fix: follow first redirect when fetching remote pact artifacts. (#80)

When a pact artifact is fetched remotely, the method in Pact::PactFile
that facilitates this will now follow a single redirect response. If
the second request results in anything but a 200 response, an error
will be raised.

lib/pact/consumer_contract/pact_file.rb

@@ -79,12 +79,37 @@ def get_remote_with_retry(uri_string, options)
 
     def get_remote(uri, options)
       request = Net::HTTP::Get.new(uri)
+      request = prepare_auth(request, options) if options[:username] || options[:token]
+
+      http = prepare_request(uri)
+      response = perform_http_request(http, request, options)
+
+      if response.is_a?(Net::HTTPRedirection)
+        uri = URI(response.header['location'])
+        req = Net::HTTP::Get.new(uri)
+        req = prepare_auth(req, options) if options[:username] || options[:token]
+
+        http = prepare_request(uri)
+        response = perform_http_request(http, req, options)
+      end
+      response
+    end
+
+    def prepare_auth(request, options)
       request.basic_auth(options[:username], options[:password]) if options[:username]
       request['Authorization'] = "Bearer #{options[:token]}" if options[:token]
+      request
+    end
+
+    def prepare_request(uri)
       http = Net::HTTP.new(uri.host, uri.port, :ENV)
       http.use_ssl = (uri.scheme == 'https')
       http.ca_file = ENV['SSL_CERT_FILE'] if ENV['SSL_CERT_FILE'] && ENV['SSL_CERT_FILE'] != ''
       http.ca_path = ENV['SSL_CERT_DIR'] if ENV['SSL_CERT_DIR'] && ENV['SSL_CERT_DIR'] != ''
+      http
+    end
+
+    def perform_http_request(http, request, options)
       http.start do |http|
         http.open_timeout = options[:open_timeout] || OPEN_TIMEOUT
         http.read_timeout = options[:read_timeout] || READ_TIMEOUT

spec/lib/pact/consumer_contract/pact_file_spec.rb

@@ -7,6 +7,7 @@ module Pact
   describe PactFile do
     describe 'render_pact' do
       let(:uri_without_userinfo) { 'http://pactbroker.com'}
+      let(:redirect_uri_without_userinfo) { 'http://alternate-pactbroker.com'}
       let(:pact_content) { 'api contract'}
 
       describe 'from a local file URI' do
@@ -106,6 +107,18 @@ def render_pact(options = {})
           end
         end
 
+        context 'with redirect' do
+          before do
+            stub_request(:get, uri_without_userinfo).to_return(status: 302, headers: {"location" => redirect_uri_without_userinfo})
+            stub_request(:get, redirect_uri_without_userinfo).to_return(status: 200, body: pact_content)
+          end
+
+          it 'succeeds' do
+            expect(PactFile).not_to receive(:delay_retry)
+            expect(render_pact).to eq(pact_content)
+          end
+        end
+
         context 'with single server error' do
           before do
             stub_request(:get, uri_without_userinfo).to_return(status: 500).