family = AF_INET;
   source.sin_addr.s_addr = INADDR_ANY;
   source.sin_port = port;