[nginx] HTTP/2: fixed flushing early hints over SSL.

[noreply at nginx.com]

details:   https://github.com/nginx/nginx/commit/50932c3c6c1d2c442ef08241443162c7a3ed58b3
branches:  master
commit:    50932c3c6c1d2c442ef08241443162c7a3ed58b3
user:      Roman Arutyunyan <arut at nginx.com>
date:      Thu, 24 Jul 2025 18:29:21 +0400
description:
HTTP/2: fixed flushing early hints over SSL.

Previously, when using HTTP/2 over SSL, an early hints HEADERS frame was
queued in SSL buffer, and might not be immediately flushed.  This resulted
in a delay of early hints delivery until the main response was sent.

The fix is to set the flush flag for the early hints HEADERS frame buffer.

---
 src/http/v2/ngx_http_v2_filter_module.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/src/http/v2/ngx_http_v2_filter_module.c b/src/http/v2/ngx_http_v2_filter_module.c
index 907906a88..6b73b1e68 100644
--- a/src/http/v2/ngx_http_v2_filter_module.c
+++ b/src/http/v2/ngx_http_v2_filter_module.c
@@ -32,7 +32,8 @@ static ngx_int_t ngx_http_v2_early_hints_filter(ngx_http_request_t *r);
 static ngx_int_t ngx_http_v2_init_stream(ngx_http_request_t *r);
 
 static ngx_http_v2_out_frame_t *ngx_http_v2_create_headers_frame(
-    ngx_http_request_t *r, u_char *pos, u_char *end, ngx_uint_t fin);
+    ngx_http_request_t *r, u_char *pos, u_char *end, ngx_uint_t fin,
+    ngx_uint_t flush);
 static ngx_http_v2_out_frame_t *ngx_http_v2_create_trailers_frame(
     ngx_http_request_t *r);
 
@@ -609,7 +610,7 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
     fin = r->header_only
           || (r->headers_out.content_length_n == 0 && !r->expect_trailers);
 
-    frame = ngx_http_v2_create_headers_frame(r, start, pos, fin);
+    frame = ngx_http_v2_create_headers_frame(r, start, pos, fin, 0);
     if (frame == NULL) {
         return NGX_ERROR;
     }
@@ -774,7 +775,7 @@ ngx_http_v2_early_hints_filter(ngx_http_request_t *r)
                                       header[i].value.len, tmp);
     }
 
-    frame = ngx_http_v2_create_headers_frame(r, start, pos, 0);
+    frame = ngx_http_v2_create_headers_frame(r, start, pos, 0, 1);
     if (frame == NULL) {
         return NGX_ERROR;
     }
@@ -825,7 +826,7 @@ ngx_http_v2_init_stream(ngx_http_request_t *r)
 
 static ngx_http_v2_out_frame_t *
 ngx_http_v2_create_headers_frame(ngx_http_request_t *r, u_char *pos,
-    u_char *end, ngx_uint_t fin)
+    u_char *end, ngx_uint_t fin, ngx_uint_t flush)
 {
     u_char                    type, flags;
     size_t                    rest, frame_size;
@@ -916,6 +917,7 @@ ngx_http_v2_create_headers_frame(ngx_http_request_t *r, u_char *pos,
         }
 
         b->last_buf = fin;
+        b->flush = flush;
         cl->next = NULL;
         frame->last = cl;
 
@@ -1038,7 +1040,7 @@ ngx_http_v2_create_trailers_frame(ngx_http_request_t *r)
                                       header[i].value.len, tmp);
     }
 
-    return ngx_http_v2_create_headers_frame(r, start, pos, 1);
+    return ngx_http_v2_create_headers_frame(r, start, pos, 1, 0);
 }