new file mode 100644
--- /dev/null
+++ b/src/core/ngx_buf.h
@@ -0,0 +1,153 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#ifndef _NGX_BUF_H_INCLUDED_
+#define _NGX_BUF_H_INCLUDED_
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+
+
+typedef void *            ngx_buf_tag_t;
+
+typedef struct ngx_buf_s  ngx_buf_t;
+
+struct ngx_buf_s {
+    u_char          *pos;
+    u_char          *last;
+    off_t            file_pos;
+    off_t            file_last;
+
+    int              type;
+    u_char          *start;         /* start of buffer */
+    u_char          *end;           /* end of buffer */
+    ngx_buf_tag_t    tag;
+    ngx_file_t      *file;
+    ngx_buf_t       *shadow;
+
+
+    /* the buf's content could be changed */
+    unsigned         temporary:1;
+
+    /*
+     * the buf's content is in a memory cache or in a read only memory
+     * and must not be changed
+     */
+    unsigned         memory:1;
+
+    /* the buf's content is mmap()ed and must not be changed */
+    unsigned         mmap:1;
+
+    unsigned         recycled:1;
+    unsigned         in_file:1;
+    unsigned         flush:1;
+    unsigned         last_buf:1;
+
+    unsigned         last_shadow:1;
+    unsigned         temp_file:1;
+
+    unsigned         zerocopy_busy:1;
+
+    /* STUB */ int   num;
+};
+
+
+typedef struct ngx_chain_s       ngx_chain_t;
+
+struct ngx_chain_s {
+    ngx_buf_t    *buf;
+    ngx_chain_t  *next;
+};
+
+
+typedef struct {
+    ngx_int_t    num;
+    size_t       size;
+} ngx_bufs_t;
+
+
+typedef int  (*ngx_output_chain_filter_pt)(void *ctx, ngx_chain_t *out);
+
+typedef struct {
+    ngx_buf_t                   *buf;
+    ngx_chain_t                 *in;
+    ngx_chain_t                 *free;
+    ngx_chain_t                 *busy;
+
+    unsigned                     sendfile;
+    unsigned                     need_in_memory;
+    unsigned                     need_in_temp;
+
+    ngx_pool_t                  *pool;
+    ngx_int_t                    allocated;
+    ngx_bufs_t                   bufs;
+    ngx_buf_tag_t                tag;
+
+    ngx_output_chain_filter_pt   output_filter;
+    void                        *filter_ctx;
+} ngx_output_chain_ctx_t;
+
+
+typedef struct {
+    ngx_chain_t                 *out;
+    ngx_chain_t                **last;
+    ngx_connection_t            *connection;
+    ngx_pool_t                  *pool;
+    off_t                        limit;
+} ngx_chain_writer_ctx_t;
+
+
+#define NGX_CHAIN_ERROR     (ngx_chain_t *) NGX_ERROR
+
+
+#define ngx_buf_in_memory(b)        (b->temporary || b->memory || b->mmap)
+#define ngx_buf_in_memory_only(b)   (ngx_buf_in_memory(b) && !b->in_file)
+#define ngx_buf_special(b)                                                   \
+        ((b->flush || b->last_buf) && !ngx_buf_in_memory(b) && !b->in_file)
+
+#define ngx_buf_size(b)                                                      \
+        (ngx_buf_in_memory(b) ? (size_t) (b->last - b->pos):                 \
+                                (size_t) (b->file_last - b->file_pos))
+
+ngx_buf_t *ngx_create_temp_buf(ngx_pool_t *pool, size_t size);
+ngx_chain_t *ngx_create_chain_of_bufs(ngx_pool_t *pool, ngx_bufs_t *bufs);
+
+
+#define ngx_alloc_buf(pool)  ngx_palloc(pool, sizeof(ngx_buf_t))
+#define ngx_calloc_buf(pool) ngx_pcalloc(pool, sizeof(ngx_buf_t))
+
+
+#define ngx_alloc_chain_link(pool) ngx_palloc(pool, sizeof(ngx_chain_t))
+
+
+#define ngx_alloc_link_and_set_buf(chain, b, pool, error)                    \
+            do {                                                             \
+                ngx_test_null(chain, ngx_alloc_chain_link(pool), error);     \
+                chain->buf = b;                                              \
+                chain->next = NULL;                                          \
+            } while (0);
+
+
+#define ngx_chain_add_link(chain, last, cl)                                  \
+            if (chain) {                                                     \
+                *last = cl;                                                  \
+            } else {                                                         \
+                chain = cl;                                                  \
+            }                                                                \
+            last = &cl->next
+
+
+ngx_int_t ngx_output_chain(ngx_output_chain_ctx_t *ctx, ngx_chain_t *in);
+ngx_int_t ngx_chain_writer(void *data, ngx_chain_t *in);
+
+ngx_int_t ngx_chain_add_copy(ngx_pool_t *pool, ngx_chain_t **chain,
+                             ngx_chain_t *in);
+void ngx_chain_update_chains(ngx_chain_t **free, ngx_chain_t **busy,
+                             ngx_chain_t **out, ngx_buf_tag_t tag);
+
+
+#endif /* _NGX_BUF_H_INCLUDED_ */