HTTP/3: server pushes.

New directives are added:
- http3_max_concurrent_pushes
- http3_push
- http3_push_preload

1 files changed, 697 insertions, 7 deletions

diff --git a/src/http/v3/ngx_http_v3_request.c b/src/http/v3/ngx_http_v3_request.c
index adc40d368..a0259be11 100644
--- a/src/http/v3/ngx_http_v3_request.c
+++ b/src/http/v3/ngx_http_v3_request.c
@@ -11,18 +11,37 @@
 
 
 /* static table indices */
+#define NGX_HTTP_V3_HEADER_AUTHORITY                 0
+#define NGX_HTTP_V3_HEADER_PATH_ROOT                 1
 #define NGX_HTTP_V3_HEADER_CONTENT_LENGTH_ZERO       4
 #define NGX_HTTP_V3_HEADER_DATE                      6
 #define NGX_HTTP_V3_HEADER_LAST_MODIFIED             10
 #define NGX_HTTP_V3_HEADER_LOCATION                  12
+#define NGX_HTTP_V3_HEADER_METHOD_GET                17
+#define NGX_HTTP_V3_HEADER_SCHEME_HTTP               22
+#define NGX_HTTP_V3_HEADER_SCHEME_HTTPS              23
 #define NGX_HTTP_V3_HEADER_STATUS_200                25
+#define NGX_HTTP_V3_HEADER_ACCEPT_ENCODING           31
 #define NGX_HTTP_V3_HEADER_CONTENT_TYPE_TEXT_PLAIN   53
 #define NGX_HTTP_V3_HEADER_VARY_ACCEPT_ENCODING      59
+#define NGX_HTTP_V3_HEADER_ACCEPT_LANGUAGE           72
 #define NGX_HTTP_V3_HEADER_SERVER                    92
+#define NGX_HTTP_V3_HEADER_USER_AGENT                95
 
 
 static ngx_int_t ngx_http_v3_process_pseudo_header(ngx_http_request_t *r,
     ngx_str_t *name, ngx_str_t *value);
+static ngx_int_t ngx_http_v3_push_resources(ngx_http_request_t *r,
+    ngx_chain_t ***out);
+static ngx_int_t ngx_http_v3_push_resource(ngx_http_request_t *r,
+    ngx_str_t *path, ngx_chain_t ***out);
+static ngx_int_t ngx_http_v3_create_push_request(
+    ngx_http_request_t *pr, ngx_str_t *path, uint64_t push_id);
+static ngx_int_t ngx_http_v3_set_push_header(ngx_http_request_t *r,
+    const char *name, ngx_str_t *value);
+static void ngx_http_v3_push_request_handler(ngx_event_t *ev);
+static ngx_chain_t *ngx_http_v3_create_push_promise(ngx_http_request_t *r,
+    ngx_str_t *path, uint64_t push_id);
 
 
 struct {
@@ -431,7 +450,7 @@ ngx_http_v3_create_header(ngx_http_request_t *r)
     ngx_buf_t                 *b;
     ngx_str_t                  host;
     ngx_uint_t                 i, port;
-    ngx_chain_t               *hl, *cl, *bl;
+    ngx_chain_t               *out, *hl, *cl, **ll;
     ngx_list_part_t           *part;
     ngx_table_elt_t           *header;
     ngx_connection_t          *c;
@@ -443,6 +462,17 @@ ngx_http_v3_create_header(ngx_http_request_t *r)
 
     ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "http3 create header");
 
+    out = NULL;
+    ll = &out;
+
+    if ((c->qs->id & NGX_QUIC_STREAM_UNIDIRECTIONAL) == 0
+        && r->method != NGX_HTTP_HEAD)
+    {
+        if (ngx_http_v3_push_resources(r, &ll) != NGX_OK) {
+            return NULL;
+        }
+    }
+
     len = ngx_http_v3_encode_header_block_prefix(NULL, 0, 0, 0);
 
     if (r->headers_out.status == NGX_HTTP_OK) {
@@ -796,6 +826,9 @@ ngx_http_v3_create_header(ngx_http_request_t *r)
     hl->buf = b;
     hl->next = cl;
 
