Add request retry preparation

lib/protocol/http/request.rb

@@ -153,6 +153,34 @@ def idempotent?
 				return false
 			end
 
+			# Prepare the request body to be sent again, if it is safe to retry.
+			# @returns [Boolean] Whether the request was prepared for retry.
+			def retry!
+				# Only idempotent request methods can be retried safely.
+				if @method == Methods::POST || @method == Methods::PATCH || @method == Methods::CONNECT
+					return false
+				end
+
+				# Requests without a body can be sent again immediately.
+				if body = @body
+					# Empty, non-rewindable bodies have nothing left to send.
+					if body.empty? && !body.rewindable?
+						return true
+					end
+
+					# Non-empty bodies must be rewindable so the same data can be sent again.
+					if !body.rewindable?
+						return false
+					end
+
+					if !body.rewind
+						return false
+					end
+				end
+
+				return true
+			end
+
 			# Convert the request to a hash, suitable for serialization.
 			#
 			# @returns [Hash] The request as a hash.

test/protocol/http/request.rb

@@ -152,6 +152,56 @@
 			end
 		end
 
+		with "PATCH request without a body" do
+			let(:request) {subject["PATCH", "/resource"]}
+
+			it "should be idempotent" do
+				expect(request).to be(:idempotent?)
+			end
+		end
+
+		with "#retry!" do
+			it "allows idempotent requests without a body" do
+				expect(request.retry!).to be == true
+			end
+
+			with "idempotent request with a rewindable body" do
+				let(:request) {subject["PUT", "/resource", body: "content"]}
+
+				it "allows retry and rewinds the body" do
+					expect(request.body.read).to be == "content"
+
+					expect(request.retry!).to be == true
+					expect(request.body.read).to be == "content"
+				end
+			end
+
+			with "idempotent request with a non-rewindable body" do
+				let(:body) {Protocol::HTTP::Body::Readable.new}
+				let(:request) {subject.new(nil, nil, "PUT", "/resource", nil, headers, body)}
+
+				it "does not allow retry" do
+					expect(request.retry!).to be == false
+				end
+			end
+
+			with "non-idempotent request" do
+				let(:request) {subject["POST", "/submit"]}
+
+				it "does not allow retry" do
+					expect(request.retry!).to be == false
+				end
+			end
+
+			with "PATCH request" do
+				let(:request) {subject["PATCH", "/resource"]}
+
+				it "does not allow retry" do
+					expect(request.retry!).to be == false
+				end
+			end
+		end
+
 		it "should have a string representation" do
 			expect(request.to_s).to be == "http://localhost: GET /index.html HTTP/1.0"
 		end