From 1fc242200f78e4219aafc5bb91de8cf0916236af Mon Sep 17 00:00:00 2001
From: Christina Ying Wang <christina@balena.io>
Date: Mon, 6 Jan 2025 14:21:27 -0800
Subject: [PATCH] Revert to regular pull immediately on delta server failure
 (code 400s)

If the delta server responds immediately with HTTP 4xx upon requesting a delta image,
this means the server is not able to supply the resource, so fall back to a regular pull
immediately.

Change-type: patch
Signed-off-by: Christina Ying Wang <christina@balena.io>
---
 src/lib/docker-utils.ts | 16 +++++++++++-----
 src/lib/errors.ts       |  2 ++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/lib/docker-utils.ts b/src/lib/docker-utils.ts
index 25845154..056c3066 100644
--- a/src/lib/docker-utils.ts
+++ b/src/lib/docker-utils.ts
@@ -12,6 +12,7 @@ import {
 	DeltaStillProcessingError,
 	ImageAuthenticationError,
 	InvalidNetGatewayError,
+	DeltaServerError,
 } from './errors';
 import * as request from './request';
 import type { EnvVarObject } from '../types';
@@ -113,11 +114,7 @@ export async function fetchDeltaWithProgress(
 	onProgress: ProgressCallback,
 	serviceName: string,
 ): Promise<string> {
-	const deltaSourceId =
-		deltaOpts.deltaSourceId != null
-			? deltaOpts.deltaSourceId
-			: deltaOpts.deltaSource;
-
+	const deltaSourceId = deltaOpts.deltaSourceId ?? deltaOpts.deltaSource;
 	const timeout = deltaOpts.deltaApplyTimeout;
 
 	const logFn = (str: string) =>
@@ -210,6 +207,10 @@ export async function fetchDeltaWithProgress(
 				}
 				break;
 			case 3:
+				// If 400s status code, throw a more specific error & revert immediately to a regular pull
+				if (res.statusCode >= 400 && res.statusCode < 500) {
+					throw new DeltaServerError(res.statusCode, res.statusMessage);
+				}
 				if (res.statusCode !== 200) {
 					throw new Error(
 						`Got ${res.statusCode} when requesting v3 delta from delta server.`,
@@ -235,6 +236,11 @@ export async function fetchDeltaWithProgress(
 		if (e instanceof OutOfSyncError) {
 			logFn('Falling back to regular pull due to delta out of sync error');
 			return await fetchImageWithProgress(imgDest, deltaOpts, onProgress);
+		} else if (e instanceof DeltaServerError) {
+			logFn(
+				`Falling back to regular pull due to delta server error (${e.statusCode})${e.statusMessage ? `: ${e.statusMessage}` : ''}`,
+			);
+			return await fetchImageWithProgress(imgDest, deltaOpts, onProgress);
 		} else {
 			logFn(`Delta failed with ${e}`);
 			throw e;
diff --git a/src/lib/errors.ts b/src/lib/errors.ts
index eb4a1a08..f7979f1f 100644
--- a/src/lib/errors.ts
+++ b/src/lib/errors.ts
@@ -70,6 +70,8 @@ export class InvalidNetGatewayError extends TypedError {}
 
 export class DeltaStillProcessingError extends TypedError {}
 
+export class DeltaServerError extends StatusError {}
+
 export class UpdatesLockedError extends TypedError {}
 
 export function isHttpConflictError(err: { statusCode: number }): boolean {