nghttpx: Add upgrade-scheme parameter to backend option

If "upgrade-scheme" parameter is present in backend option along with
"tls" paramter, HTTP/2 :scheme pseudo header field is changed to
"https" from "http" when forwarding a request to this particular
backend.  This is a workaround for a server which requests "https"
scheme on HTTP/2 connection encrypted by TLS.

src/shrpx.cc

@@ -1815,6 +1815,13 @@ Connections:
               "redirect-if-no-tls"    parameter   to    all   backends
               explicitly if this feature is desired.
 
+              If "upgrade-scheme"  parameter is used along  with "tls"
+              parameter, HTTP/2 :scheme pseudo header field is changed
+              to "https" from "http" when forwarding a request to this
+              particular backend.  This is  a workaround for a backend
+              server  which  requires  "https" :scheme  pseudo  header
+              field on TLS encrypted connection.
+
               Since ";" and ":" are  used as delimiter, <PATTERN> must
               not  contain these  characters.  Since  ";" has  special
               meaning in shell, the option value must be quoted.

src/shrpx_config.cc

@@ -814,6 +814,7 @@ struct DownstreamParams {
   bool tls;
   bool dns;
   bool redirect_if_not_tls;
+  bool upgrade_scheme;
 };
 
 namespace {
@@ -918,6 +919,8 @@ int parse_downstream_params(DownstreamParams &out,
       out.dns = true;
     } else if (util::strieq_l("redirect-if-not-tls", param)) {
       out.redirect_if_not_tls = true;
+    } else if (util::strieq_l("upgrade-scheme", param)) {
+      out.upgrade_scheme = true;
     } else if (!param.empty()) {
       LOG(ERROR) << "backend: " << param << ": unknown keyword";
       return -1;
@@ -977,6 +980,7 @@ int parse_mapping(Config *config, DownstreamAddrConfig &addr,
   addr.tls = params.tls;
   addr.sni = make_string_ref(downstreamconf.balloc, params.sni);
   addr.dns = params.dns;
+  addr.upgrade_scheme = params.upgrade_scheme;
 
   auto &routerconf = downstreamconf.router;
   auto &router = routerconf.router;

src/shrpx_config.h

@@ -461,6 +461,10 @@ struct DownstreamAddrConfig {
   bool tls;
   // true if dynamic DNS is enabled
   bool dns;
+  // true if :scheme pseudo header field should be upgraded to secure
+  // variant (e.g., "https") when forwarding request to a backend
+  // connected by TLS connection.
+  bool upgrade_scheme;
 };
 
 // Mapping hash to idx which is an index into

src/shrpx_http2_downstream_connection.cc

@@ -291,7 +291,14 @@ int Http2DownstreamConnection::push_request_headers() {
   if (req.method != HTTP_CONNECT) {
     assert(!req.scheme.empty());
 
-    nva.push_back(http2::make_nv_ls_nocopy(":scheme", req.scheme));
+    auto addr = http2session_->get_addr();
+    assert(addr);
+    // We will handle more protocol scheme upgrade in the future.
+    if (addr->tls && addr->upgrade_scheme && req.scheme == "http") {
+      nva.push_back(http2::make_nv_ll(":scheme", "https"));
+    } else {
+      nva.push_back(http2::make_nv_ls_nocopy(":scheme", req.scheme));
+    }
 
     if (req.method == HTTP_OPTIONS && req.path.empty()) {
       nva.push_back(http2::make_nv_ll(":path", "*"));

src/shrpx_worker.cc

@@ -70,10 +70,10 @@ void proc_wev_cb(struct ev_loop *loop, ev_timer *w, int revents) {
 
 // DownstreamKey is used to index SharedDownstreamAddr in order to
 // find the same configuration.
-using DownstreamKey =
-    std::tuple<std::vector<std::tuple<StringRef, StringRef, size_t, size_t,
-                                      shrpx_proto, uint16_t, bool, bool, bool>>,
-               bool, int, StringRef, StringRef, int>;
+using DownstreamKey = std::tuple<
+    std::vector<std::tuple<StringRef, StringRef, size_t, size_t, shrpx_proto,
+                           uint16_t, bool, bool, bool, bool>>,
+    bool, int, StringRef, StringRef, int>;
 
 namespace {
 DownstreamKey create_downstream_key(
@@ -93,6 +93,7 @@ DownstreamKey create_downstream_key(
     std::get<6>(*p) = a.host_unix;
     std::get<7>(*p) = a.tls;
     std::get<8>(*p) = a.dns;
+    std::get<9>(*p) = a.upgrade_scheme;
     ++p;
   }
   std::sort(std::begin(addrs), std::end(addrs));
@@ -220,6 +221,7 @@ void Worker::replace_downstream_config(
       dst_addr.fall = src_addr.fall;
       dst_addr.rise = src_addr.rise;
       dst_addr.dns = src_addr.dns;
+      dst_addr.upgrade_scheme = src_addr.upgrade_scheme;
 
       auto shared_addr_ptr = shared_addr.get();
 

src/shrpx_worker.h

@@ -115,6 +115,10 @@ struct DownstreamAddr {
   bool tls;
   // true if dynamic DNS is enabled
   bool dns;
+  // true if :scheme pseudo header field should be upgraded to secure
+  // variant (e.g., "https") when forwarding request to a backend
+  // connected by TLS connection.
+  bool upgrade_scheme;
 };
 
 // Simplified weighted fair queuing.  Actually we don't use queue here