From 1fb3950e6b59be83305095683e30c74bda8904b7 Mon Sep 17 00:00:00 2001
From: "Crom (Thibaut CHARLES)" <CromFr@gmail.com>
Date: Sun, 10 Dec 2017 15:47:17 +0100
Subject: [PATCH] User registration return M_USER_IN_USE when username is
 already taken

---
 .../dendrite/clientapi/jsonerror/jsonerror.go       |  6 ++++++
 .../dendrite/clientapi/routing/register.go          | 13 +++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go b/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go
index 07fe90304..747924188 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/jsonerror/jsonerror.go
@@ -103,6 +103,12 @@ func InvalidUsername(msg string) *MatrixError {
 	return &MatrixError{"M_INVALID_USERNAME", msg}
 }
 
+// InvalidUsername is an error returned when the client tries to register an
+// username that already exists
+func UserInUse(msg string) *MatrixError {
+	return &MatrixError{"M_USER_IN_USE", msg}
+}
+
 // GuestAccessForbidden is an error which is returned when the client is
 // forbidden from accessing a resource as a guest.
 func GuestAccessForbidden(msg string) *MatrixError {
diff --git a/src/github.com/matrix-org/dendrite/clientapi/routing/register.go b/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
index 7bd5820f9..73282d47b 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/routing/register.go
@@ -457,6 +457,19 @@ func completeRegistration(
 		}
 	}
 
+	avail, err := accountDB.CheckAccountAvailability(ctx, username)
+	if err == nil && avail == false {
+		return util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.UserInUse("Desired user ID is already taken."),
+		}
+	} else if err != nil {
+		return util.JSONResponse{
+			Code: 500,
+			JSON: jsonerror.Unknown("Failed to check account availability: " + err.Error()),
+		}
+	}
+
 	acc, err := accountDB.CreateAccount(ctx, username, password)
 	if err != nil {
 		return util.JSONResponse{