I want to change the logging level of an application (ruby).
require 'logger'
config = { :level => 'Logger::WARN' }
log = Logger.new STDOUT
log.level = Kernel.const_get config[:level]
Well, the irb wasn't happy with that and threw "NameError: wrong constant name Logger::WARN" in my face. Ugh! I was insulted.
I could do this in a case/when to solve this, or do log.level = 1, but there must be a more elegant way!
Does anyone have any ideas?
-daniel
Why don't you just use the literal constant in your config hash?
config = { :level => Logger::WARN }
Then you don't have to fool around with const_get or anything like that; you can simply do log.level = config[:level].
If it absolutely must be a string, you can drop the namespace prefix and call const_get on the Logger module:
irb(main):012:0> Logger.const_get 'WARN'
=> 2
If it really really has to be the qualified string, you might try using this blog's qualified_const_get method (which is not a built-in!).
Related
I have the following Ruby code:
module BigTime
FOO1_MONEY_PIT = 500
FOO2_MONEY_PIT = 501
class LoseMoney
##SiteName = 'FOO1'
#site_num = ##SiteName_MONEY_PIT
def other_unimportant_stuff
whatever
end
end
end
So, what I'm trying to do here is set the SiteName and then use SiteName and combine it with the string _MONEY_PIT so I can access FOO1_MONEY_PIT and store its contents (500 in this case) in #site_num. Of course, the above code doesn't work, but there must be a way I can do this?
Thanks!!
If you want to dynamically get the value of a constant, you can use Module#const_get:
module BigTime
FOO1_MONEY_PIT = 500
FOO2_MONEY_PIT = 501
class LoseMoney
##SiteName = 'FOO1'
#site_num = BigTime.const_get(:"#{##SiteName}_MONEY_PIT")
end
end
Do not, under any circumstance, use Kernel#eval for this. Kernel#eval is extremely dangerous in any context where there is even the slightest possibility that an attacker may be able to control parts of the argument.
For example, if a user can choose the name of the site, and they name their site require 'fileutils'; FileUtils.rm_rf('/'), then Ruby will happily evaluate that code, just like you told it to!
Kernel#eval is very dangerous and you should not get into the habit of just throwing an eval at a problem. It is a very specialized tool that should only be employed when there is no other option (spoiler alert: there almost always is another option), and only after a thorough security review.
Please note that dynamically constructing variable names is already a code smell by itself, regardless of whether you use eval or not. It pretty much always points to a design flaw somewhere. In general, you can almost guaranteed replace the multiple variables with a data structure. E.g. in this case something like this:
module BigTime
MONEY_PITS = {
'FOO1' => 500,
'FOO2' => 501,
}.freeze
class LoseMoney
##SiteName = 'FOO1'
#site_num = MONEY_PITS[##SiteName]
end
end
You can refactor this as to use a Hash for your name lookups, and a getter method to retrieve it for easy testing/validation. For example:
module BigTime
MONEY_PITS = { FOO1: 500, FOO2: 501 }
MONEY_PIT_SUFFIX = '_MONEY_PIT'
class LoseMoney
##site = :FOO1
def initialize
site_name
end
def site_name
#site_name ||= '%d%s' % [MONEY_PITS[##site], MONEY_PIT_SUFFIX]
end
end
end
BigTime::LoseMoney.new.site_name
#=> "500_MONEY_PIT"
I'm trying to build a class that will basically be used as a data structure for storing values/nested values. I want there to be two methods, get and set, that accept a dot-notated path to recursively set or get variables.
For example:
bag = ParamBag.new
bag.get('foo.bar') # => nil
bag.set('foo.bar', 'baz')
bag.get('foo.bar') # => 'baz'
The get method could also take a default return value if the value doesn't exist:
bag.get('foo.baz', false) # => false
I could also initialize a new ParamBag with a Hash.
How would I manage this in Ruby? I've done this in other languages, but in order to set a recursive path, I would take the value by reference, but I'm not sure how I'd do it in Ruby.
This was a fun exercise but still falls under the "you probably should not do this" category.
To accomplish what you want, OpenStruct can be used with some slight modifications.
class ParamBag < OpenStruct
def method_missing(name, *args, &block)
if super.nil?
modifiable[new_ostruct_member(name)] = ParamBag.new
end
end
end
This class will let you chain however many method calls together you would like and set any number of parameters.
Tested with Ruby 2.2.1
2.2.1 :023 > p = ParamBag.new
=> #<ParamBag>
2.2.1 :024 > p.foo
=> #<ParamBag>
2.2.1 :025 > p.foo.bar
=> #<ParamBag>
2.2.1 :026 > p.foo.bar = {}
=> {}
2.2.1 :027 > p.foo.bar
=> {}
2.2.1 :028 > p.foo.bar = 'abc'
=> "abc"
Basically, take your get and set methods away and call methods like you would normally.
I do not advise you actually do this, I would instead suggest you use OpenStruct by itself to acheive some flexibility without going too crazy. If you find yourself needing to chain a ton of methods and have them never fail, maybe take a step backwards and ask "is this really the right way to approach this problem?". If the answer to that question is a resounding yes, then ParamBag might just be perfect.
I have a YAML config file where I want to include specific ruby class/module constants instead of the actual value.
For example, instead of putting "loglevel: 0" in the config file, I want "loglevel: Logger::DEBUG".
Is there a way to have YAML decode or resolve a class or module constant like Logger::DEBUG?
This is what I've been playing with, but looking at the psych ruby code, I don't see anything that might support this.
config.yml
loglevel: !ruby/class:fixnum Logger::DEBUG
In irb
irb> require 'logger'
irb> config = YAML.load_file('config.yml')
config['loglevel'] contains "Logger::DEBUG" as a String instead of the actual value.
