Get the PostgreSQL server version from connection? - postgresql

Question

Is there anything in the modern PostgreSQL connection protocol that would indicate the server version?
And if not, is there a special low-level request that an endpoint can execute against an open connection to pull the server details that would contain the version?
I'm looking at a possible extension of node-postgres that would automatically provide the server version upon every fresh connection. And I want to know if this is at all possible.
Having to execute SELECT version() upon every new connection and then parsing it is too high-level for the base driver that manages the connection. It should be done on the protocol level.

Answer 1

After a bit of research, I found that PostgreSQL does provide server version during connection, within the start-up message.
And specifically within node-postgres driver, we can make Pool provide a custom Client that handles event parameterStatus on the connection, and exposes the server version:
const {Client, Pool} = require('pg');
class MyClient extends Client {
constructor(config) {
super(config);
this.connection.on('parameterStatus', msg => {
if (msg.parameterName === 'server_version') {
this.version = msg.parameterValue;
}
});
}
}
const cn = {
database: 'my-db',
user: 'postgres',
password: 'bla-bla',
Client: MyClient // here's our custom Client type
};
const pool = new Pool(cn);
pool.connect()
.then(client => {
console.log('Server Version:', client.version);
client.release(true);
})
.catch(console.error);
On my test PC, I use PostgreSQL v11.2, so this test outputs:
Server Version: 11.2
UPDATE - 1
Library pg-promise has been updated to support the same functionality in TypeScript. And you can find a complete example in this ticket.
UPDATE - 2
See example here:
// tests connection and returns Postgres server version,
// if successful; or else rejects with connection error:
async function testConnection() {
const c = await db.connect(); // try to connect
c.done(); // success, release connection
return c.client.serverVersion; // return server version
}