@azure/functions/src/http/httpProxy.ts

Microsoft Azure Functions NodeJS Framework

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the MIT License.

import { serialize as serializeCookie } from 'cookie';
import { EventEmitter } from 'events';
import * as http from 'http';
import * as net from 'net';
import { AzFuncSystemError, ensureErrorType } from '../errors';
import { nonNullProp } from '../utils/nonNull';
import { workerSystemLog } from '../utils/workerSystemLog';
import { HttpResponse } from './HttpResponse';

const requests: Record<string, http.IncomingMessage> = {};
const responses: Record<string, http.ServerResponse> = {};
const minPort = 55000;
const maxPort = 55025;

const invocRequestEmitter = new EventEmitter();

export async function waitForProxyRequest(invocationId: string): Promise<http.IncomingMessage> {
    return new Promise((resolve, _reject) => {
        const req = requests[invocationId];
        if (req) {
            resolve(req);
            delete requests[invocationId];
        } else {
            invocRequestEmitter.once(invocationId, () => {
                const req = requests[invocationId];
                if (req) {
                    resolve(req);
                    delete requests[invocationId];
                }
            });
        }
    });
}

const invocationIdHeader = 'x-ms-invocation-id';
export async function sendProxyResponse(invocationId: string, userRes: HttpResponse): Promise<void> {
    const proxyRes = nonNullProp(responses, invocationId);
    delete responses[invocationId];
    for (const [key, val] of userRes.headers.entries()) {
        proxyRes.setHeader(key, val);
    }
    proxyRes.setHeader(invocationIdHeader, invocationId);
    proxyRes.statusCode = userRes.status;

    if (userRes.cookies.length > 0) {
        setCookies(userRes, proxyRes);
    }

    if (userRes.body) {
        for await (const chunk of userRes.body.values()) {
            proxyRes.write(chunk);
        }
    }
    proxyRes.end();
}

function setCookies(userRes: HttpResponse, proxyRes: http.ServerResponse): void {
    const serializedCookies: string[] = userRes.cookies.map((c) => {
        let sameSite: true | false | 'lax' | 'strict' | 'none' | undefined;
        switch (c.sameSite) {
            case 'Lax':
                sameSite = 'lax';
                break;
            case 'None':
                sameSite = 'none';
                break;
            case 'Strict':
                sameSite = 'strict';
                break;
            default:
                sameSite = c.sameSite;
        }
        return serializeCookie(c.name, c.value, {
            domain: c.domain,
            path: c.path,
            expires: typeof c.expires === 'number' ? new Date(c.expires) : c.expires,
            secure: c.secure,
            httpOnly: c.httpOnly,
            sameSite: sameSite,
            maxAge: c.maxAge,
        });
    });
    proxyRes.setHeader('Set-Cookie', serializedCookies);
}

export async function setupHttpProxy(): Promise<string> {
    return new Promise((resolve, reject) => {
        const server = http.createServer();

        server.on('request', (req, res) => {
            const invocationId = req.headers[invocationIdHeader];
            if (typeof invocationId === 'string') {
                requests[invocationId] = req;
                responses[invocationId] = res;
                invocRequestEmitter.emit(invocationId);
            } else {
                workerSystemLog('error', `Http proxy request missing header ${invocationIdHeader}`);
            }
        });

        server.on('error', (err) => {
            err = ensureErrorType(err);
            workerSystemLog('error', `Http proxy error: ${err.stack || err.message}`);
        });

        server.listen(() => {
            const address = server.address();
            // Valid address has been created
            if (address !== null && typeof address === 'object') {
                if (address.port === 0) {
                    // Auto-assigned port is 0, find and bind to an open port
                    workerSystemLog('debug', `Port 0 assigned. Finding open port.`);
                    findOpenPort((openPort: number) => {
                        // Close the server and re-listen on the found open port
                        server.close();
                        server.listen(openPort, () => {
                            workerSystemLog('debug', `Server is now listening on found open port: ${openPort}`);
                        });
                        resolve(`http://localhost:${openPort}/`);
                    });
                } else {
                    // Auto-assigned port is not 0
                    workerSystemLog('debug', `Auto-assigned port is valid. Port: ${address.port}`);
                    resolve(`http://localhost:${address.port}/`);
                }
            } else {
                reject(new AzFuncSystemError('Unexpected server address during http proxy setup'));
            }
        });

        server.on('close', () => {
            workerSystemLog('information', 'Http proxy closing');
        });
    });
}

// Function to find an open port starting from a specified port
function findOpenPort(callback: (port: number) => void): void {
    const server = net.createServer();

    function tryPort(port: number) {
        if (port > maxPort) {
            // If we've reached the maximum port, throw an error
            throw new AzFuncSystemError(
                `No available ports found between ${minPort} and ${maxPort}. To enable HTTP streaming, please open a port in this range.`
            );
        }

        server.once('error', () => {
            // If the port is unavailable, increment and try the next one
            tryPort(port + 1);
        });

        // If the port is available, return it
        server.once('listening', () => {
            const address = server.address();
            if (address !== null && typeof address === 'object') {
                port = address.port;
                server.close();
                callback(port);
            }
        });

        // Try binding to the given port
        server.listen(port);
    }

    // Start trying from the specified starting port
    tryPort(minPort);
}