From 2c3719b676d1ebae19645a64721aef7d4baa0403 Mon Sep 17 00:00:00 2001
From: Maxim Dounin <mdounin@mdounin.ru>
Date: Sat, 28 Jan 2023 05:23:33 +0300
Subject: [PATCH] Fixed "zero size buf" alerts with subrequests.

Since 4611:2b6cb7528409 responses from the gzip static, flv, and mp4 modules
can be used with subrequests, though empty files were not properly handled.
Empty gzipped, flv, and mp4 files thus resulted in "zero size buf in output"
alerts.  While valid corresponding files are not expected to be empty, such
files shouldn't result in alerts.

Fix is to set b->sync on such empty subrequest responses, similarly to what
ngx_http_send_special() does.

Additionally, the static module, the ngx_http_send_response() function, and
file cache are modified to do the same instead of not sending the response
body at all in such cases, since not sending the response body at all is
believed to be at least questionable, and might break various filters
which do not expect such behaviour.
---
 src/http/modules/ngx_http_flv_module.c         | 1 +
 src/http/modules/ngx_http_gzip_static_module.c | 1 +
 src/http/modules/ngx_http_mp4_module.c         | 1 +
 src/http/modules/ngx_http_static_module.c      | 5 +----
 src/http/ngx_http_core_module.c                | 5 +----
 src/http/ngx_http_file_cache.c                 | 5 +----
 6 files changed, 6 insertions(+), 12 deletions(-)

diff --git a/src/http/modules/ngx_http_flv_module.c b/src/http/modules/ngx_http_flv_module.c
index a7ee53cbb..ef2bff433 100644
--- a/src/http/modules/ngx_http_flv_module.c
+++ b/src/http/modules/ngx_http_flv_module.c
@@ -235,6 +235,7 @@ ngx_http_flv_handler(ngx_http_request_t *r)
     b->in_file = b->file_last ? 1 : 0;
     b->last_buf = (r == r->main) ? 1 : 0;
     b->last_in_chain = 1;
+    b->sync = (b->last_buf || b->in_file) ? 0 : 1;
 
     b->file->fd = of.fd;
     b->file->name = path;
diff --git a/src/http/modules/ngx_http_gzip_static_module.c b/src/http/modules/ngx_http_gzip_static_module.c
index 0ab14636e..91b38d17b 100644
--- a/src/http/modules/ngx_http_gzip_static_module.c
+++ b/src/http/modules/ngx_http_gzip_static_module.c
@@ -273,6 +273,7 @@ ngx_http_gzip_static_handler(ngx_http_request_t *r)
     b->in_file = b->file_last ? 1 : 0;
     b->last_buf = (r == r->main) ? 1 : 0;
     b->last_in_chain = 1;
+    b->sync = (b->last_buf || b->in_file) ? 0 : 1;
 
     b->file->fd = of.fd;
     b->file->name = path;
diff --git a/src/http/modules/ngx_http_mp4_module.c b/src/http/modules/ngx_http_mp4_module.c
index 75a7315f9..03175dea2 100644
--- a/src/http/modules/ngx_http_mp4_module.c
+++ b/src/http/modules/ngx_http_mp4_module.c
@@ -714,6 +714,7 @@ ngx_http_mp4_handler(ngx_http_request_t *r)
     b->in_file = b->file_last ? 1 : 0;
     b->last_buf = (r == r->main) ? 1 : 0;
     b->last_in_chain = 1;
+    b->sync = (b->last_buf || b->in_file) ? 0 : 1;
 
     b->file->fd = of.fd;
     b->file->name = path;
diff --git a/src/http/modules/ngx_http_static_module.c b/src/http/modules/ngx_http_static_module.c
index 3e65edfdb..8b0bb1478 100644
--- a/src/http/modules/ngx_http_static_module.c
+++ b/src/http/modules/ngx_http_static_module.c
@@ -238,10 +238,6 @@ ngx_http_static_handler(ngx_http_request_t *r)
         return NGX_HTTP_INTERNAL_SERVER_ERROR;
     }
 
-    if (r != r->main && of.size == 0) {
-        return ngx_http_send_header(r);
-    }
-
     r->allow_ranges = 1;
 
     /* we need to allocate all before the header would be sent */
@@ -268,6 +264,7 @@ ngx_http_static_handler(ngx_http_request_t *r)
     b->in_file = b->file_last ? 1 : 0;
     b->last_buf = (r == r->main) ? 1 : 0;
     b->last_in_chain = 1;
+    b->sync = (b->last_buf || b->in_file) ? 0 : 1;
 
     b->file->fd = of.fd;
     b->file->name = path;
diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 6b1cb4fa4..2140e0627 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -1803,10 +1803,6 @@ ngx_http_send_response(ngx_http_request_t *r, ngx_uint_t status,
         }
     }
 
-    if (r != r->main && val.len == 0) {
-        return ngx_http_send_header(r);
-    }
-
     b = ngx_calloc_buf(r->pool);
     if (b == NULL) {
         return NGX_HTTP_INTERNAL_SERVER_ERROR;
@@ -1817,6 +1813,7 @@ ngx_http_send_response(ngx_http_request_t *r, ngx_uint_t status,
     b->memory = val.len ? 1 : 0;
     b->last_buf = (r == r->main) ? 1 : 0;
     b->last_in_chain = 1;
+    b->sync = (b->last_buf || b->memory) ? 0 : 1;
 
     out.buf = b;
     out.next = NULL;
diff --git a/src/http/ngx_http_file_cache.c b/src/http/ngx_http_file_cache.c
index 8db24f103..aa5fd1917 100644
--- a/src/http/ngx_http_file_cache.c
+++ b/src/http/ngx_http_file_cache.c
@@ -1575,10 +1575,6 @@ ngx_http_cache_send(ngx_http_request_t *r)
     ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                    "http file cache send: %s", c->file.name.data);
 
-    if (r != r->main && c->length - c->body_start == 0) {
-        return ngx_http_send_header(r);
-    }
-
     /* we need to allocate all before the header would be sent */
 
     b = ngx_calloc_buf(r->pool);
@@ -1603,6 +1599,7 @@ ngx_http_cache_send(ngx_http_request_t *r)
     b->in_file = (c->length - c->body_start) ? 1 : 0;
     b->last_buf = (r == r->main) ? 1 : 0;
     b->last_in_chain = 1;
+    b->sync = (b->last_buf || b->in_file) ? 0 : 1;
 
     b->file->fd = c->file.fd;
     b->file->name = c->file.name;