in_http: Add support for HTTP GET requests

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

This teaches Fluentd to respond nicely with "200 OK"

Signed-off-by: Fujimoto Seiji <[email protected]>

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 sends GET requests for health checking purpose.
+      # Respond with `200 OK` to accommodate it.
+      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
@@ -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)