Debugging on Rails. Mykhaylo Sorochan

kiev.rb #2

kiev

#2
.rb

Debugging on Rails
Mykhaylo Sorochan

Debugged application
Sample app for the Ruby on Rails Tutorial (Rails 4)
https://github.com/railstutorial/sample_app_rails_4

debugger
gem 'debugger'
debugger - call debugger
config - .rdebugrc

Debug location
UserController#show

def show
@user = User.find(params[:id])
debugger
@microposts = @user.microposts.paginate(page: params[:page])
end

Debugger commands
(rdb:9) help
ruby-debug help v1.6.2
Type 'help <command-name>' for help on a specific command

Available commands:
backtrace

delete

enable

help

list

pry

restart

source

undisplay

break

disable

eval

info

method

ps

save

start

up

catch

display

exit

irb

next

putl

set

step

var

condition

down

finish

jump

p

quit

show

thread

where

continue

edit

frame

kill

pp

reload

skip

trace

Program info
(rdb:4) help info
Generic command for showing things about the program being debugged.
-List of info subcommands:
-info args -- Argument variables of current stack frame
info breakpoints -- Status of user-settable breakpoints
info catch -- Exceptions that can be caught in the current stack frame
info display -- Expressions to display when program stops
info file -- Info about a particular file read in
info files -- File names and timestamps of files read in
info global_variables -- Global variables
info instance_variables -- Instance variables of the current stack frame
info line -- Line number and file name of current position in source file
info locals -- Local variables of the current stack frame
info program -- Execution status of the program
info stack -- Backtrace of the stack
info thread -- List info about thread NUM
info threads -- information of currently-known threads
info variables -- Local and instance variables of the current stack frame

Listing
(rdb:1) help list
l[ist]

list forward

l[ist] -

list backward

l[ist] =

list current line

l[ist] nn-mm

list given lines

NOTE - to turn on autolist, use 'set autolist' -> .rdebugrc

Listing: in debug
12


13

debugger

=> 14
15
16

end

Listing: l 23,25
l 23,25
[23, 25] in */sample_app_rails_4/app/controllers/users_controller.rb
23

if @user.save

24

sign_in @user

25

flash[:success] = "Welcome to the Sample App!"

Breakpoints
(rdb:4) help break
b[reak] file:line [if expr]
b[reak] class(.|#)method [if expr]
set breakpoint to some position, (optionally) if expr == true
(rdb:4) help delete
del[ete][ nnn...]

delete some or all breakpoints

Set breakpoint
(rdb:4) b ApplicationHelper#full_title
Breakpoint 1 at ApplicationHelper::full_title
(rdb:4) b 18
Breakpoint 2 file */sample_app_rails_4/app/controllers/users_controller.rb, line 18
(rdb:4) info b
Num Enb What
1 y

at ApplicationHelper:full_title

2 y

at */sample_app_rails_4/app/controllers/users_controller.rb:18

Navigate
(rdb:4) help step
s[tep][+-]?[ nnn]

step (into methods) once or nnn times

'+' forces to move to another line.
'-' is the opposite of '+' and disables the force_stepping setting.
(rdb:4) help next
n[ext][+-]?[ nnn]

step over once or nnn times,

'+' forces to move to another line.
'-' is the opposite of '+' and disables the force_stepping setting.
(rdb:4) help up
up[count]

move to higher frame

Stop at breakpoint
(rdb:4) c
Breakpoint 1 at ApplicationHelper:full_title
[-1, 8] in */sample_app_rails_4/app/helpers/application_helper.rb
1

module ApplicationHelper

2
3
=> 4
5

# Returns the full title on a per-page basis.
def full_title(page_title)
base_title = "Ruby on Rails Tutorial Sample App"

Display
(rdb:4) help display
disp[lay] <expression>

add expression into display expression list

disp[lay]

display expression list

(rdb:4) help undisplay
undisp[lay][ nnn]
Cancel some expressions to be displayed when program stops.

Display configured
4
=> 5
6

def full_title(page_title)
if page_title.empty?

