job-info: avoid error response on failed rpc

Problem: Common usage in flux-core is to not respond with an RPC error
(such as through flux_respond_error()) if a prior RPC attempt fails (such
as through flux_respond_pack()).  This pattern is violated in several
places in job-info.

Solution: If flux_respond_pack() fails, do not call flux_respond_error()
in error handling paths.

Fixes #6498

src/modules/job-info/guest_watch.c

@@ -587,6 +587,7 @@ static void guest_namespace_watch_continuation (flux_future_t *f, void *arg)
     struct guest_watch_ctx *gw = arg;
     struct info_ctx *ctx = gw->ctx;
     const char *event;
+    bool skip_respond_error = false;
 
     if (flux_job_event_watch_get (f, &event) < 0) {
         if (errno == ENOTSUP) {
@@ -639,6 +640,7 @@ static void guest_namespace_watch_continuation (flux_future_t *f, void *arg)
     if (flux_respond_pack (ctx->h, gw->msg, "{s:s}", "event", event) < 0) {
         flux_log_error (ctx->h, "%s: flux_respond_pack",
                         __FUNCTION__);
+        skip_respond_error = true;
         goto error_cancel;
     }
 
@@ -657,6 +659,9 @@ static void guest_namespace_watch_continuation (flux_future_t *f, void *arg)
         errno = save_errno;
     }
 
+    if (skip_respond_error)
+        goto cleanup;
+
 error:
     if (flux_respond_error (ctx->h, gw->msg, errno, NULL) < 0)
         flux_log_error (ctx->h, "%s: flux_respond_error", __FUNCTION__);
@@ -763,7 +768,7 @@ static void main_namespace_lookup_continuation (flux_future_t *f, void *arg)
                                "event", tok, toklen) < 0) {
             flux_log_error (ctx->h, "%s: flux_respond_pack",
                             __FUNCTION__);
-            goto error;
+            goto cleanup;
         }
     }
 

src/modules/job-info/update.c

@@ -143,6 +143,7 @@ static void eventlog_continuation (flux_future_t *f, void *arg)
     json_t *context = NULL;
     const char *errmsg = NULL;
     const flux_msg_t *msg;
+    bool skip_respond_error = false;
 
     if (flux_rpc_get (f, NULL) < 0) {
         /* ENODATA is normal when job finishes or we've sent cancel */
@@ -196,6 +197,7 @@ static void eventlog_continuation (flux_future_t *f, void *arg)
                                        "{s:O}",
                                        uc->key, uc->update_object) < 0) {
                     flux_log_error (ctx->h, "%s: flux_respond", __FUNCTION__);
+                    skip_respond_error = true;
                     goto error_cancel;
                 }
                 msg = flux_msglist_next (uc->msglist);
@@ -212,6 +214,9 @@ static void eventlog_continuation (flux_future_t *f, void *arg)
      * freed */
     eventlog_watch_cancel (uc);
 
+    if (skip_respond_error)
+        goto cleanup;
+
 error:
     msg = flux_msglist_first (uc->msglist);
     while (msg) {
@@ -360,7 +365,7 @@ static void lookup_continuation (flux_future_t *f, void *arg)
         if (flux_respond_pack (uc->ctx->h, msg, "{s:O}",
                                uc->key, uc->update_object) < 0) {
             flux_log_error (ctx->h, "%s: flux_respond", __FUNCTION__);
-            goto error;
+            goto cleanup;
         }
 
     next:
@@ -520,7 +525,7 @@ void update_watch_cb (flux_t *h,
                                    "{s:O}",
                                    uc->key, uc->update_object) < 0) {
                 flux_log_error (ctx->h, "%s: flux_respond", __FUNCTION__);
-                goto error;
+                goto cleanup;
             }
         }
         /* if uc->update_object has not been set, the initial lookup
@@ -536,6 +541,7 @@ void update_watch_cb (flux_t *h,
 error:
     if (flux_respond_error (h, msg, errno, errmsg) < 0)
         flux_log_error (h, "%s: flux_respond_error", __FUNCTION__);
+cleanup:
     free (index_key);
 }
 

src/modules/job-info/watch.c

@@ -224,6 +224,7 @@ static void watch_continuation (flux_future_t *f, void *arg)
     const char *tok;
     size_t toklen;
     const char *errmsg = NULL;
+    bool skip_respond_error = false;
 
     if (flux_kvs_lookup_get (f, &s) < 0) {
         if (errno != ENOENT && errno != ENODATA && errno != ENOTSUP)
@@ -266,6 +267,7 @@ static void watch_continuation (flux_future_t *f, void *arg)
             flux_log_error (ctx->h,
                             "%s: flux_respond_pack",
                             __FUNCTION__);
+            skip_respond_error = true;
             goto error_cancel;
         }
 
@@ -306,6 +308,9 @@ static void watch_continuation (flux_future_t *f, void *arg)
         errno = save_errno;
     }
 
+    if (skip_respond_error)
+        goto cleanup;
+
 error:
     if (flux_respond_error (ctx->h, w->msg, errno, errmsg) < 0)
         flux_log_error (ctx->h, "%s: flux_respond_error", __FUNCTION__);