core: Create cache directory only when needed [GH-367]

CHANGELOG.md

@@ -34,6 +34,7 @@ BUG FIXES:
 
   * core: Errors are properly shown when adding bad floppy files. [GH-1043]
   * core: Fix some URL parsing issues on Windows.
+  * core: Create Cache directory only when it is needed. [GH-367]
   * builder/amazon-instance: Use S3Endpoint for ec2-upload-bundle arg,
       which works for every region. [GH-904]
   * builder/digitalocean: updated default image_id [GH-1032]

packer.go

@@ -106,11 +106,6 @@ func wrappedMain() int {
 		return 1
 	}
 
-	if err := os.MkdirAll(cacheDir, 0755); err != nil {
-		fmt.Fprintf(os.Stderr, "Error preparing cache directory: \n\n%s\n", err)
-		return 1
-	}
-
 	log.Printf("Setting cache directory: %s", cacheDir)
 	cache := &packer.FileCache{CacheDir: cacheDir}
 

packer/cache.go

@@ -3,6 +3,8 @@ package packer
 import (
 	"crypto/sha256"
 	"encoding/hex"
+	"log"
+	"os"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -84,6 +86,13 @@ func (f *FileCache) cachePath(key string, hashKey string) string {
 		}
 	}
 
+	// Make the cache directory. We ignore errors here, but
+	// log them in case something happens.
+	if err := os.MkdirAll(f.CacheDir, 0755); err != nil {
+		log.Printf(
+			"[ERR] Error making cacheDir: %s %s", f.CacheDir, err)
+	}
+
 	return filepath.Join(f.CacheDir, hashKey+suffix)
 }