Fallback to USER env var if user.Current failed

Also expose the error emitted by lookup failures.

conn.go

@@ -30,6 +30,7 @@ var (
 	ErrInFailedTransaction       = errors.New("pq: Could not complete operation in a failed transaction")
 	ErrSSLNotSupported           = errors.New("pq: SSL is not enabled on the server")
 	ErrSSLKeyHasWorldPermissions = errors.New("pq: Private key file has group or world access. Permissions should be u=rw (0600) or less.")
+	ErrCouldNotDetectUsername	 = errors.New("pq: Could not detect default username. Please provide one explicitly.")
 )
 
 type drv struct{}

user_posix.go

@@ -4,12 +4,21 @@
 
 package pq
 
-import "os/user"
+import (
+	"os"
+	"os/user"
+)
 
 func userCurrent() (string, error) {
 	u, err := user.Current()
-	if err != nil {
-		return "", err
+	if err == nil {
+		return u.Username, nil
 	}
-	return u.Username, nil
+
+	name := os.Getenv("USER")
+	if name != "" {
+		return name, nil
+	}
+
+	return "", ErrCouldNotDetectUsername
 }

user_windows.go

@@ -19,7 +19,7 @@ func userCurrent() (string, error) {
 	pwname_size := uint32(len(pw_name)) - 1
 	err := syscall.GetUserNameEx(syscall.NameSamCompatible, &pw_name[0], &pwname_size)
 	if err != nil {
-		return "", err
+		return "", ErrCouldNotDetectUsername
 	}
 	s := syscall.UTF16ToString(pw_name)
 	u := filepath.Base(s)