My Rails website (this problem is purely Ruby based though) uses the AWS-SES (Action mailer using AWS) gem in test/development environment, and I am catching possible errors from email deliveries like this
def try_delivering_email(options = {})
begin
yield
return false
rescue EOFError,
...
AWS::SES::ResponseError,
... => e
log_exception(e, options)
return e
end
end
Now the problem is that this gem is only defined for specific environments, in other words AWS does not exist in development, and the error checking code will therefore throw an error (haha) for undefined constant.
I have tried substuting that line for (AWS::SES::ResponseError if defined?(AWS) but then the next error I get is
class or module required for rescue clause
How can I get around this in the nicest way possible ?
The exception list of a rescue-clause doesn't have to be a literal/static list:
excs = [EOFError]
defined?(AWS) && excs << AWS::SES::Response
# ...
rescue *excs => e
The splat operator * is used here to convert an array into a list.
You can't include a conditional in a rescue clause, but you can blind rescue and then get picky about how to deal with it using conventional Ruby code:
rescue EOFError => e
log_exception(e)
e
rescue => e
if (defined?(AWS) and e.is_a?(AWS::SES::Response))
# ...
else
raise e
end
end
It's not the nicest way, but it does the job. You could always encapsulate a lot of that into some module that tests more neatly:
def loggable_exception?(e)
case (e)
when EOFError, AnotherError, EtcError
true
else
if (defined?(AWS) and e.is_a?(AWS::SES::Response))
true
else
false
end
end
end
Then you can do this as that method name should be self-explanatory:
rescue => e
if (loggable_exception?(e))
log_exception(e)
e
else
raise e
end
end
You could make this a little neater if log_exception returned the exception it was given. Don't forget Ruby is "return by default" and it doesn't need to be explicit unless you're doing it early.
Related
I have a func where when an exception was raised, I am rescuing it.
But the program continues to the next line and calls the next func create_request
But when there is exception, I do not want to continue
def validate_request_code options
if check_everything is good
#code to validate
else
errors << "something is gone bad"
end
[errors.size == 0, errors.size == 0 ? options : raise(ArgumentError, "Error while validating #{errors}")]
end
I am trying to catch/rescue the exception
def validate_request options
begin
validate_request_code options
rescue ArgumentError => e
log :error
rescue Exception => e
log :error
end
sleep 20
if options['action'] == "create"
create_request options
end
end
If by 'not continue' you mean that you want the original error to continue (i.e., you just want to take action on the way by), you can call raise inside the rescue block, which re-raises the original error.
def foo
begin
# stuff
rescue StandardError => e
# handle error
raise
end
end
You can also simply return from within the rescue block as well.
def foo
begin
# stuff
rescue StandardError => e
# handle error
return some_value
end
end
As an aside, generally you want to rescue StandardError rather than Exception. All the things that you can reasonably handle within your application are covered under the StandardError. The things outside that are things like out-of-memory, etc., that are outside your control.
Rubocop doesn't seem to like how I am handling my error. What should I do?
Lint/UselessAssignment: Useless assignment to variable - e.
rescue *exceptions_list => e
It is for the piece of code below:
def get_request(url_args = {})
http_connection(url_builder(url_args[:url], url_args[:page]))
rescue *exceptions_list => e
raise "#{e.message}"
end
The *exceptions_list that you see there is defined in a private method:
private
def exceptions_list
[
Net::HTTPBadResponse,
Net::HTTPHeaderSyntaxError,
Net::ProtocolError,
Errno::ECONNRESET,
Errno::EINVAL,
Timeout::Error,
EOFError,
SocketError
]
end
To avoid the rescue line being too long.
Question:
Having => e is pretty standard for error handling no? What should I do?
Thank you very much in advance! =)
Your example does not give Lint/UselessAssignment from rubocop, not at least with version 0.55.0
The UselessAssignment usually comes from something like this:
def do_things
..
rescue *exception_list => e # Useless assignment, e is never used in the block below.
puts "it failed :("
end
To fix this, you can remove the assignment if you're not using the raised exception for anything:
def do_things
..
rescue *exception_list
puts "it failed and i don't care why :D"
end
I know how to catch the exceptions but what we do is to put "rescue" after a suspicious section of a code. what if you had a lot functions sending a query to mysql through mysql2 gem and you want to catch their exceptions. One thing you can do is to put a "rescue" statement in each of them. but i want to do that just by one rescue statement. So I put a "rescue" in end of code and put all of code in a "begin" and "end" but it didn't work.
