new file mode 100644
--- /dev/null
+++ b/src/core/ngx_output_chain.c
@@ -0,0 +1,252 @@
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+
+
+#define NGX_NONE      1
+
+
+ngx_inline static int ngx_output_chain_need_to_copy(ngx_output_chain_ctx_t *ctx,
+                                                    ngx_hunk_t *hunk);
+static int ngx_output_chain_copy_hunk(ngx_hunk_t *dst, ngx_hunk_t *src,
+                                      int sendfile);
+
+
+int ngx_output_chain(ngx_output_chain_ctx_t *ctx, ngx_chain_t *in)
+{
+    int           rc, last;
+    ssize_t       size, hsize;
+    ngx_chain_t  *cl, *out, **last_out;
+
+    /*
+     * the short path for the case when the chain ctx->in is empty
+     * and the incoming chain is empty too or it has the single hunk
+     * that does not require the copy
+     */
+
+    if (ctx->in == NULL) {
+
+        if (in == NULL) {
+            return ctx->output_filter(ctx->output_ctx, in);
+        }
+
+        if (!ctx->copy_chain
+            && in->next == NULL
+            && (!ngx_output_chain_need_to_copy(ctx, in->hunk)))
+        {
+            return ctx->output_filter(ctx->output_ctx, in);
+        }
+    }
+
+    /* add the incoming hunk to the chain ctx->in */
+
+    if (in) {
+        if (ngx_chain_add_copy(ctx->pool, &ctx->in, in) == NGX_ERROR) {
+            return NGX_ERROR;
+        }
+    }
+
+    last = NGX_NONE;
+    last_out = &out;
+
+    for ( ;; ) {
+
+        while (ctx->in) {
+
+            if (!ngx_output_chain_need_to_copy(ctx, ctx->in->hunk)) {
+
+                /* move the chain link to the chain out */
+
+                cl = ctx->in;
+                ctx->in = cl->next;
+
+                *last_out = cl;
+                last_out = &cl->next;
+                cl->next = NULL;
+
+                continue;
+            }
+
+            if (ctx->hunk == NULL) {
+
+                /* get the free hunk */
+
+                if (ctx->free) {
+                    ctx->hunk = ctx->free->hunk;
+                    ctx->free = ctx->free->next;
+
+                } else if (ctx->hunks < ctx->bufs.num) {
+
+                    size = ctx->bufs.size;
+
+                    if (ctx->in->hunk->type & NGX_HUNK_LAST) {
+
+                        hsize = ngx_hunk_size(ctx->in->hunk);
+
+                        if (hsize < ctx->bufs.size) {
+
+                           /*
+                            * allocate small temp hunk for the small last hunk
+                            * or its small last part
+                            */
+
+                            size = hsize;
+
+                        } else if (ctx->bufs.num == 1
+                                   && (hsize < ctx->bufs.size
+                                                     + (ctx->bufs.size >> 2)))
+                        {
+                            /*
+                             * allocate a temp hunk that equals
+                             * to the last hunk if the last hunk size is lesser
+                             * than 1.25 of bufs.size and a temp hunk is single
+                             */
+
+                            size = hsize;
+                        }
+                    }
+
+                    ngx_test_null(ctx->hunk,
+                                  ngx_create_temp_hunk(ctx->pool, size, 0, 0),
+                                  NGX_ERROR);
+                    ctx->hunk->tag = ctx->tag;
+                    ctx->hunk->type |= NGX_HUNK_RECYCLED;
+                    ctx->hunks++;
+
+                } else {
+                    break;
+                }
+            }
+
+            rc = ngx_output_chain_copy_hunk(ctx->hunk, ctx->in->hunk,
+                                            ctx->sendfile);
+
+            if (rc == NGX_ERROR) {
+                return rc;
+            }
+
+            if (rc == NGX_AGAIN) {
+                if (out) {
+                    break;
+                }
+                return rc;
+            }
+
+            /* delete the completed hunk from the chain ctx->in */
+
+            if (ngx_hunk_size(ctx->in->hunk) == 0) {
+                ctx->in = ctx->in->next;
+            }
+
+            ngx_alloc_link_and_set_hunk(cl, ctx->hunk, ctx->pool, NGX_ERROR);
+            *last_out = cl;
+            last_out = &cl->next;
+            ctx->hunk = NULL;
+
+            if (ctx->free == NULL) {
+                break;
+            }
+        }
+
+        if (out == NULL && last != NGX_NONE) {
+            return last;
+        }
+
+        last = ctx->output_filter(ctx->output_ctx, out);
+
+        ngx_chain_update_chains(&ctx->free, &ctx->busy, &out, ctx->tag);
+        last_out = &out;
+    }
+}
+
+
+ngx_inline static int ngx_output_chain_need_to_copy(ngx_output_chain_ctx_t *ctx,
+                                                    ngx_hunk_t *hunk)
+{
+    if (ngx_hunk_special(hunk)) {
+        return 0;
+    }
+
+    if (!ctx->sendfile) {
+        return 1;
+    }
+
+    if (ctx->need_in_memory && (!(hunk->type & NGX_HUNK_IN_MEMORY))) {
+        return 1;
+    }
+
+
+    if (ctx->need_in_temp && (hunk->type & (NGX_HUNK_MEMORY|NGX_HUNK_MMAP))) {
+        return 1;
+    }
+
+    return 0;
+}
+
+
+static int ngx_output_chain_copy_hunk(ngx_hunk_t *dst, ngx_hunk_t *src,
+                                      int sendfile)
+{
+    ssize_t  n, size;
+
+    size = ngx_hunk_size(src);
+
+    if (size > (dst->end - dst->pos)) {
+        size = dst->end - dst->pos;
+    }
+
+    if (src->type & NGX_HUNK_IN_MEMORY) {
+        ngx_memcpy(dst->pos, src->pos, size);
+        src->pos += size;
+        dst->last += size;
+
+        if (src->type & NGX_HUNK_FILE) {
+            src->file_pos += size;
+        }
+
+        if ((src->type & NGX_HUNK_LAST) && src->pos == src->last) {
+            dst->type |= NGX_HUNK_LAST;
+        }
+
+    } else {
+        n = ngx_read_file(src->file, dst->pos, size, src->file_pos);
+
+if (n == 0) {
+ngx_log_debug(src->file->log, "READ: %qd:%qd %X:%X %X:%X" _
+              src->file_pos _ src->file_last _
+              dst->pos _ dst->last _ dst->start _ dst->end);
+}
+
+        if (n == NGX_ERROR) {
+            return n;
+        }
+
+#if (NGX_FILE_AIO_READ)
+        if (n == NGX_AGAIN) {
+            return n;
+        }
+#endif
+
+        if (n != size) {
+            ngx_log_error(NGX_LOG_ALERT, src->file->log, 0,
+                          ngx_read_file_n " reads only %d of %d from file",
+                          n, size);
+            if (n == 0) {
+                return NGX_ERROR;
+            }
+        }
+
+        src->file_pos += n;
+        dst->last += n;
+
+        if (!sendfile) {
+            dst->type &= ~NGX_HUNK_FILE;
+        }
+
+        if ((src->type & NGX_HUNK_LAST) && src->file_pos == src->file_last) {
+            dst->type |= NGX_HUNK_LAST;
+        }
+    }
+
+    return NGX_OK;
+}