restic panics if writes to the SFTP backend fail

[Crest]

Output of restic version

restic 0.1.0 (v0.1.0-561-gb8c7622)
compiled at 2016-07-19 17:07:04 with go1.6.2

Expected behavior

Restic attempts to reconnect (or aborts the backup/restore).

Actual behavior

The restic process crashes with an unhandled panic().

scan [/home/crest/old-home/crest]
scanned 11758 directories, 69525 files in 0:06
Fssh_packet_write_wait: Connection to 138.201.35.217 port 23: Broken pipe0 errors  ETA 25:54 
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x28 pc=0x6df5ce]

goroutine 24905 [running]:
panic(0x998f60, 0xc820012150)
    /usr/local/go/src/runtime/panic.go:481 +0x3e6
github.com/pkg/sftp.(*File).Write(0x0, 0xc833276000, 0x455a8b, 0x455a8b, 0xc8230d97d8, 0x0, 0x0)
    /tmp/restic-build-630373645/src/github.com/pkg/sftp/client.go:971 +0x4e
restic/backend/sftp.(*SFTP).Save(0xc82015c000, 0xa49a50, 0x4, 0xc8219eb700, 0x40, 0xc833276000, 0x455a8b, 0x455a8b, 0x800e63798, 0xc821f9cd20)
    /tmp/restic-build-630373645/src/restic/backend/sftp/sftp.go:326 +0x393
restic/repository.(*Repository).savePacker(0xc82006e720, 0xc82006d0c0, 0x0, 0x0)
    /tmp/restic-build-630373645/src/restic/repository/packer_manager.go:115 +0x747
restic/repository.(*Repository).SaveAndEncrypt(0xc82006e720, 0x10d1059b94c94e00, 0xc82d074000, 0x296810, 0x300000, 0xc8230d9e88, 0x0, 0x0, 0x0, 0x0, ...)
    /tmp/restic-build-630373645/src/restic/repository/repository.go:211 +0x76f
restic.(*Archiver).Save(0xc8242453b0, 0x296800, 0xc82d074000, 0x296810, 0x300000, 0x10d1059b94c94e0b, 0x7ca93e5baf2e869d, 0xd97bec525f202584, 0xbe8e4130b45d50cf, 0x0, ...)
    /tmp/restic-build-630373645/src/restic/archiver.go:102 +0x3d2
restic.(*Archiver).saveChunk(0xc8242453b0, 0x12fb392, 0x296810, 0xe7cfef2a00000, 0xc82d074000, 0x296810, 0x300000, 0xc8202bfa20, 0x800df0850, 0xc820188030, ...)
    /tmp/restic-build-630373645/src/restic/archiver.go:162 +0xe3
created by restic.(*Archiver).SaveFile
    /tmp/restic-build-630373645/src/restic/archiver.go:237 +0x556
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x28 pc=0x6df5ce]

goroutine 24957 [running]:
panic(0x998f60, 0xc820012150)
    /usr/local/go/src/runtime/panic.go:481 +0x3e6
github.com/pkg/sftp.(*File).Write(0x0, 0xc834ce2000, 0x9359f8, 0x9359f8, 0xc8245857d8, 0x0, 0x0)
    /tmp/restic-build-630373645/src/github.com/pkg/sftp/client.go:971 +0x4e
restic/backend/sftp.(*SFTP).Save(0xc82015c000, 0xa49a50, 0x4, 0xc821606b00, 0x40, 0xc834ce2000, 0x9359f8, 0x9359f8, 0x800e63798, 0xc824312960)
    /tmp/restic-build-630373645/src/restic/backend/sftp/sftp.go:326 +0x393
restic/repository.(*Repository).savePacker(0xc82006e720, 0xc821475780, 0x0, 0x0)
    /tmp/restic-build-630373645/src/restic/repository/packer_manager.go:115 +0x747
restic/repository.(*Repository).SaveAndEncrypt(0xc82006e720, 0xde7275ae1d9bf500, 0xc83dbaa000, 0x54dc6e, 0x5dc000, 0xc824585e88, 0x0, 0x0, 0x0, 0x0, ...)
    /tmp/restic-build-630373645/src/restic/repository/repository.go:211 +0x76f
restic.(*Archiver).Save(0xc8242453b0, 0x54dc00, 0xc83dbaa000, 0x54dc6e, 0x5dc000, 0xde7275ae1d9bf5dc, 0x10151768c2f82f8a, 0x8e2e883147f51130, 0xc821452984740b2d, 0x0, ...)
    /tmp/restic-build-630373645/src/restic/archiver.go:102 +0x3d2
restic.(*Archiver).saveChunk(0xc8242453b0, 0x18b1d95, 0x54dc6e, 0x830d359e00000, 0xc83dbaa000, 0x54dc6e, 0x5dc000, 0xc8202bfa20, 0x800df0850, 0xc820188030, ...)
    /tmp/restic-build-630373645/src/restic/archiver.go:162 +0xe3
created by restic.(*Archiver).SaveFile
    /tmp/restic-build-630373645/src/restic/archiver.go:237 +0x556

Steps to reproduce the behavior

Kill the network connection while restic is writing a backup to the SFTP backend.

[fd0]

Thanks for the report

[wscott]

I reported a similar bug #592 and the error handling of the SFTP backend was much improved. You may want to test this case again.

[fawick]

Does this panic still occur with 0.7.3?

[fd0]

I think this is a duplicate of #353, the sftp connection was dropped and restic did not disconnect. I'm closing this as a duplicate. Thanks!