From d5ed9a935f7947210f2decfed3d447044ba896a2 Mon Sep 17 00:00:00 2001
From: Benjie Gillam <benjie@jemjie.com>
Date: Sat, 17 Feb 2018 20:00:29 +0000
Subject: [PATCH] feat(pg): duck-type PG to prevent 'provide valid PG client'
 error (#168)

* feat(pg): duck-type PG to prevent clashes

* Duck-type in watch mode also

* Satisfy Flow
---
 .../src/plugins/PgIntrospectionPlugin.js      |  3 +-
 .../graphile-build-pg/src/withPgClient.js     | 40 ++++++++++++++++---
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/packages/graphile-build-pg/src/plugins/PgIntrospectionPlugin.js b/packages/graphile-build-pg/src/plugins/PgIntrospectionPlugin.js
index d269c4eb0..314a69c4d 100644
--- a/packages/graphile-build-pg/src/plugins/PgIntrospectionPlugin.js
+++ b/packages/graphile-build-pg/src/plugins/PgIntrospectionPlugin.js
@@ -6,6 +6,7 @@ import { readFile as rawReadFile } from "fs";
 import pg from "pg";
 import debugFactory from "debug";
 import chalk from "chalk";
+import { quacksLikePgPool } from "../withPgClient";
 
 import { version } from "../../package.json";
 
@@ -260,7 +261,7 @@ export default (async function PgIntrospectionPlugin(
     await stopListening();
 
     // Check we can get a pgClient
-    if (pgConfig instanceof pg.Pool) {
+    if (pgConfig instanceof pg.Pool || quacksLikePgPool(pgConfig)) {
       pgClient = await pgConfig.connect();
       releasePgClient = () => pgClient && pgClient.release();
     } else if (typeof pgConfig === "string") {
diff --git a/packages/graphile-build-pg/src/withPgClient.js b/packages/graphile-build-pg/src/withPgClient.js
index 9f48ea585..db2614ead 100644
--- a/packages/graphile-build-pg/src/withPgClient.js
+++ b/packages/graphile-build-pg/src/withPgClient.js
@@ -3,6 +3,35 @@ import pg from "pg";
 import debugFactory from "debug";
 const debug = debugFactory("graphile-build-pg");
 
+function constructorName(obj) {
+  return obj && typeof obj.constructor === "function" && obj.constructor.name;
+}
+
+// Some duck-typing
+
+function quacksLikePgClient(pgConfig: mixed): boolean {
+  // A diagnosis of exclusion
+  if (!pgConfig || typeof pgConfig !== "object") return false;
+  if (constructorName(pgConfig) !== "Client") return false;
+  if (typeof pgConfig.connect !== "function") return false;
+  if (typeof pgConfig.end !== "function") return false;
+  if (typeof pgConfig.escapeLiteral !== "function") return false;
+  if (typeof pgConfig.escapeIdentifier !== "function") return false;
+  return true;
+}
+
+export function quacksLikePgPool(pgConfig: mixed): boolean {
+  // A diagnosis of exclusion
+  if (!pgConfig || typeof pgConfig !== "object") return false;
+  if (constructorName(pgConfig) !== "Pool") return false;
+  if (!pgConfig.Client) return false;
+  if (!pgConfig.options) return false;
+  if (typeof pgConfig.connect !== "function") return false;
+  if (typeof pgConfig.end !== "function") return false;
+  if (typeof pgConfig.query !== "function") return false;
+  return true;
+}
+
 const withPgClient = async (
   pgConfig: pg.Client | pg.Pool | string = process.env.DATABASE_URL,
   fn: (pgClient: pg.Client) => *
@@ -11,18 +40,19 @@ const withPgClient = async (
     throw new Error("Nothing to do!");
   }
   let releasePgClient = () => {};
-  let pgClient;
+  let pgClient: pg.Client;
   let result;
   try {
-    if (pgConfig instanceof pg.Client) {
-      pgClient = pgConfig;
+    if (pgConfig instanceof pg.Client || quacksLikePgClient(pgConfig)) {
+      pgClient = (pgConfig: pg.Client);
       if (!pgClient.release) {
         throw new Error(
           "We only support PG clients from a PG pool (because otherwise the `await` call can hang indefinitely if an error occurs and there's no error handler)"
         );
       }
-    } else if (pgConfig instanceof pg.Pool) {
-      pgClient = await pgConfig.connect();
+    } else if (pgConfig instanceof pg.Pool || quacksLikePgPool(pgConfig)) {
+      const pgPool = (pgConfig: pg.Pool);
+      pgClient = await pgPool.connect();
       releasePgClient = () => pgClient.release();
     } else if (pgConfig === undefined || typeof pgConfig === "string") {
       pgClient = new pg.Client(pgConfig);