rclone sync crashes with “invalid memory address or nil pointer dereference” when a Proton Docs file is present

[giovanni-volpe]

While using rclone sync to keep a remote S3 bucket mirrored with a Proton Drive remote, the operation aborts as soon as a Proton Docs document is encountered. The Proton‑Drive backend panics with a runtime error (nil pointer dereference). Deleting the Docs file from the source fixes the sync, which shows that the current backend does not support Docs objects.

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Steps to Reproduce

1. Configure two remotes

rclone config                     # create a remote named “protondrive” (type: protondrive)  
rclone config                     # create a remote named “s3backup” (type: s3) pointing to your bucket

2. In the Proton Drive account, create a folder (e.g., SyncFolder) that contains at least one Proton Docs file (created from the web UI).

3. Run the sync command: rclone sync protondrive:/SyncFolder s3backup:/SyncFolder --progress

4. Observe the output. The sync stops when the Docs file is reached and rclone panics.

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Expected Behaviour

• rclone sync should either download the Docs file in a supported export format (PDF, HTML, etc.) or skip it gracefully with a clear warning.
• No panic or crash should occur, and the rest of the files should continue to sync.

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Actual Behaviour

Transferred:              0 B / 0 B, -, 0 B/s, ETA -
Checks:               247 / 249, 99%, Listed 936
Transferred:            0 / 1, 0%
Elapsed time:        13.0s
Checking:
  *xxx/xxx/xx: checking*
   xxx/xxx/xxxx: checking
Transferring:
  *xxx/xxx/XXX: transferringpanic: runtime error: invalid memory address or nil pointer dereference*
[signal 0xc0000005 code=0x0 addr=0x0 pc=0x1416ccac6]

goroutine 48 [running]:
github.com/rclone/rclone/backend/protondrive.(*Object).Open(...)
    github.com/rclone/rclone/backend/protondrive/protondrive.go:877 +0x46
...

The panic originates from backend/protondrive/protondrive.go:877 when the backend tries to open the Docs object. Removing the Docs file from the source eliminates the crash, confirming that Docs files are the trigger.

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Environment

OS | Windows 11 (64‑bit)
rclone version | v1.71.2
Proton Docs file type | native Proton Docs
Command used | rclone sync protondrive:/SyncFolder s3backup:/SyncFolder --progress

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Thanks to @tomekit for pointing me in the right direction for debugging