Add "GET /register/available?username=...." endpoint

Signed-off-by: MTRNord <mtrnord1@gmail.com>

src/github.com/matrix-org/dendrite/clientapi/readers/register.go

@@ -0,0 +1,65 @@
+package readers
+
+import (
+	"fmt"
+	"github.com/matrix-org/dendrite/clientapi/auth/storage/accounts"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/util"
+	"net/http"
+	"regexp"
+)
+
+const (
+	maxUsernameLength = 254 // http://matrix.org/speculator/spec/HEAD/intro.html#user-identifiers TODO account for domain
+)
+
+var validUsernameRegex = regexp.MustCompile(`^[0-9a-zA-Z_\-./]+$`)
+
+func validate(username string) *util.JSONResponse {
+	if len(username) > maxUsernameLength {
+		return &util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.BadJSON(fmt.Sprintf("'username' >%d characters", maxUsernameLength)),
+		}
+	} else if !validUsernameRegex.MatchString(username) {
+		return &util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.InvalidUsername("User ID can only contain characters a-z, 0-9, or '_-./'"),
+		}
+	} else if username[0] == '_' { // Regex checks its not a zero length string
+		return &util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.InvalidUsername("User ID can't start with a '_'"),
+		}
+	}
+	return nil
+}
+
+type availableResponse struct {
+	Available bool `json:"available"`
+}
+
+func RegisterAvailable(
+	req *http.Request,
+	accountDB *accounts.Database,
+) util.JSONResponse {
+	username := req.URL.Query().Get("username")
+
+	if resErr := validate(username); resErr != nil {
+		return *resErr
+	}
+
+	if _, resErr := accountDB.GetProfileByLocalpart(req.Context(), username); resErr == nil {
+		return util.JSONResponse{
+			Code: 400,
+			JSON: jsonerror.InvalidUsername("A different user ID has already been registered for this session"),
+		}
+	}
+
+	return util.JSONResponse{
+		Code: 200,
+		JSON: availableResponse{
+			Available: true,
+		},
+	}
+}

src/github.com/matrix-org/dendrite/clientapi/routing/routing.go

@@ -131,6 +131,10 @@ func Setup(
 		return writers.LegacyRegister(req, accountDB, deviceDB, &cfg)
 	})).Methods("POST", "OPTIONS")
 
+	r0mux.Handle("/register/available", common.MakeExternalAPI("registerAvailable", func(req *http.Request) util.JSONResponse {
+		return readers.RegisterAvailable(req, accountDB)
+	})).Methods("GET", "OPTIONS")
+
 	r0mux.Handle("/directory/room/{roomAlias}",
 		common.MakeAuthAPI("directory_room", deviceDB, func(req *http.Request, device *authtypes.Device) util.JSONResponse {
 			vars := mux.Vars(req)