gRPC Status Details (custom error data) with Swift (grpc-objc)

ExampleClient.swift

func ping() {
	let req = PingRequest()
	ExampleService.ping(with: req) { (response, error) in

		if let error = error {
			var title = "Unknown error"
			var message = error.localizedDescription

			for detail in try! RPCStatus.from(error)?.details ?? [] {
				switch detail {
				case let detail as AlertMessage:
					title = detail.title
					message = detail.message
				default:
					break
				}
			}

			// use title, message to show an alert

			return
		}

		// use response
	}
}

RPCStatus+Extension.swift

import ExampleRPCSDK

let knownErrorDetailClasses = [
	RPCRetryInfo.self,
	RPCDebugInfo.self,
	RPCQuotaFailure.self,
	RPCPreconditionFailure.self,
	RPCBadRequest.self,
	RPCRequestInfo.self,
	RPCResourceInfo.self,
	RPCHelp.self,
	RPCLocalizedMessage.self,

	AlertMessage.self, // Custom
]

extension RPCStatus {

	class func from(_ error: Error) throws -> RPCStatus? {
		let nserr = error as NSError
		guard let trailerMetadata = nserr.userInfo[kGRPCTrailersKey as! AnyHashable] as? Dictionary<String, AnyObject> else {
			return nil
		}
		guard let bin = trailerMetadata["grpc-status-details-bin"] as? Data else {
			return nil
		}
		return try RPCStatus(data: bin)
	}

	var details: Array<AnyObject> {
		return detailsArray
			.flatMap({ $0 as? GPBAny })
			.flatMap({ detail -> AnyObject? in
				for knownType in knownErrorDetailClasses {
					if let t = try? detail.unpackMessageClass(knownType) {
						return t
					}
				}
				return nil
			})
	}

}