Should return the provider by parsing the json in the box metadata file

post-processor/vagrant-cloud/post-processor.go

@@ -8,10 +8,10 @@ import (
 	"archive/tar"
 	"compress/gzip"
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"io/ioutil"
-	"log"
 	"os"
 	"strings"
 
@@ -244,12 +244,18 @@ func providerFromVagrantBox(boxfile string) (providerName string, err error) {
 	}
 	tr := tar.NewReader(ar)
 
+	// The metadata.json file in the tar archive contains a 'provider' key
+	type metadata struct {
+		ProviderName string `json:"provider"`
+	}
+	md := metadata{}
+
 	// Loop through the files in the archive and read the provider
 	// information from the boxes metadata.json file
 	for {
 		hdr, err := tr.Next()
 		if err == io.EOF {
-			if providerName == "" {
+			if md.ProviderName == "" {
 				return "", fmt.Errorf("Error: Provider info was not found in box: %s", boxfile)
 			}
 			break
@@ -263,11 +269,12 @@ func providerFromVagrantBox(boxfile string) (providerName string, err error) {
 			if err != nil {
 				return "", fmt.Errorf("Error reading contents of metadata.json file from box file: %s", err)
 			}
-			// TODO: Parse the json for the provider
+			err = json.Unmarshal(contents, &md)
-			log.Printf("Contents: %s", contents)
+			if err != nil {
+				return "", fmt.Errorf("Error parsing metadata.json file: %s", err)
+			}
 			break
 		}
 	}
-
+	return md.ProviderName, nil
-	return "", nil
 }

post-processor/vagrant-cloud/post-processor_test.go

@@ -14,6 +14,7 @@ import (
 	"testing"
 
 	"github.com/hashicorp/packer/packer"
+	"github.com/stretchr/testify/assert"
 )
 
 type tarFiles []struct {
@@ -286,6 +287,26 @@ func TestProviderFromVagrantBox_no_metadata(t *testing.T) {
 	t.Logf("%s", err)
 }
 
+func TestProviderFromVagrantBox_metadata_ok(t *testing.T) {
+	// Good: The box contains the metadata.json file with the required
+	// 'provider' key/value
+	expectedProvider := "virtualbox"
+	files := tarFiles{
+		{"foo.txt", "This is a foo file"},
+		{"bar.txt", "This is a bar file"},
+		{"metadata.json", `{"provider":"` + expectedProvider + `"}`},
+	}
+	boxfile, err := createBox(files)
+	if err != nil {
+		t.Fatalf("Error creating test box: %s", err)
+	}
+	defer os.Remove(boxfile.Name())
+
+	provider, err := providerFromVagrantBox(boxfile.Name())
+	assert.Equal(t, expectedProvider, provider, "Error: Expected provider: '%s'. Got '%s'", expectedProvider, provider)
+	t.Logf("Expected provider '%s'. Got provider '%s'", expectedProvider, provider)
+}
+
 func newBoxFile() (boxfile *os.File, err error) {
 	boxfile, err = ioutil.TempFile(os.TempDir(), "test*.box")
 	if err != nil {