details: https://hg.nginx.org/nginx/rev/0ef2bc0ec9c9
branches:
changeset: 7545:0ef2bc0ec9c9
user: Maxim Dounin <mdounin@mdounin.ru>
date: Wed Jul 31 17:29:00 2019 +0300
description:
Gzip: fixed "zero size buf" alerts after ac5a741d39cf.

After ac5a741d39cf it is now possible that after zstream.avail_out
reaches 0 and we allocate additional buffer, there will be no more data
to put into this buffer, triggering "zero size buf" alert. Fix is to
reset b->temporary flag in this case.

Additionally, an optimization added to avoid allocating additional buffer
in this case, by checking if last deflate() call returned Z_STREAM_END.
Note that checking for Z_STREAM_END by itself is not enough to fix alerts,
as deflate() can return Z_STREAM_END without producing any output if the
buffer is smaller than gzip trailer.

Reported by Witold Filipczyk,
http://mailman.nginx.org/pipermail/nginx-devel/2019-July/012469.html.

diffstat:

src/http/modules/ngx_http_gzip_filter_module.c | 15 +++++++++++----
1 files changed, 11 insertions(+), 4 deletions(-)

diffs (43 lines):

diff --git a/src/http/modules/ngx_http_gzip_filter_module.c b/src/http/modules/ngx_http_gzip_filter_module.c
--- a/src/http/modules/ngx_http_gzip_filter_module.c
+++ b/src/http/modules/ngx_http_gzip_filter_module.c
@@ -778,7 +778,7 @@ ngx_http_gzip_filter_deflate(ngx_http_re

ctx->out_buf->last = ctx->zstream.next_out;

- if (ctx->zstream.avail_out == 0) {
+ if (ctx->zstream.avail_out == 0 && rc != Z_STREAM_END) {

/* zlib wants to output some more gzipped data */

@@ -868,6 +868,7 @@ ngx_http_gzip_filter_deflate_end(ngx_htt
ngx_http_gzip_ctx_t *ctx)
{
int rc;
+ ngx_buf_t *b;
ngx_chain_t *cl;

ctx->zin = ctx->zstream.total_in;
@@ -888,13 +889,19 @@ ngx_http_gzip_filter_deflate_end(ngx_htt
return NGX_ERROR;
}

- cl->buf = ctx->out_buf;
+ b = ctx->out_buf;
+
+ if (ngx_buf_size(b) == 0) {
+ b->temporary = 0;
+ }
+
+ b->last_buf = 1;
+
+ cl->buf = b;
cl->next = NULL;
*ctx->last_out = cl;
ctx->last_out = &cl->next;

- ctx->out_buf->last_buf = 1;
-
ctx->zstream.avail_in = 0;
ctx->zstream.avail_out = 0;

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