Module: MCPClient::ElicitationValidator

Defined in:
lib/mcp_client/elicitation_validator.rb

Overview

Validates elicitation schemas and content per MCP 2025-11-25 spec. Schemas are restricted to flat objects with primitive property types:

string (with optional enum, pattern, format, minLength, maxLength)
number / integer (with optional minimum, maximum)
boolean
array (multi-select enum only, with items containing enum or anyOf)

Constant Summary collapse

PRIMITIVE_TYPES =

Allowed primitive types for schema properties

%w[string number integer boolean].freeze
STRING_FORMATS =

Allowed string formats per MCP spec

%w[email uri date date-time].freeze
PATTERN_MATCH_TIMEOUT =

Wall-clock budget for ALL pattern matching in a single validate_content call. The requestedSchema comes from the remote server, so an expensive expression must not be able to monopolize the calling thread.

The budget covers the whole operation, not each match: a per-match limit multiplies, since the server also controls how many fields it declares.

1.0
MIN_PATTERN_MATCH_TIMEOUT =

Floor for an individual match, so a nearly-exhausted budget still makes progress rather than failing every remaining field.

0.01

Class Method Summary collapse

Class Method Details

.parseable?(klass, value) ⇒ Boolean

Returns whether the value parses.

Parameters:

  • klass (Class) —

    Date or Time

  • value (String) —

    candidate ISO 8601 value

Returns:

  • (Boolean) —

    whether the value parses



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# File 'lib/mcp_client/elicitation_validator.rb', line 282

def self.parseable?(klass, value)
  klass.iso8601(value)
  true
rescue ArgumentError
  false
end

.pattern_budget_remaining(deadline) ⇒ Float

Time left in the validation-wide pattern budget.

Parameters:

  • deadline (Float, nil) —

    monotonic deadline, or nil for a lone match

Returns:

  • (Float) —

    seconds available for the next match; 0.0 when exhausted



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# File 'lib/mcp_client/elicitation_validator.rb', line 243

def self.pattern_budget_remaining(deadline)
  return PATTERN_MATCH_TIMEOUT unless deadline

  remaining = deadline - Process.clock_gettime(Process::CLOCK_MONOTONIC)
  return 0.0 if remaining <= 0

  [remaining, MIN_PATTERN_MATCH_TIMEOUT].max
end

.valid_uri?(value) ⇒ Boolean

Returns whether the value is an absolute URI.

Parameters:

  • value (String) —

    candidate URI

Returns:

  • (Boolean) —

    whether the value is an absolute URI



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# File 'lib/mcp_client/elicitation_validator.rb', line 272

def self.valid_uri?(value)
  uri = URI.parse(value)
  !uri.scheme.nil?
rescue URI::InvalidURIError
  false
end

.validate_array_property(name, prop) ⇒ Array<String>

Validate an array property (multi-select enum only).

Parameters:

  • name (String) —

    property name

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 107

def self.validate_array_property(name, prop)
  errors = []
  items = prop['items']

  unless items.is_a?(Hash)
    errors << "Property '#{name}' array type requires 'items' definition"
    return errors
  end

  has_enum = items['enum'].is_a?(Array)
  has_any_of = items['anyOf'].is_a?(Array)

  errors << "Property '#{name}' array items must have 'enum' or 'anyOf'" unless has_enum || has_any_of

  errors
end

.validate_array_value(field, value, prop) ⇒ Array<String>

Validate an array value against its property schema (multi-select enum).

Parameters:

  • field (String) —

    field name

  • value (Object) —

    the value

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 316

def self.validate_array_value(field, value, prop)
  errors = []

  unless value.is_a?(Array)
    errors << "Field '#{field}' must be an array"
    return errors
  end

  items = prop['items'] || {}
  allowed = if items['enum'].is_a?(Array)
              items['enum']
            elsif items['anyOf'].is_a?(Array)
              items['anyOf'].map { |o| o['const'] }
            end

  if allowed
    value.each do |v|
      errors << "Field '#{field}' contains invalid value '#{v}'" unless allowed.include?(v)
    end
  end

  if prop['minItems'] && value.length < prop['minItems']
    errors << "Field '#{field}' must have at least #{prop['minItems']} items"
  end

  if prop['maxItems'] && value.length > prop['maxItems']
    errors << "Field '#{field}' must have at most #{prop['maxItems']} items"
  end

  errors
end

.validate_content(content, schema) ⇒ Array<String>

Validate content against a requestedSchema. Returns an array of error messages (empty if valid).

