feat: Message#previous to get responses in negotiation

HTTP::Message#previous keeps previous response in negotiation.  For
redirection, authorization negotiation and retry from custom filter.

Closes #234.

lib/httpclient.rb

@@ -954,6 +954,7 @@ def do_request(method, uri, query, body, header, &block)
     end
     retry_count = @session_manager.protocol_retry_count
     proxy = no_proxy?(uri) ? nil : @proxy
+    previous = nil
     while retry_count > 0
       body.pos = pos if pos
       req = create_request(method, uri, query, body, header)
@@ -962,9 +963,10 @@ def do_request(method, uri, query, body, header, &block)
           do_get_block(req, proxy, conn, &block)
         end
         res = conn.pop
+        res.previous = previous
         break
       rescue RetryableResponse
-        res = conn.pop
+        previous = conn.pop
         retry_count -= 1
       end
     end
@@ -1029,15 +1031,18 @@ def follow_redirect(method, uri, query, body, header, &block)
       pos = body.pos rescue nil
     end
     retry_number = 0
+    previous = nil
     while retry_number < @follow_redirect_count
       body.pos = pos if pos
       res = do_request(method, uri, query, body, header, &filtered_block)
+      res.previous = previous
       if res.redirect?
         if res.header['location'].empty?
           raise BadResponseError.new("Missing Location header for redirect", res)
         end
         method = :get if res.see_other? # See RFC2616 10.3.4
         uri = urify(@redirect_uri_callback.call(uri, res))
+        previous = res
         retry_number += 1
       else
         return res

test/test_auth.rb

@@ -146,7 +146,11 @@ def test_BASIC_auth
       c.www_auth.basic_auth.instance_eval { @scheme = "BASIC" }
       #
       c.set_auth("http://localhost:#{serverport}/", 'admin', 'admin')
-      assert_equal('basic_auth OK', c.get_content("http://localhost:#{serverport}/basic_auth"))
+      res = c.get("http://localhost:#{serverport}/basic_auth")
+      assert_equal('basic_auth OK', res.content)
+      assert_equal(200, res.status)
+      assert_equal(401, res.previous.status)
+      assert_equal(nil, res.previous.previous)
     ensure
       @basic_auth.instance_eval { @auth_scheme = webrick_backup }
     end

test/test_httpclient.rb

@@ -710,7 +710,13 @@ def test_head_follow_redirect
   def test_get_follow_redirect
     assert_equal('hello', @client.get(serverurl + 'hello', :follow_redirect => true).body)
     assert_equal('hello', @client.get(serverurl + 'redirect1', :follow_redirect => true).body)
-    assert_equal('hello', @client.get(serverurl + 'redirect2', :follow_redirect => true).body)
+
+    res = @client.get(serverurl + 'redirect2', :follow_redirect => true)
+    assert_equal('hello', res.body)
+    assert_equal("http://localhost:#{@serverport}/hello", res.header.request_uri.to_s)
+    assert_equal("http://localhost:#{@serverport}/redirect3", res.previous.header.request_uri.to_s)
+    assert_equal("http://localhost:#{@serverport}/redirect2", res.previous.previous.header.request_uri.to_s)
+    assert_equal(nil, res.previous.previous.previous)
   end
 
   def test_get_async