I am working on an application for chatting. I wondering how to design the API for getting messages from a server.
When the application loads the chat window, I display the last 20 messages from the server using the endpoint:
/messages?user1={user1Id}&user2={user2Id}&page=0
Secondly, I allow user to load and display previous messages when the users scrolls to the top using the same endpoint but with different page (1)
/messages?user1={user1Id}&user2={user2Id}&page=1
But this design doesn't work correctly when users start to send messages to each others. The reason is that the endpoint returns the messages using descending order. Invoking the endpoint will give different result sets before sending/receiving a message and after.
My goal is to get always 20 previous messages when a user scrolls through conversation history.
How would you implement this in a clean way (including the REST API design)? I can imagine some solutions, but they seem dirty to me.
REST does not scale well for real time applications. It takes too many resources to open the HTTP connection again and again. Better to use websockets for it.
As of the upper problem if you start pagination with the latest message, not with the first message, then I would not wonder that it changes. To keep the pages after it you need to send the message id you started with. So for example: GET ...&count=20&latest=1, after that you get a 20 list of messages, you get the message id of the latest one and do the pagination with GET ...&count=20&basePoint={messageId}&page=0 to always get the exact same page no matter that you got new messages. After that you continue with GET ...&count=20&basePoint={messageId}&page=1 and so on... You will have negative pages GET ...&count=20&basePoint={messageId}&page=-1 if there are newer messages. Though I don't know any chatting application which uses pagination this way.
What I would do is GET ...&count=20&latest=1 and get the 20th message and do GET ...&count=20&before={messageId_20th} after that get the last message again from that list which is the 40th and do GET ...&count=20&before={messageId_40th} and so on. To get the new messages you can do GET ...&count=20&latest=1 again or GET ...&count=20&after={messageId_1st}.
None of the above is really good if you are using a caching mechanism in the client. I would add something like key frames in videos, so key messages. For example every 20th message can be a key message. I would do caching based on the key message ids so the responses could be cacheable, something like GET ...&count=20&latest=1 would return messages and one in the middle of the list would have a property of keyMessage=true. I would start the next request from the last key message something like GET ...&count=20&before={messageId_lastKey}, so the response will be cacheable.
Another way of doing this is starting pagination from the very first message. So when you do GET ...&count=20&latest=1 it will write the index of the message, something like 1234th message. You can do caching based on every 20th message just like in the key message solution, but instead of the message ids, you can do GET ...&count=20&to=1220 and merge the pages on the client. Or if you really want to spare with data, then GET ...&from=1201&to=1220&before=1215 or GET ...&from=1201&to=1220&last=1214 or GET ...&from=1201&to=1214, etc... And continue normal pagination with GET ...&count=20&to=1200 or GET ...&from=1181&to=1200.
What is good with the upper fixed pages approach, that you can use range headers too. For example GET .../latest would return the last 20 message with the header of Content-Range: messages 1215-1234/1234. After that you can do GET .../ Range: messages=1201-1214 and GET .../ Range: messages=1181-1200 and so on... When the total message count is updated in the response Content-Range: messages 1181-1200/1245, then you can automagically download the new message with GET .../ Range: messages=1235-1245 or with GET .../ Range: messages=1235- if you expect the 1245 to change meanwhile. You can do the same thing with the URI too, but if you have a standard solution like range headers it is better to use it instead of reinventing the wheel.
As of the &user1={user1Id}&user2={user2Id} part I would order it based on alphabet, so always user1 would be earlier in alphabetic order than user2, something like &user1=B&user2=A -> &user1=A&user2=B. So that will be properly cacheable too, not necassarily on the client, but you can add a server side cache too, so if the two participating users try to get the same conversation recently it won't be queried from the database again. Another way of doing this is adding a conversation id, which can be random unique or generated from the two user ids, but it must be always the same for the two users e.g. /conversations/A+B or /conversations/x23542asda. I would do the latter, because if you start support conversations with multiple users it is better to have a dedicated conversation identifier. Another thing you can support is having multiple topic related conversations between the two users, so you won't need to do /conversations/A+B/{topic} just use a unique id and search for conversations before creating a new one, so either /conversations?participants[]=A&participants[]=B&topic={topic} will give you an empty list or a list with a single conversation. This could be used to list coversations of a single user /conversations?participants[]=A or list conversations of a single user in a certain topic /conversations?participants[]=A&topic={topic}.
