Use nc6 in MSP tests instead of nc

On OS-X (BSD), nc6 appears to be the only available variant of
netcat that matches the Linux version.

Introduces a guard function to catch invocations of nc6 when
setup_netcat6 has not been called in the fixture.  Introduce
guard functions to prevent invocations of nc and netcat.

testdefs.sh

@@ -903,7 +903,39 @@ setup_curl() {
          ;;
       esac
       fail "curl(1) version $2 is not adequate (expecting $minversion or higher)"
+}
+
+# Setup function:
+# - ensure that the netcat6 nc6(1) utility is available
+setup_netcat6() {
+   NETCAT6=$(type -P nc6) || error "nc6(1) command is not present"
+   local minversion="${1:-1.0}"
+   local ver="$("$NETCAT6" --version | tr '\n' ' ')"
+   case "$ver" in
+   nc6\ version\ *)
+      set -- $ver
+      tfw_cmp_version "$3" "$minversion"
+      case $? in
+      0|2)
+         export NETCAT6
+         return 0
+         ;;
+      esac
+      error "$NETCAT6 version $3 is not adequate (expecting $minversion or higher)"
       ;;
    esac
-   fail "cannot parse output of curl --version: $ver"
+   error "cannot parse output of $NETCAT6 --version: $ver"
+}
+
+# Guard functions.
+NETCAT6=
+nc6() {
+   [ -x "$NETCAT6" ] || error "missing call to setup_netcat6 in the fixture"
+   "$NETCAT6" "$@"
+}
+nc() {
+   error "do not use nc; instead use nc6(1) after calling setup_netcat6 in the fixture"
+}
+netcat() {
+   error "do not use netcat; instead use nc6(1) after calling setup_netcat6 in the fixture"
 }

tests/msp

@@ -181,6 +181,7 @@ test_keep_alive() {
 doc_forward="Forward TCP connections to a remote server"
 setup_forward() {
    setup_common
+   setup_netcat6
    start_servald_instances +A +B
 }
 client_forward() {
@@ -194,7 +195,7 @@ test_forward() {
    set_instance +B
    fork %connect client_forward 2048 $SIDA
    sleep 1
-   executeOk nc -q 30 -v 127.0.0.1 2048 < <(echo "Hello from the client")
+   executeOk nc6 -q 30 -v 127.0.0.1 2048 < <(echo "Hello from the client")
    assertStdoutGrep --matches=1 "^Hello from the server$"
    fork_wait %listen %connect
 }
@@ -202,6 +203,7 @@ test_forward() {
 doc_tcp_tunnel="Tunnel a tcp connection"
 setup_tcp_tunnel() {
    setup_common
+   setup_netcat6
    start_servald_instances +A +B
 }
 server_forward() {
@@ -210,7 +212,7 @@ server_forward() {
    tfw_cat --stderr
 }
 nc_listen() {
-   execute nc -q -1 -v -l -p $1 < <(echo "Hello from the server")
+   execute nc6 -q -1 -v -l -p $1 < <(echo "Hello from the server")
    tfw_cat --stdout --stderr
 }
 test_tcp_tunnel() {
@@ -220,7 +222,7 @@ test_tcp_tunnel() {
    set_instance +B
    fork %client client_forward 6001 $SIDA
    sleep 1
-   executeOk nc -q 10 -v 127.0.0.1 6001 < <(echo "Hello from the client")
+   executeOk nc6 -q 10 -v 127.0.0.1 6001 < <(echo "Hello from the client")
    tfw_cat --stdout --stderr
    assertStdoutGrep --matches=1 "^Hello from the server$"
    fork_wait %listen %server %client
@@ -285,6 +287,7 @@ test_refused(){
 doc_terminate="Terminate a connection mid stream"
 setup_terminate() {
    setup_common
+   setup_netcat6
    start_servald_instances +A +B
 }
 client_terminate() {
@@ -303,8 +306,8 @@ test_terminate() {
    set_instance +B
    fork %mspconnect client_terminate
    sleep 1
-# todo capture nc output nicely, while still being able to terminate it
+# todo capture nc6 output nicely, while still being able to terminate it
-   fork %ncconnect nc -q 0 -v 127.0.0.1 3001
+   fork %ncconnect nc6 -q 0 -v 127.0.0.1 3001
    fork_terminate %ncconnect
    fork_wait %msplisten %mspconnect %ncconnect
 }