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

Class Method Summary collapse

Class Method Details

.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 91

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 230

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 113

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

  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))
  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 208

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 65

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 44

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 21

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_value(field, value, prop) ⇒ 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 165

def self.validate_string_value(field, value, prop)
  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

  if prop['pattern']
    begin
      unless value.match?(Regexp.new(prop['pattern']))
        errors << "Field '#{field}' must match pattern '#{prop['pattern']}'"
      end
    rescue RegexpError
      # Skip pattern validation if the pattern is invalid
    end
  end

  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
end

.validate_value(field, value, prop) ⇒ 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 142

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

  case type
  when 'string'
    errors.concat(validate_string_value(field, value, prop))
  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