feat(pglite-socket): handle CancelRequest wire protocol message

Rebased onto main, which now handles SSLRequest (replies 'N') via the
extracted handleSslRequest() method (#990).

Adapts the remaining CancelRequest handling to that same style as requested
in review: adds named CANCEL_REQUEST_CODE / CANCEL_REQUEST_LENGTH constants
(no magic numbers) and extracts the logic into a dedicated handleCancelRequest()
method called from the handleData() loop alongside handleSslRequest().

PGlite has no backend process to signal, so the request is consumed and
silently ignored (the protocol expects no response). Drops the now-redundant
inline SSL handling and SSL-specific tests (covered by upstream's
ssl-request.test.ts); keeps a CancelRequest integration test.

Author: bookernath

.changeset/cancel-request-handling.md

@@ -0,0 +1,7 @@
+---
+'@electric-sql/pglite-socket': minor
+---
+
+Handle PostgreSQL CancelRequest wire protocol messages
+
+Added support for the CancelRequest message that some clients and connection proxies send during the connection startup phase. PGlite has no backend process to cancel, so the request is consumed and silently ignored (the protocol expects no response), which prevents it from being misinterpreted as a malformed startup/typed message. This complements the existing SSLRequest handling.

packages/pglite-socket/src/index.ts

@@ -5,6 +5,8 @@ import { type Server, type Socket, createServer } from 'net'
 export const CONNECTION_QUEUE_TIMEOUT = 60000 // 60 seconds
 export const SSL_REQUEST_CODE = 80877103
 export const SSL_REQUEST_LENGTH = 8
+export const CANCEL_REQUEST_CODE = 80877102
+export const CANCEL_REQUEST_LENGTH = 16
 
 /**
  * Represents a queued query waiting for PGlite access
@@ -346,6 +348,26 @@ export class PGLiteSocketHandler extends EventTarget {
     return false
   }
 
+  // CancelRequest arrives on its own connection during startup, before any
+  // typed message. PGlite has no backend process to signal, so we consume the
+  // message and silently drop it (the wire protocol expects no response).
+  private handleCancelRequest(): boolean {
+    if (this.messageBuffer.length < CANCEL_REQUEST_LENGTH) {
+      return false
+    }
+
+    const len = this.messageBuffer.readInt32BE(0)
+    const code = this.messageBuffer.readInt32BE(4)
+
+    if (len === CANCEL_REQUEST_LENGTH && code === CANCEL_REQUEST_CODE) {
+      this.messageBuffer = this.messageBuffer.slice(CANCEL_REQUEST_LENGTH)
+      this.log('handleData: CancelRequest received, ignoring (not supported)')
+      return true
+    }
+
+    return false
+  }
+
   private async handleData(data: Buffer): Promise<number> {
     if (!this.socket || !this.active) {
       this.log(`handleData: no active socket, ignoring data`)
@@ -368,6 +390,10 @@ export class PGLiteSocketHandler extends EventTarget {
           continue
         }
 
+        if (this.handleCancelRequest()) {
+          continue
+        }
+
         // Determine message length
         let messageLength = 0
         let isComplete = false

packages/pglite-socket/tests/query-with-node-pg.test.ts

@@ -11,6 +11,7 @@ import { Client } from 'pg'
 import { PGlite } from '@electric-sql/pglite'
 import { PGLiteSocketServer } from '../src'
 import { spawn, ChildProcess } from 'node:child_process'
+import { createConnection } from 'node:net'
 import { fileURLToPath } from 'node:url'
 import { dirname, join } from 'node:path'
 import fs from 'fs'
@@ -792,6 +793,36 @@ describe(`PGLite Socket Server`, () => {
         // swallow
       }
     }, 30000)
+
+    it('should handle CancelRequest without crashing', async () => {
+      // Test raw CancelRequest wire protocol handling
+      const socket = createConnection({ host: '127.0.0.1', port: TEST_PORT })
+
+      await new Promise<void>((resolve, reject) => {
+        socket.on('connect', resolve)
+        socket.on('error', reject)
+      })
+
+      // Send CancelRequest: [length=16][code=80877102 (0x04D2162E)][processID=0][secretKey=0]
+      const cancelRequest = Buffer.alloc(16)
+      cancelRequest.writeInt32BE(16, 0)
+      cancelRequest.writeInt32BE(80877102, 4)
+      cancelRequest.writeInt32BE(0, 8) // processID
+      cancelRequest.writeInt32BE(0, 12) // secretKey
+      socket.write(cancelRequest)
+
+      // Wait briefly for server to process (no response expected)
+      await new Promise((resolve) => setTimeout(resolve, 200))
+
+      socket.destroy()
+
+      // Verify server still works after receiving CancelRequest
+      const testClient = new Client(connectionConfig)
+      await testClient.connect()
+      const result = await testClient.query('SELECT 1 as one')
+      expect(result.rows[0].one).toBe(1)
+      await testClient.end()
+    })
   })
 
   describe('with extensions via CLI', () => {