feat: allow overriding HTTP parser body length via env var

[ngdangdat]

Summary

Make Plug.Parsers's :length configurable via APP_HTTP_MAX_BODY_LENGTH (defaults to the current 8 MB).

Reference: Plug.Parsers — Options — :length sets the maximum body length the parser accepts; it defaults to 8_000_000 bytes.

Why

Pushing a Terraform state larger than 8 MB fails with:

Acquiring state lock. This may take a few moments...
Failed to persist state: HTTP error: 413

ls -lah errored.tfstate
-rw-rw-r-- 1 michael michael 8.0M Apr 29 06:24 errored.tfstate

The errored.tfstate is exactly 8.0M, which trips Plug.Parsers's default :length of 8_000_000 bytes in lib/lynx_web/endpoint.ex:52. State files in real-world projects routinely grow past that, so the cap needs to be tunable per-deployment.

Change

Wired the limit through application config (sitting next to the existing LynxWeb.Endpoint config keys, matching the APP_HOST pattern already there):

# config/config.exs
config :lynx, LynxWeb.Endpoint,
  ...
  http_max_body_length: String.to_integer(System.get_env("APP_HTTP_MAX_BODY_LENGTH") || "8000000")

# lib/lynx_web/endpoint.ex
@max_body_length Application.compile_env(
                   :lynx,
                   [__MODULE__, :http_max_body_length],
                   8_000_000
                 )

plug Plug.Parsers,
  parsers: [:urlencoded, :multipart, :json],
  pass: ["*/*"],
  length: @max_body_length,
  json_decoder: Phoenix.json_library()

Default behavior is unchanged. Operators bumping into 413s can set e.g. APP_HTTP_MAX_BODY_LENGTH=104857600 for 100 MB before building/booting the app.

Note: because Application.compile_env/3 resolves at compile time, the env var needs to be set when the release is built — same lifecycle as the other env-driven config keys here (APP_HOST, APP_SECRET).

Tests

test/lynx_web/endpoint_test.exs covers:

• :http_max_body_length defaults to 8_000_000 so existing deployments are unaffected.
• The configured value is accepted by Plug.Parsers.init/1 as :length.

Test plan

• mix test test/lynx_web/endpoint_test.exs is green.
• Boot without the env var — uploads up to 8 MB still work, >8 MB returns 413 (current behavior).
• Set APP_HTTP_MAX_BODY_LENGTH=33554432 and confirm a ~16 MB tfstate push succeeds.

[ngdangdat]

Hi @Clivern,

Please help to review the PR when you have time. I'm facing this issue when using Lynx in my production environment 🙇

tofu apply
...
Acquiring state lock. This may take a few moments...
Failed to persist state: HTTP error: 413

Thank you in advance!

[Clivern]

lgtm

[Clivern]

Created a new docker image https://hub.docker.com/layers/clivern/lynx/0.12.10/images/sha256-80a0def2cc281d450052ba9d5bbdc229cfdebef009d680d5e299ea5f395731b9