Support build under wasm and/or js

[paralin]

Fixes the following build error under GOOS=js GOARCH=wasm go build -v:

package github.com/go-git/go-git/v5        
        imports github.com/go-git/go-billy/v5/osfs
        imports golang.org/x/sys/unix: build constraints exclude all Go files in /home/paralin/go/pkg/mod/golang.org/x/sys@v0.0.0-20200302150141-5c8b2ff67527/unix

[paralin]

[mcuadros]

Will be better if you submit the fix to go-billy instead of replace it with your fork.

[paralin]

@mcuadros go-git/go-billy#15

The line can be deleted once this is merged

[mcuadros]

After an intensive reach, sadly is not just easy as replace one package to make work properly go-git with wasm. Maybe clone works, but many other functionally doesn't. The current results of running the root package test suites are:

OOPS: 136 passed, 135 FAILED, 1 PANICKED, 11 MISSED

I am working on this branch to try to get go-git fully compatible with wasm:
https://github.com/go-git/go-git/tree/wasm

[paralin]

@mcuadros Thanks for looking into this. What is it about wasm that is causing the difference in behavior?

[mcuadros]

In your example, you execute a very small part of the go-git dataset. The tests are using os.Mkdir and some other not implemented functions. As well some parts of the code are using call directly to some not implemented functions. So I am fixing every test and functionality. Anyways its good to have better test suites, so...

BTW is a pitty goland doesn't use wasi.

[paralin]

So, the tests are broken, but the actual go-git functionality might not be?

Which calls are making to not implemented funcs in non test code?

I'm interested to see what the differences are here with webassembly. Yes, if the tests call os.mkdir it won't work. But which part of the non-test code is broken?

[mcuadros]

Many changes are required and the transports are really limited.
BTW can you share the code that generated the output you pasted?

[paralin]

@mcuadros The transport limit makes sense, but what other changes are required to get it to work? I'm just wondering what it is about webassembly that would cause things to not work.

The only issue I saw was the CORS issue - GitHub doesn't set cross-origin headers, so it was necessary to clone from a localhost IP address with CORS set.

// RunCloneExample attempts to perform a clone demo into the given interfaces.
func RunCloneExample(
	ctx context.Context,
	le *logrus.Entry,
	url string,
	storage storage.Storer,
	worktree billy.Filesystem,
) error {
	cloneOpts := &git.CloneOptions{
		// The (possibly remote) repository URL to clone from.
		URL: url,
		// Auth credentials, if required, to use with the remote repository.
		// Auth transport.AuthMethod
		// Name of the remote to be added, by default `origin`.
		// RemoteName string
		// Remote branch to clone.
		// ReferenceName plumbing.ReferenceName
		// Fetch only ReferenceName if true.
		// SingleBranch bool
		// No checkout of HEAD after clone if true.
		// NoCheckout bool
		// Limit fetching to the specified number of commits.
		// Depth int
		// RecurseSubmodules after the clone is created, initialize all submodules
		// within, using their default settings. This option is ignored if the
		// cloned repository does not have a worktree.
		// RecurseSubmodules SubmoduleRescursivity
		// Progress is where the human readable information sent by the server is
		// stored, if nil nothing is stored and the capability (if supported)
		// no-progress, is sent to the server to avoid send this information.
		Progress: os.Stdout,
		// Tags describe how the tags will be fetched from the remote repository,
		// by default is AllTags.
		// Tags TagMode
	}
	repo, err := git.CloneContext(
		ctx,
		storage,
		worktree,
		cloneOpts,
	)
	if err != nil {
		return err
	}
	le.Info("cloned")
	_ = repo

	files, err := worktree.ReadDir("")
	if err != nil {
		return err
	}
	for _, f := range files {
		le.Debugf(
			"%v %s",
			f.Mode().String(),
			f.Name(),
		)
	}
	return nil
}

I can make a full reproduction if it would be helpful.

[mcuadros]

Ohh, I see, that's why didn't work for me. Because of the CORS, this is a problem.

As I said the changes are mainly on the test, but for example, some packages are using user.Current for get the home or using or accessing config files without billy.

https://github.com/go-git/go-git/commits/wasm

[mcuadros]

I was able to clone a repository using this script as a proxy:

http://localhost:8081/?https://github.com/go-git/go-git.git

package main

import (
	"io"
	"net/http"
	"net/url"

	"github.com/rs/cors"
)

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		url, err := url.Parse(r.URL.RawQuery)
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}

		req := &http.Request{
			URL:    url,
			Method: r.Method,
			Body:   r.Body,
			Header: r.Header,
		}

		resp, err := http.DefaultTransport.RoundTrip(req)
		if err != nil {
			http.Error(w, err.Error(), http.StatusServiceUnavailable)
			return
		}

		defer resp.Body.Close()

		w.WriteHeader(resp.StatusCode)
		io.Copy(w, resp.Body)
	})

	handler := cors.New(cors.Options{
		AllowedOrigins: []string{"*"},
		AllowedHeaders: []string{"*"},
		Debug:          true,
	}).Handler(mux)
	http.ListenAndServe(":8081", handler)
}

[paralin]

Nice, yeah, it seems to work. Have you tried the other functionality like checkouts and merges? I'm pretty sure it should work fine. Of course, the test suite is important too.

[paralin]

@mcuadros Discovered this parallel effort in js today: https://github.com/isomorphic-git/isomorphic-git - they also mention the same CORS issue with GitHub and are trying to campaign them to add the headers.

[mcuadros]

With the latest changes on master your test code should run without any problems. I will work to create an example to document the usage under wasm to complete this effort.

[paralin]

@mcuadros Thanks for that!

[SaicharanKandukuri]

@mcuadros / @paralin trying to test out git-go in wasm

where can i find an wasm example for a simple clone

With the latest changes on master your test code should run without any problems. I will work to create an example to document the usage under wasm to complete this effort.