discover docker version automatically (fixes #47)

image/image.go

@@ -22,7 +22,7 @@ import (
 )
 
 // TODO: this file should be rethought... but since it's only for preprocessing it'll be tech debt for now.
-const dockerVersion = "1.26"
+var dockerVersion string
 
 func check(e error) {
 	if e != nil {
@@ -199,6 +199,8 @@ func InitializeData(imageID string) ([]*Layer, []*filetree.FileTree, float64, fi
 	var manifest ImageManifest
 	var layerMap = make(map[string]*filetree.FileTree)
 	var trees = make([]*filetree.FileTree, 0)
+	dockerVersion = utils.DiscoverDockerVersion()
+	logrus.Debug("Using docker version:", dockerVersion)
 
 	// pull the image if it does not exist
 	ctx := context.Background()

utils/docker.go

@@ -1,6 +1,7 @@
 package utils
 
 import (
+	"bytes"
 	"os"
 	"os/exec"
 	"strings"
@@ -30,3 +31,15 @@ func cleanArgs(s []string) []string {
 	}
 	return r
 }
+
+func DiscoverDockerVersion() string {
+	cmd := exec.Command("docker", "version", "--format", "{{.Server.APIVersion}}")
+	cmdOutput := &bytes.Buffer{}
+	cmd.Stdout = cmdOutput
+
+	err := cmd.Run()
+	if err != nil {
+		panic(err)
+	}
+	return strings.TrimSpace(string(cmdOutput.Bytes()))
+}