Here is my code and as you see there is a problem in mysql query and just because of "rescue" being end of file, it doesn't catch the exception but when I put it after that query it works.
require 'mysql2'
require 'colored'
begin
def log(string)
p "["+string.cyan+"]"
end
def err
p "["+"FAIL".red+"]"
end
def done
p "["+"DONE".red+"]"
end
class SqlClient
def initialize()
log "SqlClient/initialize"
puts "Host: \n"
#host = gets.strip
puts "User: \n"
#user = gets.strip
puts "Pass: \n"
#pass = gets.strip
#client = Mysql2::Client.new(host: #host , username: #user , password: #pass)
end
def list_databases()
puts "We are listing your databases(not just projects) \n \n \n "
#client.query("ELECT SCHEMA_NAME FROM INFORMATION_SCHEMA.SCHEMATA").each do |row|
p row["SCHEMA_NAME"]
end
puts "\n \n \n"
end
end
rescue Mysql2::Error
err
abort
end
`query': You have an error in your SQL syntax; check the manual that corresponds to your
MySQL server version for the right syntax to use near 'ELECT SCHEMA_NAME FROM
INFORMATION_SCHEMA.SCHEMATA' at line 1 (Mysql2::Error)
I'm not looking for something like:
begin
# my code
rescue # this line is right after the code which is going to have problem and we catch it.
end
I'm looking for something like this:
begin
# first method
# second method
# thrid method
# rest of code and etc ...
# now this is end of file:
rescue
end
but as you saw in my code, it didn't work.
UPDATE: I found a similar question here and it seems there will be no answer :| maybe this is a sort of ruby Weakness.
if you want to see ANY error just use e for example
begin
# your call to a method of Mysql2 gem. for example:
client = Mysql2::Client.new(:host => "localhost", :username => "root", etc...)
rescue => e
puts e.message
puts e.backtrace.inspect
end
In order to catch every exception you'd need to wrap each method call with a begin rescue end. When an exception is raised it bails out of the execution so it wouldn't hit the next methods.
To catch all errors I guess I'd do something like this. Keep in mind, this is ugly and I'd recommend for you NOT to do this, but... if you want to try, maybe try something like this:
all_errors = []
# first method you call
begin
# some error might happen here
first_response = Mysql2::Client.new(:host => "localhost", :username => "root", etc...)
rescue => e
all_errors << e
end
# second method you call
begin
# some error might happen here
second_response = Mysql2::Client.new(:host => "localhost", :username => "root", etc...)
rescue => e
all_errors << e
end
puts all_errors.inspect
After a quick search I've found: (http://coderrr.wordpress.com/2008/11/07/the-simple-way-to-print-exceptions-in-ruby/)
# catch all exceptions (anything that derives from Exception)
begin
...
rescue Exception
puts $!, $#
end
You could use an at_exit handler, which has access to the last exception in $!
like
at_exit {
puts "the exception that killed us is", $!
}
If you want to catch Exceptions "as soon as they occur" (not after they're caught) you could use ruby's "debug mode" (which outputs messages when they occur to the console) or ruby-debug see Is there any way to start the Ruby debugger on exception?
Just wrap all your code in:
begin
#yourcode
#as much as you want
rescue
end
Nobody seemed to notice it but using rescue without a class will catch all StandardError and there are so much more.
If you want to catch ALL exceptions you need to do
begin
# your code where you call SqlClient.new etc
rescue Exception => e
puts "error raised"
puts [e, e.backtrace].flatten.join("\n")
end
List of all error classes:
Exception
NoMemoryError
ScriptError
LoadError
NotImplementedError
SyntaxError
SignalException
Interrupt
StandardError
ArgumentError
IOError
EOFError
IndexError
LocalJumpError
NameError
NoMethodError
RangeError
FloatDomainError
RegexpError
RuntimeError
SecurityError
SystemCallError
SystemStackError
ThreadError
TypeError
ZeroDivisionError
SystemExit
fatal
have you tried adding an at_exit method in your class? This would allow you to do something when ruby is exiting. like in this article.
Ruby at_exit
or
From Ruby 2.0 API Docs
However beware of cleverly rescuing from an exception!
You'll start pulling your hair out down the road (or another dev will) when you try to figure out why your code isn't failing when it should be failing. I prefer to fail massively with a bright shiny sign saying the code failed here! hehe.
Good luck!
Is there a way to rescue all exceptions under a certain namespace?
