async_http_client_adapter crashes with protocol-http >= 0.59.0 — NoMethodError: undefined method 'split' for nil

[renatovico]

WebMockClientWrapper#build_request_signature calls request.headers.to_h (line 103 in async_http_client_adapter.rb). Starting with protocol-http 0.59.0, Headers#to_h invokes Header::Split.parse(value) on each header entry during merging. When a header has a nil value (which is valid in the Protocol::HTTP::Headers collection for internal/connection headers), Split.parse calls value.split(COMMA) on nil and raises:

NoMethodError: undefined method 'split' for nil
  protocol-http-0.59.0/lib/protocol/http/header/split.rb:23:in 'Protocol::HTTP::Header::Split.parse'
  protocol-http-0.59.0/lib/protocol/http/headers.rb:452:in 'Protocol::HTTP::Headers#merge_into'
  protocol-http-0.59.0/lib/protocol/http/headers.rb:473:in 'block in Protocol::HTTP::Headers#to_h'
  webmock-3.26.1/lib/webmock/http_lib_adapters/async_http_client_adapter.rb:103:in 'build_request_signature'

Steps to reproduce:

# Gemfile
gem "faraday"
gem "async-http-faraday"
gem "webmock"

# test
require "async/http/faraday/default"  # sets async-http as Faraday default adapter
require "webmock/rspec"

WebMock.disable_net_connect!

stub_request(:get, "https://example.com/test")
  .to_return(status: 200, body: '{"ok":true}')

# This crashes:
Faraday.get("https://example.com/test")
# => NoMethodError: undefined method 'split' for nil

Environment
webmock 3.26.1
protocol-http >= 0.59.0
async-http >= 0.94.0
async-http-faraday 0.22.1
Ruby 3.2+ / 3.4+

Root Cause
In async_http_client_adapter.rb line 103:

def build_request_signature(request)
  body = request.read
  request.body = ::Protocol::HTTP::Body::Buffered.wrap(body)
  WebMock::RequestSignature.new(
    request.method.downcase.to_sym,
    "#{request.scheme}://#{request.authority}#{request.path}",
    headers: request.headers.to_h,  # <--- crashes here
    body: body
  )
end

request.headers can contain entries with nil values. The protocol-http 0.59.0 Headers#to_h now strictly parses every value through header policy classes, which don't handle nil.

Suggested Fix
Filter out nil-valued headers before conversion:

def build_request_signature(request)
  body = request.read
  request.body = ::Protocol::HTTP::Body::Buffered.wrap(body)

  headers = {}
  request.headers.each do |key, value|
    headers[key] = value unless value.nil?
  end

  WebMock::RequestSignature.new(
    request.method.downcase.to_sym,
    "#{request.scheme}://#{request.authority}#{request.path}",
    headers: headers,
    body: body
  )
end

Workaround

if defined?(Async::HTTP::WebMockClientWrapper)
  module Async
    module HTTP
      class WebMockClientWrapper
        private

        def build_request_signature(request)
          body = request.read
          request.body = ::Protocol::HTTP::Body::Buffered.wrap(body)

          headers = {}
          request.headers.each do |key, value|
            headers[key] = value unless value.nil?
          end

          WebMock::RequestSignature.new(
            request.method.downcase.to_sym,
            "#{request.scheme}://#{request.authority}#{request.path}",
            headers: headers,
            body: body
          )
        end
      end
    end
  end
end

[renatovico]

@ioquatix can confirm if here fault?

[ioquatix]

Well, I'll try to take a closer look, but a nil header value is not typically valid.

[renatovico]

any update ? i can do the pull request ?