Fwd: "reverse proxy" remote-helper

Fwd: "reverse proxy" remote-helper

[Guga Figueiredo]

Hello,

I am playing around with git remote helpers trying to write a "reverse
proxy" sort of custom helper to work with a personal server and custom
protocol.
I am doing this because git, natively, already does 99% of the work
that I need, and I would like to avoid reinventing the wheel. I just
want to create a barely customized interface for a custom server.
I know I can achieve this with hooks, but I would rather keep this
configuration out of the repos.

conceptually, the command call flow should be something like this:
```
git <cmd> custom::<repo-url>
└──>git-remote-custom <repo-url> <cmd>
    └──>git <native-remote-helper> <repo-url> <cmd>
```

I have been able to implement a git remote helper in go that works on
locally stored remotes following this article by rovaugn and the git
documentation on helpers.

And have stripped it down to bare essentials to try to invoke the
native/builtin remote-helpers directly:
```go
package main

import (
    "errors"
    "fmt"
    "log"
    "net/url"
    "os"
    "os/exec"
    "regexp"
)

func Main() (er error) {

    if len(os.Args) < 3 {
       return fmt.Errorf("Usage: git-remote-custom remote-name remote-url")
    }

    remoteName := os.Args[1]
    remoteUrl := os.Args[2]

    scheme, err := parseRemoteURL(remoteUrl)
    if err != nil {
       return fmt.Errorf("Invalid remote URL %s: %v", remoteUrl, err)
    }

    // do custom stuff here ...

    // proxy through to native git remote helper
    cmd := exec.Command("git", fmt.Sprintf("remote-%s", scheme),
remoteName, remoteUrl)
    cmd.Stdin = os.Stdin
    cmd.Stdout = os.Stdout
    if err := cmd.Run(); err != nil {
       return err
    }

    return nil
}

func main() {
    if err := Main(); err != nil {
       log.Fatal(err)
    }
}

func parseRemoteURL(remoteUrl string) (string, error) {
    if u, err := url.Parse(remoteUrl); err == nil && u.Scheme != "" {
       return u.Scheme, nil
    }

    // Check for SCP-like SSH URLs first because they don't have a "scheme://"
    scpRe := regexp.MustCompile(`^[a-zA-Z0-9._@/+~-]+@[a-zA-Z0-9._@/+~-]+:[a-zA-Z0-9._@/+~-]+(\.git)?$`)
    if scpRe.MatchString(remoteUrl) {
       return "ssh", nil
    }

    return "", errors.New("invalid Git URL scheme")
}
```

and this worked for http(s):
```
$ GIT_TRACE=1 git clone custom::https://github.com/rovaughn/git-remote-grave.git
11:17:52.117674 git.c:455               trace: built-in: git clone
custom::https://github.com/rovaughn/git-remote-grave.git
Cloning into 'git-remote-grave'...
11:17:52.120021 run-command.c:668       trace: run_command: git
remote-custom origin https://github.com/rovaughn/git-remote-grave.git
11:17:52.121757 git.c:742               trace: exec: git-remote-custom
origin https://github.com/rovaughn/git-remote-grave.git
11:17:52.121792 run-command.c:668       trace: run_command:
git-remote-custom origin
https://github.com/rovaughn/git-remote-grave.git
11:17:52.666930 run-command.c:668       trace: run_command: git
index-pack --stdin -v --fix-thin '--keep=fetch-pack 21547 on pop-os'
--check-self-contained-and-connected
remote: Enumerating objects: 71, done.
11:17:52.669349 git.c:455               trace: built-in: git
index-pack --stdin -v --fix-thin '--keep=fetch-pack 21547 on pop-os'
--check-self-contained-and-connected
remote: Total 71 (delta 0), reused 0 (delta 0), pack-reused 71
Receiving objects: 100% (71/71), 48.92 KiB | 1.11 MiB/s, done.
Resolving deltas: 100% (28/28), done.
11:17:52.716950 run-command.c:668       trace: run_command: git
rev-list --objects --stdin --not --all --quiet --alternate-refs
'--progress=Checking connectivity'
11:17:52.718721 git.c:455               trace: built-in: git rev-list
--objects --stdin --not --all --quiet --alternate-refs
'--progress=Checking connectivity'
```

but `ssh` doesn't have a corresponding remote-ssh helper.

Is there a plug and play way to wrap/proxy the `ssh` protocols in a
similar way with a remote-helper? Or are there better approaches to
achieve this?

Any feedback is appreciated,
Kind regards

Guga