(rdb:4) disp
2: controller_name = users
3: base_title =

Display changed
(rdb:4) n
*/sample_app_rails_4/app/helpers/application_helper.rb:6

2: controller_name = users
3: base_title = Ruby on Rails Tutorial Sample App
[1, 10] in */sample_app_rails_4/app/helpers/application_helper.rb
5
=> 6
7

base_title

Conditional breakpoint
(rdb:8) b ApplicationHelper#full_title if page_title=="Alexander"
Breakpoint 4 at ApplicationHelper::full_title
(rdb:8) c
Breakpoint 1 at ApplicationHelper:full_title

Variables
(rdb:8) help var
v[ar] cl[ass]

show class variables of self

v[ar] co[nst] <object>

show constants of object

v[ar] g[lobal]

show global variables

v[ar] i[nstance] <object>

show instance variables of object. You may pass object id's hex as well.

v[ar] l[ocal]

show local variables

Show variables
12


13

debugger

=> 14
15

end

16
17

def new

(rdb:12) v i
@_action_has_layout = true
@_action_name = "show"
@_config = {}
@_env = {"GATEWAY_INTERFACE"=>"CGI/1.1", "PATH_INFO"=>"/users/1", "QUERY_STRING"=>"",...
@_headers = {"Content-Type"=>"text/html"}
@_lookup_context = #<ActionView::LookupContext:0x00000008e4b710 @details_key=nil, @details={:loc...
@_params = {"action"=>"show", "controller"=>"users", "id"=>"1"}
@_prefixes = ["users", "application"]
@_request = #<ActionDispatch::Request:0x00000008e4bad0 @env={"GATEWAY_INTERFACE"=>"CGI/1....
@_response = #<ActionDispatch::Response:0x00000008e4baa8 @mon_owner=nil, @mon_count=0, @mo...
@_response_body = nil
@_routes = nil
@_status = 200
@user = #<User id: 1, name: "Alexander", email: "asdf@asdf.com", created_at: "2013-11...

Remote debugger
Server
Debugger.wait_connection = true
Debugger.start_remote

Client
# rdebug --client -h 127.0.0.1
Connected.

*/sample_app_rails_4/app/controllers/users_controller.rb:14

[9, 18] in */sample_app_rails_4/app/controllers/users_controller.rb
9

end

10
11

def show

12


13

debugger

=> 14


debugger-pry
Call pry from debugger

pry-debugger
Debugger commands inside pry:
step, next, continue, breakpoints

jazz_hands
jazz_hands is an opinionated set of consolerelated gems and a bit of glue:
pry, awesome_print, hirb, pry-rails, pry-doc, pry-git,
pry-remote, pry-debugger, pry-stack_explorer, coolline,
coderay

Logging
ActiveSupport::Logger

is used for logging

Rails.root/log/[environment_name].log

Log levels
Rails.logger.level

| name

| level |

|----------+-------|
| :debug

|

0 |

| :info

|

1 |

| :warn

|

2 |

| :error

|

3 |

| :fatal

|

4 |

| :unknown |

5 |

development, testing:
production:

log_level = 0 (:debug)

log_level = 1

Messages with equal or higher level are sent to log

Write to log
logger.debug User.inspect
logger.info user.id
logger.fatal "Help!"

Tagging log messages
logger = ActiveSupport::TaggedLogging.new(Logger.new(STDOUT))
logger.tagged("USER") { logger.info "hello" }
=> [USER] hello

Tagged logging
def show
logger.tagged("USER") { logger.info @user.email }

# tail -f log/development.log|grep [USER]
[USER] asdf@asdf.com

Global variables for tracing
__FILE__

- file name

__LINE__

- line number

Some useful CLI commands
tail -n 100
tail -f
grep, less

Querying logs
# cat log/development.log|grep GET|tail -n 2
Started GET "/assets/users.js?body=1" for 127.0.0.1 at 2013-11-21 23:32:01 +0200
Started GET "/assets/application.js?body=1" for 127.0.0.1 at 2013-11-21 23:32:01 +0200

# cat log/development.log|grep GET|wc -l
574

config.log_formatter
Defines the formatter of the Rails logger.
Defaults to

ActiveSupport::Logger::SimpleFormatter

production defaults to

for all modes,

Logger::Formatter.

module ActiveSupport
class Logger < ::Logger

# Simple formatter which only displays the message.
class SimpleFormatter < ::Logger::Formatter
# This method is invoked when a log event occurs
def call(severity, timestamp, progname, msg)
"#{String === msg ? msg : msg.inspect}n"
end
end

config.log_level
Defaults to

:debug

for all modes, production defaults to

:info.

config.log_tags
See

ActionDispatch::Request

methods.

config.log_tags = [ :fullpath ]

[/users/1] Started GET "/users/1" for 127.0.0.1 at 2013-11-...
[/users/1]

ActiveRecord::SchemaMigration Load (0.1ms)

SELECT ...

[/assets/application.css?body=1] Started GET "/assets/application.css?body=1" for 127...

config.logger
Accepts a logger conforming to the interface of Log4r or the default Ruby Logger class.
Defaults to

ActiveSupport::Logger,

with auto flushing off in production mode.

