dfilter: Handle null arguments in macros better

If a null argument is given to a macro, print an error saying that
is disallowed instead of substituting the null argument (i.e., an
unquoted empty string) into the macro.
The latter almost certainly still produces a grammatical error, but it
will be something mysterious that depends on the macro definition like

"==" was unexpected in this context

instead of a useful error string.

For macros that take strings as argument, substituting a null has
never worked either, "" has always needed to be used.

As a special case, accept a single empty argument as meaning
"a macro with 0 arguments" instead of how it is currently treated,
a "macro with 1 null argument", i.e. $mymacro() for the new
function-like syntax and ${mymacro:} for the original syntax.

See 7d87367e22

epan/dfilter/dfilter-macro.c

@@ -301,6 +301,12 @@ static char* dfilter_macro_apply_recurse(const char* text, unsigned depth, df_er
 						goto on_error;
 					case ';':
 					case ',':
+						if (arg->len == 0) {
+							/* Null arguments aren't accepted */
+							if (error != NULL)
+								*error = df_error_new_msg("null argument in macro expression");
+							goto on_error;
+						}
 						g_ptr_array_add(args,g_string_free(arg,false));
 
 						arg = g_string_sized_new(32);
@@ -323,10 +329,19 @@ static char* dfilter_macro_apply_recurse(const char* text, unsigned depth, df_er
 							break;
 						}
 
-						g_ptr_array_add(args,g_string_free(arg,false));
-						g_ptr_array_add(args,NULL);
-
-						arg = NULL;
+						if (arg->len == 0) {
+							/* Null arguments aren't accepted... */
+							if (args->len != 0) {
+								/* Except $macro() or ${macro:} means zero args, not one null arg */
+								if (error != NULL)
+									*error = df_error_new_msg("null argument in macro expression");
+								goto on_error;
+							}
+						} else {
+							g_ptr_array_add(args,g_string_free(arg,false));
+							g_ptr_array_add(args,NULL);
+							arg = NULL;
+						}
 
 						resolved = dfilter_macro_resolve(name->str, (char**)args->pdata, error);
 						if (resolved == NULL)

test/suite_dfilter/group_macro.py

@@ -20,3 +20,45 @@ class TestDfilterMacro:
     def test_macro_3(self, checkDFilterCount):
         dfilter = "${private_ipv4;ip.src}"
         checkDFilterCount(dfilter, 1)
+
+class TestDfilterMacroZeroArg:
+    trace_file = "nfs.pcap"
+
+    def test_macro_1(self, checkDFilterCount):
+        dfilter = "$nfs()"
+        checkDFilterCount(dfilter, 2)
+
+    def test_macro_2(self, checkDFilterCount):
+        dfilter = "${nfs}"
+        checkDFilterCount(dfilter, 2)
+
+    def test_macro_3(self, checkDFilterCount):
+        dfilter = "${nfs:}"
+        checkDFilterCount(dfilter, 2)
+
+    def test_macro_wrong_count_1(self, checkDFilterFail):
+        dfilter = "${private_ipv4}"
+        checkDFilterFail(dfilter, "wrong number of arguments for macro")
+
+    def test_macro_wrong_count_2(self, checkDFilterFail):
+        dfilter = "${private_ipv4:}"
+        checkDFilterFail(dfilter, "wrong number of arguments for macro")
+
+    def test_macro_wrong_count_3(self, checkDFilterFail):
+        dfilter = "$private_ipv4()"
+        checkDFilterFail(dfilter, "wrong number of arguments for macro")
+
+class TestDfilterMacroNullArg:
+    trace_file = "nfs.pcap"
+
+    def test_macro_works(self, checkDFilterCount):
+        dfilter = "$ip(198.95.230.20, 2049)"
+        checkDFilterCount(dfilter, 2)
+
+    def test_macro_null_1(self, checkDFilterFail):
+        dfilter = "$ip(198.95.230.20,)"
+        checkDFilterFail(dfilter, "null argument")
+
+    def test_macro_null_2(self, checkDFilterFail):
+        dfilter = "${ip:;2049}"
+        checkDFilterFail(dfilter, "null argument")

test/suite_dfilter/test_dmacros

@@ -2,3 +2,5 @@
 "private_ipv4" $1 == 192.168.0.0/16 or $1 == 172.16.0.0/12 or $1 == 10.0.0.0/8
 "private_ethernet" $1[0] & 0x0F == 2
 "private_ipv6" ipv6 && $1 == fc00::/7
+"nfs" rpc.program == 100003
+"ip" (ip.src == $1 and (tcp.srcport == $2 or udp.srcport == $2 or sctp.srcport == $2 or dccp.srcport == $2)) or (ip.dst == $1 and (tcp.dstport == $2 or udp.dstport == $2 or sctp.dstport == $2 or dccp.dstport == $2))