cowd which runs

packages/cowbull/src/cow.txt

@@ -0,0 +1,58 @@
+The Cow Game
+============
+
+You are trying to guess a 4-nybble sequence.  Each nybble will have
+either 1 or 2 bits set, and the highest bit will never be set.  The
+game server will tell you how many nybbles in each guess were correct,
+and how many had one correct bit.  It does not tell you which
+positions
+
+
+
+The Cow Client
+==============
+
+The client connects to the Cow server running on the IPv6 address
+provided in argument 1.  If argument 2 is present, the client will
+try to run it, providing stdin and stdout as in interactive mode.
+
+In interactive mode (no argument 2), the client reads a guess in the
+form of 4 ASCII numerals, and prints the number of correct nybbles
+followed by the number of nybbles with one correct bit.
+
+Here is an example of a session:
+
+    1111
+    12
+    2222
+    10
+    4444
+    02
+    4244
+    12
+    1244
+    22
+    1255
+    cow:xylep-radar-nanox
+
+
+
+The Cow Protocol
+================
+
+cowd runs on port 3782.
+
+The client always sends 6 octets.  To request a new session, it sends
+all zeroes.  Otherwise it sends the 4-octet game identifier provided
+by the server, concatenated with a 2-octet guess.
+
+The server will respond with a new game identifier (4 octets) to a new
+game request or if the game requested is too old.  If a guess is
+incorrect, the server will respond with either a 1-octet score in
+which the high nybble is the number of correct nybbles in the guess,
+and the low nybble is the number of nybbles in the guess with one
+correct bit.  If a guess is correct, the server will respond with a
+token of length 5 octets or more.
+
+There are multiple tokens, one per number of guesses used, up to
+some maximum number of guesses defined per server instance.

packages/cowbull/src/cowd.c

@@ -1,13 +1,143 @@
 #include <stdio.h>
-#include <sys/time.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <time.h>
+#include <string.h>
+#include <sysexits.h>
+#include <arpa/inet.h>
+#include <sys/socket.h>
+
+#define TIMEOUT 30
+
+#define NTOKENS 20
+#define TOKENLEN 50
+char            tokens[NTOKENS][TOKENLEN];
+int             ntokens;
+
+struct state {
+    time_t          death;
+    uint16_t        answer;
+    uint16_t        guesses;
+};
+
+#define NSTATES 500
+struct state    states[NSTATES] = { 0 };
+
+int
+bind_port(struct in6_addr *addr, int fd, uint16_t port)
+{
+    struct sockaddr_in6 saddr = { 0 };
+
+    saddr.sin6_family = AF_INET6;
+    saddr.sin6_port = htons(port);
+    memcpy(&saddr.sin6_addr, addr, sizeof *addr);
+    return bind(fd, (struct sockaddr *) &saddr, sizeof saddr);
+}
+
+
+struct newgame {
+    uint16_t        offset;
+    uint16_t        token;
+};
 
 void
-mungle(char *str, int len)
+new_game(int sock, time_t now, struct sockaddr_in6 *from,
+         socklen_t fromlen)
 {
     int             i;
+    struct newgame  g;
 
