Travis Configuration Parser

What is this?

This project is a library for loading Travis CI build configuration.

It can create a configuration both from a normal Ruby Hash or a YAML string. These config objects generally behave like normal primitives (hashes, arrays, etc).

require 'travis/yaml'

config = Travis::Yaml.parse('language: ruby')
config = Travis::Yaml.parse(language: 'ruby')

config[:language] # ruby
config.language   # ruby

# using parse! instead of parse will print out warnings
Travis::Yaml.parse! deploy: []
# .travis.yml: missing key "language", defaulting to "ruby"
# .travis.yml: value for "deploy" section is empty, dropping

# have it generate the build matrix for you
Travis::Yaml.matrix('rvm: [jruby, 2.0.0]').each do |matrix_entry|
  puts matrix_entry.ruby
end

Why use it?

• Prevents code execution. Instead of deserializing arbitrary Ruby objects, it only deserializes primitive objects. To go even further, in contrast to SafeYAML, it only deserializes primitive objects that are expected for a certain part of the configuration.
• Prevents memory leaks. Internally, only expected values are stored in the data structure, discarding any additional data. No user input is converted to symbols (which would allow a memory based DoS attack).
• Normalization is happening in one place. Travis CI currently does config normalization in many different parts of its infrastructure, making it tedious to determine supported input formats and the resulting internal structure.
• Explicit structure. Due to the explicit configuration structure, exceptions throughout the system can be greatly reduced, since the configuration will not contain unexpected objects.
• Forgiving about user input. The parser knows the expected structure and can therefore automatically map some malformed input onto that structure. For instance, node: 1.10 does not get converted to node: 1.1 internally, because travis-yaml knows to expect a string here rather than a float.
• Built-in support for encrypted values, making it easier to support these in different parts of the system and never leak the decrypted form if configuration is being serialized.
• Extensive warning and error handling, making it possible to use this library for linting and also to display such warnings when running a build.
• Performance. Using travis-yaml to load a configuration from a YAML string is slightly faster than using psych directly and significantly faster than using safeyaml.
• Compatibility. This library is written in a way to not only be fully compatible with the current .travis.yml format, but also with the configuration data in the current Travis database and with the code interacting with the configuration data (for instance in travis-build).
• Extensibility. The configuration structure is easily extended.
• Pluggable parser. It is easy to write a new parser. This would be useful for instance for the Travis CI command line client, where one could imagine a parser for the small subset of the YAML format that is commonly in use. This would for instance allow to write a parser and serializer able to preserve comments and indentation when modifying the contents of the .travis.yml.

What is missing?

• Serialization

External API

Loading a config

config = Travis::Yaml.parse('language: ruby') # parse from a yaml string
config = Travis::Yaml.parse(language: "ruby") # parse from Ruby object

For Psych/YAML compatibility, parse is also aliased to load.

Convenience

Nodes generally behave like normal Ruby objects. Mappings accept both symbols and strings as keys. Known fields on mappings are exposed as methods.

puts config.language
puts config[:language]
puts config['language']

Warnings and errors

• errors are actual parse errors, parent elements should discard elements with errors.
• warnings are general warnings for an element, with the element still being usable. These do not include warnings for child elements (though an error in a child element becomes a warning for its immediate parent).
• nested warnings include warnings for the whole tree, they also come with key prefix (array of strings) to identify the position the error occured at.

Travis::Yaml.parse("foo: bar").nested_warnings.each do |key, warning|
  puts "#{key.join('.')}: #{warning}"
end

# will print nested warnings to stderr, will raise on top level error
Travis::Yaml.parse! "foo: bar"

Secure Variables

Secure variables are stored as Travis::Yaml::SecureString internally. A secure string has at least an encrypted_string or a decrypted_string, or both.

You can use decrypt/encrypt with a block to generate the missing string:

secret = Travis::Yaml::SecureString.new("foo")

secret.encrypted_string # => "foo"
secret.decrypted_string # => nil
secret.encrypted?       # => true
secret.decrypted?       # => false

secret.decrypt { |string| string.upcase }

secret.encrypted_string # => "foo"
secret.decrypted_string # => "FOO"
secret.encrypted?       # => true
secret.decrypted?       # => true

To avoid having to walk the whole structure manually or hardcoding the values to decrypt, these methods are also exposed on any node:

config = Travis::Yaml.load 'env: { secure: foo }'
config.decrypted? # => false

config.decrypt { |string| string.upcase }
config.decrypted?                        # => true
config.env.matrix.first.decrypted_string # => "FOO"

This can even be done right with the parse step:

content = File.read('.travis.yml')
Travis::Yaml.parse! content do |config|
  config.decrypt { |string| string.upcase }
end

Serialization

A travis-yaml document can be serialized to a few other formats via the serialize method:

pp   config.serialize(:ruby)
puts config.serialize(:json, pretty: true)

Serializer	Descriptions	Options
ruby	Corresponding Ruby objects, secure values will be SecureStrings	secure, symbol_keys
legacy	Format compatible with Travis CI's old fetch_config service	secure, symbol_keys
json	Serialize as JSON, parsable via Travis::Yaml.load	secure, pretty
yaml	Serialize as YAML, parsable via Travis::Yaml.load	secure, symbol_keys, indentation, line_width, canonical, avoid_tags

The secure option can be set to :decrypted or :encrypted, enforcing the decrypted or encrypted form of secure strings to be serialized. In some serializations, this might lead to secure strings being mapped to normal strings if set to :decrypted.