For example, I want to rescue all of the Errno::* exceptions (Errno::ECONNRESET, Errno::ETIMEDOUT). I can go ahead and list them all out on my exception line, but I was wondering if I can do something like.
begin
# my code
rescue Errno
# handle exception
end
The above idea doesn't seem to work, thus is there something similar that can work?
All the Errno exceptions subclass SystemCallError:
Module Errno is created dynamically to map these operating system errors to Ruby classes, with each error number generating its own subclass of SystemCallError. As the subclass is created in module Errno, its name will start Errno::.
So you could trap SystemCallError and then do a simple name check:
rescue SystemCallError => e
raise e if(e.class.name.start_with?('Errno::'))
# do your thing...
end
Here is another interesting alternative. Can be adapted to what you want.
Pasting most interesting part:
def match_message(regexp)
lambda{ |error| regexp === error.message }
end
begin
raise StandardError, "Error message about a socket."
rescue match_message(/socket/) => error
puts "Error #{error} matches /socket/; ignored."
end
See the original site for ruby 1.8.7 solution.
It turns out lambda not accepted my more recent ruby versions. It seems the option is to use what worked in 1.8.7 but that's IM slower (to create a new class in all comparisons. So I don't recommend using it and have not even tried it:
def exceptions_matching(&block)
Class.new do
def self.===(other)
#block.call(other)
end
end.tap do |c|
c.instance_variable_set(:#block, block)
end
end
begin
raise "FOOBAR: We're all doomed!"
rescue exceptions_matching { |e| e.message =~ /^FOOBAR/ }
puts "rescued!"
end
If somebody knows when ruby removed lambda support in rescue please comment.
All classes under Errno are subclasses of SystemCallError. And all subclasses of SystemCallError are classes under Errno. The 2 sets are identical, so just rescue SystemCallError. This assumes that you're not using an external lib that adds to one and not the other.
Verify the identity of the 2 sets (using active_support):
Errno.constants.map {|name|
Errno.const_get(name)
}.select{|const|
Class === const
}.uniq.map(&:to_s).sort ==
SystemCallError.subclasses.map(&:to_s).sort
This returns true for me.
So, applied to your example:
begin
# my code
rescue SystemCallError
# handle exception
end
Here is a more generic solution, in the case you wanted to rescue some Errno types and not others.
Create a custom module to be included by all the error classes we want to rescue
module MyErrnoModule; end
Customize this array to your liking, up to the "each" call.
Errno.constants.map {|name|
Errno.const_get(name)
}.select{|const|
Class === const
}.uniq.each {|klass|
klass.class_eval {
include MyErrnoModule
}
}
Test:
begin
raise Errno::EPERM
rescue MyErrnoModule
p "rescued #{$!.inspect}"
end
Test result:
"rescued #<Errno::EPERM: Operation not permitted>"
I would guess this performs slightly better than a solution that needs to check the name of the exception.
My application (Ruby 1.9.2) may raise different exceptions, including net-connection breaks. I rescue Exception => e, then do case/when to handle them in defferent ways, but several errors go through my cases straight to else.
rescue Exception => e
p e.class
case e.class
when Errno::ECONNRESET
p 1
when Errno::ECONNRESET,Errno::ECONNABORTED,Errno::ETIMEDOUT
p 2
else
p 3
end
end
Prints:
Errno::ECONNRESET
3
This is because of how the === operator works on the class Class
The case statement internally calls the === method on the object you are evaluating against. If you want to test for e class, you just test against e, not e.class. That's because e.class would fall into the when Class case, because, well, e.class is a Class.
rescue Exception => e
case e
when Errno::ECONNRESET
p 1
when Errno::ECONNRESET,Errno::ECONNABORTED,Errno::ETIMEDOUT
p 2
else
p 3
end
end
Yeah, Ruby can have weird semantics sometimes
Well it depends upon whether you referencing the class or the constant.
I have for instance had to use the following case statement to get a certain type of detection working
def fail(exception_error)
exception = exception_error
case exception.class
when /HTTPClient::ConnectTimeoutError.new/
status = 'CONNECTION TIMEOUT'
connection_status = 'DOWN'
else
status = 'UNKNOWN FAILURE'
connection_status = 'DOWN'
end
But that's because I'm working with the actual Exception Class not the constant.
HTTPCLient is raising an actual class object:
class TimeoutError < RuntimeError
end
class ConnectTimeoutError < TimeoutError
end
Here's a puzzling fact:
error = HTTPClient::ConnectTimeoutError.new
HTTPClient::ConnectTimeoutError === error
#=> true
error === HTTPClient::ConnectTimeoutError
#=> false
Not sure what to make of that.