plumbing: transport/http, add support for custom proxy URLs

Add support for custom HTTP and HTTPS proxies for each session.

The tests require server certificate and a matching private key to be
able to run a TLS server and test HTTPS proxy functionality. The cert
and the key are stored in `plumbing/transport/http/testdata/certs` and
were generated using the following command:
`openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout server.key -out server.crt`
Note: All details were left empty, except for the FQDN for which
example.com was used.

Signed-off-by: Sanskar Jaiswal <jaiswalsanskar078@gmail.com>

2 files changed, 115 insertions, 0 deletions

diff --git a/plumbing/transport/http/internal/test/proxy_test.go b/plumbing/transport/http/internal/test/proxy_test.go
new file mode 100644
index 0000000..6ae2943
--- /dev/null
+++ b/plumbing/transport/http/internal/test/proxy_test.go
@@ -0,0 +1,72 @@
+package test
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net"
+	nethttp "net/http"
+	"os"
+	"sync/atomic"
+	"testing"
+
+	"github.com/elazarl/goproxy"
+
+	"github.com/go-git/go-git/v5/plumbing/transport"
+	"github.com/go-git/go-git/v5/plumbing/transport/http"
+
+	. "gopkg.in/check.v1"
+)
+
+// Hook up gocheck into the "go test" runner.
+func Test(t *testing.T) { TestingT(t) }
+
+type ProxySuite struct{}
+
+var _ = Suite(&ProxySuite{})
+
+var proxiedRequests int32
+
+// This test tests proxy support via an env var, i.e. `HTTPS_PROXY`.
+// Its located in a separate package because golang caches the value
+// of proxy env vars leading to misleading/unexpected test results.
+func (s *ProxySuite) TestAdvertisedReferences(c *C) {
+	proxy := goproxy.NewProxyHttpServer()
+	proxy.Verbose = true
+	SetupHTTPSProxy(proxy, &proxiedRequests)
+	httpsListener, err := net.Listen("tcp", ":0")
+	c.Assert(err, IsNil)
+	defer httpsListener.Close()
+	httpProxyAddr := fmt.Sprintf("localhost:%d", httpsListener.Addr().(*net.TCPAddr).Port)
+
+	proxyServer := nethttp.Server{
+		Addr:    httpProxyAddr,
+		Handler: proxy,
+		// Due to how golang manages http/2 when provided with custom TLS config,
+		// servers and clients running in the same process leads to issues.
+		// Ref: https://github.com/golang/go/issues/21336
+		TLSConfig: &tls.Config{
+			NextProtos: []string{"http/1.1"},
+		},
+	}
+	go proxyServer.ServeTLS(httpsListener, "../../testdata/certs/server.crt", "../../testdata/certs/server.key")
+	defer proxyServer.Close()
+	os.Setenv("HTTPS_PROXY", fmt.Sprintf("https://user:pass@%s", httpProxyAddr))
+	defer os.Unsetenv("HTTPS_PROXY")
+
+	endpoint, err := transport.NewEndpoint("https://github.com/git-fixtures/basic.git")
+	c.Assert(err, IsNil)
+	endpoint.InsecureSkipTLS = true
+
+	client := http.DefaultClient
+	session, err := client.NewUploadPackSession(endpoint, nil)
+	c.Assert(err, IsNil)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	info, err := session.AdvertisedReferencesContext(ctx)
+	c.Assert(err, IsNil)
+	c.Assert(info, NotNil)
+	proxyUsed := atomic.LoadInt32(&proxiedRequests) > 0
+	c.Assert(proxyUsed, Equals, true)
+}
diff --git a/plumbing/transport/http/internal/test/test_utils.go b/plumbing/transport/http/internal/test/test_utils.go
new file mode 100644
index 0000000..6665fb3
--- /dev/null
+++ b/plumbing/transport/http/internal/test/test_utils.go
@@ -0,0 +1,43 @@
+package test
+
+import (
+	"encoding/base64"
+	"strings"
+	"sync/atomic"
+
+	"github.com/elazarl/goproxy"
+)
+
+func SetupHTTPSProxy(proxy *goproxy.ProxyHttpServer, proxiedRequests *int32) {
+	var proxyHandler goproxy.FuncHttpsHandler = func(host string, ctx *goproxy.ProxyCtx) (*goproxy.ConnectAction, string) {
+		if strings.Contains(host, "github.com") {
+			user, pass, _ := ParseBasicAuth(ctx.Req.Header.Get("Proxy-Authorization"))
+			if user != "user" || pass != "pass" {
+				return goproxy.RejectConnect, host
+			}
+			atomic.AddInt32(proxiedRequests, 1)
+			return goproxy.OkConnect, host
+		}
+		// Reject if it isn't our request.
+		return goproxy.RejectConnect, host
+	}
+	proxy.OnRequest().HandleConnect(proxyHandler)
+}
+
+// adapted from https://github.com/golang/go/blob/2ef70d9d0f98832c8103a7968b195e560a8bb262/src/net/http/request.go#L959
+func ParseBasicAuth(auth string) (username, password string, ok bool) {
+	const prefix = "Basic "
+	if len(auth) < len(prefix) || !strings.EqualFold(auth[:len(prefix)], prefix) {
+		return "", "", false
+	}
+	c, err := base64.StdEncoding.DecodeString(auth[len(prefix):])
+	if err != nil {
+		return "", "", false
+	}
+	cs := string(c)
+	username, password, ok = strings.Cut(cs, ":")
+	if !ok {
+		return "", "", false
+	}
+	return username, password, true
+}