I recently learned about the Connection:Keep-Alive header, which supposedly instructs the server to maintain the connection between the client and server for a while to reduce the overhead of establishing a new connection with each request. However, when I tried adding this header to my requests, the socket connection still closed after each request.
I'm puzzled by why this is happening. Could it be that I misunderstood something about Connection:Keep-Alive, or perhaps I implemented it incorrectly?
Client:
const http = require("http");
const options = {
port: 4000,
headers: {
connection: "keep-alive",
},
};
function request() {
console.log(`making a request`);
const req = http.request(options, (res) => {
console.log(`STATUS: ${res.statusCode}`);
console.log(`HEADERS: ${JSON.stringify(res.headers)}`);
res.setEncoding("utf8");
res.on("data", (chunk) => {
console.log(`BODY: ${chunk}`);
});
res.on("end", () => {
console.log("No more data in response.");
});
});
req.on("error", (e) => {
console.error(`problem with request: ${e.message}`);
});
req.end();
}
setInterval(() => {
request();
}, 3000);
Server:
const http = require("http");
const server = http.createServer((req, res) => {
setTimeout(() => {
res.end();
}, 500);
});
server.on("connection", function (socket) {
socket.id = Date.now();
console.log(
"A new connection was made by a client." + ` SOCKET ${socket.id}`
);
socket.on("end", function () {
console.log(
`SOCKET ${socket.id} END: other end of the socket sends a FIN packet`
);
});
socket.on("timeout", function () {
console.log(`SOCKET ${socket.id} TIMEOUT`);
});
socket.on("error", function (error) {
console.log(`SOCKET ${socket.id} ERROR: ` + JSON.stringify(error));
});
socket.on("close", function (had_error) {
console.log(`SOCKET ${socket.id} CLOSED. IT WAS ERROR: ` + had_error);
});
});
server.on("clientError", (err, socket) => {
socket.end("HTTP/1.1 400 Bad Request\r\n\r\n");
});
server.listen(4000);
Here's what I observed on the client side:
Client:
making a request
STATUS: 200
HEADERS: {"date":"Thu, 09 Apr 2020 13:05:44 GMT","connection":"keep-alive","content-length":"81"}
No more data in response.
making a request
STATUS: 200
HEADERS: {"date":"Thu, 09 Apr 2020 13:05:47 GMT","connection":"keep-alive","content-length":"81"}
No more data in response.
making a request
STATUS: 200
HEADERS: {"date":"Thu, 09 Apr 2020 13:05:50 GMT","connection":"keep-alive","content-length":"81"}
No more data in response.
and Server:
A new connection was made by a client. SOCKET 1586437543111
{ connection: 'keep-alive', host: 'localhost:1234' }
SOCKET 1586437543111 END: other end of the socket sends a FIN packet
SOCKET 1586437543111 CLOSED. IT WAS ERROR: false
A new connection was made by a client. SOCKET 1586437546091
{ connection: 'keep-alive', host: 'localhost:1234' }
SOCKET 1586437546091 END: other end of the socket sends a FIN packet
SOCKET 1586437546091 CLOSED. IT WAS ERROR: false
A new connection was made by a client. SOCKET 1586437549095
{ connection: 'keep-alive', host: 'localhost:1234' }
SOCKET 1586437549095 END: other end of the socket sends a FIN packet
SOCKET 1586437549095 CLOSED. IT WAS ERROR: false
NodeJS version: 10.15.0
Another confusing aspect for me arises when using telnet localhost 1234 to make a request:
GET / HTTP/1.1
Connection: Keep-Alive
Host: localhost
Surprisingly, the connection remains open without closing and no new connections are established as anticipated. Could it be that telnet interprets Connection: Keep-Alive itself and maintains the connection?