Handle client errors in pool.query (#131)

If an error not related to the query occurs, the client is emitting an
error event.

Forward this event to the callback.

index.js

@@ -316,13 +316,31 @@ class Pool extends EventEmitter {
     }
     const response = promisify(this.Promise, cb)
     cb = response.callback
+
     this.connect((err, client) => {
       if (err) {
         return cb(err)
       }
+
+      let clientReleased = false
+      const onError = (err) => {
+        if (clientReleased) {
+          return
+        }
+        clientReleased = true
+        client.release(err)
+        cb(err)
+      }
+
+      client.once('error', onError)
       this.log('dispatching query')
       client.query(text, values, (err, res) => {
         this.log('query dispatched')
+        client.removeListener('error', onError)
+        if (clientReleased) {
+          return
+        }
+        clientReleased = true
         client.release(err)
         if (err) {
           return cb(err)

test/error-handling.js

@@ -226,4 +226,19 @@ describe('pool error handling', function () {
       })
     })
   })
+
+  it('handles post-checkout client failures in pool.query', (done) => {
+    const pool = new Pool({ max: 1 })
+    pool.on('error', () => {
+      // We double close the connection in this test, prevent exception caused by that
+    })
+    pool.query('SELECT pg_sleep(5)', [], (err) => {
+      expect(err).to.be.an(Error)
+      done()
+    })
+
+    setTimeout(() => {
+      pool._clients[0].end()
+    }, 1000)
+  })
 })