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README
Overview
This package provides a collection of utilities on top of the packages optparse-applicative, aeson, and yaml for configuring libraries and applications in a composable way.
The main features are
- compositional configuration management with integration of command line option parsing and configuration files, validation of configurations, and loading of configurations from remote locations,
- a
Setup.hs
file that generates aPkgInfo
module for each component of a package that provide information about the package and the build, and - a set of types for configuration of HTTP services and clients along with aeson instances and command line option parsers.
The ultimate goal for this package is a general framework for compositional configuration management for software components. Instead of designing such a framework from scratch the approach of this package is to first explore design and implementation patterns based on practical examples and by gluing together existing technology.
Therefor at the current state this package mostly provides operators and coding patterns for writing stylish boilerplate code.
Once we feel that the developed patterns cover a sufficient portion of real world requirements we plan to rewrite this package such that the boilerplate is hidden behind a clean and simple DSL.
Installation
Assuming that you have a recent version version of GHC
and Cabal
installed in your system this package can be install from Hackage
via
cabal install configuration-tools
If you don't need support for remote configuration files this package can be build with a much smaller set of dependencies via
cabal install -f-remote-configs configuration-tools
The package can be tested via
git clone https://github.com/alephcloud/hs-configuration-tools.git
cd hs-configurationt-tools
cabal configure --enable-tests
cabal build
cabal test
If you have issues building this package, first ensure that the installed
version of the Cabal
library matches the version that is used by
your cabal
binary. You may compare the results of cabal info Cabal
and
cabal --version
.
Configuration Management
The goal of this package is to make management of configurations easy by providing an idiomatic style of defining and deploying configurations.
For each data type that is used as a configuration type the following must be provided:
a default value,
a
FromJSON
instance that yields a function that takes a value and updates that value with the parsed values,a
ToJSON
instance, andan options parser that yields a function that takes a value and updates that value with the values provided as command line options.
Optionally, a function for validating the configuration value may be provided.
The package provides operators and functions that make the implementation of these requisites easy for the common case that the configuration is encoded mainly through nested records.
In addition to the user defined command line options the following options are recognized by the application:
--config-file
parses the given file as a --possibly partial-- configuration in YAML or JSON format. The file location can be provided either as a local file system path or as a remote HTTP or HTTPS URL. In addition a list of static configuration file locations can be defined in the code.If this option is provided more than a single time the configuration files are loaded in the order as the respective options appear on the command line, where settings that are loaded later have precedence over earlier settings. Files from static locations are loaded before files that are specified on the command line.
print-config
configures the application and prints the configuration in YAML format to standard out and exits. The printed configuration is exactly the configuration that otherwise would be used to run the application.print-config-as (full|minimal|diff)
Configures the application and prints the configuration in YAML format to standard out and exits. The printed configuration is exactly the configuration that otherwise would be used to run the application.Arguments:
-
full
: print the complete configuration. Same as--print-config
. -
minimal
: print a minimal configuration that contains only those settings that are different from the default setting. -
diff
: print a YAML document that shows the difference between the default configuration and the actual configuration.
-
--help, -h, -?
prints a help message and exits.
If the package is build with -f+remote-configs
the following two options are
available. They affect how configuration files are loaded from remote URLs.
--config-https-insecure=true|false
Bypass certificate validation for all HTTPS connections to all services.--config-https-allow-cert=HOSTNAME:PORT:FINGERPRINT
Unconditionally trust the certificate for connecting to the service.
The operators provided in this package assume that lenses are provided for field of the configuration record types.
An complete usage example can be found in the file example/Example.hs of the cabal package.
Usage Example
Remark: there are unicode equivalents for some operators available in
Configuration.Utils
that lead to better aligned and more readable code.
We start with language extensions and imports.
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE FlexibleInstances #-}
module Main
( main
) where
import Configuration.Utils
import Data.Monoid
Next we define the types that are used for the configuration of our application. In this contrived example these types define a simplified version of HTTP URLs.
data Auth = Auth
{ _user :: !String
, _pwd :: !String
}
We have to define lenses for the configuration types. Here we do it explicitly.
Alternatively one could have used TemplateHaskell along with makeLenses
from
the module Control.Lens
from the lens
package.
user :: Functor f => (String -> f String) -> Auth -> f Auth
user f s = (\u โ s { _user = u }) <$> f (_user s)
pwd :: Functor f => (String -> f String) -> Auth -> f Auth
pwd f s = (\p -> s { _pwd = p }) <$> f (_pwd s)
(Note, that the module Configuration.Utils
defines its own type synonyms for
lenses. If you import Control.Lens
you should hide Lens
and Lens'
from
either module.)
