Class: AtlasRb::Middleware::RaiseOnReadError

Inherits:
Faraday::Middleware
  • Object
show all
Defined in:
lib/atlas_rb/middleware/raise_on_read_error.rb

Overview

Raises ResourceError when a read comes back non-2xx, so no read binding can hand an error body back as if it were data.

Why a middleware rather than a guard per binding

Resource.fetch_resource enforces this contract for the typed single-resource finds, but a binding has to opt in by routing through it, and the read surface is about thirty methods wide. The failures that come of forgetting are the ones hardest to attribute: JSON.parse on an error envelope yields a Hash with no payload key, so the caller dereferences nil far from the cause; a binding returning a raw body hands the error text to whatever renders it. Enforcing at the transport means a binding cannot forget.

Scope: reads only

Keyed on the request method, because SAFE_METHODS is what "a read" means on the wire. The write path has its own guard (Resource.write_resource, which names the verb and path in a NotFoundError), and several write bindings — tombstone, destroy, complete — deliberately return the raw response so their caller can read a 422 discriminator Atlas owns as a wire contract. Raising on those would take that away.

The two POST-shaped reads (Resource.find_many, Blob.find_many_versions) are out of reach here, so they call FaradayHelper#read_body — which applies the same mapping — directly.

Statuses that pass through

  • 404 — "absent" is a legitimate answer to a read, so the binding answers nil. That holds for a list read too: "no such container" and "an empty container" mean different things to a UI.
  • 410 — a tombstone arrives as 410 Gone with its full body, so it is a returnable answer rather than an error envelope.

Ordering

Register this before the typed translators (RaiseOnStaleResource, RaiseOnResourceError, RaiseOnReadOnlyMode). Faraday runs on_complete innermost-first, so the handler registered earliest runs last — which is where this one belongs: a maintenance 503 must stay a ReadOnlyModeError and a refused re-parent must stay a ForbiddenError, not become a generic ResourceError.

Constant Summary collapse

SAFE_METHODS =

Request methods this middleware treats as reads.

i[get head].freeze
PASS_THROUGH =

Read statuses that are answers rather than failures.

[404, 410].freeze

Instance Method Summary collapse

Instance Method Details

#on_complete(env) ⇒ void

This method returns an undefined value.

Parameters:

  • env (Faraday::Env) —

    the completed response environment.

Raises:



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# File 'lib/atlas_rb/middleware/raise_on_read_error.rb', line 61

def on_complete(env)
  return unless SAFE_METHODS.include?(env.method)
  return if env.status < 400 || PASS_THROUGH.include?(env.status)
  return if streaming?(env)

  raise AtlasRb::ResourceError.new(
    "#{env.method.to_s.upcase} #{env.url&.path} → #{env.status}: #{env.body}",
    response: env.response
  )
end