nghttpd: Add --trailer to send trailer header fields

src/HttpServer.cc

@@ -809,6 +809,7 @@ void Http2Handler::terminate_session(uint32_t error_code) {
 ssize_t file_read_callback(nghttp2_session *session, int32_t stream_id,
                            uint8_t *buf, size_t length, uint32_t *data_flags,
                            nghttp2_data_source *source, void *user_data) {
+  int rv;
   auto hd = static_cast<Http2Handler *>(user_data);
   auto stream = hd->get_stream(stream_id);
 
@@ -829,6 +830,20 @@ ssize_t file_read_callback(nghttp2_session *session, int32_t stream_id,
   if (nread == 0 || stream->body_left <= 0) {
     *data_flags |= NGHTTP2_DATA_FLAG_EOF;
 
+    auto config = hd->get_config();
+    if (!config->trailer.empty()) {
+      *data_flags |= NGHTTP2_DATA_FLAG_NO_END_STREAM;
+      std::vector<nghttp2_nv> nva;
+      nva.reserve(config->trailer.size());
+      for (auto &kv : config->trailer) {
+        nva.push_back(http2::make_nv(kv.name, kv.value, kv.no_index));
+      }
+      rv = nghttp2_submit_trailer(session, stream_id, nva.data(), nva.size());
+      if (rv != 0) {
+        *data_flags &= ~NGHTTP2_DATA_FLAG_NO_END_STREAM;
+      }
+    }
+
     if (nghttp2_session_get_stream_remote_close(session, stream_id) == 0) {
       remove_stream_read_timeout(stream);
       remove_stream_write_timeout(stream);

src/HttpServer.h

@@ -50,6 +50,7 @@ namespace nghttp2 {
 
 struct Config {
   std::map<std::string, std::vector<std::string>> push;
+  Headers trailer;
   std::string htdocs;
   std::string host;
   std::string private_key_file;

src/nghttpd.cc

@@ -140,6 +140,11 @@ Options:
   --early-response
               Start sending response when request HEADERS is received,
               rather than complete request is received.
+  --trailer=<HEADER>
+              Add a trailer  header to a response.   <HEADER> must not
+              include pseudo header field  (header field name starting
+              with ':').  The  trailer is sent only if  a response has
+              body part.  Example: --trailer 'foo: bar'.
   --version   Display version information and exit.
   -h, --help  Display this help and exit.
 
@@ -170,6 +175,7 @@ int main(int argc, char **argv) {
         {"version", no_argument, &flag, 3},
         {"dh-param-file", required_argument, &flag, 4},
         {"early-response", no_argument, &flag, 5},
+        {"trailer", required_argument, &flag, 6},
         {nullptr, 0, nullptr, 0}};
     int option_index = 0;
     int c = getopt_long(argc, argv, "DVb:c:d:ehn:p:va:", long_options,
@@ -254,6 +260,30 @@ int main(int argc, char **argv) {
         // early-response
         config.early_response = true;
         break;
+      case 6: {
+        // trailer option
+        auto header = optarg;
+        auto value = strchr(optarg, ':');
+        if (!value) {
+          std::cerr << "--trailer: invalid header: " << optarg << std::endl;
+          exit(EXIT_FAILURE);
+        }
+        *value = 0;
+        value++;
+        while (isspace(*value)) {
+          value++;
+        }
+        if (*value == 0) {
+          // This could also be a valid case for suppressing a header
+          // similar to curl
+          std::cerr << "--trailer: invalid header - value missing: " << optarg
+                    << std::endl;
+          exit(EXIT_FAILURE);
+        }
+        config.trailer.emplace_back(header, value, false);
+        util::inp_strlower(config.trailer.back().name);
+        break;
+      }
       }
       break;
     default: