fix(sharing): answer malformed request URLs instead of crashing the server

handle() is dispatched via `void`, so a throw before its try/catch is an
unhandled rejection on a LAN-facing server. A request target the HTTP
parser accepts but the WHATWG URL parser rejects (unterminated IPv6 host
like //[::1) threw at new URL() and hung/killed the process. Parse inside
a guard and answer 400. Mutation-checked: the test times out with an
unhandled error before the fix, passes after.

src/sharing/share-server.ts

@@ -73,11 +73,22 @@ export class ShareServer {
   }
 
   private async handle(req: IncomingMessage, res: ServerResponse): Promise<void> {
-    const url = new URL(req.url ?? '/', 'https://localhost')
     const json = (code: number, body: unknown): void => {
       res.writeHead(code, { 'content-type': 'application/json' })
       res.end(JSON.stringify(body))
     }
+    // handle() is dispatched with `void` (see the createServer callback), so a
+    // throw here is an UNHANDLED rejection, not a caught 500. A request target
+    // the HTTP parser accepts but the WHATWG URL parser rejects - e.g. an
+    // unterminated IPv6 host like `//[::1` - would otherwise crash this
+    // LAN-facing server. Parse inside the guard and answer 400 instead.
+    let url: URL
+    try {
+      url = new URL(req.url ?? '/', 'https://localhost')
+    } catch {
+      json(400, { error: 'malformed request URL' })
+      return
+    }
     try {
       await this.route(url, req, res, json)
     } catch (err) {

tests/sharing/malformed-request.test.ts

@@ -0,0 +1,58 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest'
+import { connect as tlsConnect } from 'tls'
+
+import { generateIdentity, type Identity } from '../../src/sharing/identity.js'
+import { PeerStore } from '../../src/sharing/pairing.js'
+import { ShareServer } from '../../src/sharing/share-server.js'
+
+// The share server listens on the LAN for device pairing and is dispatched via
+// `void this.handle(...)`, so a throw inside handle() is an UNHANDLED rejection.
+// A request target the HTTP parser accepts but the WHATWG URL parser rejects
+// (an unterminated IPv6 host) used to throw at `new URL(...)` before the
+// try/catch, which could crash the host process. The server must instead answer
+// and stay alive.
+describe('share server: malformed request URL does not crash the process', () => {
+  let server: ShareServer
+  let serverId: Identity
+  let clientId: Identity
+  let port: number
+
+  beforeAll(async () => {
+    serverId = await generateIdentity('Server')
+    clientId = await generateIdentity('Client')
+    server = new ShareServer({ identity: serverId, peers: new PeerStore(), getUsage: async () => ({ current: { cost: 1 } }) })
+    port = await server.listen(0, '127.0.0.1')
+  })
+
+  afterAll(async () => {
+    await server.close()
+  })
+
+  // Send one raw HTTP request line over mTLS and resolve with the response head.
+  function rawRequest(line: string): Promise<string> {
+    return new Promise((resolve, reject) => {
+      const socket = tlsConnect(
+        { host: '127.0.0.1', port, key: clientId.key, cert: clientId.cert, rejectUnauthorized: false },
+        () => socket.write(`${line}\r\nHost: localhost\r\nConnection: close\r\n\r\n`),
+      )
+      let buf = ''
+      socket.setTimeout(4000, () => { socket.destroy(); reject(new Error('timed out (server hung)')) })
+      socket.on('data', (d) => { buf += d.toString() })
+      socket.on('end', () => resolve(buf))
+      socket.on('error', reject)
+    })
+  }
+
+  it('answers an unterminated-IPv6 target instead of hanging or crashing', async () => {
+    // `new URL('//[::1', 'https://localhost')` throws TypeError; llhttp accepts
+    // the target, so this exercises the exact pre-try throw path.
+    const res = await rawRequest('GET //[::1 HTTP/1.1')
+    expect(res).toMatch(/^HTTP\/1\.1 400/)
+  })
+
+  it('is still alive for a valid request afterward', async () => {
+    const res = await rawRequest('GET /api/peer/hello HTTP/1.1')
+    expect(res).toMatch(/^HTTP\/1\.1 200/)
+    expect(res).toContain(serverId.fingerprint)
+  })
+})