Living Without Exceptions

Living without Exceptions Radoslav Stankov 07/09/2019

Radoslav Stankov @rstankov rstankov.com

https://tips.rstankov.com

" Happy Friday # Bug Duty ⚔ Strike Team 4
8 20 developers count

1 developers count " Happy Friday

% Fix bugs & Fix exceptions ' Bump dependancies (
Pay technical dept ) Catchup on projects " Happy Friday

“Have process around exceptions.” * Rado's tip

Back to basics

http://exceptionalruby.com/

def perform do_something rescue end

def perform do_something rescue SpecificError end

def perform do_something rescue SpecificError # NOTE(rstankov): Reason to return
nil nil end

nil nil end Your name, not mine +

nil nil end

def perform do_something rescue Timeout::Error # NOTE(rstankov): WiFi Sucks nil
end

“Be explicit around the exceptions. Handle speciﬁc errors and have
explanations of why they happen.” * Rado's tip

Monitoring

“Split web and background processes errors into separate projects” *
Rado's tip

＃engineering-exceptions

“Have a Slack channel where every new exception is being
logged. Log deployments in this channel as well, so you can correlate.” * Rado's tip

– Brian Kernighan and Rob Pike, The Practice of Programming
“Exceptions shouldn't be expected” Use exceptions only for exceptional situations. […] Exceptions are often overused. Because they distort the ﬂow of control, they can lead to convoluted constructions that are prone to bugs. It is hardly exceptional to fail to open a ﬁle; generating an exception in this case strikes us as over-engineering.

Sentry.configure do |config| # Note(rstankov): Exclude unactionable errors config.excluded_exceptions =
[ 'Rack::Timeout::RequestExpiryError', 'Rack::Timeout::RequestTimeoutException', 'ActionController::RoutingError', 'ActionController::InvalidAuthenticityToken', 'ActionDispatch::ParamsParser::ParseError', 'Sidekiq::Shutdown', ] end

“Reduce noise. See only exceptional errors in your tracker.” *
Rado's tip

ArgumentError: invalid byte sequence in UTF-8 &

# NOTE(rstankov): Fix invalid byte sequence in UTF-8. More info:
# - https://robots.thoughtbot.com/fight-back-utf-8-invalid-byte-sequences module Handle::InvalidByteSequence extend self def call(string) return if string.nil? string.encode('UTF-8', 'binary', invalid: :replace, undef: :replace, replace: '' ) end end

“I put most of the code related to exceptions in
a single module named Handle” * Rado's tip

account.subscription.status

account.subscription&.status

, Steps to ﬁx -

✅ Check for other accounts without a subscription , Steps
to ﬁx -

✅ Check for other accounts without a subscription ✅ Find
out why those accounts don't have a subscription , Steps to ﬁx -

out why those accounts don't have a subscription ✅ Fix this / , Steps to ﬁx -

out why those accounts don't have a subscription ✅ Fix this / ✅ Add missing subscriptions to accounts , Steps to ﬁx -

“Don't hide exceptions. Fix root causes.” * Rado's tip

if account.ship_subscription.blank? ErrorReporting.capture "Missing ship subscription", account_id: account.id return :no_subscription
end

“I have a module named ErrorReporting, which helps me capture
errors that won't get to the user and provides a centralized place for error tracking.” * Rado's tip

https://graphql.org/

Which query causes this issue? 0

class Frontend::GraphqlController < Frontend::BaseController before_action :authenticate def index render json:
Graph::Schema.execute(query, variables: variables, context: context) rescue => e handle_error e end private def authenticate # ...   ErrorReporting.assign_user(@user) end  def handle_error(error) if Rails.env.development? logger.error error.message logger.error error.backtrace.join("\n") render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 elsif Rails.env.test? p error.message p error.backtrace render json: { error: { message: error.message, backtrace: error.backtrace } }, status: 500 else ErrorReporting.capture(e, query: query) render json: { error: { message: 'SERVER_ERROR' }, data: {} }, status: 500 end end end

“Invest in your monitoring and exception traceability. When you have
a hard time racing an exception. Ask yourself - what more information I need? 0 Then add it.” * Tip

https://sidekiq.org/

Use action

Use action Achievements::Job

Use action Achievements::Job Achievement  (unique)

class Achievements::Job < ApplicationJob def perform(achievement, user) Achievements::Create.call achievement, user
end end

Use action Achievements::Job Achievement  (unique) Use action Achievements::Job Achievement  (unique)

Use action Achievements::Job Achievement  (unique) Use action Achievements::Job Achievement  (unique)
&

Use action Achievements::Job Achievement  (unique) Use action Achievements::Job PG::UniqueViolation &

class Achievements::Job < ApplicationJob def perform(achievement, user) Achievements::Create.call achievement, user
end end

class Achievements::Job < ApplicationJob def perform(achievement, user) Handle::RaceCondition.call do Achievements::Create.call
achievement, user end end end

module Handle::RaceCondition extend self UNIQUE_ACTIVE_RECORD_ERROR = 'has already been taken'.freeze
def call retries ||= 2 yield rescue ActiveRecord::RecordNotUnique, PG::UniqueViolation retries -= 1 raise unless retries.nonzero? retry rescue ActiveRecord::RecordInvalid => e raise unless e.message.include? UNIQUE_ACTIVE_RECORD_ERROR retries -= 1 raise unless retries.nonzero? retry end end

class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event) end
end

Errno::ECONNRESET &

class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event) end
end

class Notifications::DeliverJob < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)  rescue
Errno::ECONNRESET  retry_job end end

Errno:: EOFError &

Errno::ECONNRESET, EOFError  retry_job end end

Errno::ECONNRESET, EOFError, Timeout::Error  retry_job end end

Errno::ECONNRESET, EOFError, Timeout::Error, ... 1  retry_job end end

module Handle::NetworkErrors extend self ERRORS = [ EOFError, Errno::ECONNRESET, Errno::EINVAL,
Net::HTTPBadResponse, Net::HTTPHeaderSyntaxError, Net::ProtocolError, Timeout::Error, # ... ] def ===(error) ERRORS.any? { |error_class| error_class === error } end end

class Notifications::Deliver < ApplicationJob queue_as :notifications def perform(event) Notifications::Deliver.call(event)  rescue
Handle::NetworkErrors retry_job end end

class Notifications::Deliver::Job < ApplicationJob retry_on(*::Handle::NetworkErrors::ERRORS, wait: 2.minutes, attempts: 5) queue_as
:notifications def perform(event) Notifications::Deliver.call(event) end end

class Notifications::Deliver::Job < ApplicationJob include Handle::Job::NetworkErrors queue_as :notifications def perform(event)
Notifications::Deliver.call(event) end end

module Handle::Job::NetworkErrors def self.included(job) job.retry_on( *::Handle::NetworkErrors::ERRORS, wait: 2.minutes, attempts: 50
) do |job, exception| ErrorReporting.job_discarded(job, exception) end end end

module Handle::NetworkErrors extend self ERRORS = [ # ... Faraday::ConnectionFailed,
Faraday::TimeoutError, RestClient::BadGateway, RestClient::BadRequest, # ... ] def ===(error) ERRORS.any? { |error_class| error_class === error } end end

ActiveJob::DeserializationError &

class Notifications::ScheduleJob < ApplicationJob queue_as :notifications def perform(kind:, object:, subscriber_id:)
Notifications::Schedule.call( kind: kind, object: object, subscriber_id: subscriber_id, ) end end

class Notifications::ScheduleJob < ApplicationJob include Handle::Job::DeserializationError queue_as :notifications def perform(kind:,
object:, subscriber_id:) Notifications::Schedule.call( kind: kind, object: object, subscriber_id: subscriber_id, ) end end

“Have tooling around handling common exceptions. Make it a no-brainer
to process everyday errors.” * Rado's tip

* Be explicit around the exceptions * Reduce noise *
Don't hide exceptions * Invest in your monitoring * Have tooling around handling exceptions 3 Recap

https://tips.rstankov.com/p/tips-exceptions

Living Without Exceptions

Living Without Exceptions

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