Generally speaking, for "system design" questions, there isn't any one correct answer. Multiple approaches can be considered, based on their pros and cons. You've mentioned you want a clean way to retrieve messages, so your expectation might be different from mine.
Here is a simple approach/idea to get you started:
Have a field in your database that can be used to order messages. It could be a timestamp, a message_id, or something else that you want. Let's call this m_id for now.
On your client, have a field that tracks the m_id of the earliest message currently available locally on the client. This key (let's call it earliest_m_id) will be used to query the database, because you can simply fetch x number of messages before the earliest_m_id.
This would solve your issue of incorrect messages being fetched. Using paging will not work, since pages will continuously change with the exchange of messages.
Related
At my company we have a DELETE endpoint which (obviously) deletes some data that the user selects on the client side. Currently we are doing another get request to refresh the data on this page after the deletion requests completes successfully (So we don't have two conflicting states on client/server side).
A developer at our company wants to now change the DELETE endpoint to return the updated state after the data is successfully deleted, so we can just use this response value to update our client side.
This makes sense to me (As we can avoid another GET call) but from other threads the general consensus is that we should return an empty response.
Can someone explain to me why this is the case? I've looked around it seems like people are mostly saying 'because that is how REST is supposed to be' which doesn't really seem like a good reason.
I want to attach a button for a media group
To do this, I intercept the message and see if there is the same mediaGroup_id, then I save the file_id to the database
After all messages from this media group have been received, I send them to a group in a separate channel (here is the problem) -> how can I determine that this is the last message from the media group, I had a stupid idea to create a job with a delay of several seconds, enough time to receive the entire media group, and then send the entire media group in this job, however, I am worried about the reliability of this method, and for sure it will be buggy if one day I have to use asynchronous
Then, in the main channel, I send a message containing a link to the media group and a button, as I wanted
Is there some way to do this more elegantly?
That actually sounds rather reasonable and in fact I know a bot that does something very similar. The idea why this works, is that TG apparently first uploads all the media files and then sends all messages at once rather then looping over "upload, then send".
I want to reduce the number of requests from Telegram to my server and make the bot receive only messages with images, URLs or documents. I use webhook.
If this is achievable, then how?
It is possible to some extend through the allowed_updates parameter of the https://core.telegram.org/bots/api#setwebhook method:
List the types of updates you want your bot to receive. For example, specify [“message”, “edited_channel_post”, “callback_query”] to only receive updates of these types. See Update for a complete list of available update types. Specify an empty list to receive all updates regardless of type (default). If not specified, the previous setting will be used.
Very sadly though it is not possible to receive only updates with urls, since this is text.
If you want to reduce the amount of requests made, than you could attempt to use the getUpdates method. Sorry :/
I have an activity feed system that uses Redis sorted sets.
Events happen and a message is placed into a sorted set for each relevant user, with a timestamp for the score.
The messages are then distributed to the users, either when they log in, or through a push if the user is currently logged in.
I'd like to differentiate between messages that have been "read" by the user and ones that are still unread.
From my understanding, I can't just have a "read/unread" property as part of the member as changing it would cause the member to be different and therefore be added a second time, instead of replacing the current member.
So, what I'm thinking is that for each user, I have to sorted sets - an "unread" set and a "read" set.
When new events come in, they're added to the "unread" set
When the user reads a message, I add the message to the read set and remove it from the unread set.
A little less sure on how to deliver them. I can't just union them as I lose the distinction between read/unread unless I inverse the score on the unread ones, for instance.
Returning the two sets individually (and merging them in code) makes paging difficult. I'd like to be able to the 20 most recent messages regardless of read/unread status.
So, questions:
Is the read set/unread set way the best way to do it? Is there a better way?
What's the best way to return subsets of the merged/union'd data.
Thanks!
Instead of trying to update the member, you could just pop it and insert a new version. Should be no problem, because you know both member and its timestamp.
I am building an API and am a little unsure whether it would be better to have a request that brings back all information relating to a resource, or just bring back info separately according to tasks that need carrying out. For example, I have a messages resource and am struggling to decide whether to bring back all message information in one go. OR have a separate request for unread messages, a separate request for a list of messages and another request for a single message.
What is the proper way? I am tempted to keep them all separate but then worrya bout having to do too many requests.
Stop worrying and just do.
I like to keep things separate in the beginning, and at some point, I realise that request x always followed by request y, so I'll just merge those two. You won't know what you'll need until you're working on it...