restic: Backblaze B2 unexpected end of JSON input

Output of restic version

restic 0.7.3
compiled with go1.9 on linux/amd64

How did you run restic exactly?

I tried to back up some fairly large (~ 200GB in total) VM images using restic using restic backup --force /mnt/backup/dump/

I used these environment variables:

RESTIC_REPOSITORY "b2:<bucket_name:<path_to_backup>"
B2_ACCOUNT_ID="<some_account_id>"
B2_ACCOUNT_KEY "<some_account_key"
RESTIC_PASSWORD "<very_secret_password>"

I tried this multiple times, but restic always fails with an error after < 30 minutes.

error while saving data to the repo: unexpected end of JSON input
Close
github.com/restic/restic/internal/backend/b2.(*b2Backend).Save
        src/github.com/restic/restic/internal/backend/b2/b2.go:250
github.com/restic/restic/internal/repository.(*Repository).savePacker
        src/github.com/restic/restic/internal/repository/packer_manager.go:122
github.com/restic/restic/internal/repository.(*Repository).SaveAndEncrypt
        src/github.com/restic/restic/internal/repository/repository.go:203
github.com/restic/restic/internal/repository.(*Repository).SaveBlob
        src/github.com/restic/restic/internal/repository/repository.go:529
github.com/restic/restic/internal/archiver.(*Archiver).Save
        src/github.com/restic/restic/internal/archiver/archiver.go:104
github.com/restic/restic/internal/archiver.(*Archiver).saveChunk
        src/github.com/restic/restic/internal/archiver/archiver.go:161
runtime.goexit
        /usr/local/go/src/runtime/asm_amd64.s:2337
panic: Close: unexpected end of JSON input

goroutine 40839 [running]:
github.com/restic/restic/internal/archiver.(*Archiver).saveChunk(0xc4202ca1e0, 0xdff020, 0xc4200140c8, 0x619ae385, 0x12516a, 0x1b98a15d300000, 0xc4333fa000, 0x12516a, 0x5e4000, 0xc420080840, ...)
        src/github.com/restic/restic/internal/archiver/archiver.go:166 +0x41b
created by github.com/restic/restic/internal/archiver.(*Archiver).SaveFile
        src/github.com/restic/restic/internal/archiver/archiver.go:240 +0x3d0

What backend/server/service did you use?

Backlaze B2

Expected behavior

I’d like restic to finish the backup without an error or aborting.

Actual behavior

The backup fails with an error every time.

Steps to reproduce the behavior

• Setup a restic repository on Backblaze B2
• Backup a folder with some large files (~ 200GB across 20 files in my case)
• Observe error message

Do you have any idea what may have caused this?

I found some issues only with a similar error. It seems, that this is caused by a invalid API response from B2. In the linked post the solution was to retry the backup, but this does not work in my case. The backup fails every time.