Module: RailsAiContext::OutputGuard

Defined in:
lib/rails_ai_context/output_guard.rb

Overview

Redirects $stdout to $stderr for the duration of a block. The stdio MCP transport carries JSON-RPC on stdout, so anything the host app prints while booting (initializer puts, gem banners, deprecation warnings) corrupts the protocol handshake and the client reports a dead server.

Swaps the $stdout global AND reopens file descriptor 1 onto $stderr's target. The global swap catches puts/print (which read $stdout); the fd reopen additionally catches code that writes through the STDOUT constant directly, and any subprocess that inherits fd 1 from this process. Code that dup'd fd 1 before this method runs holds its own descriptor pointing at the original target and stays out of reach either way.

The fd reopen only happens when $stderr is backed by a real file descriptor. Unit specs commonly swap $stderr for a StringIO, and STDOUT.reopen(StringIO) raises TypeError - that case falls back to the global-swap-only behavior above.

Dependency-free on purpose: standalone mode loads this file before the host app's Bundler.setup runs, so it must not pull in the rest of the gem.

Class Method Summary collapse

Class Method Details

.quarantine_stdout ⇒ Object 



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# File 'lib/rails_ai_context/output_guard.rb', line 24

def self.quarantine_stdout
  original = $stdout
  saved_stdout = reopenable_target? ? STDOUT.dup : nil
  STDOUT.reopen($stderr) if saved_stdout
  $stdout = $stderr
  yield
ensure
  if saved_stdout
    STDOUT.reopen(saved_stdout)
    saved_stdout.close
  end
  $stdout = original
end