We must provide a default value. If there is no reasonable default the
respective value could, for instance, be wrapped into Maybe
. Here we
use the monoid identity value of the type.
defaultAuth :: Auth
defaultAuth = Auth
{ _user = ""
, _pwd = ""
}
Now we define an aeson FromJSON
instance that yields a function that updates a given Auth
value with the
values from the parsed JSON value. The <*<
operator is functional composition
lifted for applicative functors and %
is a version of $
with a different
precedence that helps to reduce the use of parenthesis in applicative style
code.
instance FromJSON (Auth -> Auth) where
parseJSON = withObject "Auth" $ \o -> id
<$< user ..: "user" % o
<*< pwd ..: "pwd" % o
The ToJSON
instance is needed to print the configuration (as YAML document)
when the user provides the --print-config
command line option.
instance ToJSON Auth where
toJSON a = object
[ "user" .= _user a
, "pwd" .= _pwd a
]
Finally we define a command line option parser using the machinery from
the optparse-applicative
package. Similar to the FromJSON
instance the parser does not yield a value
directly but instead yields a function that updates a given Auth
value with
the value from the command line.
pAuth :: MParser Auth
pAuth = id
<$< user .:: strOption
% long "user"
<> help "user name"
<*< pwd .:: strOption
% long "pwd"
<> help "password for user"
You may consult the documentation of the optparse-applicative package for further information on how to define command line options.
The following definitions for the HttpURL
are similar to definitions for
the Auth
type above. In addition it is demonstrated how to deal with nested
configuration types. Mainly the usage of ..:
is replaced by %.:
and
.::
is replaced by %::
.
data HttpURL = HttpURL
{ _auth :: !Auth
, _domain :: !String
, _path :: !String
}
auth :: Functor f => (Auth -> f Auth) -> HttpURL -> f HttpURL
auth f s = (\u โ s { _auth = u }) <$> f (_auth s)
domain :: Functor f => (String -> f String) -> HttpURL -> f HttpURL
domain f s = (\u โ s { _domain = u }) <$> f (_domain s)
path :: Functor f => (String -> f String) -> HttpURL -> f HttpURL
path f s = (\u โ s { _path = u }) <$> f (_path s)
defaultHttpURL :: HttpURL
defaultHttpURL = HttpURL
{ _auth = defaultAuth
, _domain = ""
, _path = ""
}
instance FromJSON (HttpURL -> HttpURL) where
parseJSON = withObject "HttpURL" $ \o -> id
<$< auth %.: "auth" % o
<*< domain ..: "domain" % o
<*< path ..: "path" % o
instance ToJSON HttpURL where
toJSON a = object
[ "auth" .= _auth a
, "domain" .= _domain a
, "path" .= _path a
]
pHttpURL :: MParser HttpURL
pHttpURL = id
<$< auth %:: pAuth
<*< domain .:: strOption
% long "domain"
<> short 'd'
<> help "HTTP domain"
<*< path .:: strOption
% long "path"
<> help "HTTP URL path"
Now that everything is set up the configuration can be used to create a
ProgramInfo
value. The ProgramInfo
value is than use with the
runWithConfiguratin
function to wrap a main function that takes an HttpURL
argument with configuration file and command line parsing.
mainInfo :: ProgramInfo HttpURL
mainInfo = programInfo "HTTP URL" pHttpURL defaultHttpURL
main :: IO ()
main = runWithConfiguration mainInfo $ \conf -> do
putStrLn
$ "http://"
<> (_user . _auth) conf
<> ":"
<> (_pwd . _auth) conf
<> "@"
<> _domain conf
<> "/"
<> _path conf
Using Sum Types as Configuration Types
Sum types can not be used as configuration types in the same way as product types. The reason is that the nondeterminism in the choice of a term for the type is not restricted to the chosen constructor arguments but in addition there is non-determinism in the choice of the constructor, too.
An update function for a product type can be defined point-wise as a mapping from constructor parameters to values. An update for a sum type must take the constructor context into account. Moreover, when applied to a given default value the function may not be applicable at all if the default value uses a different constructor context than what the update assumes.
For the future we plan to provide a general solution for configurations of sum
types which would be based on the possibility to define default values for more
than a single constructor. For now one must restrict configurations of sum types
to yield constant values instead of point-wise (partial) updates. In practice
this means that for a type a
one has to provide an FromJSON
instance for a
and use the ..:
operator. Similarly for the option parser one has to define a
parser that yields an a
and use it with the .::
operator.
