Add clientapi tests (#2916)

This PR
- adds several tests for the clientapi, mostly around `/register` and
auth fallback.
- removes the now deprecated `homeserver` field from responses to
`/register` and `/login`
- slightly refactors auth fallback handling

internal/validate.go

@@ -15,30 +15,96 @@
 package internal
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
+	"regexp"
 
 	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 )
 
-const minPasswordLength = 8 // http://matrix.org/docs/spec/client_server/r0.2.0.html#password-based
+const (
+	maxUsernameLength = 254 // http://matrix.org/speculator/spec/HEAD/intro.html#user-identifiers TODO account for domain
 
-const maxPasswordLength = 512 // https://github.com/matrix-org/synapse/blob/v0.20.0/synapse/rest/client/v2_alpha/register.py#L161
+	minPasswordLength = 8   // http://matrix.org/docs/spec/client_server/r0.2.0.html#password-based
+	maxPasswordLength = 512 // https://github.com/matrix-org/synapse/blob/v0.20.0/synapse/rest/client/v2_alpha/register.py#L161
+)
 
-// ValidatePassword returns an error response if the password is invalid
-func ValidatePassword(password string) *util.JSONResponse {
+var (
+	ErrPasswordTooLong    = fmt.Errorf("password too long: max %d characters", maxPasswordLength)
+	ErrPasswordWeak       = fmt.Errorf("password too weak: min %d characters", minPasswordLength)
+	ErrUsernameTooLong    = fmt.Errorf("username exceeds the maximum length of %d characters", maxUsernameLength)
+	ErrUsernameInvalid    = errors.New("username can only contain characters a-z, 0-9, or '_-./='")
+	ErrUsernameUnderscore = errors.New("username cannot start with a '_'")
+	validUsernameRegex    = regexp.MustCompile(`^[0-9a-z_\-=./]+$`)
+)
+
+// ValidatePassword returns an error if the password is invalid
+func ValidatePassword(password string) error {
 	// https://github.com/matrix-org/synapse/blob/v0.20.0/synapse/rest/client/v2_alpha/register.py#L161
 	if len(password) > maxPasswordLength {
-		return &util.JSONResponse{
-			Code: http.StatusBadRequest,
-			JSON: jsonerror.BadJSON(fmt.Sprintf("password too long: max %d characters", maxPasswordLength)),
-		}
+		return ErrPasswordTooLong
 	} else if len(password) > 0 && len(password) < minPasswordLength {
+		return ErrPasswordWeak
+	}
+	return nil
+}
+
+// PasswordResponse returns a util.JSONResponse for a given error, if any.
+func PasswordResponse(err error) *util.JSONResponse {
+	switch err {
+	case ErrPasswordWeak:
 		return &util.JSONResponse{
 			Code: http.StatusBadRequest,
-			JSON: jsonerror.WeakPassword(fmt.Sprintf("password too weak: min %d chars", minPasswordLength)),
+			JSON: jsonerror.WeakPassword(ErrPasswordWeak.Error()),
+		}
+	case ErrPasswordTooLong:
+		return &util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON(ErrPasswordTooLong.Error()),
 		}
 	}
 	return nil
 }
+
+// ValidateUsername returns an error if the username is invalid
+func ValidateUsername(localpart string, domain gomatrixserverlib.ServerName) error {
+	// https://github.com/matrix-org/synapse/blob/v0.20.0/synapse/rest/client/v2_alpha/register.py#L161
+	if id := fmt.Sprintf("@%s:%s", localpart, domain); len(id) > maxUsernameLength {
+		return ErrUsernameTooLong
+	} else if !validUsernameRegex.MatchString(localpart) {
+		return ErrUsernameInvalid
+	} else if localpart[0] == '_' { // Regex checks its not a zero length string
+		return ErrUsernameUnderscore
+	}
+	return nil
+}
+
+// UsernameResponse returns a util.JSONResponse for the given error, if any.
+func UsernameResponse(err error) *util.JSONResponse {
+	switch err {
+	case ErrUsernameTooLong:
+		return &util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON(err.Error()),
+		}
+	case ErrUsernameInvalid, ErrUsernameUnderscore:
+		return &util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.InvalidUsername(err.Error()),
+		}
+	}
+	return nil
+}
+
+// ValidateApplicationServiceUsername returns an error if the username is invalid for an application service
+func ValidateApplicationServiceUsername(localpart string, domain gomatrixserverlib.ServerName) error {
+	if id := fmt.Sprintf("@%s:%s", localpart, domain); len(id) > maxUsernameLength {
+		return ErrUsernameTooLong
+	} else if !validUsernameRegex.MatchString(localpart) {
+		return ErrUsernameInvalid
+	}
+	return nil
+}