new file mode 100644
--- /dev/null
+++ b/src/event/ngx_event_pipe.c
@@ -0,0 +1,771 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_event.h>
+#include <ngx_event_pipe.h>
+
+
+static ngx_int_t ngx_event_pipe_read_upstream(ngx_event_pipe_t *p);
+static ngx_int_t ngx_event_pipe_write_to_downstream(ngx_event_pipe_t *p);
+
+static ngx_int_t ngx_event_pipe_write_chain_to_temp_file(ngx_event_pipe_t *p);
+ngx_inline static void ngx_event_pipe_remove_shadow_links(ngx_buf_t *buf);
+ngx_inline static void ngx_event_pipe_free_shadow_raw_buf(ngx_chain_t **free,
+                                                          ngx_buf_t *buf);
+ngx_inline static void ngx_event_pipe_add_free_buf(ngx_chain_t **chain,
+                                                   ngx_chain_t *cl);
+static ngx_int_t ngx_event_pipe_drain_chains(ngx_event_pipe_t *p);
+
+
+ngx_int_t ngx_event_pipe(ngx_event_pipe_t *p, int do_write)
+{
+    u_int         flags;
+    ngx_event_t  *rev, *wev;
+
+    for ( ;; ) {
+        if (do_write) {
+            if (ngx_event_pipe_write_to_downstream(p) == NGX_ABORT) {
+                return NGX_ABORT;
+            }
+        }
+
+        p->read = 0;
+        p->upstream_blocked = 0;
+
+        if (ngx_event_pipe_read_upstream(p) == NGX_ABORT) {
+            return NGX_ABORT;
+        }
+
+        if (!p->read && !p->upstream_blocked) {
+            break;
+        }
+
+        do_write = 1;
+    }
+
+    if (p->upstream->fd != -1) {
+        rev = p->upstream->read;
+
+        flags = (rev->eof || rev->error) ? NGX_CLOSE_EVENT : 0;
+
+        if (ngx_handle_read_event(rev, flags) == NGX_ERROR) {
+            return NGX_ABORT;
+        }
+
+        if (rev->active) {
+            ngx_add_timer(rev, p->read_timeout);
+        }
+    }
+
+    if (p->downstream->fd != -1) {
+        wev = p->downstream->write;
+        wev->available = p->send_lowat;
+        if (ngx_handle_write_event(wev, NGX_LOWAT_EVENT) == NGX_ERROR) {
+            return NGX_ABORT;
+        }
+
+        if (wev->active) {
+            ngx_add_timer(wev, p->send_timeout);
+        }
+    }
+
+    return NGX_OK;
+}
+
+
+ngx_int_t ngx_event_pipe_read_upstream(ngx_event_pipe_t *p)
+{
+    int           n, rc, size;
+    ngx_buf_t    *b;
+    ngx_chain_t  *chain, *cl, *tl;
+
+    if (p->upstream_eof || p->upstream_error || p->upstream_done) {
+        return NGX_OK;
+    }
+
+    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                   "pipe read upstream: %d", p->upstream->read->ready);
+
+    for ( ;; ) {
+
+        if (p->upstream_eof || p->upstream_error || p->upstream_done) {
+            break;
+        }
+
+        if (p->preread_bufs == NULL && !p->upstream->read->ready) {
+            break;
+        }
+
+        if (p->preread_bufs) {
+
+            /* use the pre-read bufs if they exist */
+
+            chain = p->preread_bufs;
+            p->preread_bufs = NULL;
+            n = p->preread_size;
+
+            ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                           "pipe preread: %d", n);
+
+            if (n) {
+                p->read = 1;
+            }
+
+        } else {
+
+            /*
+             * kqueue notifies about the end of file or a pending error.
+             * This test allows not to allocate a buf on these conditions
+             * and not to call ngx_recv_chain().
