grpc-ecosystem/grpc-gateway · error

unknown field type %v

Error message

unknown field type %v

What it means

Type-mapping error in genopenapi renderServices: a path parameter's target field type (pt) has no mapping in primitiveSchema, so the generator cannot determine the OpenAPI paramType/paramFormat. The failing input is an unusual proto field kind (e.g. group or unmapped WKT) used as a path parameter.

Source

Thrown at protoc-gen-openapiv2/internal/genopenapi/template.go:1662

						paramFormat = ""
						enumNames = listEnumNames(reg, enum)
						if reg.GetEnumsAsInts() {
							paramType = "integer"
							paramFormat = ""
							enumNames = listEnumNumbers(reg, enum)
						}

						schema := schemaOfField(parameter.Target, reg, customRefs)
						desc = schema.Description
						defaultValue = schema.Default
						example = schema.Example
						schemaPattern = schema.Pattern
						extensions = schema.extensions
					default:
						var ok bool
						paramType, paramFormat, ok = primitiveSchema(pt)
						if !ok {
							return fmt.Errorf("unknown field type %v", pt)
						}

						schema := schemaOfField(parameter.Target, reg, customRefs)
						desc = schema.Description
						defaultValue = schema.Default
						example = schema.Example
						schemaPattern = schema.Pattern
						extensions = schema.extensions
						// If there is no mandatory format based on the field,
						// allow it to be overridden by the user
						if paramFormat == "" {
							paramFormat = schema.Format
						}
					}

					if parameter.IsRepeated() {
						core := schemaCore{Type: paramType, Format: paramFormat}
						if parameter.IsEnum() {

View on GitHub (pinned to a58a4436a3)

Solutions

1. Use a primitive or supported enum/message type for the path parameter.
2. Add/update type mappings or upgrade grpc-gateway for wider type support.
3. Move the value into the body/query where richer schema rendering applies.

When it happens

Trigger: Thrown at protoc-gen-openapiv2/internal/genopenapi/template.go:1662 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grpc-ecosystem/grpc-gateway@a58a4436a3 (2026-09-02). Data as JSON: /api/errors/5cd70b45dbf74a40. Report an issue: GitHub.