# HG changeset patch
# User Maxim Dounin <mdounin@mdounin.ru>
# Date 1315324342 -14400
# Node ID 4cf0af103bc382a78f894302d1706929a79df4bb
# Parent  d603ce98fada855f0100b422b7b5672fd22fabea
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://mailman.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;