Handle errors: allow to return Twirp::Error from handlers, and also raise Twitp::Error exceptions

lib/twirp/error.rb

@@ -29,7 +29,12 @@ module Twirp
   ERROR_CODES = ERROR_CODES_TO_HTTP_STATUS.keys
 
   # Twirp::Error represents a valid error from a Twirp service
-	class Error
+	class Error < StandardError
+
+    # Wrap an arbitrary error as a Twirp :internal
+    def self.InternalWith(err)
+      self.new :internal, err.message, "cause" => err.class.name
+    end
 
     # Initialize a Twirp::Error
     # The code MUST be one of the valid ERROR_CODES Symbols (e.g. :internal, :not_found, :permission_denied ...).
@@ -74,6 +79,10 @@ module Twirp
       JSON.generate(as_json)
     end
 
+    def to_s
+      "Twirp::Error code:#{code} msg:#{msg.inspect} meta:#{meta.inspect}"
+    end
+
     private
 
     def validate_code(code)
@@ -99,7 +108,7 @@ module Twirp
 
     def validate_meta_key_value(key, value)
       if !key.is_a?(String) || !value.is_a?(String)
-        raise ArgumentError.new("Twirp::Error meta must be a Hash with String keys and values")
+        raise ArgumentError.new("Twirp::Error meta must be a Hash with String keys and values. Invalid key<#{key.class}>: #{key.inspect}, value<#{value.class}>: #{value.inspect}")
       end
     end
 

lib/twirp/service.rb

@@ -85,15 +85,23 @@ module Twirp
 
     # Rack app handler.
     def call(env)
-      req = Rack::Request.new(env)
-      rpc, content_type, bad_route = parse_rack_request(req)
-      if bad_route
-        return error_response(bad_route)
+      begin
+        req = Rack::Request.new(env)
+        rpc, content_type, bad_route = parse_rack_request(req)
+        if bad_route
+          return error_response(bad_route)
+        end
+        
+        proto_req = decode_request(rpc[:request_class], content_type, req.body.read)
+        resp = @handler.send(rpc[:handler_method], proto_req)
+        return rack_response_from_handler(rpc, content_type, resp)
+
+      rescue Twirp::Error => twerr
+        error_response(twerr)
+      rescue StandardError => err
+        puts err.backtrace
+        error_response(Twirp::Error.InternalWith(err))
       end
-      
-      proto_req = decode_request(rpc[:request_class], content_type, req.body.read)
-      resp = @handler.send(rpc[:handler_method], proto_req)
-      return rack_response_from_handler(rpc, content_type, resp)
     end
 
     def path_prefix

test/service_test.rb

@@ -133,7 +133,7 @@ class ServiceTest < Minitest::Test
     status, headers, body = haberdasher_service.call(env)
 
     assert_equal 404, status
-    assert_equal 'application/json', headers['Content-Type'] # error messages are always JSON, even for Protobuf requests
+    assert_equal 'application/json', headers['Content-Type'] # error responses are always JSON, even for Protobuf requests
     assert_equal({
       "code" => 'bad_route', 
       "msg" => 'Invalid route. Expected format: POST {BaseURL}/twirp/(package.)?{Service}/{Method}',
@@ -180,6 +180,38 @@ class ServiceTest < Minitest::Test
     assert_equal Example::Hat.new(inches: 0, color: ""), Example::Hat.decode(body[0])
   end
 
+  # Handler should be able to return Twirp::Exception values, that will trigger error responses
+  def test_handler_returns_twirp_exception
+    svc = Example::Haberdasher.new(HaberdasherHandler.new do |size|
+      return Twirp::Error.new(:invalid_argument, "I don't like that size")
+    end)
+
+    env = proto_req "/twirp/example.Haberdasher/MakeHat", Example::Size.new(inches: 666)
+    status, headers, body = svc.call(env)
+    assert_equal 400, status
+    assert_equal 'application/json', headers['Content-Type'] # error responses are always JSON, even for Protobuf requests
+    assert_equal({
+      "code" => 'invalid_argument', 
+      "msg" => "I don't like that size",
+    }, JSON.parse(body[0]))
+  end
+
+  # Handler should be able to raise a Twirp::Exception, that will trigger error responses
+  def test_handler_raises_twirp_exception
+    svc = Example::Haberdasher.new(HaberdasherHandler.new do |size|
+      raise Twirp::Error.new(:invalid_argument, "I don't like that size")
+    end)
+
+    env = proto_req "/twirp/example.Haberdasher/MakeHat", Example::Size.new(inches: 666)
+    status, headers, body = svc.call(env)
+    assert_equal 400, status
+    assert_equal 'application/json', headers['Content-Type'] # error responses are always JSON, even for Protobuf requests
+    assert_equal({
+      "code" => 'invalid_argument', 
+      "msg" => "I don't like that size",
+    }, JSON.parse(body[0]))
+  end
+
 
   # Test Helpers
   # ------------