in_http: Add support for HTTP GET requests

Requested by Josh Keegan. Evidently Azure App uses HTTP GET to check
if the HTTP server is working all right. Since Fluentd responds with
"400 Bad Requests" to GET requests, it does not work well.

This commit teaches Fluentd to respond nicely with a plain "200 OK"

Signed-off-by: Fujimoto Seiji <fujimoto@ceptord.net>

lib/fluent/plugin/in_http.rb

@@ -461,6 +461,12 @@ def on_body(chunk)
       RES_200_STATUS = "200 OK".freeze
       RES_403_STATUS = "403 Forbidden".freeze
 
+      # Azure App Service uses `GET /` as a health check.
+      # Simply return `200 OK` here.
+      def handle_get_request
+          return send_response_and_close(RES_200_STATUS, {}, "")
+      end
+
       # Web browsers can send an OPTIONS request before performing POST
       # to check if cross-origin requests are supported.
       def handle_options_request
@@ -469,7 +475,7 @@ def handle_options_request
           return send_response_and_close(RES_403_STATUS, {}, "")
         end
 
-        # in_http does not support HTTP methods except POST
+        # in_http does not support HTTP methods except POST and GET
         if @access_control_request_method != 'POST'
           return send_response_and_close(RES_403_STATUS, {}, "")
         end
@@ -494,6 +500,10 @@ def handle_options_request
       def on_message_complete
         return if closing?
 
+        if @parser.http_method == 'GET'.freeze
+          return handle_get_request()
+        end
+
         if @parser.http_method == 'OPTIONS'.freeze
           return handle_options_request()
         end

test/plugin/test_in_http.rb

@@ -770,6 +770,15 @@ def test_cors_allowed_wildcard
     end
   end
 
+  def test_get_request
+    d = create_driver(CONFIG)
+
+    d.run do
+      res = get("/cors.test", {}, {})
+      assert_equal "200", res.code
+    end
+  end
+
   def test_cors_preflight
     d = create_driver(CONFIG + 'cors_allow_origins ["*"]')
 
@@ -985,6 +994,12 @@ def test_if_content_type_is_initialized_properly
     assert_equal $test_in_http_connection_object_ids[0], $test_in_http_connection_object_ids[1]
   end
 
+  def get(path, params, header = {})
+    http = Net::HTTP.new("127.0.0.1", PORT)
+    req = Net::HTTP::Get.new(path, header)
+    http.request(req)
+  end
+
   def options(path, params, header = {})
     http = Net::HTTP.new("127.0.0.1", PORT)
     req = Net::HTTP::Options.new(path, header)