1 Error Reporting
The Rails error reporter provides a standard way to collect errors that occur in your application and report them to your preferred service or location (e.g. you could report the errors to a monitoring service such as Sentry).
It aims to replace boilerplate error-handling code like this:
begin
do_something
rescue SomethingIsBroken => error
MyErrorReportingService.notify(error)
end
with a consistent interface:
Rails.error.handle(SomethingIsBroken) do
do_something
end
Rails wraps all executions (such as HTTP requests, jobs, and rails runner invocations) in the error reporter, so any unhandled errors raised in your app will automatically be reported to your error-reporting service via their subscribers.
This means that third-party error-reporting libraries no longer need to insert a Rack middleware or do any monkey-patching to capture unhandled errors. Libraries that use Active Support can also use this to non-intrusively report warnings that would previously have been lost in logs.
Using the Rails error reporter is optional, as other means of capturing errors still work.
1.1 Subscribing to the Reporter
To use the error reporter with an external service, you need a subscriber. A
subscriber can be any Ruby object with a report
method. When an error occurs
in your application or is manually reported, the Rails error reporter will call
this method with the error object and some options.
Some error-reporting libraries, such as Sentry's and Honeybadger's, automatically register a subscriber for you.
You may also create a custom subscriber. For example:
# config/initializers/error_subscriber.rb
class ErrorSubscriber
def report(error, handled:, severity:, context:, source: nil)
MyErrorReportingService.report_error(error, context: context, handled: handled, level: severity)
end
end
After defining the subscriber class, you can register it by calling the
Rails.error.subscribe
method:
Rails.error.subscribe(ErrorSubscriber.new)
You can register as many subscribers as you wish. Rails will call them in the order in which they were registered.
It is also possible to unregister a subscriber by calling
Rails.error.unsubscribe
.
This may be useful if you'd like to replace or remove a subscriber added by one
of your dependencies. Both subscribe
and unsubscribe
can take either a
subscriber or a class as follows:
subscriber = ErrorSubscriber.new
Rails.error.unsubscribe(subscriber)
# or
Rails.error.unsubscribe(ErrorSubscriber)
The Rails error reporter will always call registered subscribers, regardless of your environment. However, many error-reporting services only report errors in production by default. You should configure and test your setup across environments as needed.
1.2 Using the Error Reporter
Rails error reporter has four methods that allow you to report methods in different ways:
Rails.error.handle
Rails.error.record
Rails.error.report
Rails.error.unexpected
1.2.1 Reporting and Swallowing Errors
The
Rails.error.handle
method will report any error raised within the block. It will then swallow
the error, and the rest of your code outside the block will continue as normal.
result = Rails.error.handle do
1 + '1' # raises TypeError
end
result # => nil
1 + 1 # This will be executed
If no error is raised in the block, Rails.error.handle
will return the result
of the block, otherwise it will return nil
. You can override this by providing
a fallback
:
user = Rails.error.handle(fallback: -> { User.anonymous }) do
User.find_by(params[:id])
end
1.2.2 Reporting and Re-raising Errors
The
Rails.error.record
method will report errors to all registered subscribers and then re-raise
the error, meaning that the rest of your code won't execute.
Rails.error.record do
1 + '1' # raises TypeError
end
1 + 1 # This won't be executed
If no error is raised in the block, Rails.error.record
will return the result
of the block.
1.2.3 Manually Reporting Errors
You can also manually report errors by calling
Rails.error.report
:
begin
# code
rescue StandardError => e
Rails.error.report(e)
end
Any options you pass will be passed on to the error subscribers.
1.2.4 Reporting Unexpected Errors
You can report any unexpected error by calling
Rails.error.unexpected
.
When called in production, this method will return nil after the error is reported and the execution of your code will continue.
When called in development, the error will be wrapped in a new error class (to ensure it's not being rescued higher in the stack) and surfaced to the developer for debugging.
For example:
def edit
if published?
Rails.error.unexpected("[BUG] Attempting to edit a published article, that shouldn't be possible")
false
end
# ...
end
This method is intended to gracefully handle any errors that may occur in production, but that aren't anticipated to be the result of typical use.
1.3 Error-reporting Options
The reporting APIs #handle
, #record
, and #report
support the following
options, which are then passed along to all registered subscribers:
handled
: aBoolean
to indicate if the error was handled. This is set totrue
by default.#record
sets this tofalse
.severity
: aSymbol
describing the severity of the error. Expected values are::error
,:warning
, and:info
.#handle
sets this to:warning
, while#record
sets it to:error
.context
: aHash
to provide more context about the error, like request or user detailssource
: aString
about the source of the error. The default source is"application"
. Errors reported by internal libraries may set other sources; the Redis cache library may use"redis_cache_store.active_support"
, for instance. Your subscriber can use the source to ignore errors you aren't interested in.
Rails.error.handle(context: { user_id: user.id }, severity: :info) do
# ...
end
1.4 Setting Context Globally
In addition to setting context through the context
option, you can use
Rails.error.set_context
.
For example:
Rails.error.set_context(section: "checkout", user_id: @user.id)
Any context set this way will be merged with the context
option
Rails.error.set_context(a: 1)
Rails.error.handle(context: { b: 2 }) { raise }
# The reported context will be: {:a=>1, :b=>2}
Rails.error.handle(context: { b: 3 }) { raise }
# The reported context will be: {:a=>1, :b=>3}
1.5 Filtering by Error Classes
With Rails.error.handle
and Rails.error.record
, you can also choose to only
report errors of certain classes. For example:
Rails.error.handle(IOError) do
1 + '1' # raises TypeError
end
1 + 1 # TypeErrors are not IOErrors, so this will *not* be executed
Here, the TypeError
will not be captured by the Rails error reporter. Only
instances of IOError
and its descendants will be reported. Any other errors
will be raised as normal.
1.6 Disabling Notifications
You can prevent a subscriber from being notified of errors for the duration of a
block by calling
Rails.error.disable
.
Similarly to subscribe
and unsubscribe
, you can pass in either the
subscriber itself, or its class.
Rails.error.disable(ErrorSubscriber) do
1 + '1' # TypeError will not be reported via the ErrorSubscriber
end
This can also be helpful for third-party error reporting services who may want to manage error handling a different way, or higher in the stack.
2 Error-reporting Libraries
Error-reporting libraries can register their subscribers in a Railtie:
module MySdk
class Railtie < ::Rails::Railtie
initializer "my_sdk.error_subscribe" do
Rails.error.subscribe(MyErrorSubscriber.new)
end
end
end
If you register an error subscriber, but still have other error mechanisms like a Rack middleware, you may end up with errors reported multiple times. You should either remove your other mechanisms or adjust your report functionality so it skips reporting an error it has seen before.
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