The new method combines both step into a single wrapper function. Thus
it ensures that both are always called in pairs. As an additional
benefit this slightly reduces the boilerplate to upload blobs.
Those methods now only allow modifying snapshots. Internal data types
used by the repository are now read-only. The repository-internal code
can bypass the restrictions by wrapping the repository in an
`internalRepository` type.
The restriction itself is implemented by using a new datatype
WriteableFileType in the SaveUnpacked and RemoveUnpacked methods. This
statically ensures that code cannot bypass the access restrictions.
The test changes are somewhat noisy as some of them modify repository
internals and therefore require some way to bypass the access
restrictions. This works by capturing an `internalRepository` or
`Backend` when creating the Repository using a test helper function.
use the same index size for compressed and uncompressed indexes.
Otherwise, decoding the index of a compressed repository requires
significantly more memory.
LoadRaw also includes improved context cancellation handling similar to the
implementation in repository.LoadUnpacked.
The removed cache backend test will be added again later on.
This method had a buffer argument, but that was nil at all call sites.
That's removed, and instead LoadUnpacked now reuses whatever it
allocates inside its retry loop.
TestRepository and its variants always returned no-op cleanup functions.
If they ever do need to do cleanup, using testing.T.Cleanup is easier
than passing these functions around.
Sending data through a channel at very high frequency is extremely
inefficient. Thus use simple callbacks instead of channels.
> name old time/op new time/op delta
> MasterIndexEach-16 6.68s ±24% 0.96s ± 2% -85.64% (p=0.008 n=5+5)
For large pack sizes we might be only interested in the first and last
blob of a pack file. Thus stream a pack file in multiple parts if the
gaps between requested blobs grow too large.
