Return 502 instead of 500 when failing to proxy requests in the dev server

[segevfiner]

Description

Instead of returning 500 when the upstream server in not available in the Vite dev server proxying, return 502 (Bad Gateway), which allows to detect this case more cleanly in frontend code and retry.

Suggested solution

Modify:

vite/packages/vite/src/node/server/middlewares/proxy.ts

Lines 97 to 121 in 44b5bdf

	proxy.on('error', (err, _req, res) => {
	// When it is ws proxy, res is net.Socket
	if ('req' in res) {
	config.logger.error(
	`${colors.red(`http proxy error: ${res.req.url}`)}\n${err.stack}`,
	{
	timestamp: true,
	error: err,
	},
	)
	if (!res.headersSent && !res.writableEnded) {
	res
	.writeHead(500, {
	'Content-Type': 'text/plain',
	})
	.end()
	}
	} else {
	config.logger.error(`${colors.red(`ws proxy error:`)}\n${err.stack}`, {
	timestamp: true,
	error: err,
	})
	res.end()
	}
	})

To return 502 instead of 500, or maybe only for applicable error types.

Alternative

Check for and retry on 500, which is less accurate, and only fits for development mode

Additional context

No response

Validations

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