Why am I setting headers twice - node.js

Question

I am recieving this error: Cannot set headers after they are sent to the client
I take that to mean the code is attempting to set the response headers more than once. This is the code, but I cant seem to find out where the headers are being set twice.
async function createTrip(request, response) {
const { vehicleId, driverId, startedAt, expectedReturn } = request.body
let driver, vehicle
//validation
await pool.query(
'SELECT * FROM Vehicle WHERE id = $1',
[vehicleId],
(error, results) => {
if (error) {
throw `ERROR::createTrip threw an error: ${error}`
}
if (results.rowCount === 0) {
return response.send({ status: 404, message: `vehicle with id ${vehicleId} does not exist.` })
} else if (results.rows[0].in_use) {
return response.send(403).send({ status: 403, message: `vehicle with id ${vehicleId} is not available for rental` })
} else {
vehicle = results.rows[0]
}
}
)
await pool.query(
'SELECT * FROM Driver WHERE id = $1',
[driverId],
(error, results) => {
if (error) {
throw new Error(`ERROR::createTrip threw an error: ${error}`)
} else if (results.rowCount === 0) {
return response.status(404).send({ status: 404, message: `driver with id ${driverId} does not exist` })
} else {
driver = results.rows[0]
}
}
)
//event
await pool.query(
'INSERT INTO Trip (status,started_at, expected_return, driver, vehicle) VALUES ($1,$2,$3,$4,$5) RETURNING *',
['active', startedAt, expectedReturn, driverId, vehicleId],
(error, results) => {
if (error) {
throw `ERROR::createTrip threw an error: ${error}`
} else {
return response.status(200).send({ id: results.rows[0].id, status: results.rows[0].status, startedAt, expectedReturn, driver, vehicle })
}
}
)
await pool.query(
'UPDATE Vehicle SET in_use = TRUE WHERE id = $1',
[vehicleId],
(error) =>{
if(error){
throw `ERROR::createTrip threw an error: ${error}`
}
}
)
}

Answer 1

Your createTrip function does four queries. Each of those queries results in a response potentially being called. You should do all the processing from all the queries you need to inside a try/catch block. Then, instead of sending a response when rowCount === 0 for example, throw an error, catch it in the catch block and send the response from there.