Does postgREST support request middleware?

[FelixZY]

Does postgREST support request middleware?

Basically, I would like to be able to take some action(s) for incoming requests, e.g. log requests to a special table, log the request body for query optimization (graphql), intercept requests and yield pre-calculated responses (caching), verify request parameters, etc.. I'm using hosted postgREST, meaning I do not have direct access to the host and logs; SQL only.

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Implementation suggestions

In case this is not supported, I was thinking that maybe a workflow like this could work:

• Enable request logging via a custom configuration parameter. This would cause all requests to be logged to a special table
• The table would contain special fields to indicate the state of the request. These fields would allow for middleware to intercept requests at different stages (e.g. pre-request vs post-request). See also https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/readyState and https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/readystatechange_event
• "Middleware" could be created by adding hooks to this table. A middleware which wishes to return early could, for example, raise a special sqlstate or mutate the fields of the log entry to indicate the desired result.

While this does cause some overhead and may not be practical for read-only replicas, it would be a great help for people using managed postgREST, e.g. via Supabase.

[FelixZY]

Yes, postgREST supports request interception:

• https://postgrest.org/en/v12/references/transactions.html#pre-request
• https://postgrest.org/en/v12/references/configuration.html#db-pre-request
• https://gist.github.com/FelixZY/0aef530690458b381b8100afa19202c8#file-supabase_api_auth-sql-L893-L896

Note that GET requests cause the database to be opened in a read only state, meaning it is not possible to perform writes (such as logging to a table) during such requests from this hook.

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I find this solution to have some flaws:

• Only one function may be defined as "middleware"
• It is not possible to perform writes for GET requests