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> Could you explain with more details what properties of HTTP makes it hard to deal with complex data? There are a few but one of the first that comes to mind

> Could you explain with more details what properties of HTTP makes it hard to deal with complex data? There are a few but one of the first that comes to mind is what happens if two users modify different fields/properties of the same resource at the same time? If you want to support concurrent editing by multiple users, you need a way to either automatically resolve conflicts or to avoid conflicts altogether. With REST over HTTP, because updates typically involve overwriting the whole resource in a single POST or PUT, one user will fully overwrite the changes made by the other user; even if they were editing different fields of the same resource.

spinningarrow 8y ago
But is that a failing of HTTP? “Updates typically involve overwriting the whole resource” because of how many APIs implement updates; they could for example use PATCH instead. I believe GraphQL mutations also allow updating individual fields.
lucideer 8y ago
You seem to be describing a use-case for HTTP PATCH. What is there about what you're describing that's more difficult with PATCH than alternative protocols? Unless of course you have two users directly editing the same field simultaneously, but this is a direct conflict case that any underlying implementations will have to have their own strategy for—HTTP wouldn't be any different to anything else here.
- jondubois 8y ago
  That's true, PATCH would solve that specific writing aspect of the problem, but there is still the issue that each user would not know that the other user has changed another property; we need some kind of server push mechanism to inform users that the underlying data has changed. Also, if users update one field at a time, it's more expensive to have one HTTP request per field (considering the HTTP headers overhead and potentially having to open a new connection) rather than using one WebSocket frame per update.
  - jungturk 8y ago
    Server-sent events might be a good fit here. Note that SSE belongs to the content layer (HTML) rather than the transfer layer (HTTP) so its specifically about notifications to active clients about content changes to resources they're observing. Here's someone describing their experience with it: https://medium.com/axiomzenteam/websockets-http-2-and-sse-5c24ae4d9d96 https://medium.com/axiomzenteam/websockets-http-2-and-sse-5c...
    - jondubois 8y ago
      The fact that the SSE connection is unidirectional makes it impossible to quickly and efficiently detect disconnection from the server-side; this costs extra in terms of performance. Also, SSEs make it essentially impossible to implement features like real-time user online/offline presence and automatic renewal of authentication tokens (without closing the previous real-time/SSE connection).
      - jungturk 8y ago
        Good points about the limitations - SSE certainly won't be useful for lots of scenarios and you might prefer resorting to traditional approaches in those scenarios (in lieu of or in concert with an SSE channel).
  - icebraining 8y ago
    there is still the issue that each user would not know that the other user has changed another property; we need some kind of server push mechanism to inform users that the underlying data has changed If the data occasionally changes, you can just respond to the update request with a 409 Conflict reporting the problem and allowing the user to fix it. If it's changing so fast that it requires real-time updates, the user can't probably keep up either, so you should re-think your mechanism.
drchickensalad 8y ago
Other than patch, there's also etags and match headers that are frequently used and well supported.
rasteau 8y ago
> what happens if two users modify different fields/properties of the same resource at the same time? https://tools.ietf.org/html/rfc7231#section-6.5.8 https://tools.ietf.org/html/rfc7231#section-6.5.8 6.5.8. 409 Conflict The 409 (Conflict) status code indicates that the request could not be completed due to a conflict with the current state of the target resource. This code is used in situations where the user might be able to resolve the conflict and resubmit the request. The server SHOULD generate a payload that includes enough information for a user to recognize the source of the conflict. Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the representation being PUT included changes to a resource that conflict with those made by an earlier (third-party) request, the origin server might use a 409 response to indicate that it can't complete the request. In this case, the response representation would likely contain information useful for merging the differences based on the revision history. Conflict resolution is inherently a consequence of the application-specific semantics of a "conflict". If the notion of "conflict" exists -- i.e., it is not obviated by application design[1] -- then conflict resolution is pushed to the caller. That said, it may be reasonable to develop reusable conflict resolution mechanisms for reusable definitions of "conflict", allowing for composition of separate concerns as needed. This seems preferable to inventing a new system that binds concerns together with a single, irrevocable notion of "conflict". [1] Using PATCH does not obviate conflicts that the application design otherwise allows.