-    for (i = 0; i < len; i += 1) {
+    for (g.offset = 0; g.offset < NSTATES; g.offset += 1) {
-        str[i] ^= 0xff;
+        struct state   *s = &states[g.offset];
+
+        if (s->death < now) {
+            s->death = now + TIMEOUT;
+            s->guesses = 0;
+            s->answer = 0;
+
+            for (i = 0; i < 4; i += 1) {
+                s->answer = (s->answer << 4) | ((random() % 6) + 1);
+            }
+            break;
+        }
+    }
+
+    if (g.offset < NSTATES) {
+        sendto(sock, &g, sizeof(g), 0, (struct sockaddr *) from, fromlen);
+    }
+}
+
+struct guess {
+    uint16_t        offset;
+    uint16_t        token;
+    uint16_t        guess;
+};
+
+void
+loop(int sock)
+{
+    struct guess    g;
+    struct state   *cur;
+    struct sockaddr_in6 from;
+    socklen_t       fromlen = sizeof from;
+    time_t          now = time(NULL);
+
+    /*
+     * Read guess 
+     */
+    {
+        ssize_t         inlen;
+
+        inlen = recvfrom(sock, &g, sizeof g, 0,
+                         (struct sockaddr *) &from, &fromlen);
+        if (inlen != sizeof g) {
+            return;
+        }
+    }
+
+    /*
+     * Bounds check 
+     */
+    if (g.offset >= NSTATES) {
+        g.offset = 0;
+    }
+    cur = &states[g.offset];
+
+    if ((g.token != cur->answer) || /* Wrong token? */
+        (cur->death < now) ||   /* Old game? */
+        (cur->guesses++ > 100)) {       /* Too dumb? */
+        /*
+         * Start a new game 
+         */
+        new_game(sock, now, &from, fromlen);
+        return;
+    } else {
+        uint8_t         reply;
+        int i;
+
+        for (i = 0; i < 4; i += 1) {
+            int             s = (g.guess >> (i * 4)) & 0xf;
+            int             a = (cur->answer >> (i * 4)) & 0xf;
+            if ((s < 1) || (s > 7)) {
+                reply = 0;
+                break;
+            } else if (s == a) {
+                reply += 0x10;
+            } else if (s & a) {
+                reply += 0x01;
+            }
+        }
+
+        if (reply == 0x40) {
+            if (cur->guesses > ntokens) {
+                sendto(sock, tokens[cur->guesses],
+                       strlen(tokens[cur->guesses]), 0,
+                       (struct sockaddr *) &from, fromlen);
+            }
+        } else {
+            sendto(sock, &reply, sizeof reply, 0, (struct sockaddr *) &from,
+                   fromlen);
+        }
     }
 }
 
@@ -15,13 +145,39 @@ int
 main(int argc, char *argv[])
 {
     long            answer = 0;
+    int             sock;
     int             i;
+    struct in6_addr addr;
 
-    {
+    srand(time(NULL));
-        struct timeval tv;
 
-        gettimeofday(&tv, NULL);
+    if (argc > 1) {
-        srandom(tv.tv_usec);
+        if (0 >= inet_pton(AF_INET6, argv[1], &addr)) {
+            fprintf(stderr, "invalid address: %s\n", argv[1]);
+            return EX_IOERR;
+        }
+    } else {
+        memcpy(&addr, &in6addr_any, sizeof addr);
+    }
+
+    /*
+     * Read in tokens 
+     */
+    for (ntokens = 0; ntokens < NTOKENS; ntokens += 1) {
+        if (NULL == fgets(tokens[ntokens], TOKENLEN, stdin)) {
+            break;
+        }
+    }
+    printf("Read %d tokens.\n", ntokens);
+
+    /*
+     * Set up socket 
+     */
+    sock = socket(AF_INET6, SOCK_DGRAM, 0);
+    i = bind_port(&addr, sock, 3782);
+    if (-1 == i) {
+        perror("Bind port 3782");
+        return EX_IOERR;
     }
 
     for (i = 0; i < 4; i += 1) {
@@ -29,31 +185,7 @@ main(int argc, char *argv[])
     }
 
     while (1) {
-        char line[20];
+        loop(sock);
-        long guess;
-        int ret = 0;
-
-        if (NULL == fgets(line, sizeof(line), stdin)) {
-            break;
-        }
-
-        guess = strtol(line, NULL, 16);
-
-        for (i = 0; i < 4; i += 1) {
-            int g = (guess  >> (i*4)) & 0xf;
-            int a = (answer >> (i*4)) & 0xf;
-
-            if ((g < 1) || (g > 7)) {
-                ret = 0;
-                break;
-            } else if (g == a) {
-                ret += 0x10;
-            } else if (g & a) {
-                ret += 0x01;
-            }
-        }
-
-        printf("%02x\n", ret);
     }
 
     return 0;