Feature: make log contain source address of unknown site

So far, log would contain just the (reasonably unique) identifier
of the astray originator, but it's hard or downright impossible
to unambiguously recover the original address just with this piece
of knowledge.  Hence to allow for convenient tracking such cases
down, log also the source address if possible.

Technically, we are abusing the fact that said identifiers are supposed
to be non-negative (most significant bit set to zero) while the proper
OK state is indicated with zero and proper error condition mostly with
negative integers.  So these identifiers fit nicely into the positive
integer area, except for:
- zero identifier <-- we flip all the bits but MSB to 1 in this case
- malformed identifiers with MSB=1 <-- we flip MSB to 0

Also, we make sure that remaining error conditions not following the
rule and being indicated with positive integers are now indicated
with negative ones.

This convention is also mentioned in the function declaration's comment.

src/attr.c

@@ -464,7 +464,7 @@ int attr_recv(void *buf, struct booth_site *source)
 		log_warn("got invalid ticket name %s from %s",
 				msg->attr.tkt_id, site_string(source));
 		source->invalid_cnt++;
-		return 1;
+		return -1;
 	}
 
 	return 0;

src/raft.c

@@ -402,13 +402,13 @@ static int process_REVOKE (
 		tk_log_error("%s wants to revoke ticket, "
 				"but it is not granted there (ignoring)",
 				site_string(sender));
-		return 1;
+		return -1;
 	} else if (tk->state != ST_FOLLOWER) {
 		tk_log_error("unexpected ticket revoke from %s "
 				"(in state %s) (ignoring)",
 				site_string(sender),
 				state_to_string(tk->state));
-		return 1;
+		return -1;
 	} else {
 		tk_log_info("%s revokes ticket",
 				site_string(tk->leader));

src/transport.c

@@ -23,13 +23,15 @@
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <netdb.h>  /* getnameinfo */
 #include <poll.h>
 #include <arpa/inet.h>
 #include <asm/types.h>
 #include <linux/rtnetlink.h>
 #include <net/if.h>
 #include <netinet/in.h>
 #include <netinet/tcp.h>
+#include <sys/socket.h>  /* getnameinfo */
 #include "b_config.h"
 #include "attr.h"
 #include "auth.h"
@@ -50,7 +52,12 @@
 
 struct booth_site *local = NULL;
 
-
+/* function to be called when handling booth-group-internal messages;
+ * it's expected to return 0 to indicate success, negative integer
+ * to indicate silent (or possibly already complained about) error,
+ * or positive integer to indicate sender's ID that will then be
+ * emitted in the error log message together with the real source
+ * address if this is available */
 static int (*deliver_fn) (void *msg, int msglen);
 
 
@@ -779,7 +786,15 @@ static void process_recv(int ci)
 	if (rv == -1)
 		return;
 
-	deliver_fn((void*)msg, rv);
+	rv = deliver_fn((void*)msg, rv);
+	if (rv > 0) {
+		if (getnameinfo((struct sockaddr *)&sa, sa_len,
+				buffer, sizeof(buffer), NULL, 0,
+				NI_NUMERICHOST) == 0)
+			log_error("unknown sender: %08x (real: %s)", rv, buffer);
+		else
+			log_error("unknown sender: %08x", rv);
+	}
 }
 
 static int booth_udp_init(void *f)
@@ -1051,7 +1066,7 @@ int send_header_plus(int fd, struct boothc_hdr_msg *msg, void *data, int len)
 	return rv;
 }
 
-/* UDP message receiver. */
+/* UDP message receiver (see also deliver_fn declaration's comment) */
 int message_recv(void *msg, int msglen)
 {
 	uint32_t from;
@@ -1062,8 +1077,10 @@ int message_recv(void *msg, int msglen)
 
 	from = ntohl(header->from);
 	if (!find_site_by_id(from, &source)) {
-		log_error("unknown sender: %08x", from);
-		return -1;
+		/* caller knows the actual source address, pass
+		   the (assuredly) positive number and let it report */
+		from = from ? from : ~from;  /* avoid 0 (success) */
+		return from & (~0U >> 1);  /* avoid negative (error code} */
 	}
 
 	time(&source->last_recv);