From bb07437e0af8c41d5acf2dec6f59a0cb33fe461a Mon Sep 17 00:00:00 2001
From: Gajus Kuizinas <gajus@gajus.com>
Date: Thu, 12 Dec 2019 09:55:20 +0000
Subject: [PATCH] feat: add error to the observe callback (fixes #1) BREAKING
 CHANGE: observer callback signature change.

---
 README.md                               | 30 ++++++++++++++-----------
 package.json                            |  3 ++-
 src/factories/createResourceObserver.js | 27 ++++++++++++++++------
 src/types.js                            |  6 ++++-
 4 files changed, 44 insertions(+), 22 deletions(-)

diff --git a/README.md b/README.md
index eb71118..5c74a17 100644
--- a/README.md
+++ b/README.md
@@ -150,19 +150,23 @@ const main = async () => {
   if (isKubernetesCredentialsPresent()) {
     const resourceObserver = createResourceObserver();
 
-    resourceObserver.observe((podResourceSpecification, podResourceUsage) => {
-      for (const containerResourceSpecification of podResourceSpecification.containers) {
-        if (containerResourceSpecification.resources.limits && containerResourceSpecification.resources.limits.memory) {
-          const containerResourceUsage = podResourceUsage.containers.find((container) => {
-            return container.name === containerResourceSpecification.name;
-          });
-
-          if (!containerResourceUsage) {
-            throw new Error('Unexpected state.');
-          }
-
-          if (containerResourceUsage.usage.memory / containerResourceSpecification.resources.limits.memory > MAXIMUM_MEMORY_USAGE) {
-            lightship.shutdown();
+    resourceObserver.observe((error, podResourceSpecification, podResourceUsage) => {
+      if (error) {
+        // Handle error.
+      } else {
+        for (const containerResourceSpecification of podResourceSpecification.containers) {
+          if (containerResourceSpecification.resources.limits && containerResourceSpecification.resources.limits.memory) {
+            const containerResourceUsage = podResourceUsage.containers.find((container) => {
+              return container.name === containerResourceSpecification.name;
+            });
+
+            if (!containerResourceUsage) {
+              throw new Error('Unexpected state.');
+            }
+
+            if (containerResourceUsage.usage.memory / containerResourceSpecification.resources.limits.memory > MAXIMUM_MEMORY_USAGE) {
+              lightship.shutdown();
+            }
           }
         }
       }
diff --git a/package.json b/package.json
index 519efe8..cf88b47 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,8 @@
   "dependencies": {
     "bytes-iec": "^3.1.0",
     "got": "^9.6.0",
-    "roarr": "^2.14.6"
+    "roarr": "^2.14.6",
+    "serialize-error": "^5.0.0"
   },
   "description": "Retrieves & observes Kubernetes Pod resource (CPU, memory) utilisation.",
   "devDependencies": {
diff --git a/src/factories/createResourceObserver.js b/src/factories/createResourceObserver.js
index b292d18..f3a0ccd 100644
--- a/src/factories/createResourceObserver.js
+++ b/src/factories/createResourceObserver.js
@@ -1,5 +1,8 @@
 // @flow
 
+import {
+  serializeError,
+} from 'serialize-error';
 import {
   getCredentials,
   getPodResourceSpecification,
@@ -69,15 +72,25 @@ export default () => {
         const context = await ready;
 
         const podResourceSpecification = context.podResourceSpecification;
-        const podResourceUsage = await getPodResourceUsage();
 
-        log.debug({
-          podResourceSpecification,
-          podResourceUsage,
-        }, 'observed resource usage');
+        try {
+          const podResourceUsage = await getPodResourceUsage();
+
+          log.debug({
+            podResourceSpecification,
+            podResourceUsage,
+          }, 'observed resource usage');
+
+          // eslint-disable-next-line callback-return
+          callback(null, podResourceSpecification, podResourceUsage);
+        } catch (error) {
+          log.error({
+            error: serializeError(error),
+          }, 'cannot get resource usage');
 
-        // eslint-disable-next-line callback-return
-        callback(podResourceSpecification, podResourceUsage);
+          // eslint-disable-next-line callback-return
+          callback(error, null, null);
+        }
 
         timeout = setTimeout(() => {
           tick();
diff --git a/src/types.js b/src/types.js
index 8480522..19cfec8 100644
--- a/src/types.js
+++ b/src/types.js
@@ -36,4 +36,8 @@ export type PodResourceSpecificationType = {|
   +name: string,
 |};
 
-export type IntervalCallbackType = (podResourceSpecification: PodResourceSpecificationType, podResourceUsage: PodResourceUsageType) => void;
+export type IntervalCallbackType = (
+  error: Error | null,
+  podResourceSpecification: PodResourceSpecificationType | null,
+  podResourceUsage: PodResourceUsageType | null
+) => void;