[PATCH 10 of 10] Upstream: fixed parsing of split status lines

[Maxim Dounin]

# HG changeset patch
# User Sergey Kandaurov <pluknet at nginx.com>
# Date 1777489340 -14400
#      Wed Apr 29 23:02:20 2026 +0400
# Node ID b454cd489cfd4e42ba3d45e0f34587bedd6cd463
# Parent  f4515f0ba7bcf8f0c7ed6e4e2024c051b39c31f1
Upstream: fixed parsing of split status lines.

If the first response line was split across reads and it didn't appear
a status line, the portion already processed was lost.  The change
introduces a new field for proper backtracking on status line fallback.

Obtained from (with minor changes):
https://github.com/nginx/nginx/commit/5f86648ef8c969e98aa2f7b938472296b12055be

diff --git a/src/http/modules/ngx_http_proxy_module.c b/src/http/modules/ngx_http_proxy_module.c
--- a/src/http/modules/ngx_http_proxy_module.c
+++ b/src/http/modules/ngx_http_proxy_module.c
@@ -1862,6 +1862,8 @@ ngx_http_proxy_process_status_line(ngx_h
         u->headers_in.status_n = 200;
         u->headers_in.connection_close = 1;
 
+        u->buffer.pos = ctx->status.line_start;
+
         return NGX_OK;
     }
 
diff --git a/src/http/modules/ngx_http_scgi_module.c b/src/http/modules/ngx_http_scgi_module.c
--- a/src/http/modules/ngx_http_scgi_module.c
+++ b/src/http/modules/ngx_http_scgi_module.c
@@ -1016,6 +1016,7 @@ ngx_http_scgi_process_status_line(ngx_ht
 
     if (rc == NGX_ERROR) {
         u->process_header = ngx_http_scgi_process_header;
+        u->buffer.pos = status->line_start;
         r->state = 0;
         return ngx_http_scgi_process_header(r);
     }
diff --git a/src/http/modules/ngx_http_uwsgi_module.c b/src/http/modules/ngx_http_uwsgi_module.c
--- a/src/http/modules/ngx_http_uwsgi_module.c
+++ b/src/http/modules/ngx_http_uwsgi_module.c
@@ -1245,6 +1245,7 @@ ngx_http_uwsgi_process_status_line(ngx_h
 
     if (rc == NGX_ERROR) {
         u->process_header = ngx_http_uwsgi_process_header;
+        u->buffer.pos = status->line_start;
         r->state = 0;
         return ngx_http_uwsgi_process_header(r);
     }
diff --git a/src/http/ngx_http.h b/src/http/ngx_http.h
--- a/src/http/ngx_http.h
+++ b/src/http/ngx_http.h
@@ -72,6 +72,7 @@ struct ngx_http_chunked_s {
 typedef struct {
     ngx_uint_t           http_version;
     ngx_uint_t           code;
+    u_char              *line_start;
     u_char              *start;
     u_char              *end;
 } ngx_http_status_t;
diff --git a/src/http/ngx_http_parse.c b/src/http/ngx_http_parse.c
--- a/src/http/ngx_http_parse.c
+++ b/src/http/ngx_http_parse.c
@@ -1663,6 +1663,8 @@ ngx_http_parse_status_line(ngx_http_requ
 
         /* "HTTP/" */
         case sw_start:
+            status->line_start = p;
+
             switch (ch) {
             case 'H':
                 state = sw_H;