Defining Structure

Good starting points for getting into the code are the root node and the language node.

A parsed configuration is very similar to a syntax tree. To create a new node type, you should inherit from one of the abstract types. Internal vocabulary is taken from the YAML spec rather than the Ruby names (ie, sequence vs array, mapping vs hash).

Scalar Values

Most of the time, scalar values are just strings. In fact, if you create a new scalar node class and don't specify and other supported type, it will treat everything as string.

module Travis::Yaml::Nodes
  class Example < Scalar
  end
end

This will parse foo to "foo" and 1.10 to 1.10. This will also generate a warning and discard values like !float 1.10.

Value Types

You can also allow other types and change the default type unsupported implicit types are cast to.

module Travis::Yaml::Nodes
  class Example < Scalar
    cast :str, :binary, :int
    default_type :int
  end
end

Available types are str, binary, bool, float, int, time, regexp, secure and null.

Default Value

It is also possible to give a scalar a default value.

module Travis::Yaml::Nodes
  class Example < Scalar
    default_value "example"
  end
end

This is handy when using it for a required entry in a mapping (for instance, language is required, but has a default).

Fixed Value Set

For entries that have a well defined set of values, you can inherit from FixedValue:

module Travis::Yaml::Nodes
  class Example < FixedValue
    ignore_case

    default_value :example
    value :foo, :bar, baz: :bar
  end
end

This will, for example, map FOO to "foo", baz to "bar", and blah to "example" (and generate a warning about blah being not supported).

Shorthands

There are shorthands for creating Scalar and FixedValue subclasses:

module Travis::Yaml::Nodes
  class Example < Map
    map :foo, to: Scalar[:int]
    map :bar, to: FixedValue[:foo, :bar]
  end
end

Sequences

Sequences correspond to Ruby arrays. If you pass in a scalar or mapping instead of a sequence, it will be treated as if it was a sequence with a single entry of that value.

module Travis::Yaml::Nodes
  class ExampleList < Sequence
    type ExampleValue # node type, defaults to Scalar
  end
end

Mappings

Mappings correspond to hashes in Ruby.

module Travis::Yaml::Nodes
  class ExampleMapping < Mapping
    # map the value for the "example" key to an Example node
    # map the value for the "other" key to an Other node
    map :example, :other

    # map the values for "foo" and "bar" to a Scalar
    map :foo, :bar, to: Scalar

    # map "list" to a Sequence, keep it even if it's empty
    map :list, to: Sequence, drop_empty: false

    # require "setting" to be present
    map :setting, required: true

    # make "option" an alias for "setting"
    map :option, to: :setting

    # if a scalar is passed in instead of a mapping, treat it as
    # the value of "setting" ("foo" becomes { setting: "foo" })
    prefix_scalar :setting
  end
end

Open Mappings

Sometimes it is not possible to define all available keys for a mapping. You can solve this by using an open mapping:

module Travis::Yaml::Nodes
  class ExampleMapping < OpenMapping
    # node type for entries not specified (defaults to Scalar)
    default_type ExampleValue

    # map "setting" to Setting node, make it a requirement
    map :setting, required: true
  end
end

You can also limit the possible keys by overriding accept_key?.

module Travis::Yaml::Nodes
  class ExampleMapping < OpenMapping
    default_type ExampleValue

    def accept_key?(key)
      key.start_with? "example_"
    end
  end
end

Additional Verification

Besides the generated warnings, validations and normalizations inherent to the structure, you can define your own checks and normalizations by overriding the verify method.

module Travis::Yaml::Nodes
  class Example < Scalar
    def verify
      if value == "foo"
        warning "foo is deprecated, using bar instead"
        self.value = "bar"
      end
      super
    end
  end
end

The warning method will generate track a warning, so it can be presented to the user later on. The error method will lead to the node being removed from its parent node. It will also propagate the error message as a warning in the parent node.

Nested Warnings

When reflecting upon a node, warnings and errors will only contain the messages for that specific node. To get all the warnings for the entire tree, use nested_warnings, which will also give you the path (as array of strings).

config.nested_warnings.each do |path, message|
  p path      # ["my", "example", "key"]
  p message   # "this is the warning"
end

Requirements

This project requires Ruby 1.9.3 or 2.0.0 and Psych ~> 2.0 (part of the stdlib).