From 4818998e502ad9f0d6c2fa260474a99118dcc5fa Mon Sep 17 00:00:00 2001
From: Sorunome <mail@sorunome.de>
Date: Thu, 7 Oct 2021 14:33:36 +0200
Subject: [PATCH] feat: advertise the low-bandwidth proxy in the /versions
 response

---
 cmd/proxy/proxy.go | 54 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/cmd/proxy/proxy.go b/cmd/proxy/proxy.go
index fdc392d..e392b32 100644
--- a/cmd/proxy/proxy.go
+++ b/cmd/proxy/proxy.go
@@ -19,11 +19,13 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net/http"
 	"net/http/httputil"
 	"net/url"
+	"strings"
 	"sync/atomic"
 	"time"
 
@@ -165,6 +167,25 @@ func writeResponse(cfg *Config, res *http.Response, w http.ResponseWriter) []byt
 				}
 			}
 		}
+		if res.Request.URL.Path == "/_matrix/client/versions" {
+			dtlsPortParts := strings.Split(cfg.ListenDTLS, ":")
+			tuples := []struct {
+				Key string
+				Value interface{}
+			}{
+				{`org\.matrix\.msc3079\.low_bandwidth.dtls`, dtlsPortParts[len(dtlsPortParts) - 1]},
+				{`org\.matrix\.msc3079\.low_bandwidth.cbor_enum_version`, 1},
+				{`org\.matrix\.msc3079\.low_bandwidth.coap_enum_version`, 1},
+			}
+			for _, t := range tuples {
+				jsonBody2, err := sjson.SetBytes(jsonBody, t.Key, t.Value)
+				if err != nil {
+					logrus.WithError(err).Error("failed to advertise low-bandwidth support")
+				} else {
+					jsonBody = jsonBody2
+				}
+			}
+		}
 		if len(jsonBody) > 0 {
 			resBody, err = cfg.CBORCodec.JSONToCBOR(bytes.NewBuffer(jsonBody))
 			if err != nil {
@@ -291,6 +312,39 @@ func RunProxyServer(cfg *Config) error {
 				logrus.Infof("TCP proxy %v", req.URL.String())
 				req.Host = localURL.Host
 			},
+			ModifyResponse: func(res *http.Response) error {
+				if res.Request.URL.Path == "/_matrix/client/versions" {
+					logrus.Info("Got versions response....")
+					jsonBody, err := ioutil.ReadAll(res.Body)
+					if err != nil {
+						logrus.WithError(err).Error("failed to read the remote response body")
+						return nil
+					}
+					dtlsPortParts := strings.Split(cfg.ListenDTLS, ":")
+					tuples := []struct {
+						Key string
+						Value interface{}
+					}{
+						{`org\.matrix\.msc3079\.low_bandwidth.dtls`, dtlsPortParts[len(dtlsPortParts) - 1]},
+						{`org\.matrix\.msc3079\.low_bandwidth.cbor_enum_version`, 1},
+						{`org\.matrix\.msc3079\.low_bandwidth.coap_enum_version`, 1},
+					}
+					for _, t := range tuples {
+						jsonBody2, err := sjson.SetBytes(jsonBody, t.Key, t.Value)
+						if err != nil {
+							logrus.WithError(err).Error("failed to advertise low-bandwidth support")
+						} else {
+							jsonBody = jsonBody2
+						}
+					}
+					buf := bytes.NewBufferString("")
+					buf.Write(jsonBody)
+					res.Body = ioutil.NopCloser(buf)
+					res.Header["Content-Length"] = []string{fmt.Sprint(buf.Len())}
+					logrus.Info("Done modifying response")
+				}
+				return nil
+			},
 		}
 		if cfg.AdvertiseOnHTTPS {
 			tlsServer := &http.Server{