"https" address causes zsync download to fail with error 'could not read control file from URL'

[Sai Vinoba]

How to reproduce:
1. Go to cdimage.ubuntu.com, choose any flavor and navigate to release or daily-live folder.
2. Copy (link address of) the .zsync file.
3. Open a terminal and try to perform zsync download with the copied zsync URL.

Expected:
Zsync download happens normally.

Actual:
Zsync download fails with error '...could not read control file from URL'.

Below is an example error (for Ubuntu 21.10 20210507 daily build iso):

```
zsync https://cdimage.ubuntu.com/ubuntu/daily-live/20210507/impish-desktop-amd64.iso.zsync
failed on url https://cdimage.ubuntu.com/ubuntu/daily-live/20210507/impish-desktop-amd64.iso.zsync
could not read control file from URL https://cdimage.ubuntu.com/ubuntu/daily-live/20210507/impish-desktop-amd64.iso.zsync
```

If we change the protocol to `http` instead of `https` the zsync function works.

This is happening for all flavors.

Suggested solution: Change/keep all zsync file's address to use `http` till (if) zsync software supports `https` protocol.

[Bryan Quigley (bryanquigley)]

Apparently this has been known for a while: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=459706

[Steve Langasek (vorlon)]

Reassigning to the zsync package then, since this is not an error in the infrastructure.

[Bryan Quigley (bryanquigley)]

zsync is no longer maintained.
https://github.com/cph6/zsync/issues/15#issuecomment-835307920 - but zsync2 exists..

[Sai Vinoba (saivinob)]

@vorlon, while it may not be an *error* on infrastructure side, the infrastructure team *can* provide solution i.e., by changing the link address of zsync files from 'https' to 'http'.

If we check the linked debian bug report, they are not interested in implementing 'https' feature in zsync for 'overload' concerns. If infrastructure team passes the issue to package, it will be open forever.

[Matthew Fearnley (matthew-w-fearnley)]

I've been wondering if it's worth making a small patch to zsync so it at least rejects HTTPS with a clear error message? (I was confused by this for a while..)

If I did, where would be the best place to submit it?

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Norbert (nrbrtx)]

I'm using Ubuntu 18.04.6 LTS.

Here

```
zsync https://cdimage.ubuntu.com/daily-canary/current/jammy-desktop-canary-amd64.iso.zsync
```

fails with

```
failed on url https://cdimage.ubuntu.com/daily-canary/current/jammy-desktop-canary-amd64.iso.zsync
could not read control file from URL https://cdimage.ubuntu.com/daily-canary/current/jammy-desktop-canary-amd64.iso.zsync
```

Also it should be noted that pages https://cdimage.ubuntu.com/daily-canary/current/ like has a link to http://zsync.moria.org.uk/ which works normally, so still available.

[wontfix (wontfix)]

The concerns from the Debian and Fedora bug reports from over a decade ago, shouldn't exist in 2023.
https://istlsfastyet.com/

[geole0 (geole0)]

Hello

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu Noble Numbat (development branch)
Release: 24.04
Codename: noble

sudo zsync https://cdimage.ubuntu.com/daily-live/current/noble-desktop-amd64.iso.zsync
failed on url https://cdimage.ubuntu.com/daily-live/current/noble-desktop-amd64.iso.zsync
could not read control file from URL https://cdimage.ubuntu.com/daily-live/current/noble-desktop-amd64.iso.zsync
a@a:~$ sudo zsync http:
failed on url http:
could not read control file from URL http:

and seems good with
a@a:~$ sudo zsync http://cdimage.ubuntu.com/daily-live/current/noble-desktop-amd64.iso.zsync
#################### 100.0% 1223.2 kBps DONE

No relevent local data found - I will be downloading the whole file. If that's not what you want, CTRL-C out. You should specify the local file is the old version of the file to download with -i (you might have to decompress it with gzip -d first). Or perhaps you just have no data that helps download the file
downloading from http://cdimage.ubuntu.com/daily-live/current/noble-desktop-amd64.iso:
#------------------- 5.2% 32.8 kBps ETA
#------------------- 8.6% 1288.1 kBps 66:49 ETA ^C

[Simon (coopersimon)]

there should be an warning message in the zsync program if you attempt to use https, since it appears to not be supported in all cases.