Do not return broken clients to the pool (#2083)

* Prevent requeuing a broken client

If a client is not queryable, the pool should prevent requeuing instead
of strictly enforcing errors to be propagated back to it.

* Write tests for change

* Use node 13.6 in travis

Some weird behavior changed w/ async iteration in node 13.7...I'm not sure if this was an unintentional break or not but it definitely diverges in behavior from node 12 and earlier versions in node 13...so for now going to run tests on 13.6 to unblock the tests from running while I track this down.

* Update packages/pg-pool/test/releasing-clients.js

Co-Authored-By: Charmander <~@charmander.me>

* Update .travis.yml

Co-authored-by: Johannes Würbach <johannes.wuerbach@googlemail.com>
Co-authored-by: Charmander <~@charmander.me>

.travis.yml

@@ -10,7 +10,10 @@ env:
 node_js:
   - lts/dubnium
   - lts/erbium
-  - 13
+  # node 13.7 seems to have changed behavior of async iterators exiting early on streams
+  # if 13.8 still has this problem when it comes down I'll talk to the node team about the change
+  # in the mean time...peg to 13.6 
+  - 13.6
 
 addons:
   postgresql: "10"

packages/pg-pool/index.js

@@ -25,6 +25,10 @@ class PendingItem {
   }
 }
 
+function throwOnDoubleRelease () {
+  throw new Error('Release called on client which has already been released to the pool.')
+}
+
 function promisify (Promise, callback) {
   if (callback) {
     return { callback: callback, result: undefined }
@@ -244,7 +248,7 @@ class Pool extends EventEmitter {
 
     client.release = (err) => {
       if (released) {
-        throw new Error('Release called on client which has already been released to the pool.')
+        throwOnDoubleRelease()
       }
 
       released = true
@@ -280,7 +284,8 @@ class Pool extends EventEmitter {
   _release (client, idleListener, err) {
     client.on('error', idleListener)
 
-    if (err || this.ending) {
+    // TODO(bmc): expose a proper, public interface _queryable and _ending
+    if (err || this.ending || !client._queryable || client._ending) {
       this._remove(client)
       this._pulseQueue()
       return

packages/pg-pool/test/releasing-clients.js

@@ -0,0 +1,54 @@
+const Pool = require('../')
+
+const expect = require('expect.js')
+const net = require('net')
+
+describe('releasing clients', () => {
+  it('removes a client which cannot be queried', async () => {
+    // make a pool w/ only 1 client
+    const pool = new Pool({ max: 1 })
+    expect(pool.totalCount).to.eql(0)
+    const client = await pool.connect()
+    expect(pool.totalCount).to.eql(1)
+    expect(pool.idleCount).to.eql(0)
+    // reach into the client and sever its connection
+    client.connection.end()
+
+    // wait for the client to error out
+    const err = await new Promise((resolve) => client.once('error', resolve))
+    expect(err).to.be.ok()
+    expect(pool.totalCount).to.eql(1)
+    expect(pool.idleCount).to.eql(0)
+
+    // try to return it to the pool - this removes it because its broken
+    client.release()
+    expect(pool.totalCount).to.eql(0)
+    expect(pool.idleCount).to.eql(0)
+
+    // make sure pool still works
+    const { rows } = await pool.query('SELECT NOW()')
+    expect(rows).to.have.length(1)
+    await pool.end()
+  })
+
+  it('removes a client which is ending', async () => {
+    // make a pool w/ only 1 client
+    const pool = new Pool({ max: 1 })
+    expect(pool.totalCount).to.eql(0)
+    const client = await pool.connect()
+    expect(pool.totalCount).to.eql(1)
+    expect(pool.idleCount).to.eql(0)
+    // end the client gracefully (but you shouldn't do this with pooled clients)
+    client.end()
+
+    // try to return it to the pool
+    client.release()
+    expect(pool.totalCount).to.eql(0)
+    expect(pool.idleCount).to.eql(0)
+
+    // make sure pool still works
+    const { rows } = await pool.query('SELECT NOW()')
+    expect(rows).to.have.length(1)
+    await pool.end()
+  })
+})