proposal: x/mod: create proxy package

[jcbhmr]

Proposal Details

Create a golang.org/x/mod/proxy package similar in goal to the golang.org/x/mod/sumdb package.

Why? To make it easy to setup, test, and develop your own https://modproxy.example.com/ Go module proxy for <meta name="go-import" content="example.com/awesome mod https://modproxy.example.com"> custom module proxies and/or GOPROXY=https://goproxy.example.com caching module proxies. I appreciate the https://pkg.go.dev/golang.org/x/mod/sumdb#Client and https://pkg.go.dev/golang.org/x/mod/sumdb#Server structs so that I can just plug-and-play some type MyServerOps struct {}, sumdb.NewServer(&MyServerOps{}) and then http.ListenAndServe(blahblah) and it works for testing. I also like being able to use a client very easily. I would appreciate a similar thing for module proxies.

This was mentioned in #31761:

golang.org/x/mod/proxy: go module proxy client and server protocol (like x/mod/sumdb; not written yet)

golang.org/x/mod/index: go module index client and server protocol (like x/mod/sumdb; not written yet)

golang.org/x/mod/gomodproxy: command: trivial go module proxy for reference and trivial uses (not published yet; maybe also “go mod proxy”)

So I think this isn't that far out. I am willing to contribute code to do this.

[gabyhelp]

Related Issues

• proposal: x/mod: new repo for module mechanics #31761 (closed)
• proposal: make go/src/cmd/go/internal/module part of the standard library as go/module #30980 (closed)
• proposal: cmd/go: add .proxy endpoint to the module proxy spec #35400

Related Code Changes

• cmd/go: fix typo in sumdb cache path

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

There are quite a few third party packages that already do this, for example https://pkg.go.dev/github.com/goproxy/goproxy
what does yet another implementation bring?

[jcbhmr]

You're right that https://pkg.go.dev/github.com/goproxy/goproxy does offer a solution to GOPROXY=https://goproxy.example.com/ and maybe (unsure how well it works & fits) <meta name="go-import" content="example.com/awesome mod https://modproxy.example.com">.

That's one half you're right that can be left out. What about the client side of things? I really liked the symmetry of sumdb.Client and sumdb.Server. I liked the look of http://pkg.go.dev/cmd/go/internal/modfetch#Lookup (assuming I am able to provide a ClientOps thing like https://pkg.go.dev/golang.org/x/mod/sumdb#NewClient) and I was hoping that something like it could be exposed in x/mod/proxy or something alongside a basic server implementation (which you've pointed out now might be redundant) too.