I can do an eval on it like so:
irb> p eval config['loglevel']
0
==> 0
I'm just wondering if there's a way to have YAML eval it? I'm okay with doing it in my code after doing a YAML load, but I wanted to make sure I left no stone unturned in my, what has turned into a lengthy, quest ;-).
Not sure of a YAML way, but best not to use eval...
In Ruby 2+
Object.const_get 'Logger::DEBUG'
Or the old school
def const_lookup const_name
const_name.split('::').inject(Object) do |rec, name|
rec.const_get(name)
end
end
const_lookup 'Logger::DEBUG'
Looks like you can do it for classes/modules but not their constants
2.0.0-p247 :046 > YAML.load("!ruby/class 'String'")
=> String
2.0.0-p247 :047 > YAML.load("!ruby/class 'String'").class
=> Class
2.0.0-p247 :065 > YAML.load("!ruby/class 'Logger'")
=> Logger
When using Tempfile Ruby is creating a file with a thread-safe and inter-process-safe name. I only need a file name in that way.
I was wondering if there is a more straight forward approach way than:
t = Tempfile.new(['fleischwurst', '.png'])
temp_path = t.path
t.close
t.unlink
Dir::Tmpname.create
You could use Dir::Tmpname.create. It figures out what temporary directory to use (unless you pass it a directory). It's a little ugly to use given that it expects a block:
require 'tmpdir'
# => true
Dir::Tmpname.create(['prefix-', '.ext']) {}
# => "/tmp/prefix-20190827-1-87n9iu.ext"
Dir::Tmpname.create(['prefix-', '.ext'], '/my/custom/directory') {}
# => "/my/custom/directory/prefix-20190827-1-11x2u0h.ext"
The block is there for code to test if the file exists and raise an Errno::EEXIST so that a new name can be generated with incrementing value appended on the end.
The Rails Solution
The solution implemented by Ruby on Rails is short and similar to the solution originally implemented in Ruby:
require 'tmpdir'
# => true
File.join(Dir.tmpdir, "YOUR_PREFIX-#{Time.now.strftime("%Y%m%d")}-#{$$}-#{rand(0x100000000).to_s(36)}-YOUR_SUFFIX")
=> "/tmp/YOUR_PREFIX-20190827-1-wyouwg-YOUR_SUFFIX"
File.join(Dir.tmpdir, "YOUR_PREFIX-#{Time.now.strftime("%Y%m%d")}-#{$$}-#{rand(0x100000000).to_s(36)}-YOUR_SUFFIX")
=> "/tmp/YOUR_PREFIX-20190827-1-140far-YOUR_SUFFIX"
Dir::Tmpname.make_tmpname (Ruby 2.5.0 and earlier)
Dir::Tmpname.make_tmpname was removed in Ruby 2.5.0. Prior to Ruby 2.4.4 it could accept a directory path as a prefix, but as of Ruby 2.4.4, directory separators are removed.
Digging in tempfile.rb you'll notice that Tempfile includes Dir::Tmpname. Inside you'll find make_tmpname which does what you ask for.
require 'tmpdir'
# => true
File.join(Dir.tmpdir, Dir::Tmpname.make_tmpname("prefix-", nil))
# => "/tmp/prefix-20190827-1-dfhvld"
File.join(Dir.tmpdir, Dir::Tmpname.make_tmpname(["prefix-", ".ext"], nil))
# => "/tmp/prefix-20190827-1-19zjck1.ext"
File.join(Dir.tmpdir, Dir::Tmpname.make_tmpname(["prefix-", ".ext"], "suffix"))
# => "/tmp/prefix-20190827-1-f5ipo7-suffix.ext"
Since Dir::Tmpname.make_tmpname was removed in Ruby 2.5.0, this one falls back to using SecureRandom:
require "tmpdir"
def generate_temp_filename(ext=".png")
filename = begin
Dir::Tmpname.make_tmpname(["x", ext], nil)
rescue NoMethodError
require "securerandom"
"#{SecureRandom.urlsafe_base64}#{ext}"
end
File.join(Dir.tmpdir, filename)
end
Since you only need the filename, what about using the SecureRandom for that:
require 'securerandom'
filename = "#{SecureRandom.hex(6)}.png" #=> "0f04dd94addf.png"
You can also use SecureRandom.alphanumeric
I found the Dir:Tmpname solution did not work for me. When evaluating this:
Dir::Tmpname.make_tmpname "/tmp/blob", nil
Under MRI Ruby 1.9.3p194 I get:
uninitialized constant Dir::Tmpname (NameError)
Under JRuby 1.7.5 (1.9.3p393) I get:
NameError: uninitialized constant Dir::Tmpname
You might try something like this:
def temp_name(file_name='', ext='', dir=nil)
id = Thread.current.hash * Time.now.to_i % 2**32
name = "%s%d.%s" % [file_name, id, ext]
dir ? File.join(dir, name) : name
end
As you may know Logger:Application has constants (Logger::DEBUG, Logger::WARN etc...)
My log level is a string in my config. Passing that string to my logger gives error. I'll have to override the level method to accept a string.
log = Logger.new($CONFIG.log.file, $CONFIG.log.freq)
log.level = $CONFIG.log.level ## << Error
#log.level = Logger::WARN ## < manually settings it as example in doc.
how would you set the logging level dynamically?
Use const_get:
log_level = 'WARN'
log.level = Logger.const_get(log_level) #=> 2 (which is the value of Logger::WARN)
Be careful with your input though, as Logger::Error & Logger::ERROR are not the same thing.