Rails console
rails c
rails c --sandbox

irb
pry

rake routes
> all_routes = Rails.application.routes.routes
> require 'action_dispatch/routing/inspector'
> inspector = ActionDispatch::Routing::RoutesInspector.new(all_routes)

All routes
> puts inspector.format(ActionDispatch::Routing::ConsoleFormatter.new)
Prefix Verb

URI Pattern

Controller#Action

following_user GET

/users/:id/following(.:format) users#following

followers_user GET

/users/:id/followers(.:format) users#followers

users GET

/users(.:format)

users#index

/users(.:format)

users#create

/users/new(.:format)

users#new

/users/:id/edit(.:format)

users#edit

/users/:id(.:format)

users#show

PATCH


users#update

PUT


users#update

POST
new_user GET
edit_user GET
user GET

DELETE /users/:id(.:format)
sessions POST
new_session GET

/sessions(.:format)

sessions#create

/sessions/new(.:format)

sessions#new

session DELETE /sessions/:id(.:format)
microposts POST

/microposts(.:format)

micropost DELETE /microposts/:id(.:format)
relationships POST

/relationships(.:format)

relationship DELETE /relationships/:id(.:format)
root GET
signup GET

users#destroy

sessions#destroy
microposts#create
microposts#destroy
relationships#create
relationships#destroy

/

static_pages#home

/signup(.:format)

users#new

Routes for controller
> puts inspector.format(ActionDispatch::Routing::ConsoleFormatter.new, 'microposts')
Prefix Verb
microposts POST

URI Pattern

Controller#Action

/microposts(.:format)

microposts#create

micropost DELETE /microposts/:id(.:format) microposts#destroy

Filtering routes: GET
> puts inspector.format(ActionDispatch::Routing::ConsoleFormatter.new, 'users').lines.grep(/GET/).join
following_user GET

/users/:id/following(.:format) users#following

followers_user GET

/users/:id/followers(.:format) users#followers

users GET
new_user GET
edit_user GET
user GET
signup GET

/users(.:format)

users#index

/users/new(.:format)

users#new

/users/:id/edit(.:format)

users#edit


users#show

/signup(.:format)

users#new

Filtering routes: /relation/
> puts inspector.format(ActionDispatch::Routing::ConsoleFormatter.new).lines.grep(/relation/).join
relationships POST

/relationships(.:format)

relationship DELETE /relationships/:id(.:format)

relationships#create
relationships#destroy

Matching routes
> r = Rails.application.routes
> r.recognize_path "/users/47"
=> {:action=>"show", :controller=>"users", :id=>"47"}
> r.recognize_path "/users/87", :method => "PUT"
=> {:action=>"update", :controller=>"users", :id=>"87"}
> r.recognize_path "/users/47.json"
=> {:action=>"show", :controller=>"users", :id=>"47", :format=>"json"}

Named routes
> app.users_path
=> "/users"
> app.users_path(:json)
=> "/users.json"
> app.user_path(1)
=> "/users/1"
> app.user_path(1, :xml)
=> "/users/1.xml"
> app.user_path(1, :count => 4)
=> "/users/1?count=4"

Making requests
> app
=> #<ActionDispatch::Integration::Session:...>

> app.reset!

Get requests
> app.get '/users/1/edit'

Started GET "/users/1/edit" for 127.0.0.1 at 2013-11-26 23:24:18 +0200
Processing by UsersController#edit as HTML
Parameters: {"id"=>"1"}
Redirected to http://localhost:3000/signin
Filter chain halted as :signed_in_user rendered or redirected
Completed 302 Found in 3ms (ActiveRecord: 0.4ms)

> app.response.body
=> "<html><body>You are being <a href="http://localhost:3000/signin">redirected</a>.</body></html>"

> app.get_via_redirect '/users/1/edit'

Redirected to http://localhost:3000/signin
...
Started GET "/signin" for 127.0.0.1 at 2013-11-26 23:26:44 +0200

Session cookies
> app.cookies
=> #<Rack::Test::CookieJar...

> app.cookies.to_hash
=> {"_sample_app_session"=>"RC9j...

app.cookies - received/sent cookies

Post requests: signin
> app.response.body.lines.grep /csrf-token/
=> ["<meta content="n+9uCcG2JJmgwhnNcp4s9jTwOU55RAPOdtAHWstcpKQ=" name="csrf-token" />n"]

> app.post '/sessions', :authenticity_token => 'n+9uCcG2JJmgwhnNcp4s9jTwOU55RAPOdtAHWstcpKQ=',
'session[email]' => 'asdf@asdf.com', 'session[password]' => '123456'

