security: simplify choose_mech

Coverity CID 1299424 identified dead code because of checks that could
never equal true (if the mechanism's name was NULL).

Simplified the function by removing a level of pointers and removing the
loop and array that weren't used.

lib/security.c

@@ -109,13 +109,6 @@ static char level_to_char(int level) {
   return 'P';
 }
 
-static const struct Curl_sec_client_mech * const mechs[] = {
-#ifdef HAVE_GSSAPI
-  &Curl_krb5_client_mech,
-#endif
-  NULL
-};
-
 /* Send an FTP command defined by |message| and the optional arguments. The
    function returns the ftp_code. If an error occurs, -1 is returned. */
 static int ftp_send_command(struct connectdata *conn, const char *message, ...)
@@ -484,36 +477,29 @@ static CURLcode choose_mech(struct connectdata *conn)
 {
   int ret;
   struct SessionHandle *data = conn->data;
-  const struct Curl_sec_client_mech * const *mech;
   void *tmp_allocation;
-  const char *mech_name;
+  const struct Curl_sec_client_mech *mech = &Curl_krb5_client_mech;
 
-  for(mech = mechs; (*mech); ++mech) {
+  do {
-    mech_name = (*mech)->name;
+    tmp_allocation = realloc(conn->app_data, mech->size);
-    /* We have no mechanism with a NULL name but keep this check */
-    DEBUGASSERT(mech_name != NULL);
-    if(mech_name == NULL) {
-      infof(data, "Skipping mechanism with empty name (%p)\n", (void *)mech);
-      continue;
-    }
-    tmp_allocation = realloc(conn->app_data, (*mech)->size);
     if(tmp_allocation == NULL) {
-      failf(data, "Failed realloc of size %u", (*mech)->size);
+      failf(data, "Failed realloc of size %u", mech->size);
       mech = NULL;
       return CURLE_OUT_OF_MEMORY;
     }
     conn->app_data = tmp_allocation;
 
-    if((*mech)->init) {
+    if(mech->init) {
-      ret = (*mech)->init(conn->app_data);
+      ret = mech->init(conn->app_data);
-      if(ret != 0) {
+      if(ret) {
-        infof(data, "Failed initialization for %s. Skipping it.\n", mech_name);
+        infof(data, "Failed initialization for %s. Skipping it.\n",
+              mech->name);
         continue;
       }
     }
 
-    infof(data, "Trying mechanism %s...\n", mech_name);
+    infof(data, "Trying mechanism %s...\n", mech->name);
-    ret = ftp_send_command(conn, "AUTH %s", mech_name);
+    ret = ftp_send_command(conn, "AUTH %s", mech->name);
     if(ret < 0)
       /* FIXME: This error is too generic but it is OK for now. */
       return CURLE_COULDNT_CONNECT;
@@ -522,11 +508,11 @@ static CURLcode choose_mech(struct connectdata *conn)
       switch(ret) {
       case 504:
         infof(data, "Mechanism %s is not supported by the server (server "
-                    "returned ftp code: 504).\n", mech_name);
+                    "returned ftp code: 504).\n", mech->name);
         break;
       case 534:
         infof(data, "Mechanism %s was rejected by the server (server returned "
-                    "ftp code: 534).\n", mech_name);
+                    "ftp code: 534).\n", mech->name);
         break;
       default:
         if(ret/100 == 5) {
@@ -539,7 +525,7 @@ static CURLcode choose_mech(struct connectdata *conn)
     }
 
     /* Authenticate */
-    ret = (*mech)->auth(conn->app_data, conn);
+    ret = mech->auth(conn->app_data, conn);
 
     if(ret == AUTH_CONTINUE)
       continue;
@@ -549,7 +535,7 @@ static CURLcode choose_mech(struct connectdata *conn)
     }
     DEBUGASSERT(ret == AUTH_OK);
 
-    conn->mech = *mech;
+    conn->mech = mech;
     conn->sec_complete = 1;
     conn->recv[FIRSTSOCKET] = sec_recv;
     conn->send[FIRSTSOCKET] = sec_send;
@@ -559,10 +545,10 @@ static CURLcode choose_mech(struct connectdata *conn)
     /* Set the requested protection level */
     /* BLOCKING */
     (void)sec_set_protection_level(conn);
-    break;
-  }
 
-  return *mech != NULL ? CURLE_OK : CURLE_FAILED_INIT;
+  } WHILE_FALSE;
+
+  return CURLE_OK;
 }
 
 CURLcode