Parameters:

  • content (Hash) —

    the response content

  • schema (Hash) —

    the requestedSchema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 129

def self.validate_content(content, schema)
  errors = []
  return errors unless content.is_a?(Hash) && schema.is_a?(Hash)

  # One deadline covers every field's pattern in this call.
  deadline = Process.clock_gettime(Process::CLOCK_MONOTONIC) + PATTERN_MATCH_TIMEOUT

  properties = schema['properties'] || {}
  required = Array(schema['required'])

  # Check required fields
  required.each do |field|
    field_s = field.to_s
    errors << "Missing required field '#{field_s}'" unless content.key?(field_s) || content.key?(field_s.to_sym)
  end

  # Validate each provided field
  content.each do |field, value|
    prop = properties[field.to_s]
    next unless prop.is_a?(Hash)

    errors.concat(validate_value(field.to_s, value, prop, deadline))
  end

  errors
end

.validate_number_value(field, value, prop) ⇒ Array<String>

Validate a number value against its property schema.

Parameters:

  • field (String) —

    field name

  • value (Object) —

    the value

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 294

def self.validate_number_value(field, value, prop)
  errors = []

  unless value.is_a?(Numeric)
    errors << "Field '#{field}' must be a number"
    return errors
  end

  errors << "Field '#{field}' must be an integer" if prop['type'] == 'integer' && !value.is_a?(Integer)

  errors << "Field '#{field}' must be >= #{prop['minimum']}" if prop['minimum'] && value < prop['minimum']

  errors << "Field '#{field}' must be <= #{prop['maximum']}" if prop['maximum'] && value > prop['maximum']

  errors
end

.validate_primitive_property(name, prop) ⇒ Array<String>

Validate a primitive property (string, number, integer, boolean).

Parameters:

  • name (String) —

    property name

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 81

def self.validate_primitive_property(name, prop)
  errors = []
  type = prop['type']

  case type
  when 'string'
    if prop['format'] && !STRING_FORMATS.include?(prop['format'])
      errors << "Property '#{name}' has unsupported format '#{prop['format']}'"
    end
    errors << "Property '#{name}' enum must be an array" if prop['enum'] && !prop['enum'].is_a?(Array)
  when 'number', 'integer'
    if prop.key?('minimum') && !prop['minimum'].is_a?(Numeric)
      errors << "Property '#{name}' minimum must be numeric"
    end
    if prop.key?('maximum') && !prop['maximum'].is_a?(Numeric)
      errors << "Property '#{name}' maximum must be numeric"
    end
  end

  errors
end

.validate_property(name, prop) ⇒ Array<String>

Validate a single property definition.

Parameters:

  • name (String) —

    property name

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 60

def self.validate_property(name, prop)
  errors = []
  return errors unless prop.is_a?(Hash)

  type = prop['type']

  if type == 'array'
    errors.concat(validate_array_property(name, prop))
  elsif PRIMITIVE_TYPES.include?(type)
    errors.concat(validate_primitive_property(name, prop))
  else
    errors << "Property '#{name}' has unsupported type '#{type}'"
  end

  errors
end

.validate_schema(schema) ⇒ Array<String>

Validate that a requestedSchema conforms to MCP elicitation constraints. Returns an array of error messages (empty if valid).

Parameters:

  • schema (Hash) —

    the requestedSchema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 37

def self.validate_schema(schema)
  errors = []
  return errors unless schema.is_a?(Hash)

  unless schema['type'] == 'object'
    errors << "Schema type must be 'object', got '#{schema['type']}'"
    return errors
  end

  properties = schema['properties']
  return errors unless properties.is_a?(Hash)

  properties.each do |name, prop|
    errors.concat(validate_property(name, prop))
  end

  errors
end

.validate_string_format(field, value, format) ⇒ Array<String>

Validate a string value against the schema's format constraint. The MCP elicitation schema supports email, uri, date, and date-time.

