complete url if location header is relative path

spec/redirect_spec.cr

@@ -6,6 +6,10 @@ WebMock.stub(:post, "http://example.com/post")
   .with(body: "email=foobar", headers: {"Content-Type" => "application/x-www-form-urlencoded"})
   .to_return(status: 302, body: "redirect", headers: {"Location" => "http://example.com/redirect"})
 
+WebMock.stub(:post, "http://example.com/post2")
+  .with(body: "email=foobar", headers: {"Content-Type" => "application/x-www-form-urlencoded"})
+  .to_return(status: 302, body: "redirect", headers: {"Location" => "/redirect"})
+
 describe "Mechanize redirect test" do
   it "redirect" do
     agent = Mechanize.new
@@ -14,4 +18,12 @@ describe "Mechanize redirect test" do
     page.body.should eq("success")
     page.code.should eq(200)
   end
+
+  it "redirect with relative path" do
+    agent = Mechanize.new
+    query = {"email" => "foobar"}
+    page = agent.post("http://example.com/post2", query: query)
+    page.body.should eq("success")
+    page.code.should eq(200)
+  end
 end

src/mechanize/http/agent.cr

@@ -32,15 +32,15 @@ module MechanizeCr
         save_response_cookies(response, uri, page)
 
         if response && response.status.redirection?
-          return follow_redirect(response, headers)
+          return follow_redirect(response, headers, page)
         end
 
         page
       end
 
-      private def follow_redirect(response, headers)
+      private def follow_redirect(response, headers, referer)
         redirect_url = response.headers["location"]
-        uri = URI.parse(redirect_url)
+        uri = resolve_url(redirect_url, referer)
 
         # Make sure we are not copying over the POST headers from the original request
         headers.delete("Content-MD5")