The module Configuration.Utils.Maybe
provides tools for dealing with
Maybe
values.
Package and Build Information
The module Configuration.Utils.Setup
an example Setup.hs
script that hooks
into the cabal build process at the end of the configuration phase and generates
a module with package information for each component of the cabal package.
The modules are created in the autogen build directory where also the Path_
module is created by cabal's simple build setup. This is usually the directory
./dist/build/autogen
.
For a library component the module is named just PkgInfo
. For all
other components the module is named PkgInfo_COMPONENT_NAME
where
COMPONENT_NAME
is the name of the component with -
characters replaced by
_
.
For instance, if a cabal package contains a library and an executable that
is called my-app, the following modules are created: PkgInfo
and PkgInfo_my_app
.
Usage as Setup Script
There are two ways how this module can be used:
Copy the code of this module into a file called
Setup.hs
in the root directory of your package.If the configuration-tools package is already installed in the system where the build is done, following code can be used as
Setup.hs
script:module Main (main) where import Configuration.Utils.Setup
With both methods the field Build-Type
in the package description (cabal) file
must be set to Custom
:
Build-Type: Custom
Integration With Configuration.Utils
You can integrate the information provided by the PkgInfo
modules with the
command line interface of an application by importing the respective module for
the component and using the runWithPkgInfoConfiguration
function from the
module Configuration.Utils
as show in the following example:
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE FlexibleInstances #-}
module Main
( main
) where
import Configuration.Utils
import PkgInfo
instance FromJSON (() -> ()) where parseJSON _ = pure id
mainInfo :: ProgramInfo ()
mainInfo = programInfo "Hello World" (pure id) ()
main :: IO ()
main = runWithPkgInfoConfiguration mainInfo pkgInfo . const $ putStrLn "hello world"
With that the resulting application supports the following additional command line options:
--version, -v
prints the version of the application and exits.--info, -i
prints a short info message for the application and exits.--long-info
print a detailed info message for the application and exits. Beside component name, package name, version, revision, and copyright the message also contain information about the compiler that was used for the build, the build architecture, build flags, the author, the license type, and a list of all direct and indirect dependencies along with their licenses and copyrights.--license
prints the text of the license of the application and exits.
Here is the example output of --long-info
for the example
examples/Trivial.hs
from this package:
trivial-0.2.6 (package configuration-tools-0.2.6 revision 2cc860c)
Copyright (c) 2014 AlephCloud, Inc.
Author: Lars Kuhtz <[email protected]>
License: MIT
Homepage: https://github.com/alephcloud/hs-configuration-tools
Build with: ghc-7.8.3 (x86_64-osx)
Build flags:
Optimisation: normal
Dependencies:
Cabal-1.20.0.2 [BSD3, 2003-2006, Isaac Jones 2005-2011, Duncan Coutts]
MonadRandom-0.3 [OtherLicense]
aeson-0.8.0.0 [BSD3, (c) 2011-2014 Bryan O'Sullivan (c) 2011 MailRank, Inc.]
ansi-terminal-0.6.1.1 [BSD3]
ansi-wl-pprint-0.6.7.1 [BSD3]
array-0.5.0.0 [BSD3]
attoparsec-0.12.1.0 [BSD3]
base-4.7.0.1 [BSD3]
base-unicode-symbols-0.2.2.4 [BSD3, 2009โ2011 Roel van Dijk <[email protected]>]
bifunctors-4.1.1.1 [BSD3, Copyright (C) 2008-2013 Edward A. Kmett]
rts-1.0 [BSD3]
bytestring-0.10.4.0 [BSD3, Copyright (c) Don Stewart 2005-2009, (c) Duncan Coutts 2006-2013, (c) David Roundy 2003-2005, (c) Jasper Van der Jeugt 2010, (c) Simon Meier 2010-2013.]
case-insensitive-1.2.0.0 [BSD3, 2011 Bas van Dijk]
comonad-4.2.2 [BSD3, Copyright (C) 2008-2014 Edward A. Kmett, Copyright (C) 2004-2008 Dave Menendez]
conduit-1.2.0.2 [MIT]
containers-0.5.5.1 [BSD3]
contravariant-1.2 [BSD3, Copyright (C) 2007-2014 Edward A. Kmett]
deepseq-1.3.0.2 [BSD3]
directory-1.2.1.0 [BSD3]
distributive-0.4.4 [BSD3, Copyright (C) 2011-2014 Edward A. Kmett]
dlist-0.7.1 [BSD3, 2006-2009 Don Stewart, 2013 Sean Leather]
either-4.3.1 [BSD3, Copyright (C) 2008-2014 Edward A. Kmett]
errors-1.4.7 [BSD3, 2012, 2013 Gabriel Gonzalez]
exceptions-0.6.1 [BSD3, Copyright (C) 2013-2014 Edward A. Kmett Copyright (C) 2012 Google Inc.]
