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When making a backup, use the same checksum for any chunks it re-uses
or creates. This is for performance: if we allowed two checksums to be
used, we would have to compute the checksum for a chunk twice, and
potentially look up both on the server. This is just a lot of work.
Instead, we use only one. The trade-off here is that when (not if) the
user wants to switch to a new checksum type, they'll have to do a full
backup, uploading all their data to the server, even when it's already
there, just with a different checksum. Hopefully this will be rare.
Full backups always use the built-in, hardcoded default checksum, and
incremental backups use whatever the previous backup used. The default
is still SHA256, but this commit add code to support BLAKE2 if we
decide to switch that as a default. It's also easy to add support for
others, now. BLAKE2 was added to verify that Obnam can actually handle
the checksum changing (manual test: not in the test suite).
I don't think users need to be offered even the option of choosing a
checksum algorithm to use. When one cares about both security and
performance, choosing a checksum requires specialist, expert
knowledge. Obnam developers should choose the default. Giving users a
knob they can twiddle just makes it that much harder to configure and
use Obnam. If the choice Obnam developers have made is shown to be
sub-optimal, it seems better to change the default for everyone,
rather than hope that every user changes their configuration to gain
the benefit.
Experience has shown that people mostly don't change the default
configuration, and that they are especially bad at choosing well when
security is a concern.
(Obnam is free software. Expert users can choose their checksum by
changing the source code. I'm not fundamentally limiting anyone's
freedom or choice here.)
Users can switch to a new default algorithm by triggering a full
backup with the new "obnam backup --full".
Sponsored-by: author
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Backups made with this version can't be restored with old clients, and
vice version.
Sponsored-by: author
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The way this is currently implemented resulted in a lot of code
duplication in src/generation.rs. This should be refactored later. My
first attempt to do it by adding a trait for a schema variant failed.
Sponsored-by: author
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This makes the code clearer and allows for catching more errors,
albeit at runtime, such as using the wrong column name.
Sponsored-by: author
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Also, make it an error for a public symbol to not be documented.
Sponsored-by: author
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This reads a passphrase and derives two passwords from that, and
stores them next to the configuration file. The passwords aren't yet
used for anything, that will come later.
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This means that a function that parses step bindings can't return an
error that the document is missing a title. Such an error return would
be nonsensical, and we use the Rust type system to prevent it, at a
small cost of being a bit verbose.
Additional benefit is that the library portion of Obnam doesn't return
anyhow::Result values anymore.
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This speeds startup a lot. However, the backup repository needs to be
re-created from scratch and internal APIs have change in incompatible
ways.
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This uses the previous, latest generation as a guideline to see what
is new or changed.
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