[PR] perf(ctx): cache parsed request body to avoid repeated decode for post_arg.* [apisix]

["AlinsRan (via GitHub)" <gi...@apache.org>]

AlinsRan opened a new pull request, #13356:
URL: https://github.com/apache/apisix/pull/13356

   ## Summary
   
   When multiple `post_arg.*` variables are evaluated in a single request
   (e.g. `vars` expressions in route matching), each access independently
   triggers a full body read + `json.decode` cycle. For large request
   bodies at high QPS, this causes unnecessary repeated CPU and memory
   overhead.
   
   ## Changes
   
   Split `get_parsed_request_body` into two layers:
   
   - `_get_parsed_request_body(ctx)` — pure parsing logic, no side effects
   - `get_parsed_request_body(ctx)` — wrapper that adds a per-request ctx cache
   
   On the first access, the decoded table is stored in `ctx._parsed_request_body`.
   Subsequent accesses to different `post_arg.*` keys within the same request
   reuse the cached result, so `json.decode` runs at most once per request.
   
   Errors are intentionally **not cached**: plugins may call
   `ngx.req.set_body_data()` in later phases, so a transient parse failure
   should not be permanently frozen for the request lifetime.
   
   ## Tests
   
   Added TEST 3/4 in `t/core/ctx3.t`: a route with three different
   `post_arg.*` keys, verifying all fields are read correctly and that
   the `reuse parsed request body from ctx cache` debug log appears
   exactly twice (for the second and third key accesses).


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Re: [PR] perf(ctx): cache parsed request body to avoid repeated decode for post_arg.* [apisix]

["AlinsRan (via GitHub)" <gi...@apache.org>]

AlinsRan merged PR #13356:
URL: https://github.com/apache/apisix/pull/13356


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Re: [PR] perf(ctx): cache parsed request body to avoid repeated decode for post_arg.* [apisix]

["AlinsRan (via GitHub)" <gi...@apache.org>]

AlinsRan commented on PR #13356:
URL: https://github.com/apache/apisix/pull/13356#issuecomment-4427473004

   The body rewrite cache invalidation approach (body version counter + `patch.lua` monkey-patching + `set_body_data` hook) has been reverted from this PR.
   
   The existing variable-level cache in `ctx.__index` has the same limitation — it does not invalidate on `set_body_data` either — so fixing it only for the body-level cache would be inconsistent and add complexity without addressing the general problem. That is a separate concern for a future PR.
   
   This PR now contains only the core optimization: `get_parsed_request_body` caches the parsed body table in `ctx` for the request lifetime, so `json.decode` is called at most once per request regardless of how many different `post_arg.*` keys are accessed.


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