packer continues to build even if iso_checksum_url download fails

[avx-rvandegrift]

Overview of the Issue

I'm using a remote checksum file. packer had a network error while downloading the file, but it still continued. All of the expected images were built, but packer exited with an error code (so github actions saw a failure).

Either:

1. packer couldn't verify the checksum but continued anyhow (scary, since I can't be sure what it was working with)
2. packer retried download and succeeded, but still exited with a failure (merely annoying, since now I have to re-run)

Reproduction Steps

Hard to reproduce - depends on checksum file download failure.

Plugin and Packer version

I'm using packer 1.8.7 in Github actions by way of hashicorp/setup-packer@v2.0.0 with the qemu builder.

Simplified Packer Buildfile

The relevant part of my sources is:

source "qemu" "img-boot" {
  iso_url      = "https://cloud-images.ubuntu.com/releases/22.04/release-20230815/ubuntu-22.04-server-cloudimg-amd64.img"
  iso_checksum = "file:https://cloud-images.ubuntu.com/releases/22.04/release-20230815/SHA256SUMS"
}

Operating system and Environment details

Running in github actions on ubuntu-latest-8-cores with nested kvm enabled.

Log Fragments and crash.log files

Relevant bit of logs:

2023-08-28T22:15:57.7721333Z packer init .
2023-08-28T22:15:58.6280791Z packer build -force -on-error=cleanup -parallel-builds=8 .
2023-08-28T22:18:02.3983059Z Error: 1 error(s) occurred:
2023-08-28T22:18:02.3983728Z
2023-08-28T22:18:02.4012220Z * Error downloading checksum file: Get "https://cloud-images.ubuntu.com/releases/22.04/release-20230815/SHA256SUMS": read tcp 10.0.0.41:35328->185.12
5.190.37:443: read: connection reset by peer in "file:https://cloud-images.ubuntu.com/releases/22.04/release-20230815/SHA256SUMS"
2023-08-28T22:18:02.4013305Z
2023-08-28T22:18:02.4013671Z   on sources.pkr.hcl line 3:
2023-08-28T22:18:02.4014241Z   (source code not available)
2023-08-28T22:18:02.4014650Z
2023-08-28T22:18:02.4014681Z
2023-08-28T22:18:02.4015103Z A.qemu.img-boot: output will be in this color.
... (more builds)
2023-08-28T22:18:02.4018647Z
2023-08-28T22:18:02.4028391Z ==> A.qemu.img-boot: Retrieving ISO
2023-08-28T22:18:02.4030680Z ==> A.qemu.img-boot: Trying https://cloud-images.ubuntu.com/releases/22.04/release-20230815/ubuntu-22.04-server-cloudimg-amd64.img
2023-08-28T22:18:49.8774666Z ==> A.qemu.img-boot: Trying https://cloud-images.ubuntu.com/releases/22.04/release-20230815/ubuntu-22.04-server-cloudimg-amd64.img?checksum=sha256%3A870bd58b5c1e9da3de5e44987de88cb6a877f15eaccc977a0898f015407ba402
2023-08-28T22:18:52.1919550Z ==> A.qemu.img-boot: https://cloud-images.ubuntu.com/releases/22.04/release-20230815/ubuntu-22.04-server-cloudimg-amd64.img?checksum=sha
256%3A870bd58b5c1e9da3de5e44987de88cb6a877f15eaccc977a0898f015407ba402 => /home/runner/.cache/packer/33aa0e70378232c3b3a9a5dd7e96ed4bc6c5b82c.iso
... (lots of build output snipped)
2023-08-28T22:43:20.7996419Z ==> A.qemu.img-boot: Running post-processor:  (type manifest)
2023-08-28T22:43:20.8042924Z Build 'A.qemu.img-boot' finished after 25 minutes 18 seconds.
2023-08-28T22:47:01.3340662Z
2023-08-28T22:47:01.3398578Z ==> Wait completed after 28 minutes 58 seconds
2023-08-28T22:47:01.3398911Z
2023-08-28T22:47:01.3399221Z ==> Builds finished. The artifacts of successful builds are:
... (list of artifacts snipped)