Add ability to set Content-Type and Content-Length HTTP headers

According to the Rack documentation, those headers are not supported through the HTTP_ variables:
https://www.rubydoc.info/github/rack/rack/file/SPEC#The_Environment

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [1.4.0] - unreleased
 - Support non-GET requests via REQUEST_METHOD and setting body via REQUEST_BODY
+- Add ability to set Content-Type and Content-Length headers via CONTENT_TYPE and CONTENT_LENGTH env vars (they don't work with HTTP_ variables)
 
 
 ## [1.3.4]

README.md

@@ -438,6 +438,8 @@ $ HTTP_AUTHORIZATION="Basic YWRtaW46c2VjcmV0\n" \
   PATH_TO_HIT=/foo_secret bundle exec derailed exec perf:ips
 ```
 
+The `Content-Type` and `Content-Length` headers are a bit different. To set those, ignore the HTTP_ prefix, use the `CONTENT_TYPE` and `CONTENT_LENGTH` variables.
+
 ### Performing non-GET requests
 
 If the endpoint being tested is not a GET request, you can set the `REQUEST_METHOD` variable with the HTTP method you want (e.g. POST, PUT, PATCH, DELETE).
@@ -446,7 +448,8 @@ To set the request body, you can use the `REQUEST_BODY`.
 
 ```
 $ REQUEST_METHOD=POST \
-  REQUEST_BODY="user%5Bemail%5D=foo%40bar.com&user%password%5D=123456&user%password_confirmation%5D=123456" \
+  REQUEST_BODY="{\"user\":{\"email\":\"foo@bar.com\",\"password\":\"123456\",\"password_confirmation\":\"123456\"}}" \
+  CONTENT_TYPE="application/json" \
   PATH_TO_HIT=/users \
   bundle exec derailed exec perf:test
 ```

lib/derailed_benchmarks/tasks.rb

@@ -75,12 +75,22 @@
     puts "Endpoint: #{ PATH_TO_HIT.inspect }"
 
     # See https://www.rubydoc.info/github/rack/rack/file/SPEC#The_Environment
+    # All HTTP_ variables are accepted in the Rack environment hash, except HTTP_CONTENT_TYPE and HTTP_CONTENT_LENGTH.
+    # For those, the HTTP_ prefix has to be removed.
     HTTP_HEADER_PREFIX = "HTTP_".freeze
-    RACK_ENV_HASH = ENV.select { |key| key.start_with?(HTTP_HEADER_PREFIX) }
+    HTTP_HEADER_REGEXP = /^#{HTTP_HEADER_PREFIX}.+|CONTENT_(TYPE|LENGTH)$/
+    RACK_ENV_HASH = ENV.select { |key| key =~ HTTP_HEADER_REGEXP }
 
     HTTP_HEADERS = RACK_ENV_HASH.keys.inject({}) do |hash, rack_header_name|
       # e.g. "HTTP_ACCEPT_CHARSET" -> "Accept-Charset"
-      header_name = rack_header_name[HTTP_HEADER_PREFIX.size..-1].split("_").map(&:downcase).map(&:capitalize).join("-")
+      upper_case_header_name =
+        if rack_header_name.start_with?(HTTP_HEADER_PREFIX)
+          rack_header_name[HTTP_HEADER_PREFIX.size..-1]
+        else
+          rack_header_name
+        end
+
+      header_name = upper_case_header_name.split("_").map(&:downcase).map(&:capitalize).join("-")
 
       hash[header_name] = RACK_ENV_HASH[rack_header_name]
       hash

test/integration/tasks_test.rb

@@ -83,6 +83,25 @@ def rake(cmd, options = {})
     assert_match 'HTTP headers: {"Authorization"=>"Basic YWRtaW46c2VjcmV0\n", "Cache-Control"=>"no-cache"}', result
   end
 
+  test 'CONTENT_TYPE' do
+    env = {
+      "REQUEST_METHOD" => "POST",
+      "PATH_TO_HIT" => "users",
+      "CONTENT_TYPE" => "application/json",
+      "REQUEST_BODY" => '{"user":{"email":"foo@bar.com","password":"123456","password_confirmation":"123456"}}',
+      "TEST_COUNT" => "2"
+    }
+
+    result = rake "perf:test", env: env
+    assert_match 'Body: {"user":{"email":"foo@bar.com","password":"123456","password_confirmation":"123456"}}', result
+    assert_match 'HTTP headers: {"Content-Type"=>"application/json"}', result
+
+    env["USE_SERVER"] = "webrick"
+    result = rake "perf:test", env: env
+    assert_match 'Body: {"user":{"email":"foo@bar.com","password":"123456","password_confirmation":"123456"}}', result
+    assert_match 'HTTP headers: {"Content-Type"=>"application/json"}', result
+  end
+
   test 'REQUEST_METHOD and REQUEST_BODY' do
     env = {
       "REQUEST_METHOD" => "POST",