+    *ll = hl;
+    ll = &cl->next;
+
     if (r->headers_out.content_length_n >= 0 && !r->header_only) {
         len = ngx_http_v3_encode_varlen_int(NULL, NGX_HTTP_V3_FRAME_DATA)
               + ngx_http_v3_encode_varlen_int(NULL,
@@ -811,17 +844,18 @@ ngx_http_v3_create_header(ngx_http_request_t *r)
         b->last = (u_char *) ngx_http_v3_encode_varlen_int(b->last,
                                               r->headers_out.content_length_n);
 
-        bl = ngx_alloc_chain_link(c->pool);
-        if (bl == NULL) {
+        cl = ngx_alloc_chain_link(c->pool);
+        if (cl == NULL) {
             return NULL;
         }
 
-        bl->buf = b;
-        bl->next = NULL;
-        cl->next = bl;
+        cl->buf = b;
+        cl->next = NULL;
+
+        *ll = cl;
     }
 
-    return hl;
+    return out;
 }
 
 
@@ -853,3 +887,659 @@ ngx_http_v3_create_trailers(ngx_http_request_t *r)
 
     return cl;
 }
+
+
+static ngx_int_t
+ngx_http_v3_push_resources(ngx_http_request_t *r, ngx_chain_t ***out)
+{
+    u_char                     *start, *end, *last;
+    ngx_str_t                   path;
+    ngx_int_t                   rc;
+    ngx_uint_t                  i, push;
+    ngx_table_elt_t           **h;
+    ngx_http_v3_loc_conf_t     *h3lcf;
+    ngx_http_complex_value_t   *pushes;
+
+    h3lcf = ngx_http_get_module_loc_conf(r, ngx_http_v3_module);
+
+    if (h3lcf->pushes) {
+        pushes = h3lcf->pushes->elts;
+
+        for (i = 0; i < h3lcf->pushes->nelts; i++) {
+
+            if (ngx_http_complex_value(r, &pushes[i], &path) != NGX_OK) {
+                return NGX_ERROR;
+            }
+
+            if (path.len == 0) {
+                continue;
+            }
+
+            if (path.len == 3 && ngx_strncmp(path.data, "off", 3) == 0) {
+                continue;
+            }
+
+            rc = ngx_http_v3_push_resource(r, &path, out);
+
+            if (rc == NGX_ERROR) {
+                return NGX_ERROR;
+            }
+
+            if (rc == NGX_ABORT) {
+                return NGX_OK;
+            }
+
+            /* NGX_OK, NGX_DECLINED */
+        }
+    }
+
+    if (!h3lcf->push_preload) {
+        return NGX_OK;
+    }
+
+    h = r->headers_out.link.elts;
+
+    for (i = 0; i < r->headers_out.link.nelts; i++) {
+
+        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                       "http3 parse link: \"%V\"", &h[i]->value);
+
+        start = h[i]->value.data;
+        end = h[i]->value.data + h[i]->value.len;
+
+    next_link:
+
+        while (start < end && *start == ' ') { start++; }
+
+        if (start == end || *start++ != '<') {
+            continue;
+        }
+
+        while (start < end && *start == ' ') { start++; }
+
+        for (last = start; last < end && *last != '>'; last++) {
+            /* void */
+        }
+
+        if (last == start || last == end) {
+            continue;
+        }
+
+        path.len = last - start;
+        path.data = start;
+
+        start = last + 1;
+
+        while (start < end && *start == ' ') { start++; }
+
+        if (start == end) {
+            continue;
+        }
+
+        if (*start == ',') {
+            start++;
+            goto next_link;
+        }
+
+        if (*start++ != ';') {
+            continue;
+        }
+
+        last = ngx_strlchr(start, end, ',');
+
+        if (last == NULL) {
+            last = end;
+        }
+
+        push = 0;
+
+        for ( ;; ) {
+
+            while (start < last && *start == ' ') { start++; }
+
+            if (last - start >= 6
+                && ngx_strncasecmp(start, (u_char *) "nopush", 6) == 0)
+            {
+                start += 6;
+
+                if (start == last || *start == ' ' || *start == ';') {
+                    push = 0;
+                    break;
+                }
+
+                goto next_param;
+            }
+
+            if (last - start >= 11
+                && ngx_strncasecmp(start, (u_char *) "rel=preload", 11) == 0)
