ircd: enforce unique nicknames (433), announce renames, fold case

NICK overwrote the nick with whatever was asked for, so two clients could
both be "alice": /NAMES listed her twice and a private message only ever
reached whichever slot came first in the table.

- A nick already held by another client is refused with 433
  ERR_NICKNAMEINUSE and the client keeps the one it had. Unregistered
  clients simply stay unregistered until they pick a free one, which is what
  every client already expects.
- A NICK from a registered client is a rename: it is announced to the client
  and to its channel, so nobody's user list goes stale.
- IRC names fold case, so "Alice" is "alice" - for the uniqueness check, for
  PRIVMSG by nick, and for channels ("#GB" is "#gb"). One irceq() replaces
  the exact-match compare that was used for all three.

gbos's own irc(1) already retries 433 by appending '_', so two Game Boys with
the default nick now sort themselves out: verified with a GB running ircd, a
laptop client holding "sl0pboy", and a second GB arriving as "sl0pboy_" -
both in #gbos, messages crossing both ways.

1 files changed, 42 insertions, 10 deletions

diff --git a/usr/ircd.c b/usr/ircd.c
index b960dd6..eccaf82 100644
--- a/usr/ircd.c
+++ b/usr/ircd.c
@@ -41,13 +41,6 @@ static unsigned char mlen;
 static char line[INBUF]; /* the line being dispatched */
 
 /* ---- tiny string helpers -------------------------------------------------- */
-static unsigned char seq(const char *a, const char *b) {
-    while (*a && *a == *b) {
-        a++;
-        b++;
-    }
-    return (unsigned char)(*a == *b);
-}
 static unsigned char up(char c) { return (unsigned char)((c >= 'a' && c <= 'z') ? c - 32 : c); }
 /* case-insensitive compare of a command word */
 static unsigned char cmdis(const char *w, const char *name) {
@@ -58,6 +51,16 @@ static unsigned char cmdis(const char *w, const char *name) {
     }
     return (unsigned char)(*w == 0);
 }
+/* IRC names - nicknames AND channels - are case-insensitive, so "Alice" and
+   "alice" are one person, "#GB" and "#gb" one channel. (RFC 1459 also folds
+   []\\~ onto {}|^; plain ASCII is close enough for a Game Boy.) */
+static unsigned char irceq(const char *a, const char *b) {
+    while (*a && up(*a) == up(*b)) {
+        a++;
+        b++;
+    }
+    return (unsigned char)(*a == 0 && *b == 0);
+}
 static void scpy(char *d, const char *s, unsigned char max) {
     unsigned char i = 0;
     while (s[i] && i < max - 1) {
@@ -100,7 +103,15 @@ static void bcast(const char *chan, unsigned char except) {
     unsigned char i;
     if (!chan[0]) return;
     for (i = 0; i < MAXCL; i++)
-        if (cused[i] && creg[i] && i != except && seq(cchan[i], chan)) msend(i);
+        if (cused[i] && creg[i] && i != except && irceq(cchan[i], chan)) msend(i);
+}
+
+/* is `n` already in use by some OTHER client? */
+static unsigned char nick_taken(const char *n, unsigned char except) {
+    unsigned char i;
+    for (i = 0; i < MAXCL; i++)
+        if (cused[i] && i != except && cnick[i][0] && irceq(cnick[i], n)) return 1;
+    return 0;
 }
 
 static void logline(const char *a, const char *b) {
@@ -163,7 +174,7 @@ static void names(unsigned char ci) {
     m(cchan[ci]);
     m(" :");
     for (i = 0; i < MAXCL; i++)
-        if (cused[i] && creg[i] && seq(cchan[i], cchan[ci])) {
+        if (cused[i] && creg[i] && irceq(cchan[i], cchan[ci])) {
             m(cnick[i]);
             m(" ");
         }
@@ -204,6 +215,27 @@ static void dispatch(unsigned char ci) {
 
     if (cmdis(cmd, "NICK")) {
         if (!a1[0]) return;
+        if (nick_taken(a1, ci)) { /* 433: keep the nick they have */
+            mnumeric(ci, "433");
+            m(a1);
+            m(" :Nickname is already in use");
+            mend();
+            msend(ci);
+            return;
+        }
+        if (irceq(cnick[ci], a1)) { /* same nick, only case: just take it */
+            scpy(cnick[ci], a1, NICKSZ);
+            return;
+        }
+        if (creg[ci]) { /* a rename: everyone must be told */
+            mprefix(ci);
+            m("NICK :");
+            m(a1);
+            mend();
+            msend(ci);
+            bcast(cchan[ci], ci);
+            logline(cnick[ci], " renamed");
+        }
         scpy(cnick[ci], a1, NICKSZ);
         if (cgotu[ci] && !creg[ci]) welcome(ci);
         return;
@@ -279,7 +311,7 @@ static void dispatch(unsigned char ci) {
             nl();
         } else {
             for (i = 0; i < MAXCL; i++) /* to one nick */
-                if (cused[i] && creg[i] && seq(cnick[i], a1)) msend(i);
+                if (cused[i] && creg[i] && irceq(cnick[i], a1)) msend(i);
         }
         return;
     }