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content: cleanup service and interfaces

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After implementing pull, a few changes are required to the content store
interface to make sure that the implementation works smoothly.
Specifically, we work to make sure the predeclaration path for digests
works the same between remote and local writers. Before, we were
hesitent to require the the size and digest up front, but it became
clear that having this provided significant benefit.

There are also several cleanups related to naming. We now call the
expected digest `Expected` consistently across the board and `Total` is
used to mark the expected size.

This whole effort comes together to provide a very smooth status
reporting workflow for image pull and push. This will be more obvious
when the bulk of pull code lands.

There are a few other changes to make `content.WriteBlob` more broadly
useful. In accordance with addition for predeclaring expected size when
getting a `Writer`, `WriteBlob` now supports this fully. It will also
resume downloads if provided an `io.Seeker` or `io.ReaderAt`. Coupled
with the `httpReadSeeker` from `docker/distribution`, we should only be
a lines of code away from resumable downloads.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day 2017-02-21 23:41:11 -08:00
parent 0a5544d8c4
commit c062a85782
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GPG key ID: 67B3DED84EDC823F
15 changed files with 568 additions and 337 deletions
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8
remotes/remote.go
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@ -5,7 +5,7 @@ import (
"io"
)
type Remote interface {
type Fetcher interface {
// Fetch the resource identified by id. The id is opaque to the remote, but
// may typically be a tag or a digest.
//
@ -32,8 +32,10 @@ type Remote interface {
Fetch(ctx context.Context, id string, hints ...string) (io.ReadCloser, error)
}
type RemoteFunc func(context.Context, string, ...string) (io.ReadCloser, error)
// FetcherFunc allows package users to implement a Fetcher with just a
// function.
type FetcherFunc func(context.Context, string, ...string) (io.ReadCloser, error)
func (fn RemoteFunc) Fetch(ctx context.Context, object string, hints ...string) (io.ReadCloser, error) {
func (fn FetcherFunc) Fetch(ctx context.Context, object string, hints ...string) (io.ReadCloser, error) {
return fn(ctx, object, hints...)
}