+             */
+
+            if (p->upstream->read->available == 0
+                && p->upstream->read->pending_eof)
+            {
+                p->upstream->read->ready = 0;
+                p->upstream->read->eof = 0;
+                p->upstream_eof = 1;
+                p->read = 1;
+
+#if (HAVE_KQUEUE)
+                if (p->upstream->read->kq_errno) {
+                    p->upstream->read->error = 1;
+                    p->upstream_error = 1;
+                    p->upstream_eof = 0;
+
+                    ngx_log_error(NGX_LOG_ERR, p->log,
+                                  p->upstream->read->kq_errno,
+                                  "readv() failed");
+                }
+#endif
+
+                break;
+            }
+
+            if (p->free_raw_bufs) {
+
+                /* use the free bufs if they exist */
+
+                chain = p->free_raw_bufs;
+                if (p->single_buf) {
+                    p->free_raw_bufs = p->free_raw_bufs->next;
+                    chain->next = NULL;
+                } else {
+                    p->free_raw_bufs = NULL;
+                }
+
+            } else if (p->allocated < p->bufs.num) {
+
+                /* allocate a new buf if it's still allowed */
+
+                if (!(b = ngx_create_temp_buf(p->pool, p->bufs.size))) {
+                    return NGX_ABORT;
+                }
+
+                p->allocated++;
+
+                ngx_alloc_link_and_set_buf(tl, b, p->pool, NGX_ABORT);
+                chain = tl;
+
+            } else if (!p->cachable && p->downstream->write->ready) {
+
+                /*
+                 * if the bufs are not needed to be saved in a cache and
+                 * a downstream is ready then write the bufs to a downstream
+                 */
+
+                p->upstream_blocked = 1;
+
+                ngx_log_debug0(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                               "pipe downstream ready");
+
+                break;
+
+            } else if (p->cachable
+                       || p->temp_file->offset < p->max_temp_file_size)
+            {
+
+                /*
+                 * if it's allowed then save some bufs from r->in
+                 * to a temporary file, and add them to a r->out chain
+                 */
+
+                rc = ngx_event_pipe_write_chain_to_temp_file(p);
+
+                ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                               "pipe temp offset: %d", p->temp_file->offset);
+
+                if (rc == NGX_AGAIN) {
+                    if (ngx_event_flags & NGX_USE_LEVEL_EVENT
+                        && p->upstream->read->active
+                        && p->upstream->read->ready)
+                    {
+                        if (ngx_del_event(p->upstream->read, NGX_READ_EVENT, 0)
+                                                                  == NGX_ERROR)
+                        {
+                            return NGX_ABORT;
+                        }
+                    }
+                }
+
+                if (rc != NGX_OK) {
+                    return rc;
+                }
+
+                chain = p->free_raw_bufs;
+                if (p->single_buf) {
+                    p->free_raw_bufs = p->free_raw_bufs->next;
+                    chain->next = NULL;
+                } else {
+                    p->free_raw_bufs = NULL;
+                }
+
+            } else {
+
+                /* if there're no bufs to read in then disable a level event */
+
+                ngx_log_debug0(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                               "no pipe bufs to read in");
+    
+                break;
+            }
+
+            n = ngx_recv_chain(p->upstream, chain);
+
+            ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                           "pipe recv chain: %d", n);
+
+            if (p->free_raw_bufs) {
+                chain->next = p->free_raw_bufs;
+            }
+            p->free_raw_bufs = chain;
+
+            if (n == NGX_ERROR) {
+                p->upstream_error = 1;
+                return NGX_ERROR;
+            }
+
+            if (n == NGX_AGAIN) {
+                if (p->single_buf) {
+                    ngx_event_pipe_remove_shadow_links(chain->buf);
+                }
+
+                break;
+            }
+
+            p->read = 1;
+
+            if (n == 0) {
+                p->upstream_eof = 1;
+                break;
+            }
+        }
+
+        p->read_length += n;
+        cl = chain;
+
+        while (cl && n > 0) {
+
+            ngx_event_pipe_remove_shadow_links(cl->buf);
+
+            size = cl->buf->end - cl->buf->last;
+
+            if (n >= size) {
+                cl->buf->last = cl->buf->end;
+
+                /* STUB */ cl->buf->num = p->num++;
+
+                if (p->input_filter(p, cl->buf) == NGX_ERROR) {
+                    return NGX_ABORT;
+                }
+
+                n -= size;
+                cl = cl->next;
+
+            } else {
+                cl->buf->last += n;
