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fix: harden egress proxy error handling #23

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Merged
abnegate merged 2 commits into from
Oct 22, 2026
Merged

fix: harden egress proxy error handling #23

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fe41ba2
fix: harden egress proxy error handling
cursoragent Oct 22, 2026
267c7fb
test: use a status message both Bun versions reject
cursoragent Oct 22, 2026
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245 changes: 152 additions & 93 deletions src/utils/egress.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -133,6 +133,41 @@ function parseAuthority(
return { hostname: url.hostname, port };
}

function failResponse(res: http.ServerResponse, status = 502): void {
if (res.destroyed || res.writableEnded) {
return;
}
if (res.headersSent) {
res.destroy();
return;
}
try {
// A rejected writeHead can leave an unusable status line on `res`.
res.statusCode = status;
res.statusMessage = "Bad Gateway";
const socket = res.socket;
res.writeHead(status).end(() => {
socket?.end();
});
} catch {
res.destroy();
}
}

function failSocket(
socket: net.Socket,
statusLine = "HTTP/1.1 502 Bad Gateway",
): void {
if (socket.destroyed) {
return;
}
try {
socket.end(`${statusLine}\r\nContent-Length: 0\r\n\r\n`);
} catch {
socket.destroy();
}
}

/**
* A guard per capture pins each host to its first answer for the capture, so a
* page cannot flip a host between public and private mid-capture, and records
Expand Down Expand Up @@ -176,113 +211,137 @@ export async function startEgressGuard({
};

const server = http.createServer(async (req, res) => {
track(req.socket);
// Bun stalls on the second absolute-form request of a kept-alive
// connection, so make the browser open a new one for each request.
res.setHeader("Connection", "close");

let target: URL;
try {
target = new URL(req.url ?? "");
} catch {
res.writeHead(400).end();
return;
}
if (target.protocol !== "http:") {
res.writeHead(400).end();
return;
}
track(req.socket);
// Bun stalls on the second absolute-form request of a kept-alive
// connection, so make the browser open a new one for each request.
res.setHeader("Connection", "close");
req.on("error", () => failResponse(res));

const port = target.port === "" ? 80 : Number(target.port);
const resolution = await resolve(target.hostname);
if (resolution.status === "private") {
refuse(target.hostname, port);
res
.writeHead(403, { "Content-Type": "text/plain" })
.end("Destination is not publicly routable.");
return;
}
if (resolution.status === "unresolved") {
res.writeHead(502).end();
return;
}
let target: URL;
try {
target = new URL(req.url ?? "");
} catch {
res.writeHead(400).end();
return;
}
if (target.protocol !== "http:") {
res.writeHead(400).end();
return;
}

const [address] = preferIpv4(resolution.addresses);
const upstream = http.request(
{
host: address.address,
family: address.family,
port,
method: req.method,
path: `${target.pathname}${target.search}`,
headers: { ...forwardHeaders(req.headers), host: target.host },
},
(upstreamRes) => {
res.writeHead(
upstreamRes.statusCode ?? 502,
upstreamRes.statusMessage,
forwardHeaders(upstreamRes.headers),
);
upstreamRes.pipe(res);
},
);
upstream.setTimeout(IDLE_TIMEOUT_MS, () => upstream.destroy());
res.once("close", () => upstream.destroy());
upstream.on("error", () => {
if (res.headersSent) {
res.destroy();
} else {
const port = target.port === "" ? 80 : Number(target.port);
const resolution = await resolve(target.hostname);
if (resolution.status === "private") {
refuse(target.hostname, port);
res
.writeHead(403, { "Content-Type": "text/plain" })
.end("Destination is not publicly routable.");
return;
}
if (resolution.status === "unresolved") {
res.writeHead(502).end();
return;
}
});
req.pipe(upstream);

const [address] = preferIpv4(resolution.addresses);
const upstream = http.request(
{
host: address.address,
family: address.family,
port,
method: req.method,
path: `${target.pathname}${target.search}`,
headers: { ...forwardHeaders(req.headers), host: target.host },
},
(upstreamRes) => {
const abort = () => {
failResponse(res);
upstreamRes.destroy();
};
upstreamRes.on("error", abort);
try {
res.writeHead(
upstreamRes.statusCode ?? 502,
upstreamRes.statusMessage,
forwardHeaders(upstreamRes.headers),
);
upstreamRes.pipe(res);
} catch {
abort();
}
},
);
upstream.setTimeout(IDLE_TIMEOUT_MS, () => upstream.destroy());
res.once("close", () => upstream.destroy());
upstream.on("error", () => failResponse(res));
req.pipe(upstream);
} catch {
failResponse(res);
}
});

// HTTPS, and WebSockets of either scheme, arrive as CONNECT tunnels.
server.on("connect", async (req, socket: net.Socket, head: Buffer) => {
track(socket);
let upstream: net.Socket | undefined;
let established = false;
try {
track(socket);
req.on("error", () => socket.destroy());

const target = parseAuthority(req.url ?? "");
if (!target) {
socket.end("HTTP/1.1 400 Bad Request\r\nContent-Length: 0\r\n\r\n");
return;
}
const target = parseAuthority(req.url ?? "");
if (!target) {
failSocket(socket, "HTTP/1.1 400 Bad Request");
return;
}

const resolution = await resolve(target.hostname);
if (resolution.status === "private") {
refuse(target.hostname, target.port);
socket.end("HTTP/1.1 403 Forbidden\r\nContent-Length: 0\r\n\r\n");
return;
}
if (resolution.status === "unresolved") {
socket.end("HTTP/1.1 502 Bad Gateway\r\nContent-Length: 0\r\n\r\n");
return;
}
const resolution = await resolve(target.hostname);
if (resolution.status === "private") {
refuse(target.hostname, target.port);
failSocket(socket, "HTTP/1.1 403 Forbidden");
return;
}
if (resolution.status === "unresolved") {
failSocket(socket);
return;
}

let upstream: net.Socket;
try {
upstream = await connectToAny(
preferIpv4(resolution.addresses),
target.port,
);
} catch {
socket.end("HTTP/1.1 502 Bad Gateway\r\nContent-Length: 0\r\n\r\n");
return;
}
if (socket.destroyed) {
upstream.destroy();
return;
}
track(upstream);
upstream.once("close", () => socket.destroy());
socket.once("close", () => upstream.destroy());
try {
upstream = await connectToAny(
preferIpv4(resolution.addresses),
target.port,
);
} catch {
failSocket(socket);
return;
}
if (!upstream) {
failSocket(socket);
return;
}
if (socket.destroyed) {
upstream.destroy();
return;
}
track(upstream);
upstream.once("close", () => socket.destroy());
socket.once("close", () => upstream?.destroy());

socket.write("HTTP/1.1 200 Connection Established\r\n\r\n");
if (head.length > 0) {
upstream.write(head);
socket.write("HTTP/1.1 200 Connection Established\r\n\r\n");
established = true;
if (head.length > 0) {
upstream.write(head);
}
upstream.pipe(socket);
socket.pipe(upstream);
} catch {
upstream?.destroy();
if (established) {
socket.destroy();
} else {
failSocket(socket);
}
}
upstream.pipe(socket);
socket.pipe(upstream);
});

await new Promise<void>((resolve, reject) => {
Expand Down
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