Cursor: avoid closing connection twice if error received after destroy() (brianc#2836)

* Cursor: avoid closing connection twice if error received after destroy()

Includes test case from @nathanjcochran

* Resolve lint violations

* revert fix to check tests fail without it

* Re-introdce fix

This reverts commit 5f5d42a.

---------

Co-authored-by: alxndrsn <alxndrsn>

Author: alxndrsn

packages/pg-cursor/index.js

@@ -151,6 +151,9 @@ class Cursor extends EventEmitter {
   }
 
   handleError(msg) {
+    // If this cursor has already closed, don't try to handle the error.
+    if (this.state === 'done') return
+
     // If we're in an initialized state we've never been submitted
     // and don't have a connection instance reference yet.
     // This can happen if you queue a stream and close the client before

packages/pg-query-stream/test/error.ts

@@ -89,4 +89,85 @@ describe('error recovery', () => {
       await client.end()
     })
   })
+
+  it('should work if used after timeout error', async () => {
+    const pool = new Pool({ max: 1, connectionTimeoutMillis: 400, statement_timeout: 400 })
+
+    const res1 = await pool.query('SELECT 1 AS a')
+    assert.deepStrictEqual(res1.rows, [{ a: 1 }])
+
+    const query = new QueryStream('SELECT 2 AS b')
+    const client = await pool.connect()
+    const stream = await client.query(query)
+
+    await assert.rejects(() => pool.query('SELECT TRUE'), { message: 'timeout exceeded when trying to connect' })
+
+    await stream.destroy()
+    await client.release()
+
+    const res2 = await pool.query('SELECT 4 AS d')
+    assert.deepStrictEqual(res2.rows, [{ d: 4 }])
+
+    await pool.end()
+  })
+
+  it('should work if used after syntax error', async () => {
+    const pool = new Pool({ max: 1, statement_timeout: 100 }) // statement_timeout is required here, so maybe this is just another timeout error?
+
+    const res1 = await pool.query('SELECT 1 AS a')
+    assert.deepStrictEqual(res1.rows, [{ a: 1 }])
+
+    const query = new QueryStream('SELECT 2 AS b')
+    const client = await pool.connect()
+    const stream = await client.query(query)
+
+    await new Promise((resolve) => setTimeout(resolve, 10))
+
+    await stream.destroy()
+    await client.release()
+
+    const res2 = await pool.query('SELECT 4 AS d')
+    assert.deepStrictEqual(res2.rows, [{ d: 4 }])
+
+    await pool.end()
+  })
+
+  it('should work after cancelling query', async () => {
+    const pool = new Pool()
+    const conn = await pool.connect()
+
+    // Get connection PID for sake of pg_cancel_backend() call
+    const result = await conn.query('SELECT pg_backend_pid() AS pid;')
+    const { pid } = result.rows[0]
+
+    const stream = conn.query(new QueryStream('SELECT pg_sleep(10);'))
+    stream.on('data', (chunk) => {
+      // Switches stream into readableFlowing === true mode
+    })
+    stream.on('error', (err) => {
+      // Errors are expected due to pg_cancel_backend() call
+    })
+
+    // Create a promise that is resolved when the stream is closed
+    const closed = new Promise((res) => {
+      stream.on('close', res)
+    })
+
+    // Wait 100ms before cancelling the query
+    await new Promise((res) => setTimeout(res, 100))
+
+    // Cancel pg_sleep(10) query
+    await pool.query('SELECT pg_cancel_backend($1);', [pid])
+
+    // Destroy stream and wait for it to be closed
+    stream.destroy()
+    await closed
+
+    // Subsequent query on same connection should succeed
+    const res = await conn.query('SELECT 1 AS a;')
+    assert.deepStrictEqual(res.rows, [{ a: 1 }])
+
+    conn.release()
+    await pool.end()
+  })
 })