19eecaab12
With this changeset we introduce several new things. The first is the top-level dist command. This is a toolkit that implements various distribution primitives, such as fetching, unpacking and ingesting. The first component to this is a simple `fetch` command. It is a low-level command that takes a "remote", identified by a `locator`, and an object identifier. Keyed by the locator, this tool can identify a remote implementation to fetch the content and write it back to standard out. By allowing this to be the unit of pluggability in fetching content, we can have quite a bit of flexibility in how we retrieve images. The current `fetch` implementation provides anonymous access to docker hub images, through the namespace `docker.io`. As an example, one can fetch the manifest for `redis` with the following command: ``` $ ./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json ``` Note that we have provided a mediatype "hint", nudging the fetch implementation to grab the correct endpoint. We can hash the output of that to fetch the same content by digest: ``` $ ./dist fetch docker.io/library/redis sha256:$(./dist fetch docker.io/library/redis latest mediatype:application/vnd.docker.distribution.manifest.v2+json | shasum -a256) ``` Note that the hint is now elided, since we have affixed the content to a particular hash. If you are not yet entertained, let's bring `jq` and `xargs` into the mix for maximum fun. The following incantation fetches the same manifest and downloads all layers into the convenience of `/dev/null`: ``` $ ./dist fetch docker.io/library/redis sha256:a027a470aa2b9b41cc2539847a97b8a14794ebd0a4c7c5d64e390df6bde56c73 | jq -r '.layers[] | .digest' | xargs -n1 -P10 ./dist fetch docker.io/library/redis > /dev/null ``` This is just the beginning. We should be able to centralize configuration around fetch to implement a number of distribution methodologies that have been challenging or impossible up to this point. The `locator`, mentioned earlier, is a schemaless URL that provides a host and path that can be used to resolve the remote. By dispatching on this common identifier, we should be able to support almost any protocol and discovery mechanism imaginable. When this is more solidified, we can roll these up into higher-level operations that can be orchestrated through the `dist` tool or via GRPC. What a time to be alive! Signed-off-by: Stephen J Day <stephen.day@docker.com>
74 lines
2.1 KiB
Go
74 lines
2.1 KiB
Go
// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build go1.7
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// Package ctxhttp provides helper functions for performing context-aware HTTP requests.
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package ctxhttp // import "golang.org/x/net/context/ctxhttp"
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import (
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"io"
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"net/http"
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"net/url"
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"strings"
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"golang.org/x/net/context"
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)
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// Do sends an HTTP request with the provided http.Client and returns
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// an HTTP response.
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//
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// If the client is nil, http.DefaultClient is used.
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//
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// The provided ctx must be non-nil. If it is canceled or times out,
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// ctx.Err() will be returned.
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func Do(ctx context.Context, client *http.Client, req *http.Request) (*http.Response, error) {
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if client == nil {
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client = http.DefaultClient
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}
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resp, err := client.Do(req.WithContext(ctx))
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// If we got an error, and the context has been canceled,
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// the context's error is probably more useful.
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if err != nil {
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select {
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case <-ctx.Done():
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err = ctx.Err()
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default:
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}
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}
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return resp, err
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}
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// Get issues a GET request via the Do function.
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func Get(ctx context.Context, client *http.Client, url string) (*http.Response, error) {
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req, err := http.NewRequest("GET", url, nil)
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if err != nil {
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return nil, err
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}
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return Do(ctx, client, req)
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}
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// Head issues a HEAD request via the Do function.
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func Head(ctx context.Context, client *http.Client, url string) (*http.Response, error) {
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req, err := http.NewRequest("HEAD", url, nil)
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if err != nil {
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return nil, err
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}
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return Do(ctx, client, req)
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}
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// Post issues a POST request via the Do function.
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func Post(ctx context.Context, client *http.Client, url string, bodyType string, body io.Reader) (*http.Response, error) {
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req, err := http.NewRequest("POST", url, body)
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if err != nil {
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return nil, err
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}
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req.Header.Set("Content-Type", bodyType)
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return Do(ctx, client, req)
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}
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// PostForm issues a POST request via the Do function.
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func PostForm(ctx context.Context, client *http.Client, url string, data url.Values) (*http.Response, error) {
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return Post(ctx, client, url, "application/x-www-form-urlencoded", strings.NewReader(data.Encode()))
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}
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