Upstream: early hints support.

The change implements processing upstream early hints response in
ngx_http_proxy_module and ngx_http_grpc_module.  A new directive
"early_hints" enables sending early hints to the client.  By default,
sending early hints is disabled.

Example:

    map $http_sec_fetch_mode $early_hints {
        navigate $http2$http3;
    }

    early_hints $early_hints;

    proxy_pass http://example.com;

1 files changed, 41 insertions, 0 deletions

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 92c3eae8a..2d62674d9 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -670,6 +670,13 @@ static ngx_command_t  ngx_http_core_commands[] = {
       offsetof(ngx_http_core_loc_conf_t, etag),
       NULL },
 
+    { ngx_string("early_hints"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_1MORE,
+      ngx_http_set_predicate_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_core_loc_conf_t, early_hints),
+      NULL },
+
     { ngx_string("error_page"),
       NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_HTTP_LIF_CONF
                         |NGX_CONF_2MORE,
@@ -1858,6 +1865,37 @@ ngx_http_send_header(ngx_http_request_t *r)
 
 
 ngx_int_t
+ngx_http_send_early_hints(ngx_http_request_t *r)
+{
+    ngx_int_t                  rc;
+    ngx_http_core_loc_conf_t  *clcf;
+
+    if (r->post_action) {
+        return NGX_OK;
+    }
+
+    if (r->header_sent) {
+        ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
+                      "header already sent");
+        return NGX_ERROR;
+    }
+
+    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);
+
+    rc = ngx_http_test_predicates(r, clcf->early_hints);
+
+    if (rc != NGX_DECLINED) {
+        return rc;
+    }
+
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "http send early hints \"%V?%V\"", &r->uri, &r->args);
+
+    return ngx_http_top_early_hints_filter(r);
+}
+
+
+ngx_int_t
 ngx_http_output_filter(ngx_http_request_t *r, ngx_chain_t *in)
 {
     ngx_int_t          rc;
@@ -3637,6 +3675,7 @@ ngx_http_core_create_loc_conf(ngx_conf_t *cf)
     clcf->chunked_transfer_encoding = NGX_CONF_UNSET;
     clcf->etag = NGX_CONF_UNSET;
     clcf->server_tokens = NGX_CONF_UNSET_UINT;
+    clcf->early_hints = NGX_CONF_UNSET_PTR;
     clcf->types_hash_max_size = NGX_CONF_UNSET_UINT;
     clcf->types_hash_bucket_size = NGX_CONF_UNSET_UINT;
 
@@ -3917,6 +3956,8 @@ ngx_http_core_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
     ngx_conf_merge_uint_value(conf->server_tokens, prev->server_tokens,
                               NGX_HTTP_SERVER_TOKENS_ON);
 
+    ngx_conf_merge_ptr_value(conf->early_hints, prev->early_hints, NULL);
+
     ngx_conf_merge_ptr_value(conf->open_file_cache,
                               prev->open_file_cache, NULL);