+            {
+                start += 11;
+
+                if (start == last || *start == ' ' || *start == ';') {
+                    push = 1;
+                }
+
+                goto next_param;
+            }
+
+            if (last - start >= 4
+                && ngx_strncasecmp(start, (u_char *) "rel=", 4) == 0)
+            {
+                start += 4;
+
+                while (start < last && *start == ' ') { start++; }
+
+                if (start == last || *start++ != '"') {
+                    goto next_param;
+                }
+
+                for ( ;; ) {
+
+                    while (start < last && *start == ' ') { start++; }
+
+                    if (last - start >= 7
+                        && ngx_strncasecmp(start, (u_char *) "preload", 7) == 0)
+                    {
+                        start += 7;
+
+                        if (start < last && (*start == ' ' || *start == '"')) {
+                            push = 1;
+                            break;
+                        }
+                    }
+
+                    while (start < last && *start != ' ' && *start != '"') {
+                        start++;
+                    }
+
+                    if (start == last) {
+                        break;
+                    }
+
+                    if (*start == '"') {
+                        break;
+                    }
+
+                    start++;
+                }
+            }
+
+        next_param:
+
+            start = ngx_strlchr(start, last, ';');
+
+            if (start == NULL) {
+                break;
+            }
+
+            start++;
+        }
+
+        if (push) {
+            while (path.len && path.data[path.len - 1] == ' ') {
+                path.len--;
+            }
+        }
+
+        if (push && path.len
+            && !(path.len > 1 && path.data[0] == '/' && path.data[1] == '/'))
+        {
+            rc = ngx_http_v3_push_resource(r, &path, out);
+
+            if (rc == NGX_ERROR) {
+                return NGX_ERROR;
+            }
+
+            if (rc == NGX_ABORT) {
+                return NGX_OK;
+            }
+
+            /* NGX_OK, NGX_DECLINED */
+        }
+
+        if (last < end) {
+            start = last + 1;
+            goto next_link;
+        }
+    }
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
+ngx_http_v3_push_resource(ngx_http_request_t *r, ngx_str_t *path,
+    ngx_chain_t ***ll)
+{
+    uint64_t                   push_id;
+    ngx_int_t                  rc;
+    ngx_chain_t               *cl;
+    ngx_connection_t          *c;
+    ngx_http_v3_srv_conf_t    *h3scf;
+    ngx_http_v3_connection_t  *h3c;
+
+    c = r->connection;
+    h3c = c->qs->parent->data;
+    h3scf = ngx_http_get_module_srv_conf(r, ngx_http_v3_module);
+
+    ngx_log_debug5(NGX_LOG_DEBUG_HTTP, c->log, 0,
+                   "http3 push \"%V\" pushing:%ui/%ui id:%uL/%uL",
+                   path, h3c->npushing, h3scf->max_concurrent_pushes,
+                   h3c->next_push_id, h3c->max_push_id);
+
+    if (!ngx_path_separator(path->data[0])) {
+        ngx_log_error(NGX_LOG_WARN, c->log, 0,
+                      "non-absolute path \"%V\" not pushed", path);
+        return NGX_DECLINED;
+    }
+
+    if (h3c->next_push_id > h3c->max_push_id) {
+        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
+                       "http3 abort pushes due to max_push_id");
+        return NGX_ABORT;
+    }
+
+    if (h3c->npushing >= h3scf->max_concurrent_pushes) {
+        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0,
+                       "http3 abort pushes due to max_concurrent_pushes");
+        return NGX_ABORT;
+    }
+
+    push_id = h3c->next_push_id++;
+
+    rc = ngx_http_v3_create_push_request(r, path, push_id);
+    if (rc != NGX_OK) {
+        return rc;
+    }
+
+    cl = ngx_http_v3_create_push_promise(r, path, push_id);
+    if (cl == NULL) {
