iso_checksum_url does not work with relative checksum path to ISO on Windows 7

$ ./packer version Packer v1.3.3
Host platform (not working): Windows 7 64 Bit
Host platform (working): Fedora 28 64 Bit (4.19.15-200.fc28.x86_64)

Packer 1.3.3 fails to check the ISO checksum with iso_checksum_url (at least for virtualbox-iso) on Windows 7, Linux is working fine. This issue might be related to the relative path from the checksum file URL to the ISO URL.

Debug logs from Windows and Linux will follow as a comment.

Relevant line in http://archive.ubuntu.com/ubuntu/dists/bionic/main/installer-amd64/current/images/SHA256SUMS

bed8a55ae2a657f8349fe3271097cff3a5b8c3d1048cf258568f1601976fa30d  ./netboot/mini.iso

Template JSON file:

{
  "variables": {
    "ubuntu_mirror": "http://archive.ubuntu.com/ubuntu/dists/",
    "ubuntu_codename": "bionic",
    "username": "test",
    "password": "test"
  },
  "builders": [
    {
      "type": "virtualbox-iso",
      "vm_name": "test_vm",
      "iso_checksum_type": "sha256",
      "iso_checksum_url": "{{ user `ubuntu_mirror` }}{{ user `ubuntu_codename` }}/main/installer-amd64/current/images/SHA256SUMS",
      "iso_url": "{{ user `ubuntu_mirror` }}{{ user `ubuntu_codename` }}/main/installer-amd64/current/images/netboot/mini.iso",
      "boot_wait": "5s",
      "ssh_username": "{{ user `username` }}",
      "ssh_password": "{{ user `password` }}",
      "ssh_wait_timeout": "5s",
      "shutdown_command": "echo {{ user `password` }} | sudo -S shutdown -P now"
    }
  ]
}

hashicorp / packer

iso_checksum_url does not work with relative checksum path to ISO on Windows 7 #7217