This puts the image parsing code (mostly) back to how it was before. The

regex solution is extremely complex, which makes it hard to debug and
understand; the original switches and
commenting lay out the various cases in a straightforward fashion. Plus,
implementing namespace/repo support in the original code was a simple
strings.Join call.

builtin/providers/docker/resource_docker_image_funcs.go

@@ -3,7 +3,6 @@ package docker
 import (
 	"fmt"
 	"strings"
-	"regexp"
 
 	dc "github.com/fsouza/go-dockerclient"
 	"github.com/hashicorp/terraform/helper/schema"
@@ -76,28 +75,36 @@ func pullImage(data *Data, client *dc.Client, image string) error {
 
 	pullOpts := dc.PullImageOptions{}
 
-	// 
-	// Breaks apart an image string into host:port, repo, and tag components
-	regex := "^(?:(?P<host>(?:[\\w-]+(?:\\.[\\w-]+)+)(?::[\\d]+)?)/)?(?P<repo>[\\w.-]+(?:/[\\w.-]*)*)*(?::(?P<tag>[\\w.-]*))?"
-	r, _ := regexp.Compile(regex)
-
-	// Result is in form [[image, host, repo, tag]], so we get the head of the 
-	// outer list to pass the inner list to result
-	result := r.FindAllStringSubmatch(image, -1)[0]
-
-	// If the host is not an empty string, then the image is using a private registry
-	if (result[1] != "") {
-		pullOpts.Registry = result[1]
-		// The repository for a private registry should take the form of host/repo rather than just repo
-		pullOpts.Repository = result[1] + "/" + result[2]
-	} else if (result[2] != "") {
-		// Local registries, or the main docker registry will have an image named as just 'repo'
-		pullOpts.Repository = result[2]
-	}
+	splitImageName := strings.Split(image, ":")
+	switch len(splitImageName) {
+
+	// It's in registry:port/username/repo:tag or registry:port/repo:tag format
+	case 3:
+		splitPortRepo := strings.Split(splitImageName[1], "/")
+		pullOpts.Registry = splitImageName[0] + ":" + splitPortRepo[0]
+		pullOpts.Tag = splitImageName[2]
+		pullOpts.Repository = strings.Join(splitPortRepo[1:], "/")
+
+	// It's either registry:port/username/repo, registry:port/repo,
+	// or repo:tag with default registry
+	case 2:
+		splitPortRepo := strings.Split(splitImageName[1], "/")
+		switch len(splitPortRepo) {
+		// repo:tag
+		case 1:
+			pullOpts.Repository = splitImageName[0]
+			pullOpts.Tag = splitImageName[1]
+
+		// registry:port/username/repo or registry:port/repo
+		default:
+			pullOpts.Registry = splitImageName[0] + ":" + splitPortRepo[0]
+			pullOpts.Repository = strings.Join(splitPortRepo[1:], "/")
+			pullOpts.Tag = "latest"
+		}
 
-	// If there was a tag specified, then set it
-	if (result[3] != "") {
-		pullOpts.Tag = result[3]
+	// Plain username/repo or repo
+	default:
+		pullOpts.Repository = image
 	}
 
 	if err := client.PullImage(pullOpts, dc.AuthConfiguration{}); err != nil {