+        return NGX_ERROR;
+    }
+
+    for (**ll = cl; **ll; *ll = &(**ll)->next);
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t
+ngx_http_v3_create_push_request(ngx_http_request_t *pr, ngx_str_t *path,
+    uint64_t push_id)
+{
+    ngx_pool_t                *pool;
+    ngx_connection_t          *c, *pc;
+    ngx_http_request_t        *r;
+    ngx_http_log_ctx_t        *ctx;
+    ngx_http_connection_t     *hc;
+    ngx_http_core_srv_conf_t  *cscf;
+    ngx_http_v3_connection_t  *h3c;
+
+    pc = pr->connection;
+
+    r = NULL;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, pc->log, 0,
+                   "http3 create push request id:%uL", push_id);
+
+    c = ngx_http_v3_create_push_stream(pc, push_id);
+    if (c == NULL) {
+        return NGX_ABORT;
+    }
+
+    hc = ngx_palloc(c->pool, sizeof(ngx_http_connection_t));
+    if (hc == NULL) {
+        goto failed;
+    }
+
+    h3c = c->qs->parent->data;
+    ngx_memcpy(hc, h3c, sizeof(ngx_http_connection_t));
+    c->data = hc;
+
+    ctx = ngx_palloc(c->pool, sizeof(ngx_http_log_ctx_t));
+    if (ctx == NULL) {
+        goto failed;
+    }
+
+    ctx->connection = c;
+    ctx->request = NULL;
+    ctx->current_request = NULL;
+
+    c->log->handler = ngx_http_log_error;
+    c->log->data = ctx;
+    c->log->action = "processing pushed request headers";
+
+    c->log_error = NGX_ERROR_INFO;
+
+    r = ngx_http_create_request(c);
+    if (r == NULL) {
+        goto failed;
+    }
+
+    c->data = r;
+
+    ngx_str_set(&r->http_protocol, "HTTP/3.0");
+
+    r->method_name = ngx_http_core_get_method;
+    r->method = NGX_HTTP_GET;
+
+    cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
+
+    r->header_in = ngx_create_temp_buf(r->pool,
+                                       cscf->client_header_buffer_size);
+    if (r->header_in == NULL) {
+        goto failed;
+    }
+
+    if (ngx_list_init(&r->headers_in.headers, r->pool, 4,
+                      sizeof(ngx_table_elt_t))
+        != NGX_OK)
+    {
+        goto failed;
+    }
+
+    r->headers_in.connection_type = NGX_HTTP_CONNECTION_CLOSE;
+
+    r->schema.data = ngx_pstrdup(r->pool, &pr->schema);
+    if (r->schema.data == NULL) {
+        goto failed;
+    }
+
+    r->schema.len = pr->schema.len;
+
+    r->uri_start = ngx_pstrdup(r->pool, path);
+    if (r->uri_start == NULL) {
+        goto failed;
+    }
+
+    r->uri_end = r->uri_start + path->len;
+
+    if (ngx_http_parse_uri(r) != NGX_OK) {
+        goto failed;
+    }
+
+    if (ngx_http_process_request_uri(r) != NGX_OK) {
+        goto failed;
+    }
+
+    if (ngx_http_v3_set_push_header(r, "host", &pr->headers_in.server)
+        != NGX_OK)
+    {
+        goto failed;
+    }
+
+    if (pr->headers_in.accept_encoding) {
+        if (ngx_http_v3_set_push_header(r, "accept-encoding",
+                                        &pr->headers_in.accept_encoding->value)
+            != NGX_OK)
+        {
+            goto failed;
+        }
+    }
+
+    if (pr->headers_in.accept_language) {
+        if (ngx_http_v3_set_push_header(r, "accept-language",
+                                        &pr->headers_in.accept_language->value)
+            != NGX_OK)
+        {
+            goto failed;
+        }
+    }
+
+    if (pr->headers_in.user_agent) {
+        if (ngx_http_v3_set_push_header(r, "user-agent",
+                                        &pr->headers_in.user_agent->value)
+            != NGX_OK)
+        {
+            goto failed;
+        }
+    }
+
+    c->read->handler = ngx_http_v3_push_request_handler;
+    c->read->handler = ngx_http_v3_push_request_handler;
+
+    ngx_post_event(c->read, &ngx_posted_events);
+
+    return NGX_OK;
+
+failed:
+
+    if (r) {
+        ngx_http_free_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
+    }
+
+    c->destroyed = 1;
+
+    pool = c->pool;
+
+    ngx_close_connection(c);
+
+    ngx_destroy_pool(pool);
+
+    return NGX_ERROR;
+}
+
+
