Handle HTTP redirection.

spec/web_finger/client_spec.cr

@@ -35,6 +35,8 @@ class HTTP::Client
       raise Socket::Addrinfo::Error.new(LibC::EAI_NONAME, "No address found", url.host)
     end
     case url.query || url.path
+    when /redirect/
+      yield HTTP::Client::Response.new(302, headers: HTTP::Headers{"Location" => "https://elsewhere/"})
     when /not-found/
       yield HTTP::Client::Response.new(404)
     when /internal-server-error/
@@ -128,6 +130,11 @@ Spectator.describe WebFinger::Client do
       end
     end
 
+    it "redirects" do
+      WebFinger::Client.query("acct:redirect@example.com")
+      expect(HTTP::Client.history.map(&.host)).to contain("elsewhere")
+    end
+
     it "makes an HTTP request to the account domain" do
       WebFinger::Client.query("acct:foobar@example.com")
       expect(HTTP::Client.history.map(&.host)).to contain("example.com")

src/web_finger/client.cr

@@ -10,6 +10,10 @@ module WebFinger
   class NotFoundError < Error
   end
 
+  # Redirection failed.
+  class RedirectionError < Error
+  end
+
   # The client.
   module Client
     # Returns the result of querying for the specified account.
@@ -20,10 +24,11 @@ module WebFinger
     #     w = WebFinger.query("acct:toddsundsted@epiktistes.com") # => #<WebFinger::Result:0x108d...>
     #     w.link("http://webfinger.net/rel/profile-page").href # => "https://epiktistes.com/@toddsundsted"
     #
-    # Raises `WebFinger::NotFoundError` if the account does not
-    # exist. Otherwise, returns `WebFinger::Result`.
+    # Raises `WebFinger::NotFoundError` if the account does not exist
+    # and `WebFinger::RedirectionError` if redirection failed.
+    # Otherwise, returns `WebFinger::Result`.
     #
-    def self.query(account)
+    def self.query(account, attempts = 10)
       unless account =~ /^([^@]+)@([^@]+)$/
         raise Error.new("invalid account: #{account}")
       end
@@ -38,25 +43,36 @@ module WebFinger
 
       url = template.gsub("{uri}", URI.encode_www_form(account))
 
-      HTTP::Client.get(url) do |response|
-        case (code = response.status_code)
-        when 200
-          mt = response.mime_type.try(&.media_type)
-          if mt =~ /xml/
-            Result.from_xml(response.body_io)
-          elsif mt =~ /json/
-            Result.from_json(response.body_io)
-          elsif response.body_io.peek.try(&.first) == 123 # sniff for '{'
-            Result.from_json(response.body_io)
+      attempts.times do |i|
+        HTTP::Client.get(url) do |response|
+          case (code = response.status_code)
+          when 200
+            mt = response.mime_type.try(&.media_type)
+            result =
+              if mt =~ /xml/
+                Result.from_xml(response.body_io)
+              elsif mt =~ /json/
+                Result.from_json(response.body_io)
+              elsif response.body_io.peek.try(&.first) == 123 # sniff for '{'
+                Result.from_json(response.body_io)
+              else
+                Result.from_xml(response.body_io)
+              end
+            return result
+          when 300, 301, 302, 303, 307, 308
+            if (tmp = response.headers["Location"]?) && (url = tmp)
+              next
+            else
+              break
+            end
+          when 404
+            raise NotFoundError.new("not found [#{code}]: #{url}")
           else
-            Result.from_xml(response.body_io)
+            raise Error.new("error [#{code}]: #{url}")
           end
-        when 404
-          raise NotFoundError.new("not found [#{code}]: #{url}")
-        else
-          raise Error.new("error [#{code}]: #{url}")
         end
       end
+      raise RedirectionError.new("redirection failed: #{url}")
     rescue ex : Socket::Addrinfo::Error
       raise NotFoundError.new(ex.message)
     end