Optimized chain link usage (ticket #2614).

Previously chain links could sometimes be dropped instead of being reused,
which could result in increased memory consumption during long requests.

A similar chain link issue in ngx_http_gzip_filter_module was fixed in
da46bfc484ef (1.11.10).

Based on a patch by Sangmin Lee.

src/core/ngx_output_chain.c

@@ -117,7 +117,10 @@ ngx_output_chain(ngx_output_chain_ctx_t *ctx, ngx_chain_t *in)
 
                 ngx_debug_point();
 
-                ctx->in = ctx->in->next;
+                cl = ctx->in;
+                ctx->in = cl->next;
+
+                ngx_free_chain(ctx->pool, cl);
 
                 continue;
             }
@@ -203,7 +206,10 @@ ngx_output_chain(ngx_output_chain_ctx_t *ctx, ngx_chain_t *in)
             /* delete the completed buf from the ctx->in chain */
 
             if (ngx_buf_size(ctx->in->buf) == 0) {
-                ctx->in = ctx->in->next;
+                cl = ctx->in;
+                ctx->in = cl->next;
+
+                ngx_free_chain(ctx->pool, cl);
             }
 
             cl = ngx_alloc_chain_link(ctx->pool);

src/http/modules/ngx_http_grpc_module.c

@@ -1231,7 +1231,7 @@ ngx_http_grpc_body_output_filter(void *data, ngx_chain_t *in)
     ngx_buf_t              *b;
     ngx_int_t               rc;
     ngx_uint_t              next, last;
-    ngx_chain_t            *cl, *out, **ll;
+    ngx_chain_t            *cl, *out, *ln, **ll;
     ngx_http_upstream_t    *u;
     ngx_http_grpc_ctx_t    *ctx;
     ngx_http_grpc_frame_t  *f;
@@ -1459,7 +1459,10 @@ ngx_http_grpc_body_output_filter(void *data, ngx_chain_t *in)
             last = 1;
         }
 
+        ln = in;
         in = in->next;
+
+        ngx_free_chain(r->pool, ln);
     }
 
     ctx->in = in;

src/http/modules/ngx_http_gunzip_filter_module.c

@@ -333,6 +333,8 @@ static ngx_int_t
 ngx_http_gunzip_filter_add_data(ngx_http_request_t *r,
     ngx_http_gunzip_ctx_t *ctx)
 {
+    ngx_chain_t  *cl;
+
     if (ctx->zstream.avail_in || ctx->flush != Z_NO_FLUSH || ctx->redo) {
         return NGX_OK;
     }
@@ -344,8 +346,11 @@ ngx_http_gunzip_filter_add_data(ngx_http_request_t *r,
         return NGX_DECLINED;
     }
 
-    ctx->in_buf = ctx->in->buf;
+    cl = ctx->in;
-    ctx->in = ctx->in->next;
+    ctx->in_buf = cl->buf;
+    ctx->in = cl->next;
+
+    ngx_free_chain(r->pool, cl);
 
     ctx->zstream.next_in = ctx->in_buf->pos;
     ctx->zstream.avail_in = ctx->in_buf->last - ctx->in_buf->pos;
@@ -374,6 +379,7 @@ static ngx_int_t
 ngx_http_gunzip_filter_get_buf(ngx_http_request_t *r,
     ngx_http_gunzip_ctx_t *ctx)
 {
+    ngx_chain_t             *cl;
     ngx_http_gunzip_conf_t  *conf;
 
     if (ctx->zstream.avail_out) {
@@ -383,8 +389,12 @@ ngx_http_gunzip_filter_get_buf(ngx_http_request_t *r,
     conf = ngx_http_get_module_loc_conf(r, ngx_http_gunzip_filter_module);
 
     if (ctx->free) {
-        ctx->out_buf = ctx->free->buf;
+
-        ctx->free = ctx->free->next;
+        cl = ctx->free;
+        ctx->out_buf = cl->buf;
+        ctx->free = cl->next;
+
+        ngx_free_chain(r->pool, cl);
 
         ctx->out_buf->flush = 0;
 

src/http/modules/ngx_http_gzip_filter_module.c

@@ -985,10 +985,14 @@ static void
 ngx_http_gzip_filter_free_copy_buf(ngx_http_request_t *r,
     ngx_http_gzip_ctx_t *ctx)
 {
-    ngx_chain_t  *cl;
+    ngx_chain_t  *cl, *ln;
 
-    for (cl = ctx->copied; cl; cl = cl->next) {
+    for (cl = ctx->copied; cl; /* void */) {
-        ngx_pfree(r->pool, cl->buf->start);
+        ln = cl;
+        cl = cl->next;
+
+        ngx_pfree(r->pool, ln->buf->start);
+        ngx_free_chain(r->pool, ln);
     }
 
     ctx->copied = NULL;

src/http/modules/ngx_http_ssi_filter_module.c

@@ -482,9 +482,13 @@ ngx_http_ssi_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
     while (ctx->in || ctx->buf) {
 
         if (ctx->buf == NULL) {
-            ctx->buf = ctx->in->buf;
+
-            ctx->in = ctx->in->next;
+            cl = ctx->in;
+            ctx->buf = cl->buf;
+            ctx->in = cl->next;
             ctx->pos = ctx->buf->pos;
+
+            ngx_free_chain(r->pool, cl);
         }
 
         if (ctx->state == ssi_start_state) {

src/http/modules/ngx_http_sub_filter_module.c

@@ -335,9 +335,13 @@ ngx_http_sub_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
     while (ctx->in || ctx->buf) {
 
         if (ctx->buf == NULL) {
-            ctx->buf = ctx->in->buf;
+
-            ctx->in = ctx->in->next;
+            cl = ctx->in;
+            ctx->buf = cl->buf;
+            ctx->in = cl->next;
             ctx->pos = ctx->buf->pos;
+
+            ngx_free_chain(r->pool, cl);
         }
 
         if (ctx->buf->flush || ctx->buf->recycled) {