54 lines
2.1 KiB
Markdown
54 lines
2.1 KiB
Markdown
# Architecture
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This document describes the high-level architecture of PostgREST.
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## Bird's Eye View
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On the highest level, PostgREST processes the user HTTP request, if it's accepted it generates a SQL query, executes it, and produces a response.
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## Code Map
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This section talks briefly about various important modules.
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The starting points of the program are `main/Main.hs` -> `src/PostgREST/CLI.hs` -> `src/PostgREST/App.hs`.
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`App.hs` is then in charge of composing the different modules.
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### Auth
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It authenticates the request using JWT.
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### ApiRequest
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PostgREST operates over two types of resources: database relations (tables or views) and database functions; providing different representations (depending on the media type)
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for them.
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This module is in charge of representing the operation over an `ApiRequest` type. It parses the URL querystring following PostgREST syntax, the request headers, and the request body
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(if possible it avoids parsing the body and sends it directly to the db).
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A request might be rejected at this level if it's invalid. For example when providing an unknown media type to PostgREST or using an unknown HTTP method.
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### Plan
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Using the Schema Cache, this module enables more complex functionality (like resource embedding) by enriching the ApiRequest. It generates intermediate Plan types
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that then will be used for the next step.
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A request might be rejected at this level if it's invalid. For example when doing resource embedding on a nonexistent resource.
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### Query
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This module generates SQL queries that are parametrized and prepared. Only at this stage a connection from the pool might be used.
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A query might fail (and be rollbacked) at this level if it doesn't comply to certain conditions, e.g. by not returning a single row when a ``Accept: application/vnd.pgrst.object``
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header is specified.
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### SchemaCache
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This queries the PostgreSQL system catalogs and caches the results into a SchemaCache type, which then is used by the other modules.
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### Admin
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Admin server exposed in another port, it provides health checks.
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