How to call a service through a menu-driven application in Ballerina - api

Question

I have a file main.bal which contains the prints the menu and deals with user input. gmail_service.bal file contains a hello service which has the ability to send emails.
main.bal
function main(string... args) {
int c = 0;
while ( c != 2) {
// print options menu to choose from
io:println("-------------------------------------------------------------------------");
io:println("1. Email");
io:println("2. Exit");
io:println("-------------------------------------------------------------------------");
// read user's choice
string choice = io:readln("Enter choice 1 - 2: ");
c = check <int>choice;
if (c == 1) {
//code to send email
}
if (c == 2) {
break;
}
}
}
gmail_service.bal
// A system package containing protocol access constructs
// Package objects referenced with 'http:' in code
import ballerina/http;
import ballerina/io;
import wso2/gmail;
import ballerina/config;
endpoint gmail:Client gmailEP {
clientConfig:{
auth:{
accessToken:config:getAsString("accessToken"),
clientId:config:getAsString("clientId"),
clientSecret:config:getAsString("clientSecret"),
refreshToken:config:getAsString("refreshToken")
}
}
};
documentation {
A service endpoint represents a listener.
}
endpoint http:Listener listener {
port:9090
};
documentation {
A service is a network-accessible API
Advertised on '/hello', port comes from listener endpoint
}
#http:ServiceConfig {
basePath: "/"
}
service<http:Service> hello bind listener {
#http:ResourceConfig {
methods: ["POST"],
path: "/"
}
documentation {
A resource is an invokable API method
Accessible at '/hello/sayHello
'caller' is the client invoking this resource
P{{caller}} Server Connector
P{{request}} Request
}
sayHello (endpoint caller, http:Request request) {
gmail:MessageRequest messageRequest;
messageRequest.recipient = "abc#gmail.com";
messageRequest.sender = "efg#gmail.com";
messageRequest.cc = "";
messageRequest.subject = "Email-Subject";
messageRequest.messageBody = "Email Message Body Text";
//Set the content type of the mail as TEXT_PLAIN or TEXT_HTML.
messageRequest.contentType = gmail:TEXT_PLAIN;
//Send the message.
var sendMessageResponse = gmailEP -> sendMessage("efg#gmail.com", messageRequest);
}
}
How can I invoke the gmail service when the user enters "1"?

Answer 1

In Ballerina, we interact with network-accessible points such as services through endpoints. For example, the your Gmail service source, you have used two endpoints: a listener endpoint and a client endpoint. The listener endpoint is used to bind your hello service to a port and the client endpoint is used to invoke a 3rd party API (the Gmail API).
Similarly, to invoke your hello service from your main() function, you need to create an HTTP client endpoint for the service. You will be interacting with your service through this endpoint. The modified source for main.bal would look something like below. Note that a payload hasn't been set to the POST request since the request body is not used anywhere in the hello service.
import ballerina/http;
import ballerina/io;
endpoint http:Client emailClient {
url: "http://localhost:9090"
};
function main(string... args) {
int c = 0;
while ( c != 2) {
// print options menu to choose from
io:println("-------------------------------------------------------------------------");
io:println("1. Email");
io:println("2. Exit");
io:println("-------------------------------------------------------------------------");
// read user's choice
string choice = io:readln("Enter choice 1 - 2: ");
c = check <int>choice;
if (c == 1) {
http:Response response = check emailClient->post("/", ());
// Do whatever you want with the response
}
if (c == 2) {
break;
}
}
}