job-info: validate keys array on lookup

Problem: Throughout lookup code there are checks if the values
within the keys array are strings.  It would be simpler if this
check was only done once.

Check that the keys array is an array and contains only strings
within the primary lookup callback.

Author: chu11

src/modules/job-info/lookup.c

@@ -131,12 +131,7 @@ static int lookup_keys (struct lookup_ctx *l)
     }
 
     json_array_foreach (l->keys, index, key) {
-        const char *keystr;
-        if (!(keystr = json_string_value (key))) {
-            errno = EINVAL;
-            goto error;
-        }
-        if (lookup_key (l, fall, keystr) < 0)
+        if (lookup_key (l, fall, json_string_value (key)) < 0)
             goto error;
     }
 
@@ -197,14 +192,9 @@ static void info_lookup_continuation (flux_future_t *fall, void *arg)
 
     json_array_foreach (l->keys, index, key) {
         flux_future_t *f;
-        const char *keystr;
+        const char *keystr = json_string_value (key); /* validated earlier */
         json_t *str = NULL;
 
-        if (!(keystr = json_string_value (key))) {
-            errno = EINVAL;
-            goto error;
-        }
-
         if (!(f = flux_future_get_child (fall, keystr))) {
             flux_log_error (ctx->h, "%s: flux_future_get_child", __FUNCTION__);
             goto error;
@@ -279,12 +269,7 @@ static int check_keys_for_eventlog (struct lookup_ctx *l)
     }
 
     json_array_foreach (l->keys, index, key) {
-        const char *keystr;
-        if (!(keystr = json_string_value (key))) {
-            errno = EINVAL;
-            return -1;
-        }
-        if (streq (keystr, "eventlog"))
+        if (streq (json_string_value (key), "eventlog"))
             return 0;
     }
 
@@ -297,6 +282,8 @@ void lookup_cb (flux_t *h, flux_msg_handler_t *mh,
 {
     struct info_ctx *ctx = arg;
     struct lookup_ctx *l = NULL;
+    size_t index;
+    json_t *key;
     json_t *keys;
     flux_jobid_t id;
     uint32_t rolemask;
@@ -318,6 +305,19 @@ void lookup_cb (flux_t *h, flux_msg_handler_t *mh,
         goto error;
     }
 
+    /* validate keys is an array and all fields are strings */
+    if (!json_is_array (keys)) {
+        errno = EPROTO;
+        goto error;
+    }
+
+    json_array_foreach (keys, index, key) {
+        if (!json_is_string (key)) {
+            errno = EPROTO;
+            goto error;
+        }
+    }
+
     if (!(l = lookup_ctx_create (ctx, msg, id, keys, flags)))
         goto error;