SquatchMail.SNS.RawBodyReader (SquatchMail v0.1.1)

A Plug.Parsers body reader that caches the raw request body in conn.assigns[:raw_body] before returning it for JSON parsing.

SquatchMail.SNS.MessageVerifier/SquatchMail.SNS.Processor.process/2 need the exact bytes SNS sent (to rebuild the signed string and, incidentally, because Processor.process/2 does its own JSON decode) - by the time Plug.Parsers hands a controller a parsed conn.params, the original body is gone unless something captured it first.

Do you need this?

Usually no. squatch_mail_dashboard pipes the webhook route through SquatchMail.SNS.RawBodyPlug, which captures the raw body automatically — hosts don't have to wire anything. This module remains as an optional Plug.Parsers :body_reader for hosts that prefer to capture the raw body at the endpoint themselves; RawBodyPlug detects an already-set conn.assigns[:raw_body] and stands down, so the two never fight.

Note that a :body_reader alone is not sufficient for SNS: SNS sends Content-Type: text/plain; charset=UTF-8, which Plug.Parsers matches no parser for, so it never invokes the :body_reader for a real SNS request. That is exactly why RawBodyPlug (which reads unconditionally, after the parsers pass the body through unread) is the reliable default.

Wiring this in (optional)

Plug.Parsers accepts a :body_reader option that must be a {module, function, args} tuple implementing the same contract as Plug.Conn.read_body/2 ({:ok, body, conn} | {:more, partial, conn} | {:error, term}), invoked once per chunk. Point it at this module wherever the host endpoint configures Plug.Parsers:

plug Plug.Parsers,
  parsers: [:json],
  json_decoder: Jason,
  body_reader: {SquatchMail.SNS.RawBodyReader, :read_body, []}

This must run before :json parsing consumes the body.

Summary

Functions

read_body(conn, opts \\ [])

Drop-in replacement for Plug.Conn.read_body/2 that additionally appends every chunk read to conn.assigns[:raw_body] (starting from ""), so the full raw body is available under that key once parsing completes - including when the body arrives in multiple chunks ({:more, ...}).

Functions

read_body(conn, opts \\ [])

@spec read_body(
  Plug.Conn.t(),
  keyword()
) ::
  {:ok, binary(), Plug.Conn.t()}
  | {:more, binary(), Plug.Conn.t()}
  | {:error, term()}