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mcp: support elicitation defaults (#644)

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Fixes #617

---------

Co-authored-by: Markus Kusano <kusano@google.com>
This commit is contained in:
Markus Kusano 2025-11-21 16:15:21 -05:00 • committed by GitHub
commit d9263f7e47
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GPG key ID: B5690EEEBB952194
1 changed files with 177 additions and 9 deletions
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28
mcp/client.go
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@ -321,10 +321,13 @@ func (c *Client) elicit(ctx context.Context, req *ElicitRequest) (*ElicitResult,
if err != nil {
return nil, jsonrpc2.NewError(codeInvalidParams, fmt.Sprintf("failed to resolve requested schema: %v", err))
}
if err := resolved.Validate(res.Content); err != nil {
return nil, jsonrpc2.NewError(codeInvalidParams, fmt.Sprintf("elicitation result content does not match requested schema: %v", err))
}
err = resolved.ApplyDefaults(&res.Content)
if err != nil {
return nil, jsonrpc2.NewError(codeInvalidParams, fmt.Sprintf("failed to apply schema defalts to elicitation result: %v", err))
}
}
return res, nil
@ -341,6 +344,9 @@ func validateElicitSchema(wireSchema any) (*jsonschema.Schema, error) {
if err := remarshal(wireSchema, &schema); err != nil {
return nil, err
}
if schema == nil {
return nil, nil
}
// The root schema must be of type "object" if specified
if schema.Type != "" && schema.Type != "object" {
@ -369,7 +375,6 @@ func validateElicitProperty(propName string, propSchema *jsonschema.Schema) erro
if len(propSchema.Properties) > 0 {
return fmt.Errorf("elicit schema property %q contains nested properties, only primitive properties are allowed", propName)
}
// Validate based on the property type - only primitives are supported
switch propSchema.Type {
case "string":
@ -439,7 +444,7 @@ func validateElicitStringProperty(propName string, propSchema *jsonschema.Schema
}
}
return nil
return validateDefaultProperty[string](propName, propSchema)
}
// validateElicitNumberProperty validates number and integer-type properties.
@ -450,19 +455,28 @@ func validateElicitNumberProperty(propName string, propSchema *jsonschema.Schema
}
}
intDefaultError := validateDefaultProperty[int](propName, propSchema)
floatDefaultError := validateDefaultProperty[float64](propName, propSchema)
if intDefaultError != nil && floatDefaultError != nil {
return fmt.Errorf("elicit schema property %q has default value that cannot be interpreted as an int or float", propName)
}
return nil
}
// validateElicitBooleanProperty validates boolean-type properties.
func validateElicitBooleanProperty(propName string, propSchema *jsonschema.Schema) error {
// Validate default value if specified - must be a valid boolean
return validateDefaultProperty[bool](propName, propSchema)
}
func validateDefaultProperty[T any](propName string, propSchema *jsonschema.Schema) error {
// Validate default value if specified - must be a valid T
if propSchema.Default != nil {
var defaultValue bool
var defaultValue T
if err := json.Unmarshal(propSchema.Default, &defaultValue); err != nil {
return fmt.Errorf("elicit schema property %q has invalid default value, must be a boolean: %v", propName, err)
return fmt.Errorf("elicit schema property %q has invalid default value, must be a %T: %v", propName, defaultValue, err)
}
}
return nil
}