API: posting new conversation: await message created (#2239)

This PR ensures a conversation is not created if we cannot create its
first message, and allows error handling before creating the conversation

Namely, when creating a new conversation with a message, the message
creation event (or error) is awaited. This is fast because we do not
wait for the full message posting (with all redis events, etc.), only
the creation event.

In doing so, it aligns the behaviour of
`front/pages/api/w/[wId]/assistant/conversations/index.ts` with
the ones of
`front/pages/api/v1/w/[wId]/assistant/conversations/index.ts`,
`front/pages/api/w/[wId]/assistant/conversations/[cId]/messages/index.ts`
and
`front/pages/api/v1/w/[wId]/assistant/conversations/[cId]/messages/index.ts`,
who were already awaiting

Required for [this task](dust-tt/tasks#128) (plan limits -- do not create the conversation if the
message cannot be created because the message limit has been reached)

front/pages/api/v1/w/[wId]/assistant/conversations/index.ts

@@ -138,8 +138,10 @@ async function handler(
       }
 
       if (message) {
-        // If a message was provided we do await for the message to be posted before returning the
-        // conversation along with the message.
+        // If a message was provided we do await for the message to be created
+        // before returning the conversation along with the message.
+        // PostUserMessageWithPubSub returns swiftly since it only waits for the
+        // initial message creation event (or error)
         const messageRes = await postUserMessageWithPubSub(auth, {
           conversation,
           content: message.content,

front/pages/api/w/[wId]/assistant/conversations/[cId]/messages/index.ts

@@ -109,8 +109,8 @@ async function handler(
 
       const { content, context, mentions } = bodyValidation.right;
 
-      // Not awaiting this promise on prupose. We want to answer "OK" to the client ASAP and process
-      // the events in the background.
+      /* postUserMessageWithPubSub returns swiftly since it only waits for the
+        initial message creation event (or error) */
       const messageRes = await postUserMessageWithPubSub(auth, {
         conversation,
         content,

front/pages/api/w/[wId]/assistant/conversations/index.ts

@@ -15,6 +15,7 @@ import { PostMessagesRequestBodySchema } from "@app/pages/api/w/[wId]/assistant/
 import {
   ConversationType,
   ConversationWithoutContentType,
+  UserMessageType,
 } from "@app/types/assistant/conversation";
 
 export const PostConversationsRequestBodySchema = t.type({
@@ -32,6 +33,7 @@ export type GetConversationsResponseBody = {
 };
 export type PostConversationsResponseBody = {
   conversation: ConversationType;
+  message?: UserMessageType;
 };
 
 async function handler(
@@ -122,11 +124,14 @@ async function handler(
         visibility,
       });
 
+      let newMessage: UserMessageType | null = null;
+
       if (message) {
-        // Not awaiting this promise on purpose. We want to answer "OK" to the client ASAP and
-        // process the events in the background. So that the client gets updated as soon as
-        // possible.
-        void postUserMessageWithPubSub(auth, {
+        /* If a message was provided we do await for the message to be created
+        before returning the conversation along with the message.
+        PostUserMessageWithPubSub returns swiftly since it only waits for the
+        initial message creation event (or error) */
+        const messageRes = await postUserMessageWithPubSub(auth, {
           conversation,
           content: message.content,
           mentions: message.mentions,
@@ -138,9 +143,14 @@ async function handler(
             profilePictureUrl: message.context.profilePictureUrl,
           },
         });
+        if (messageRes.isErr()) {
+          return apiError(req, res, messageRes.error);
+        }
+
+        newMessage = messageRes.value;
       }
 
-      res.status(200).json({ conversation });
+      res.status(200).json({ conversation, message: newMessage ?? undefined });
       return;
 
     default: