Always close the build context

This ensures all resources are released properly.

container.go

@@ -209,6 +209,7 @@ func (c *ContainerRequest) Validate() error {
 }
 
 // GetContext retrieve the build context for the request
+// Must be closed when no longer needed.
 func (c *ContainerRequest) GetContext() (io.Reader, error) {
 	var includes []string = []string{"."}
 
@@ -356,12 +357,6 @@ func (c *ContainerRequest) BuildOptions() (types.ImageBuildOptions, error) {
 	buildOptions.BuildArgs = c.GetBuildArgs()
 	buildOptions.Dockerfile = c.GetDockerfile()
 
-	buildContext, err := c.GetContext()
-	if err != nil {
-		return buildOptions, err
-	}
-	buildOptions.Context = buildContext
-
 	// Make sure the auth configs from the Dockerfile are set right after the user-defined build options.
 	authsFromDockerfile := getAuthConfigsFromDockerfile(c)
 
@@ -400,6 +395,13 @@ func (c *ContainerRequest) BuildOptions() (types.ImageBuildOptions, error) {
 		buildOptions.Labels = core.DefaultLabels(core.SessionID())
 	}
 
+	// Do this as late as possible to ensure we don't leak the context on error/panic.
+	buildContext, err := c.GetContext()
+	if err != nil {
+		return buildOptions, err
+	}
+	buildOptions.Context = buildContext
+
 	return buildOptions, nil
 }
 

docker.go

@@ -890,6 +890,7 @@ func (p *DockerProvider) BuildImage(ctx context.Context, img ImageBuildInfo) (st
 			if err != nil {
 				return types.ImageBuildResponse{}, backoff.Permanent(err)
 			}
+			defer tryClose(buildOptions.Context) // release resources in any case
 
 			resp, err := p.client.ImageBuild(ctx, buildOptions.Context, buildOptions)
 			if err != nil {
@@ -1662,3 +1663,11 @@ func isPermanentClientError(err error) bool {
 	}
 	return false
 }
+
+func tryClose(r io.Reader) error {
+	rc, ok := r.(io.Closer)
+	if ok {
+		return rc.Close()
+	}
+	return nil
+}