new rewrite function suggestion + patch, use case: DHCP assignment based on switch and port

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Hello,
I have chosen GNU radius as backend for my dhcp servers on mikrotik=20
routeros 3.x,
because it is probably most flexible implementation of radius server.

I need to do special rewriting of request in order to achieve IP address=20
assignment based on
switch and port and not mac address. For this i use dhcp option 82 on=20
switches, which sets
Agent-Remote-Id and Agent-Circuit-Id.

Agent-Remote-Id is basically mac address of the switch, and Circuit-Id=20
is basically port number and vlan.

Rewrite language is strong enough to do the transformation in case of=20
text fields. But Agent-Remote-Id
and Agent-Circuit-Id are binary. Rewrite includes function qprn, which I=20
simply modified to new function tohex.
tohex encodes all characters, so that field and gsub can be used to=20
separate useful bytes from
Agent-Remote-Id and Agent-Circuit-Id.

My rewrite configuration is:

string
decode_agent_remote_id()
{
        string agent;
        string newagent;

        agent =3D gsub("%"," ",tohex(%[Agent-Remote-Id]));

        newagent =3D=20
field(agent,3)+":"+field(agent,4)+":"+field(agent,5)+":"+field(agent,6)+"=
:"+field(agent,7)+":"+field(agent,8);
        %[Orig-User-Name] =3D %[User-Name];
        %[User-Name] =3D newagent+"port:"+field(gsub("%","=20
",tohex(%[Agent-Circuit-Id])),6);
        return 0;
}

This return user names like "00:15:77:B1:D7:10port:03"

I would like to ask to include tohex function in next release, as this=20
might be useful.


--=20

Best regards
Josef Li=C5=A1ka

CHL | system care

Phone: +420.272048055
Fax: +420.272048064
Cell: +420.776026526 denn=C4=9B 9:00 - 17:30 CEST

<https://www.chl.cz/>


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 name="phokz_tohex.patch"
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--- radius-1.6.1/radiusd/rewrite.y	2008-12-15 09:03:24.000000000 +0100
+++ radius-1.6.1-phokz/radiusd/rewrite.y	2009-04-17 17:09:15.000000000 +0200
@@ -5519,6 +5519,34 @@
 	*p = 0;
 }
 
+/* Phokz's hack */
+
+static void
+bi_tohex()
+{
+	grad_string_t arg;
+	char *p, *s, *end;
+	size_t count;
+	RWSTYPE *sp;
+	
+	mem2string(&arg, (RWSTYPE*)getarg(1));
+	end = arg.data + arg.size;
+
+	/* Each encoded character takes 3 bytes. */
+	sp = heap_reserve(sizeof(RWSTYPE) + 3*arg.size + 1);
+	sp[0] = 3*arg.size;
+	pushn((RWSTYPE) sp);
+	
+	for (p = (char*)(sp + 1), s = arg.data; s < end; s++) {
+			char buf[3];
+			snprintf(buf, sizeof buf, "%02X", *(unsigned char*)s);
+			*p++ = '%';
+			*p++ = buf[0];
+			*p++ = buf[1];
+	}
+	*p = 0;
+}
+
 static void
 bi_quote_string()
 {
@@ -5667,6 +5695,8 @@
 	/* Time functions */
 	{ bi_time, "time", Integer, "" },
 	{ bi_strftime, "strftime", String, "si" },
+        /* Phokz's hack */
+	{ bi_tohex, "tohex", String, "s" },
 	{ NULL }
 };
 

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