[PATCH 13 of 31] Gzip filter: handle empty flush buffers

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1309184986 -14400
# Node ID 3d27d8f8ccb38fb59bb9b5a613dc0c1c8a01a507
# Parent  f17d4d2f60c125d977233e9c4998459499006c32
Gzip filter: handle empty flush buffers.

Empty flush buffers are legitimate and may happen e.g. due to $r->flush()
calls in embedded perl.  If there are no data buffered in zlib deflate()
will return Z_BUF_ERROR (i.e. no progress possible) without adding anything
to output.  Don't treat Z_BUF_ERROR as fatal and correctly send empty flush
buffer if we have no data in output at all.

See this thread for details:

http://nginx.org/pipermail/nginx/2010-November/023693.html

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
@@ -758,6 +758,7 @@ static ngx_int_t
 ngx_http_gzip_filter_deflate(ngx_http_request_t *r, ngx_http_gzip_ctx_t *ctx)
 {
     int                    rc;
+    ngx_buf_t             *b;
     ngx_chain_t           *cl;
     ngx_http_gzip_conf_t  *conf;
 
@@ -769,7 +770,7 @@ ngx_http_gzip_filter_deflate(ngx_http_re
 
     rc = deflate(&ctx->zstream, ctx->flush);
 
-    if (rc != Z_OK && rc != Z_STREAM_END) {
+    if (rc != Z_OK && rc != Z_STREAM_END && rc != Z_BUF_ERROR) {
         ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
                       "deflate() failed: %d, %d", ctx->flush, rc);
         return NGX_ERROR;
@@ -818,8 +819,6 @@ ngx_http_gzip_filter_deflate(ngx_http_re
 
     if (ctx->flush == Z_SYNC_FLUSH) {
 
-        ctx->zstream.avail_out = 0;
-        ctx->out_buf->flush = 1;
         ctx->flush = Z_NO_FLUSH;
 
         cl = ngx_alloc_chain_link(r->pool);
@@ -827,7 +826,22 @@ ngx_http_gzip_filter_deflate(ngx_http_re
             return NGX_ERROR;
         }
 
-        cl->buf = ctx->out_buf;
+        b = ctx->out_buf;
+
+        if (ngx_buf_size(b) == 0) {
+
+            b = ngx_calloc_buf(ctx->request->pool);
+            if (b == NULL) {
+                return NGX_ERROR;
+            }
+
+        } else {
+            ctx->zstream.avail_out = 0;
+        }
+
+        b->flush = 1;
+
+        cl->buf = b;
         cl->next = NULL;
         *ctx->last_out = cl;
         ctx->last_out = &cl->next;