Bug 1543201 - DoH Privacy Enhancement: Do not set the User-Agent header for DoH requests r=dragana

Differential Revision: https://phabricator.services.mozilla.com/D55934

--HG--
extra : moz-landing-system : lando

modules/libpref/init/StaticPrefList.yaml

@@ -6909,6 +6909,12 @@
   value: false
   mirror: always
 
+# Whether to send the User-Agent header for TRR requests
+- name: network.trr.send_user-agent_headers
+  type: bool
+  value: false
+  mirror: always
+
 # This pref controls if TRR will still be enabled when a VPN is detected on
 # the system. Detection is not foolproof, and some VPNs may not be detected.
 # See bug 1565004 comment 3 for details.

netwerk/dns/TRR.cpp

@@ -313,6 +313,13 @@ nsresult TRR::SendHTTPRequest() {
     NS_ENSURE_SUCCESS(rv, rv);
   }
 
+  // Sanitize the request by removing the User-Agent
+  if (!StaticPrefs::network_trr_send_user_agent_headers()) {
+    rv = httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("User-Agent"),
+                                       EmptyCString(), false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
   // set the *default* response content type
   if (NS_FAILED(httpChannel->SetContentType(
           NS_LITERAL_CSTRING("application/dns-message")))) {

testing/xpcshell/moz-http2/moz-http2.js

@@ -673,7 +673,7 @@ function handleRequest(req, res) {
         });
       }
 
-      if (req.headers["accept-language"]) {
+      if (req.headers["accept-language"] || req.headers["user-agent"]) {
         // If we get this header, don't send back any response. This should
         // cause the tests to fail. This is easier then actually sending back
         // the header value into test_trr.js