Parameters:

  • field (String) —

    field name

  • value (String) —

    the value

  • format (String, nil) —

    declared format

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 258

def self.validate_string_format(field, value, format)
  valid = case format
          when 'email' then value.match?(URI::MailTo::EMAIL_REGEXP)
          when 'uri' then valid_uri?(value)
          when 'date' then parseable?(Date, value)
          when 'date-time' then parseable?(Time, value)
          else true # No format declared, or an unknown format: not validated
          end

  valid ? [] : ["Field '#{field}' must be a valid #{format}"]
end

.validate_string_pattern(field, value, pattern, deadline = nil) ⇒ Array<String>

Validate a string value against the schema's regular-expression pattern. An invalid pattern is not enforced (unchanged behavior), but matching runs under PATTERN_MATCH_TIMEOUT because the pattern comes from the remote server. A match that exceeds the budget is reported as a validation error rather than silently accepted — the value was never shown to satisfy the constraint.

Parameters:

  • field (String) —

    field name

  • value (String) —

    the value

  • pattern (String) —

    the declared pattern

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 226

def self.validate_string_pattern(field, value, pattern, deadline = nil)
  remaining = pattern_budget_remaining(deadline)
  return ["Field '#{field}' pattern matching budget exhausted"] if remaining.zero?

  return [] if value.match?(Regexp.new(pattern, timeout: remaining))

  ["Field '#{field}' must match pattern '#{pattern}'"]
rescue Regexp::TimeoutError
  ["Field '#{field}' pattern '#{pattern}' exceeded the #{PATTERN_MATCH_TIMEOUT}s matching budget"]
rescue RegexpError
  # Skip pattern validation if the pattern is invalid
  []
end

.validate_string_value(field, value, prop, deadline = nil) ⇒ Array<String>

Validate a string value against its property schema.

Parameters:

  • field (String) —

    field name

  • value (Object) —

    the value

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 184

def self.validate_string_value(field, value, prop, deadline = nil)
  errors = []

  unless value.is_a?(String)
    errors << "Field '#{field}' must be a string"
    return errors
  end

  if prop['enum'].is_a?(Array) && !prop['enum'].include?(value)
    errors << "Field '#{field}' must be one of: #{prop['enum'].join(', ')}"
  end

  if prop['oneOf'].is_a?(Array)
    allowed = prop['oneOf'].map { |o| o['const'] }
    errors << "Field '#{field}' must be one of: #{allowed.join(', ')}" unless allowed.include?(value)
  end

  errors.concat(validate_string_pattern(field, value, prop['pattern'], deadline)) if prop['pattern']

  if prop['minLength'] && value.length < prop['minLength']
    errors << "Field '#{field}' must be at least #{prop['minLength']} characters"
  end

  if prop['maxLength'] && value.length > prop['maxLength']
    errors << "Field '#{field}' must be at most #{prop['maxLength']} characters"
  end

  errors.concat(validate_string_format(field, value, prop['format']))

  errors
end

.validate_value(field, value, prop, deadline = nil) ⇒ Array<String>

Validate a single value against its property schema.

Parameters:

  • field (String) —

    field name

  • value (Object) —

    the value to validate

  • prop (Hash) —

    property schema

Returns:

  • (Array<String>) —

    validation errors



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# File 'lib/mcp_client/elicitation_validator.rb', line 161

def self.validate_value(field, value, prop, deadline = nil)
  errors = []
  type = prop['type']

  case type
  when 'string'
    errors.concat(validate_string_value(field, value, prop, deadline))
  when 'number', 'integer'
    errors.concat(validate_number_value(field, value, prop))
  when 'boolean'
    errors << "Field '#{field}' must be a boolean" unless [true, false].include?(value)
  when 'array'
    errors.concat(validate_array_value(field, value, prop))
  end

  errors
end