add system proxy config support for cli requests

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

cmd/buildx/main.go

@@ -56,6 +56,11 @@ func main() {
 		os.Exit(1)
 	}
 
+	if err := configureProxy(cmd); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+
 	if plugin.RunningStandalone() {
 		err = runStandalone(cmd)
 	} else {

cmd/buildx/proxy.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+
+	"github.com/docker/buildx/util/confutil"
+	"github.com/docker/cli/cli/command"
+	"github.com/pkg/errors"
+)
+
+func configureProxy(cmd *command.DockerCli) error {
+	fp := filepath.Join(confutil.ConfigDir(cmd), "proxy.json")
+	dt, err := os.ReadFile(fp)
+	if err != nil {
+		if os.IsNotExist(err) || os.IsPermission(err) {
+			return nil
+		}
+		return err
+	}
+	env := map[string]string{}
+	if err := json.Unmarshal(dt, &env); err != nil {
+		return errors.Wrapf(err, "failed to parse proxy config %s", fp)
+	}
+	permitted := map[string]struct{}{
+		"HTTP_PROXY":  {},
+		"HTTPS_PROXY": {},
+		"NO_PROXY":    {},
+		"FTP_PROXY":   {},
+		"ALL_PROXY":   {},
+	}
+	for k := range permitted {
+		if _, ok := os.LookupEnv(k); ok {
+			continue
+		}
+		if val, ok := env[k]; ok {
+			os.Setenv(k, val)
+		}
+	}
+	return nil
+}