Support HTTY_ERROR_LOG environment variable for server-side debug logging.

Author: ioquatix

lib/async/htty/server.rb

@@ -48,7 +48,13 @@ def self.open(app = nil, input: $stdin, output: $stdout, error: $stderr, env: EN
 				stream = ::Protocol::HTTY::Stream.new(original_input, original_output)
 				input.reopen(File::NULL)
 				output.reopen(File::NULL)
-				error.reopen(File::NULL)
+				
+				# Redirect error output to a file if specified, otherwise discard it:
+				if error_log = ENV.fetch("HTTY_ERROR_LOG", nil)
+					error.reopen(File.open(error_log, "a"))
+				else
+					error.reopen(File::NULL)
+				end
 
 				Sync do |task|
 					with_raw_terminal(original_input) do

releases.md

@@ -3,6 +3,7 @@
 ## Unreleased
 
   - Suppress errors from `send_goaway` during connection cleanup to prevent shutdown exceptions from propagating.
+  - Support redirecting server-side stderr to a file via the `HTTY_ERROR_LOG` environment variable, enabling debug logging without corrupting the HTTY byte stream.
 
 ## v0.3.0