Rack::ShowExceptions catches all exceptions raised from the app it wraps. It shows a useful backtrace with the sourcefile and clickable context, the whole Rack environment and the request data.
Be careful when you use this on public-facing sites as it could reveal information helpful to attackers.
# File lib/rack/showexceptions.rb, line 18 def initialize(app) @app = app @template = ERB.new(TEMPLATE) end
# File lib/rack/showexceptions.rb, line 23 def call(env) @app.call(env) rescue StandardError, LoadError, SyntaxError => e backtrace = pretty(env, e) [500, {"Content-Type" => "text/html", "Content-Length" => backtrace.join.size.to_s}, backtrace] end
# File lib/rack/showexceptions.rb, line 33 def pretty(env, exception) req = Rack::Request.new(env) path = (req.script_name + req.path_info).squeeze("/") frames = exception.backtrace.map { |line| frame = OpenStruct.new if line =~ %r(.*?):(\d+)(:in `(.*)')?/ frame.filename = $1 frame.lineno = $2.to_i frame.function = $4 begin lineno = frame.lineno-1 lines = ::File.readlines(frame.filename) frame.pre_context_lineno = [lineno-CONTEXT, 0].max frame.pre_context = lines[frame.pre_context_lineno...lineno] frame.context_line = lines[lineno].chomp frame.post_context_lineno = [lineno+CONTEXT, lines.size].min frame.post_context = lines[lineno+1..frame.post_context_lineno] rescue end frame else nil end }.compact env["rack.errors"].puts "#{exception.class}: #{exception.message}" env["rack.errors"].puts exception.backtrace.map { |l| "\t" + l } env["rack.errors"].flush [@template.result(binding)] end