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Add bitrot detection to "diff" command

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This introduces a new modifier to the output of the diff command. It
appears whenever two files being compared only differ in their content
but not in their metadata. As far as we know, under normal
circumstances, this should only ever happen if some kind of bitrot has
happened in the source file. The prerequisite for this detection to work
is that the right-side snapshot of the comparison has been created with
"backup --force".
This commit is contained in:
Daniel Danner 2023-10-20 20:15:53 +02:00 committed by Michael Eischer
parent 634e2a46d9
commit a7dc18e697
3 changed files with 22 additions and 1 deletions
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11
changelog/unreleased/pull-4526 Normal file
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@ -0,0 +1,11 @@
Enhancement: Add bitrot detection to `diff` command
The output of the `diff` command now includes the modifier `?` for files
to indicate bitrot in backed up files. It will appear whenever there is a
difference in content while the metadata is exactly the same. Since files with
unchanged metadata are normally not read again when creating a backup, the
detection is only effective if the right-hand side of the diff has been created
with "backup --force".
https://github.com/restic/restic/issues/805
https://github.com/restic/restic/pull/4526

9
cmd/restic/cmd_diff.go
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@ -27,6 +27,7 @@ directory:
* U The metadata (access mode, timestamps, ...) for the item was updated * U The metadata (access mode, timestamps, ...) for the item was updated
* M The file's content was modified * M The file's content was modified
* T The type was changed, e.g. a file was made a symlink * T The type was changed, e.g. a file was made a symlink
* ? Bitrot detected: The file's content has changed but all metadata is the same
To only compare files in specific subfolders, you can use the To only compare files in specific subfolders, you can use the
"<snapshotID>:<subfolder>" syntax, where "subfolder" is a path within the "<snapshotID>:<subfolder>" syntax, where "subfolder" is a path within the
@ -272,6 +273,14 @@ func (c *Comparer) diffTree(ctx context.Context, stats *DiffStatsContainer, pref
!reflect.DeepEqual(node1.Content, node2.Content) { !reflect.DeepEqual(node1.Content, node2.Content) {
mod += "M" mod += "M"
stats.ChangedFiles++ stats.ChangedFiles++
node1NilContent := node1
node2NilContent := node2
node1NilContent.Content = nil
node2NilContent.Content = nil
if node1NilContent.Equals(*node2NilContent) {
mod += "?"
}
} else if c.opts.ShowMetadata && !node1.Equals(*node2) { } else if c.opts.ShowMetadata && !node1.Equals(*node2) {
mod += "U" mod += "U"
} }

3
doc/075_scripting.rst
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@ -201,7 +201,8 @@ change
+------------------+--------------------------------------------------------------+ +------------------+--------------------------------------------------------------+
| ``modifier`` | Type of change, a concatenation of the following characters: | | ``modifier`` | Type of change, a concatenation of the following characters: |
| | "+" = added, "-" = removed, "T" = entry type changed, | | | "+" = added, "-" = removed, "T" = entry type changed, |
| | "M" = file content changed, "U" = metadata changed | | | "M" = file content changed, "U" = metadata changed, |
| | "?" = bitrot detected |
+------------------+--------------------------------------------------------------+ +------------------+--------------------------------------------------------------+
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