Announce the actual public key (pk) in Bonjour and GET /info

Same as other Airplay 2 devices do, even though it doesn't seem to be used
by any clients.

common.h

@@ -299,8 +299,7 @@ typedef struct {
   uint32_t airplay_statusflags;
   char *airplay_device_id; // for the Bonjour advertisement and the GETINFO PList
   char *airplay_pin;       // non-NULL, 4 char PIN, if required for pairing
-  char *airplay_pk;        // "pk" string in the Bonjour advertisement
-  char *airplay_pi;        //  UUID in the Bonjour advertisement and the GETINFO Plist
+  char *airplay_pi;        // UUID in the Bonjour advertisement and the GETINFO Plist
   char *airplay_gid;       // UUID in the Bonjour advertisement -- initially the same as the pi
 #endif
 } shairport_cfg;

rtsp.c

@@ -886,6 +886,19 @@ static ssize_t write_encrypted(rtsp_conn_info *conn, const void *buf, size_t cou
   free(encrypted);
   return count;
 }
+
+static void pkString_make(char *str, size_t str_size, const char *device_id) {
+  uint8_t public_key[32];
+  if (str_size < 2 * sizeof(public_key) + 1) {
+    warn("Insufficient string size");
+    str[0] = '\0';
+    return;
+  }
+  pair_public_key_get(PAIR_SERVER_HOMEKIT, public_key, device_id);
+  char *ptr = str;
+  for (size_t i = 0; i < sizeof(public_key); i++)
+    ptr += sprintf(ptr, "%02x", public_key[i]);
+}
 #endif
 
 ssize_t read_from_rtsp_connection(rtsp_conn_info *conn, void *buf, size_t count) {
@@ -1238,11 +1251,14 @@ void handle_get_info(__attribute((unused)) rtsp_conn_info *conn, rtsp_message *r
       plist_dict_set_item(response_plist, "name", plist_new_string(config.service_name));
       char *vs = get_version_string();
       plist_dict_set_item(response_plist, "model", plist_new_string(vs));
+      free(vs);
+      char pkString[128];
+      pkString_make(pkString, sizeof(pkString), config.airplay_device_id);
+      plist_dict_set_item(response_plist, "pk", plist_new_string(pkString));
       plist_to_bin(response_plist, &resp->content, &resp->contentlength);
       if (resp->contentlength == 0)
         debug(1, "GET /info Stage 1: response bplist not created!");
       plist_free(response_plist);
-      free(vs);
     }
     msg_add_header(resp, "Content-Type", "application/x-apple-binary-plist");
     debug_log_rtsp_message(2, "GET /info Stage 1 Response:", resp);
@@ -1264,6 +1280,9 @@ void handle_get_info(__attribute((unused)) rtsp_conn_info *conn, rtsp_message *r
     char *vs = get_version_string();
     plist_dict_set_item(response_plist, "model", plist_new_string(vs));
     free(vs);
+    char pkString[128];
+    pkString_make(pkString, sizeof(pkString), config.airplay_device_id);
+    plist_dict_set_item(response_plist, "pk", plist_new_string(pkString));
     plist_to_bin(response_plist, &resp->content, &resp->contentlength);
     plist_free(response_plist);
     msg_add_header(resp, "Content-Type", "application/x-apple-binary-plist");
@@ -4106,7 +4125,7 @@ void *rtsp_listen_loop(__attribute((unused)) void *arg) {
 #ifdef CONFIG_AIRPLAY_2
     *p++ = "srcvers=366.0";
     char deviceIdString[64];
-    snprintf(deviceIdString, sizeof(deviceIdString) - 1, "deviceid=%s", config.airplay_device_id);
+    snprintf(deviceIdString, sizeof(deviceIdString), "deviceid=%s", config.airplay_device_id);
     *p++ = deviceIdString;
     // features is a 64 bit number, least significant 32 bits
     char featuresString[64];
@@ -4114,8 +4133,7 @@ void *rtsp_listen_loop(__attribute((unused)) void *arg) {
     features_hi = (features_hi >> 32) & 0xffffffff;
     uint64_t features_lo = config.airplay_features;
     features_lo = features_lo & 0xffffffff;
-    // @mikebrady I don't think the -1 here (and other places) is necessary
-    snprintf(featuresString, sizeof(featuresString) - 1, "features=0x%" PRIx64 ",0x%" PRIx64 "",
+    snprintf(featuresString, sizeof(featuresString), "features=0x%" PRIx64 ",0x%" PRIx64 "",
              features_lo, features_hi);
     *p++ = featuresString;
     char statusflagsString[32];
@@ -4127,14 +4145,15 @@ void *rtsp_listen_loop(__attribute((unused)) void *arg) {
     *p++ = "fv=p20.78000.12";
     *p++ = "model=SPS";
     char piString[64];
-    snprintf(piString, sizeof(piString) - 1, "pi=%s", config.airplay_pi);
+    snprintf(piString, sizeof(piString), "pi=%s", config.airplay_pi);
     *p++ = piString;
     char gidString[64];
-    snprintf(gidString, sizeof(gidString) - 1, "gid=%s", config.airplay_gid);
+    snprintf(gidString, sizeof(gidString), "gid=%s", config.airplay_gid);
     *p++ = gidString;
     *p++ = "gcgl=0";
     char pkString[128];
-    snprintf(pkString, sizeof(pkString) - 1, "pk=%s", config.airplay_pk);
+    snprintf(pkString, sizeof(pkString), "pk=");
+    pkString_make(pkString + strlen("pk="), sizeof(pkString) - strlen("pk="), config.airplay_device_id);
     *p++ = pkString;
     *p++ = NULL;
 #else

shairport.c

@@ -1591,21 +1591,6 @@ int main(int argc, char **argv) {
   } else
     debug(1, "Started in Airplay 2 mode!");
 
-  // now make up a 32-byte "pk" string from random numbers
-  const ssize_t pk_size = 32;
-  char pk_bytes[pk_size];
-  char pk_string[pk_size * 2 + 1];
-  randombytes_buf(pk_bytes, pk_size); // using libsodium
-  char *obfp = pk_string;
-  int obfc;
-  for (obfc = 0; obfc < pk_size; obfc++) {
-    snprintf(obfp, 3, "%02X", pk_bytes[obfc]);
-    obfp += 2;
-  };
-  *obfp = 0;
-  debug(1, "pk string: \"%s\"", pk_string);
-  config.airplay_pk = strdup(pk_string);
-
   // now generate a UUID
   // from https://stackoverflow.com/questions/51053568/generating-a-random-uuid-in-c
   // with thanks