+static ngx_int_t
+ngx_http_v3_set_push_header(ngx_http_request_t *r, const char *name,
+    ngx_str_t *value)
+{
+    u_char                     *p;
+    ngx_table_elt_t            *h;
+    ngx_http_header_t          *hh;
+    ngx_http_core_main_conf_t  *cmcf;
+
+    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "http3 push header \"%s\": \"%V\"", name, value);
+
+    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
+
+    p = ngx_pnalloc(r->pool, value->len + 1);
+    if (p == NULL) {
+        return NGX_ERROR;
+    }
+
+    ngx_memcpy(p, value->data, value->len);
+    p[value->len] = '\0';
+
+    h = ngx_list_push(&r->headers_in.headers);
+    if (h == NULL) {
+        return NGX_ERROR;
+    }
+
+    h->key.data = (u_char *) name;
+    h->key.len = ngx_strlen(name);
+    h->hash = ngx_hash_key(h->key.data, h->key.len);
+    h->lowcase_key = (u_char *) name;
+    h->value.data = p;
+    h->value.len = value->len;
+
+    hh = ngx_hash_find(&cmcf->headers_in_hash, h->hash,
+                       h->lowcase_key, h->key.len);
+
+    if (hh && hh->handler(r, h, hh->offset) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    return NGX_OK;
+}
+
+
+static void
+ngx_http_v3_push_request_handler(ngx_event_t *ev)
+{
+    ngx_connection_t    *c;
+    ngx_http_request_t  *r;
+
+    c = ev->data;
+    r = c->data;
+
+    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "http3 push request handler");
+
+    ngx_http_process_request(r);
+}
+
+
+static ngx_chain_t *
+ngx_http_v3_create_push_promise(ngx_http_request_t *r, ngx_str_t *path,
+    uint64_t push_id)
+{
+    size_t        n, len;
+    ngx_buf_t    *b;
+    ngx_chain_t  *hl, *cl;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "http3 create push promise id:%uL", push_id);
+
+    len = ngx_http_v3_encode_varlen_int(NULL, push_id);
+
+    len += ngx_http_v3_encode_header_block_prefix(NULL, 0, 0, 0);
+
+    len += ngx_http_v3_encode_header_ri(NULL, 0,
+                                        NGX_HTTP_V3_HEADER_METHOD_GET);
+
+    len += ngx_http_v3_encode_header_lri(NULL, 0,
+                                         NGX_HTTP_V3_HEADER_AUTHORITY,
+                                         NULL, r->headers_in.server.len);
+
+    if (path->len == 1 && path->data[0] == '/') {
+        len += ngx_http_v3_encode_header_ri(NULL, 0,
+                                            NGX_HTTP_V3_HEADER_PATH_ROOT);
+
+    } else {
+        len += ngx_http_v3_encode_header_lri(NULL, 0,
+                                             NGX_HTTP_V3_HEADER_PATH_ROOT,
+                                             NULL, path->len);
+    }
+
+    if (r->schema.len == 5 && ngx_strncmp(r->schema.data, "https", 5) == 0) {
+        len += ngx_http_v3_encode_header_ri(NULL, 0,
+                                            NGX_HTTP_V3_HEADER_SCHEME_HTTPS);
+
+    } else if (r->schema.len == 4
+               && ngx_strncmp(r->schema.data, "http", 4) == 0)
+    {
+        len += ngx_http_v3_encode_header_ri(NULL, 0,
+                                            NGX_HTTP_V3_HEADER_SCHEME_HTTP);
+
+    } else {
+        len += ngx_http_v3_encode_header_lri(NULL, 0,
+                                             NGX_HTTP_V3_HEADER_SCHEME_HTTP,
+                                             NULL, r->schema.len);
+    }
+
+    if (r->headers_in.accept_encoding) {
+        len += ngx_http_v3_encode_header_lri(NULL, 0,
+                                     NGX_HTTP_V3_HEADER_ACCEPT_ENCODING, NULL,
+                                     r->headers_in.accept_encoding->value.len);
+    }
+
+    if (r->headers_in.accept_language) {
+        len += ngx_http_v3_encode_header_lri(NULL, 0,
+                                     NGX_HTTP_V3_HEADER_ACCEPT_LANGUAGE, NULL,
+                                     r->headers_in.accept_language->value.len);
+    }
+
+    if (r->headers_in.user_agent) {
+        len += ngx_http_v3_encode_header_lri(NULL, 0,