Started POST "/sessions" for 127.0.0.1 at 2013-11-26 23:33:01 +0200
Processing by SessionsController#create as HTML
Parameters: {"authenticity_token"=>"n+9uCcG2JJmgwhnNcp4s9jTwOU55RAPOdtAHWstcpKQ=", "session"=>{"email"
=>"asdf@asdf.com", "password"=>"[FILTERED]"}}
Redirected to http://localhost:3000/users/1/edit
Completed 302 Found in 281ms (ActiveRecord: 7.2ms)

app.post_via_redirect

Access to restricted resource
> app.get '/users/1/edit'

Processing by UsersController#edit as HTML
Completed 200 OK in 41ms (Views: 35.7ms | ActiveRecord: 0.8ms)

Call helper
> helper
=> #<ActionView::Base:... >
# ApplicationHelper#full_title
> helper.full_title "Sign Up"
=> "Ruby on Rails Tutorial Sample App | Sign Up"

Call helper with cookie
> def cookies; @cookies ||= HashWithIndifferentAccess.new(app.cookies.to_hash); end

> helper.current_user
=> #<User id: 1, name: ....

ActiveRecord logging
> ActiveRecord::Base.logger = Logger.new(STDOUT)
> ActiveRecord::Base.clear_active_connections!
> # reload!
> User.find 1
D, [2013-12-30T21:55:17.775769 #24810] DEBUG -- :
WHERE "users"."id" = ? LIMIT 1 [["id", 1]]
=> #<User id: 1, name: "hello",....

User Load (0.2ms)

SELECT "users".* FROM "users"

ActiveRecord hide logging
> ActiveRecord::Base.logger = Logger.new(nil)
> ActiveRecord::Base.clear_active_connections!
> # reload!
> User.find 1
=> #<User id: 1, name: "hello",....

Raw SQL requests
> ActiveRecord::Base.connection.select_all("select * from users")
=> #<ActiveRecord::Result:...
> puts _
{"id"=>1, "name"=>"hello", "email"=>"hello@hello.com", "created_at"=>"2013-....

.irbrc
Save your helper methods
● routes
● sql logging
● etc

CLI tools
Making HTTP requests with curl
●
●
●
●
●
●

-s silent
-v verbose
-c save cookie
-b use cookie
-data POST data
-data-urlencode URL-encode POST data

Access restricted area
curl -s -v http://localhost:3000/users/1/edit > /dev/null

> GET /users/1/edit HTTP/1.1
< HTTP/1.1 302 Found
< Location: http://localhost:3000/signin

Visit /signin, get token
curl -s -c hello_cookies http://localhost:3000/signin > /dev/null |grep csrf-token

<meta content="/t/IoUQxKVEL+KR2/HsnxTKmnALUA99jIr/LvjlgPKs=" name="csrf-token" />

Sign in
curl -s -v --data "session[email]=asdf@asdf.com;session[password]=123456"
--data-urlencode "authenticity_token=/t/IoUQxKVEL+KR2/HsnxTKmnALUA99jIr/LvjlgPKs="
-b hello_cookies -c cookies
http://localhost:3000/sessions > /dev/null

> POST /sessions HTTP/1.1
< HTTP/1.1 302 Found
< Location: http://localhost:3000/users/1

Successful access to restricted area
curl -s -v http://localhost:3000/users/1/edit -b cookies > /dev/null
> GET /users/1/edit HTTP/1.1
< HTTP/1.1 200 OK

Browser tools
●
●
●
●

console
render helpers
debug info
etc

rack-webconsole
>> User.find 1
=> #<User id: 1, name: "Alexander", email: "asdf@asdf.com", created_at: "2013-11-17 16:19:07",
updated_at: "2013-11-27 21:52:06", password_digest:
"$2a$10$MEICr2zekeBhh9HYCMLmXut3ckOsiL0TkksFWVX4asFf...", remember_token:
"cda4da34a5ee4238ddb78f20d4ec7e52b59fab4e", admin: nil>
>> helper
=> Error: undefined local variable or method `helper' for #<Rack::Webconsole::Sandbox:0x000000089cf600>
>> app
=> Error: undefined local variable or method `app' for #<Rack::Webconsole::Sandbox:0x000000089cf600>
>> Rails.root
=> #<Pathname:*/sample_app_rails_4>
>> self
=> #<Rack::Webconsole::Sandbox:0x000000089cf600 @locals={:u=>#<User id: 1, name: "Alexander"

rack-webconsole

`

- activate

rails-footnotes: disable
?footnotes=false

exception_notifier
Provides a set of notifiers for sending
notifications when errors occur in a Rack/Rails
application

letter_opener
Preview email in the browser instead of
sending it

exception_notifier + letter_opener

Debugging on Rails. Mykhaylo Sorochan

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