expand env vars

Signed-off-by: Khash Sajadi <[email protected]>

Author: khash

README.md

@@ -26,7 +26,7 @@ Add any required modules to CoreDNS code as prompted.
 
 In the Corefile, `mysql` can be configured with the following parameters:
 
-`dsn` DSN for MySQL as per https://github.com/go-sql-driver/mysql examples.
+`dsn` DSN for MySQL as per https://github.com/go-sql-driver/mysql examples. You can use `$ENV_NAME` format in the DSN, and it will be replaced with the environment variable value.
 `table_prefix` Prefix for the MySQL tables. Defaults to `coredns_`.
 `max_lifetime` Duration (in Golang format) for a SQL connection. Default is 1 minute.
 `max_open_connections` Maximum number of open connections to the database server. Default is 10.

setup.go

@@ -2,6 +2,7 @@ package coredns_mysql
 
 import (
 	"database/sql"
+	"os"
 	"strconv"
 	"time"
 
@@ -129,7 +130,7 @@ func mysqlParse(c *caddy.Controller) (*CoreDNSMySql, error) {
 }
 
 func (handler *CoreDNSMySql) db() (*sql.DB, error) {
-	db, err := sql.Open("mysql", handler.Dsn)
+	db, err := sql.Open("mysql", os.ExpandEnv(handler.Dsn))
 	if err != nil {
 		return nil, err
 	}