+                                          NGX_HTTP_V3_HEADER_USER_AGENT, NULL,
+                                          r->headers_in.user_agent->value.len);
+    }
+
+    b = ngx_create_temp_buf(r->pool, len);
+    if (b == NULL) {
+        return NULL;
+    }
+
+    b->last = (u_char *) ngx_http_v3_encode_varlen_int(b->last, push_id);
+
+    b->last = (u_char *) ngx_http_v3_encode_header_block_prefix(b->last,
+                                                                0, 0, 0);
+
+    b->last = (u_char *) ngx_http_v3_encode_header_ri(b->last, 0,
+                                                NGX_HTTP_V3_HEADER_METHOD_GET);
+
+    b->last = (u_char *) ngx_http_v3_encode_header_lri(b->last, 0,
+                                                  NGX_HTTP_V3_HEADER_AUTHORITY,
+                                                  r->headers_in.server.data,
+                                                  r->headers_in.server.len);
+
+    if (path->len == 1 && path->data[0] == '/') {
+        b->last = (u_char *) ngx_http_v3_encode_header_ri(b->last, 0,
+                                                 NGX_HTTP_V3_HEADER_PATH_ROOT);
+
+    } else {
+        b->last = (u_char *) ngx_http_v3_encode_header_lri(b->last, 0,
+                                                  NGX_HTTP_V3_HEADER_PATH_ROOT,
+                                                  path->data, path->len);
+    }
+
+    if (r->schema.len == 5 && ngx_strncmp(r->schema.data, "https", 5) == 0) {
+        b->last = (u_char *) ngx_http_v3_encode_header_ri(b->last, 0,
+                                              NGX_HTTP_V3_HEADER_SCHEME_HTTPS);
+
+    } else if (r->schema.len == 4
+               && ngx_strncmp(r->schema.data, "http", 4) == 0)
+    {
+        b->last = (u_char *) ngx_http_v3_encode_header_ri(b->last, 0,
+                                               NGX_HTTP_V3_HEADER_SCHEME_HTTP);
+
+    } else {
+        b->last = (u_char *) ngx_http_v3_encode_header_lri(b->last, 0,
+                                                NGX_HTTP_V3_HEADER_SCHEME_HTTP,
+                                                r->schema.data, r->schema.len);
+    }
+
+    if (r->headers_in.accept_encoding) {
+        b->last = (u_char *) ngx_http_v3_encode_header_lri(b->last, 0,
+                                     NGX_HTTP_V3_HEADER_ACCEPT_ENCODING,
+                                     r->headers_in.accept_encoding->value.data,
+                                     r->headers_in.accept_encoding->value.len);
+    }
+
+    if (r->headers_in.accept_language) {
+        b->last = (u_char *) ngx_http_v3_encode_header_lri(b->last, 0,
+                                     NGX_HTTP_V3_HEADER_ACCEPT_LANGUAGE,
+                                     r->headers_in.accept_language->value.data,
+                                     r->headers_in.accept_language->value.len);
+    }
+
+    if (r->headers_in.user_agent) {
+        b->last = (u_char *) ngx_http_v3_encode_header_lri(b->last, 0,
+                                          NGX_HTTP_V3_HEADER_USER_AGENT,
+                                          r->headers_in.user_agent->value.data,
+                                          r->headers_in.user_agent->value.len);
+    }
+
+    cl = ngx_alloc_chain_link(r->pool);
+    if (cl == NULL) {
+        return NULL;
+    }
+
+    cl->buf = b;
+    cl->next = NULL;
+
+    n = b->last - b->pos;
+
+    len = ngx_http_v3_encode_varlen_int(NULL, NGX_HTTP_V3_FRAME_PUSH_PROMISE)
+          + ngx_http_v3_encode_varlen_int(NULL, n);
+
+    b = ngx_create_temp_buf(r->pool, len);
+    if (b == NULL) {
+        return NULL;
+    }
+
+    b->last = (u_char *) ngx_http_v3_encode_varlen_int(b->last,
+                                               NGX_HTTP_V3_FRAME_PUSH_PROMISE);
+    b->last = (u_char *) ngx_http_v3_encode_varlen_int(b->last, n);
+
+    hl = ngx_alloc_chain_link(r->pool);
+    if (hl == NULL) {
+        return NULL;
+    }
+
+    hl->buf = b;
+    hl->next = cl;
+
+    return hl;
+}