spinningarrow 8y ago

But is that a failing of HTTP? “Updates typically involve overwriting the whole resource” because of how many APIs implement updates; they could for example use PATCH instead. I believe GraphQL mutations also allow updating individual fields.

lucideer 8y ago

You seem to be describing a use-case for HTTP PATCH. What is there about what you're describing that's more difficult with PATCH than alternative protocols? Unless of course you have two users directly editing the same field simultaneously, but this is a direct conflict case that any underlying implementations will have to have their own strategy for—HTTP wouldn't be any different to anything else here.

jondubois 8y ago
That's true, PATCH would solve that specific writing aspect of the problem, but there is still the issue that each user would not know that the other user has changed another property; we need some kind of server push mechanism to inform users that the underlying data has changed. Also, if users update one field at a time, it's more expensive to have one HTTP request per field (considering the HTTP headers overhead and potentially having to open a new connection) rather than using one WebSocket frame per update.
- jungturk 8y ago
  Server-sent events might be a good fit here. Note that SSE belongs to the content layer (HTML) rather than the transfer layer (HTTP) so its specifically about notifications to active clients about content changes to resources they're observing. Here's someone describing their experience with it: https://medium.com/axiomzenteam/websockets-http-2-and-sse-5c24ae4d9d96 https://medium.com/axiomzenteam/websockets-http-2-and-sse-5c...
  - jondubois 8y ago
    The fact that the SSE connection is unidirectional makes it impossible to quickly and efficiently detect disconnection from the server-side; this costs extra in terms of performance. Also, SSEs make it essentially impossible to implement features like real-time user online/offline presence and automatic renewal of authentication tokens (without closing the previous real-time/SSE connection).
    - jungturk 8y ago
      Good points about the limitations - SSE certainly won't be useful for lots of scenarios and you might prefer resorting to traditional approaches in those scenarios (in lieu of or in concert with an SSE channel).
- icebraining 8y ago
  there is still the issue that each user would not know that the other user has changed another property; we need some kind of server push mechanism to inform users that the underlying data has changed If the data occasionally changes, you can just respond to the update request with a 409 Conflict reporting the problem and allowing the user to fix it. If it's changing so fast that it requires real-time updates, the user can't probably keep up either, so you should re-think your mechanism.

drchickensalad 8y ago

Other than patch, there's also etags and match headers that are frequently used and well supported.

rasteau 8y ago

> what happens if two users modify different fields/properties of the same resource at the same time? https://tools.ietf.org/html/rfc7231#section-6.5.8 https://tools.ietf.org/html/rfc7231#section-6.5.8 6.5.8. 409 Conflict The 409 (Conflict) status code indicates that the request could not be completed due to a conflict with the current state of the target resource. This code is used in situations where the user might be able to resolve the conflict and resubmit the request. The server SHOULD generate a payload that includes enough information for a user to recognize the source of the conflict. Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the representation being PUT included changes to a resource that conflict with those made by an earlier (third-party) request, the origin server might use a 409 response to indicate that it can't complete the request. In this case, the response representation would likely contain information useful for merging the differences based on the revision history. Conflict resolution is inherently a consequence of the application-specific semantics of a "conflict". If the notion of "conflict" exists -- i.e., it is not obviated by application design[1] -- then conflict resolution is pushed to the caller. That said, it may be reasonable to develop reusable conflict resolution mechanisms for reusable definitions of "conflict", allowing for composition of separate concerns as needed. This seems preferable to inventing a new system that binds concerns together with a single, irrevocable notion of "conflict". [1] Using PATCH does not obviate conflicts that the application design otherwise allows.