Class: LaunchDarkly::Reference

Inherits:
Object
  • Object
show all
Defined in:
lib/ldclient-rb/reference.rb

Overview

Reference is an attribute name or path expression identifying a value within a Context.

This type is mainly intended to be used internally by LaunchDarkly SDK and service code, where efficiency is a major concern so it’s desirable to do any parsing or preprocessing just once. Applications are unlikely to need to use the Reference type directly.

It can be used to retrieve a value with LDContext.get_value_for_reference() or to identify an attribute or nested value that should be considered private.

Parsing and validation are done at the time that the Reference is constructed. If a Reference instance was created from an invalid string, it is considered invalid and its #error attribute will return a non-nil error.

## Syntax

The string representation of an attribute reference in LaunchDarkly JSON data uses the following syntax:

If the first character is not a slash, the string is interpreted literally as an attribute name. An attribute name can contain any characters, but must not be empty.

If the first character is a slash, the string is interpreted as a slash-delimited path where the first path component is an attribute name, and each subsequent path component is the name of a property in a JSON object. Any instances of the characters “/” or “~” in a path component are escaped as “~1” or “~0” respectively. This syntax deliberately resembles JSON Pointer, but no JSON Pointer behaviors other than those mentioned here are supported.

## Examples

Suppose there is a context whose JSON implementation looks like this:

{

"kind": "user",
"key": "value1",
"address": {
  "street": {
    "line1": "value2",
    "line2": "value3"
  },
  "city": "value4"
},
"good/bad": "value5"

}

The attribute references “key” and “/key” would both point to “value1”.

The attribute reference “/address/street/line1” would point to “value2”.

The attribute references “good/bad” and “/good~1bad” would both point to “value5”.

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(raw_path, components = [], error = nil) ⇒ Reference

Returns a new instance of Reference.



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# File 'lib/ldclient-rb/reference.rb', line 104

def initialize(raw_path, components = [], error = nil)
  @raw_path = raw_path
  # @type [Array<Symbol>]
  @components = components
  @error = error
end

Instance Attribute Details

#error ⇒ String? (readonly)

Returns nil for a valid Reference, or a non-nil error value for an invalid Reference.

A Reference is invalid if the input string is empty, or starts with a slash but is not a valid slash-delimited path, or starts with a slash and contains an invalid escape sequence.

Otherwise, the Reference is valid, but that does not guarantee that such an attribute exists in any given Context. For instance, Reference.create(“name”) is a valid Reference, but a specific Context might or might not have a name.

See comments on the Reference type for more details of the attribute reference syntax.

Returns:

  • (String, nil) 


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# File 'lib/ldclient-rb/reference.rb', line 89

def error
  @error
end

#raw_path ⇒ String? (readonly)

Returns the attribute reference as a string, in the same format provided to #create.

If the Reference was created with #create, this value is identical to the original string. If it was created with #create_literal, the value may be different due to unescaping (for instance, an attribute whose name is “/a” would be represented as “~1a”).

Returns:

  • (String, nil) 


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# File 'lib/ldclient-rb/reference.rb', line 102

def raw_path
  @raw_path
end

Class Method Details

.create(value) ⇒ Reference

Creates a Reference from a string. For the supported syntax and examples, see comments on the Reference type.

This constructor always returns a Reference that preserves the original string, even if validation fails, so that accessing #raw_path (or serializing the Reference to JSON) will produce the original string. If validation fails, #error will return a non-nil error and any SDK method that takes this Reference as a parameter will consider it invalid.

Parameters:

  • value (String, Symbol)

Returns:



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# File 'lib/ldclient-rb/reference.rb', line 127

def self.create(value)
  unless value.is_a?(String) || value.is_a?(Symbol)
    return new(value, [], ERR_EMPTY)
  end

  value = value.to_s if value.is_a?(Symbol)

  return new(value, [], ERR_EMPTY) if value.empty? || value == "/"

  unless value.start_with? "/"
    return new(value, [value.to_sym])
  end

  if value.end_with? "/"
    return new(value, [], ERR_DOUBLE_TRAILING_SLASH)
  end

  components = []
  value[1..].split("/").each do |component|
    if component.empty?
      return new(value, [], ERR_DOUBLE_TRAILING_SLASH)
    end

    path, error = unescape_path(component)

    if error
      return new(value, [], error)
    end

    components << path.to_sym
  end

  new(value, components)
end

.create_literal(value) ⇒ Reference

create_literal is similar to #create except that it always interprets the string as a literal attribute name, never as a slash-delimited path expression. There is no escaping or unescaping, even if the name contains literal ‘/’ or ‘~’ characters. Since an attribute name can contain any characters, this method always returns a valid Reference unless the name is empty.

For example: Reference.create_literal(“name”) is exactly equivalent to Reference.create(“name”). Reference.create_literal(“a/b”) is exactly equivalent to Reference.create(“a/b”) (since the syntax used by #create treats the whole string as a literal as long as it does not start with a slash), or to Reference.create(“/a~1b”).

Parameters:

  • value (String, Symbol)

Returns:



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# File 'lib/ldclient-rb/reference.rb', line 179

def self.create_literal(value)
  unless value.is_a?(String) || value.is_a?(Symbol)
    return new(value, [], ERR_EMPTY)
  end

  value = value.to_s if value.is_a?(Symbol)

  return new(value, [], ERR_EMPTY) if value.empty?
  return new(value, [value.to_sym]) if value[0] != '/'

  escaped = "/" + value.gsub('~', '~0').gsub('/', '~1')
  new(escaped, [value.to_sym])
end

Instance Method Details

#==(other) ⇒ Object Also known as: eql? 



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# File 'lib/ldclient-rb/reference.rb', line 232

def ==(other)
  self.error == other.error && self.components == other.components
end

#component(index) ⇒ Symbol?

Retrieves a single path component from the attribute reference.

For a simple attribute reference such as “name” with no leading slash, if index is zero, #component returns the attribute name as a symbol.

For an attribute reference with a leading slash, if index is non-negative and less than #depth, Component returns the path component as a symbol.

If index is out of range, it returns nil.

Reference.create(“a”).component(0) # returns “a” Reference.create(“/a/b”).component(1) # returns “b”

Parameters:

  • index (Integer)

Returns:

  • (Symbol, nil) 


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# File 'lib/ldclient-rb/reference.rb', line 226

def component(index)
  return nil if index < 0 || index >= depth

  @components[index]
end

#depth ⇒ Integer

Returns the number of path components in the Reference.

For a simple attribute reference such as “name” with no leading slash, this returns 1.

For an attribute reference with a leading slash, it is the number of slash-delimited path components after the initial slash. For instance, NewRef(“/a/b”).Depth() returns 2.

Returns:

  • (Integer) 


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# File 'lib/ldclient-rb/reference.rb', line 205

def depth
  @components.size
end

#hash ⇒ Object 



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# File 'lib/ldclient-rb/reference.rb', line 237

def hash
  ([error] + components).hash
end

#to_json(*args) ⇒ String

Convert the Reference to a JSON string.

Parameters:

  • args (Array)

Returns:

  • (String) 


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# File 'lib/ldclient-rb/reference.rb', line 247

def to_json(*args)
  JSON.generate(@raw_path, *args)
end