7c07610ab2
We've always, since the introduction of conflicts, had the policy that
deletes lose against any other change, for safety's sake. This is a
problem, however, because it means the sort order of versions is not a
total order.
That is, given two versions `A` and `B` that are currently in conflict,
we will sort them in a given order (let's say `A, B`, so `A < B` for
ordering purposes: we say "A wins over B" or "A is newer than B") and
consider the first in the list the winner. The loser (who has `B` on
disk) will process the conflict at some point and move the file to a
conflict copy and announce `A'` as the resolved conflict. The winner
(with `A` on disk) doesn't do anything.
However, if `A` is deleted the ordering changes. We still have `A < B`
and, of course, `Adel < A` (this is not even a conflict, just linear
order). In most sane systems this would imply the ordering `Adel < A <
B`, however in our case we in fact have `B < Adel` because any version
wins over a deleted one, so there is no logical ordering at all of the
files at this point. `Adel < A < B < Adel ???` In practice the deleted
version may end up at the head or the tail of the list, depending on the
order we do the compares.
Hence, at this point, "whatever" happens and it's not guaranteed to make
any sense. 😬
I propose that we resolve this my simply letting deletes be versions
like anything else and maintain a total ordering based on just version
vectors with the existing tie breakers like always. That means a delete
can win in a conflict situation, and the result should be that the file
is moved to a conflict copy on the losing device. I think this retains
the data safety to almost the same degree as previously, while removing
probably an entire class of strange out of sync bugs...
---
(A potential wrinkle here is that, ideally, we wouldn't even create the
conflict copy when the delete and the losing version represent the same
data -- same as when we handle normal modification conflicts. However,
the deleted FileInfo doesn't carry any information on what the contents
were, so we can't do that right now. A possible future extension would
be to carry the block list hash of the deleted data in the deleted
FileInfo and use that for this purpose, but I don't want to complicate
this PR with that. The block list hash itself also isn't a
protocol-defined thing at the moment, it's something implementation
dependent that we just use locally.)
Goals
Syncthing is a continuous file synchronization program. It synchronizes files between two or more computers. We strive to fulfill the goals below. The goals are listed in order of importance, the most important ones first. This is the summary version of the goal list - for more commentary, see the full Goals document.
Syncthing should be:
-
Safe From Data Loss
Protecting the user's data is paramount. We take every reasonable precaution to avoid corrupting the user's files.
-
Secure Against Attackers
Again, protecting the user's data is paramount. Regardless of our other goals, we must never allow the user's data to be susceptible to eavesdropping or modification by unauthorized parties.
-
Easy to Use
Syncthing should be approachable, understandable, and inclusive.
-
Automatic
User interaction should be required only when absolutely necessary.
-
Universally Available
Syncthing should run on every common computer. We are mindful that the latest technology is not always available to every individual.
-
For Individuals
Syncthing is primarily about empowering the individual user with safe, secure, and easy to use file synchronization.
-
Everything Else
There are many things we care about that don't make it on to the list. It is fine to optimize for these values, as long as they are not in conflict with the stated goals above.
Getting Started
Take a look at the getting started guide.
There are a few examples for keeping Syncthing running in the background on your system in the etc directory. There are also several GUI implementations for Windows, Mac, and Linux.
Docker
To run Syncthing in Docker, see the Docker README.
Getting in Touch
The first and best point of contact is the Forum. If you've found something that is clearly a bug, feel free to report it in the GitHub issue tracker.
If you believe that you’ve found a Syncthing-related security vulnerability, please report it by emailing security@syncthing.net. Do not report it in the Forum or issue tracker.
Building
Building Syncthing from source is easy. After extracting the source bundle from
a release or checking out git, you just need to run go run build.go and the
binaries are created in ./bin. There's a guide with more details on the
build process.
Signed Releases
Release binaries are GPG signed with the key available from https://syncthing.net/security/. There is also a built-in automatic upgrade mechanism (disabled in some distribution channels) which uses a compiled in ECDSA signature. macOS and Windows binaries are also code-signed.
Documentation
Please see the Syncthing documentation site [source].
All code is licensed under the MPLv2 License.