Add early hints support

While not part of the rack spec, this API is exposed
by both puma and falcon, and Rails use it when available.

The 103 Early Hints response code is specified in RFC 8297.

1 files changed, 29 insertions, 2 deletions

diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 45a2e97..05dad99 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -15,7 +15,7 @@ class Unicorn::HttpServer
                 :before_fork, :after_fork, :before_exec,
                 :listener_opts, :preload_app,
                 :orig_app, :config, :ready_pipe, :user,
-                :default_middleware
+                :default_middleware, :early_hints
   attr_writer   :after_worker_exit, :after_worker_ready, :worker_exec
 
   attr_reader :pid, :logger
@@ -588,6 +588,25 @@ class Unicorn::HttpServer
   rescue
   end
 
+  def e103_response_write(client, headers)
+    response = if @request.response_start_sent
+      "103 Early Hints\r\n"
+    else
+      "HTTP/1.1 103 Early Hints\r\n"
+    end
+
+    headers.each_pair do |k, vs|
+      next if !vs || vs.empty?
+      values = vs.to_s.split("\n".freeze)
+      values.each do |v|
+        response << "#{k}: #{v}\r\n"
+      end
+    end
+    response << "\r\n".freeze
+    response << "HTTP/1.1 ".freeze if @request.response_start_sent
+    client.write(response)
+  end
+
   def e100_response_write(client, env)
     # We use String#freeze to avoid allocations under Ruby 2.1+
     # Not many users hit this code path, so it's better to reduce the
@@ -602,7 +621,15 @@ class Unicorn::HttpServer
   # once a client is accepted, it is processed in its entirety here
   # in 3 easy steps: read request, call app, write app response
   def process_client(client)
-    status, headers, body = @app.call(env = @request.read(client))
+    env = @request.read(client)
+
+    if early_hints
+      env["rack.early_hints"] = lambda do |headers|
+        e103_response_write(client, headers)
+      end
+    end
+
+    status, headers, body = @app.call(env)
 
     begin
       return if @request.hijacked?