This unified construction removes most backend-specific code from
global.go. The backend registry will also enable integration tests to
use custom backends if necessary.
The SemaphoreBackend now uniformly enforces the limit of concurrent
backend operations. In addition, it unifies the parameter validation.
The List() methods no longer uses a semaphore. Restic already never runs
multiple list operations in parallel.
By managing the semaphore in a wrapper backend, the sections that hold a
semaphore token grow slightly. However, the main bottleneck is IO, so
this shouldn't make much of a difference.
The key insight that enables the SemaphoreBackend is that all of the
complex semaphore handling in `openReader()` still happens within the
original call to `Load()`. Thus, getting and releasing the semaphore
tokens can be refactored to happen directly in `Load()`. This eliminates
the need for wrapping the reader in `openReader()` to release the token.
The Test method was only used in exactly one place, namely when trying
to create a new repository it was used to check whether a config file
already exists.
Use a combination of Stat() and IsNotExist() instead.
... called backend/sema. I resisted the temptation to call the main
type sema.Phore. Also, semaphores are now passed by value to skip a
level of indirection when using them.
github.com/pkg/errors is no longer getting updates, because Go 1.13
went with the more flexible errors.{As,Is} function. Use those instead:
errors from pkg/errors already support the Unwrap interface used by 1.13
error handling. Also:
* check for io.EOF with a straight ==. That value should not be wrapped,
and the chunker (whose error is checked in the cases changed) does not
wrap it.
* Give custom Error methods pointer receivers, so there's no ambiguity
when type-switching since the value type will no longer implement error.
* Make restic.ErrAlreadyLocked private, and rename it to
alreadyLockedError to match the stdlib convention that error type
names end in Error.
* Same with rest.ErrIsNotExist => rest.notExistError.
* Make s3.Backend.IsAccessDenied a private function.
This enables the backends to request the calculation of a
backend-specific hash. For the currently supported backends this will
always be MD5. The hash calculation happens as early as possible, for
pack files this is during assembly of the pack file. That way the hash
would even capture corruptions of the temporary pack file on disk.
This adds support for the following environment variables, which were
previously missing:
OS_USER_ID User ID for keystone v3 authentication
OS_USER_DOMAIN_ID User domain ID for keystone v3 authentication
OS_PROJECT_DOMAIN_ID Project domain ID for keystone v3 authentication
OS_TRUST_ID Trust ID for keystone v3 authentication
As mentioned in issue [#1560](https://github.com/restic/restic/pull/1560#issuecomment-364689346)
this changes the signature for `backend.Save()`. It now takes a
parameter of interface type `RewindReader`, so that the backend
implementations or our `RetryBackend` middleware can reset the reader to
the beginning and then retry an upload operation.
The `RewindReader` interface also provides a `Length()` method, which is
used in the backend to get the size of the data to be saved. This
removes several ugly hacks we had to do to pull the size back out of the
`io.Reader` passed to `Save()` before. In the `s3` and `rest` backend
this is actively used.
Before, all backend implementations were required to return an error if
the file that is to be written already exists in the backend. For most
backends, that means making a request (e.g. via HTTP) and returning an
error when the file already exists.
This is not accurate, the file could have been created between the HTTP
request testing for it, and when writing starts. In addition, apart from
the `config` file in the repo, all other file names have pseudo-random
names with a very very low probability of a collision. And even if a
file name is written again, the way the restic repo is structured this
just means that the same content is placed there again. Which is not a
problem, just not very efficient.
So, this commit relaxes the requirement to return an error when the file
in the backend already exists, which allows reducing the number of API
requests and thereby the latency for remote backends.
List().
move comment regarding problematic List() backend api (it's s3's ListObjects
that has a problem, NOT swift's ObjectsWalk).
As per discussion in PR #1399.
