fix local file stating (#9660)

builder/vagrant/builder.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net/url"
 	"os"
 	"path/filepath"
 	"strings"
@@ -194,10 +195,19 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, []string, error) {
 		if b.config.GlobalID != "" {
 			errs = packer.MultiErrorAppend(errs, fmt.Errorf("You may either set global_id or source_path but not both"))
 		}
+		// We're about to open up an actual boxfile. If the file is local to the
+		// filesystem, let's make sure it exists before we get too far into the
+		// build.
 		if strings.HasSuffix(b.config.SourceBox, ".box") {
-			if _, err := os.Stat(b.config.SourceBox); err != nil {
-				errs = packer.MultiErrorAppend(errs,
-					fmt.Errorf("Source box '%s' needs to exist at time of config validation! %v", b.config.SourceBox, err))
+			// If scheme is "file" or empty, then we need to check the
+			// filesystem to make sure the box is present locally.
+			u, err := url.Parse(b.config.SourceBox)
+			if err == nil && (u.Scheme == "" || u.Scheme == "file") {
+				if _, err := os.Stat(b.config.SourceBox); err != nil {
+					errs = packer.MultiErrorAppend(errs,
+						fmt.Errorf("Source box '%s' needs to exist at time of"+
+							" config validation! %v", b.config.SourceBox, err))
+				}
 			}
 		}
 	}

builder/vagrant/builder_test.go

@@ -79,6 +79,46 @@ func TestBuilder_Prepare_ValidateSource(t *testing.T) {
 			errExpected: true,
 			reason:      "Inalid argument for teardown method",
 		},
+		{
+			config: map[string]interface{}{
+				"communicator": "ssh",
+				"source_path":  "./my.box",
+			},
+			errExpected: true,
+			reason:      "Should fail because path does not exist",
+		},
+		{
+			config: map[string]interface{}{
+				"communicator": "ssh",
+				"source_path":  "file://my.box",
+			},
+			errExpected: true,
+			reason:      "Should fail because path does not exist",
+		},
+		{
+			config: map[string]interface{}{
+				"communicator": "ssh",
+				"source_path":  "http://my.box",
+			},
+			errExpected: false,
+			reason:      "Should pass because path is not local",
+		},
+		{
+			config: map[string]interface{}{
+				"communicator": "ssh",
+				"source_path":  "https://my.box",
+			},
+			errExpected: false,
+			reason:      "Should pass because path is not local",
+		},
+		{
+			config: map[string]interface{}{
+				"communicator": "ssh",
+				"source_path":  "smb://my.box",
+			},
+			errExpected: false,
+			reason:      "Should pass because path is not local",
+		},
 	}
 
 	for _, tc := range cases {