errors: add BadRequestDetails

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

errors/details.go

@@ -0,0 +1,20 @@
+package errors
+
+import (
+	"google.golang.org/genproto/googleapis/rpc/errdetails"
+)
+
+// BadRequestDetails returns an error details for an invalid argument.
+// fd is a list of field / description pairs.
+func BadRequestDetails(fd ...string) *errdetails.BadRequest {
+	var fieldViolations []*errdetails.BadRequest_FieldViolation
+	for i := 0; i < len(fd); i += 2 {
+		fieldViolations = append(fieldViolations, &errdetails.BadRequest_FieldViolation{
+			Field:       fd[i],
+			Description: fd[i+1],
+		})
+	}
+	return &errdetails.BadRequest{
+		FieldViolations: fieldViolations,
+	}
+}