filepath-1.3.0.2 [BSD3]
free-4.9 [BSD3, Copyright (C) 2008-2013 Edward A. Kmett]
ghc-prim-0.3.1.0 [BSD3]
hashable-1.2.2.0 [BSD3]
integer-gmp-0.5.1.0 [BSD3]
lifted-base-0.2.3.0 [BSD3, (c) 2011-2012 Bas van Dijk, Anders Kaseorg]
mmorph-1.0.4 [BSD3, 2013 Gabriel Gonzalez]
monad-control-0.3.3.0 [BSD3, (c) 2011 Bas van Dijk, Anders Kaseorg]
mtl-2.2.1 [BSD3]
nats-0.2 [BSD3, Copyright (C) 2011-2014 Edward A. Kmett]
old-locale-1.0.0.6 [BSD3]
optparse-applicative-0.11.0.1 [BSD3, (c) 2012-2014 Paolo Capriotti <[email protected]>]
prelude-extras-0.4 [BSD3, Copyright (C) 2011-2014 Edward A. Kmett]
pretty-1.1.1.1 [BSD3]
primitive-0.5.3.0 [BSD3, (c) Roman Leshchinskiy 2009-2012]
process-1.2.0.0 [BSD3]
profunctors-4.2.0.1 [BSD3, Copyright (C) 2011-2014 Edward A. Kmett]
random-1.0.1.1 [BSD3]
resourcet-1.1.2.3 [BSD3]
safe-0.3.6 [BSD3, Neil Mitchell 2007-2014]
scientific-0.3.3.0 [BSD3]
semigroupoids-4.2 [BSD3, Copyright (C) 2011-2013 Edward A. Kmett]
semigroups-0.15.3 [BSD3, Copyright (C) 2011-2014 Edward A. Kmett]
stm-2.4.3 [BSD3]
syb-0.4.2 [BSD3]
tagged-0.7.2 [BSD3, 2009-2013 Edward A. Kmett]
template-haskell-2.9.0.0 [BSD3]
text-1.1.1.3 [BSD3, 2009-2011 Bryan O'Sullivan, 2008-2009 Tom Harper]
time-1.4.2 [BSD3]
transformers-0.4.1.0 [BSD3]
transformers-base-0.4.3 [BSD3, 2011 Mikhail Vorozhtsov <[email protected]>, Bas van Dijk <[email protected]>]
transformers-compat-0.3.3.4 [BSD3, Copyright (C) 2012 Edward A. Kmett]
unix-2.7.0.1 [BSD3]
unordered-containers-0.2.5.0 [BSD3, 2010-2014 Johan Tibell 2010 Edward Z. Yang]
vector-0.10.11.0 [BSD3, (c) Roman Leshchinskiy 2008-2012]
void-0.6.1 [BSD3, Copyright (C) 2008-2013 Edward A. Kmett]
yaml-0.8.9.1 [BSD3]
Configuration Types for HTTP Services and Clients
The module Configuration.Utils.Http
contains some types for configuring HTTP
services and clients. Currently these types only provide the most basic
configuration settings. This will probably be extended in the future. Feel free
to submit patches for missing settings.
TODO
This package is in an early stage of development and more features are planned.
Simplify specification of Configuration data types by integrating the aeson instances and the option parser.
Come up with a story for sum types. We may use the following approach: The definition of the default should include alternate values for each constructor. Effectively, this means to map the sum type onto a product type by interpreting the summands as factors. For mapping back from the product type to the original sum type one has to provide a choice of the constructor. Intuitively, a sum type can be represented as a tree where the leafs partition the type into classes of value with the same constructors. By providing a default value for each such class partial configurations that are defined through point-wise updates can always be applied in a meaningful way.
Include help text as comments in YAML serialization of configuration values.
Provide operators (or at least examples) for more scenarios (like required options)
Nicer error messages if parsing fails.
Support JSON encoded configuration files.
Support mode where JSON/YAML parsing fails when unexpected properties are encountered.
Include default values in help message.
Use 'helpDoc' to highlight "meta-options", like options that enable optional configuration values through usage of the
maybeOption
function.Add functionality optparse-applicative that allows to group options.
*Note that all licence references and agreements mentioned in the configuration-tools README section above
are relevant to that project's source code only.