account_file can be verbatim JSON string

builder/googlecompute/account.go

@@ -2,7 +2,10 @@ package googlecompute
 
 import (
 	"encoding/json"
+	"fmt"
+	"io/ioutil"
 	"os"
+	"strings"
 )
 
 // accountFile represents the structure of the account file JSON file.
@@ -13,13 +16,37 @@ type accountFile struct {
 	ClientId     string `json:"client_id"`
 }
 
-func loadJSON(result interface{}, path string) error {
-	f, err := os.Open(path)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	dec := json.NewDecoder(f)
+func parseJSON(result interface{}, text string) error {
+	r := strings.NewReader(text)
+	dec := json.NewDecoder(r)
 	return dec.Decode(result)
 }
+
+func processAccountFile(account_file *accountFile, text string) error {
+	// Assume text is a JSON string
+	if err := parseJSON(account_file, text); err != nil {
+		// If text was not JSON, assume it is a file path instead
+		if _, err := os.Stat(text); os.IsNotExist(err) {
+			return fmt.Errorf(
+				"account_file path does not exist: %s",
+				text)
+		}
+
+		b, err := ioutil.ReadFile(text)
+		if err != nil {
+			return fmt.Errorf(
+				"Error reading account_file from path '%s': %s",
+				text, err)
+		}
+
+		contents := string(b)
+
+		if err := parseJSON(account_file, contents); err != nil {
+			return fmt.Errorf(
+				"Error parsing account file '%s': %s",
+				contents, err)
+		}
+	}
+
+	return nil
+}

builder/googlecompute/config.go

@@ -131,9 +131,8 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	c.stateTimeout = stateTimeout
 
 	if c.AccountFile != "" {
-		if err := loadJSON(&c.account, c.AccountFile); err != nil {
-			errs = packer.MultiErrorAppend(
-				errs, fmt.Errorf("Failed parsing account file: %s", err))
+		if err := processAccountFile(&c.account, c.AccountFile); err != nil {
+			errs = packer.MultiErrorAppend(errs, err)
 		}
 	}
 

website/source/docs/builders/googlecompute.html.markdown

@@ -77,7 +77,9 @@ straightforwarded, it is documented here.
 
 Below is a fully functioning example. It doesn't do anything useful, since no
 provisioners are defined, but it will effectively repackage an existing GCE
-image. The account file is obtained in the previous section.
+image. The account_file is obtained in the previous section.  If it parses as
+JSON it is assumed to be the file itself, otherwise it is assumed to be
+the path to the file containing the JSON.
 
 ``` {.javascript}
 {