Support environment variables in docker-container driver

Fixes #169

Signed-off-by: Sune Keller <absukl@almbrand.dk>

driver/docker-container/driver.go

@@ -29,6 +29,7 @@ type Driver struct {
 	factory driver.Factory
 	netMode string
 	image   string
+	env     []string
 }
 
 func (d *Driver) Bootstrap(ctx context.Context, l progress.Logger) error {
@@ -57,6 +58,7 @@ func (d *Driver) create(ctx context.Context, l progress.SubLogger) error {
 	if d.image != "" {
 		imageName = d.image
 	}
+	env := d.env
 	if err := l.Wrap("pulling image "+imageName, func() error {
 		rc, err := d.DockerAPI.ImageCreate(ctx, imageName, types.ImageCreateOptions{})
 		if err != nil {
@@ -70,6 +72,7 @@ func (d *Driver) create(ctx context.Context, l progress.SubLogger) error {
 
 	cfg := &container.Config{
 		Image: imageName,
+		Env:   env,
 	}
 	if d.InitConfig.BuildkitFlags != nil {
 		cfg.Cmd = d.InitConfig.BuildkitFlags

driver/docker-container/factory.go

@@ -2,6 +2,8 @@ package docker
 
 import (
 	"context"
+	"fmt"
+	"strings"
 
 	"github.com/docker/buildx/driver"
 	dockerclient "github.com/docker/docker/client"
@@ -39,14 +41,20 @@ func (f *factory) New(ctx context.Context, cfg driver.InitConfig) (driver.Driver
 	}
 	d := &Driver{factory: f, InitConfig: cfg}
 	for k, v := range cfg.DriverOpts {
-		switch k {
-		case "network":
+		switch {
+		case k == "network":
 			d.netMode = v
 			if v == "host" {
 				d.InitConfig.BuildkitFlags = append(d.InitConfig.BuildkitFlags, "--allow-insecure-entitlement=network.host")
 			}
-		case "image":
+		case k == "image":
 			d.image = v
+		case strings.HasPrefix(k, "env."):
+			envName := strings.TrimPrefix(k, "env.")
+			if envName == "" {
+				return nil, errors.Errorf("invalid env option %q, expecting env.FOO=bar", k)
+			}
+			d.env = append(d.env, fmt.Sprintf("%s=%s", envName, v))
 		default:
 			return nil, errors.Errorf("invalid driver option %s for docker-container driver", k)
 		}