+                n = 0;
+            }
+        }
+
+        p->free_raw_bufs = cl;
+    }
+
+#if (NGX_DEBUG)
+
+    if (p->in || p->busy || p->free_raw_bufs) {
+        ngx_log_debug0(NGX_LOG_DEBUG_EVENT, p->log, 0, "pipe buf");
+    }
+
+    for (cl = p->in; cl; cl = cl->next) {
+        ngx_log_debug3(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "pipe buf in " PTR_FMT ", pos " PTR_FMT ", size: %d",
+                       cl->buf->start, cl->buf->pos,
+                       cl->buf->last - cl->buf->pos);
+    }
+
+    for (cl = p->busy; cl; cl = cl->next) {
+        ngx_log_debug3(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "pipe buf busy " PTR_FMT ", pos " PTR_FMT ", size: %d",
+                       cl->buf->start, cl->buf->pos,
+                       cl->buf->last - cl->buf->pos);
+    }
+
+    for (cl = p->free_raw_bufs; cl; cl = cl->next) {
+        ngx_log_debug3(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "pipe buf free " PTR_FMT ", last " PTR_FMT ", size: %d",
+                       cl->buf->start, cl->buf->last,
+                       cl->buf->end - cl->buf->last);
+    }
+
+#endif
+
+    if ((p->upstream_eof || p->upstream_error) && p->free_raw_bufs) {
+
+        /* STUB */ p->free_raw_bufs->buf->num = p->num++;
+
+        if (p->input_filter(p, p->free_raw_bufs->buf) == NGX_ERROR) {
+            return NGX_ABORT;
+        }
+
+        p->free_raw_bufs = p->free_raw_bufs->next;
+
+        if (p->free_bufs) {
+            for (cl = p->free_raw_bufs; cl; cl = cl->next) {
+                ngx_pfree(p->pool, cl->buf->start); 
+            }
+        }
+    }
+
+    if (p->cachable && p->in) {
+        if (ngx_event_pipe_write_chain_to_temp_file(p) == NGX_ABORT) {
+            return NGX_ABORT;
+        }
+    }
+
+    return NGX_OK;
+}
+
+
+ngx_int_t ngx_event_pipe_write_to_downstream(ngx_event_pipe_t *p)
+{
+    size_t        bsize;
+    ngx_uint_t    flush;
+    ngx_buf_t    *b;
+    ngx_chain_t  *out, **ll, *cl, *tl;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                   "pipe write downstream: %d", p->downstream->write->ready);
+
+    for ( ;; ) {
+        if (p->downstream_error) {
+            return ngx_event_pipe_drain_chains(p);
+        }
+
+        if (p->upstream_eof || p->upstream_error || p->upstream_done) {
+
+            /* pass the p->out and p->in chains to the output filter */
+
+            if (p->out) {
+                ngx_log_debug0(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                               "pipe write downstream flush out");
+
+                if (p->output_filter(p->output_ctx, p->out) == NGX_ERROR) {
+                    p->downstream_error = 1;
+                    return ngx_event_pipe_drain_chains(p);
+                }
+
+                p->out = NULL;
+            }
+
+            if (p->in) {
+                ngx_log_debug0(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                               "pipe write downstream flush in");
+
+                if (p->output_filter(p->output_ctx, p->in) == NGX_ERROR) {
+                    p->downstream_error = 1;
+                    return ngx_event_pipe_drain_chains(p);
+                }
+
+                p->in = NULL;
+            }
+
+            ngx_log_debug0(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                           "pipe write downstream done");
+
+            /* TODO: free unused bufs */
+
+            p->downstream_done = 1;
+            break;
+        }
+
+        if (!p->downstream->write->ready) {
+            break;
+        }
+
+        /* bsize is the size of the busy bufs */
+
+        bsize = 0;
+
+        for (cl = p->busy; cl; cl = cl->next) {
+            bsize += cl->buf->end - cl->buf->start;
+        }
+
+        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "pipe write busy: " SIZE_T_FMT, bsize);
+
+        out = NULL;
+        ll = NULL;
+        flush = 0;
+
+        for ( ;; ) {
+            if (p->out) {
+                cl = p->out;
+
+                if (bsize + ngx_buf_size(cl->buf) > p->busy_size) {
+                    flush = 1;
+                    break;
+                }
+
+                p->out = p->out->next;
+                ngx_event_pipe_free_shadow_raw_buf(&p->free_raw_bufs,
+                                                   cl->buf);
+
+            } else if (!p->cachable && p->in) {
+                cl = p->in;
+
+                if (bsize + ngx_buf_size(cl->buf) > p->busy_size) {
+                    flush = 1;
+                    break;
+                }
+
+                p->in = p->in->next;
+
+            } else {
+                break;
+            }
+
+            bsize += ngx_buf_size(cl->buf);
+            cl->next = NULL;
+            ngx_chain_add_link(out, ll, cl);
+        }
+
+        ngx_log_debug2(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "pipe write: out:" PTR_FMT ", f:%d", out, flush);
+
+        if (out == NULL && !flush) {
+            break;
+        }
+
+        if (p->output_filter(p->output_ctx, out) == NGX_ERROR) {
+            p->downstream_error = 1;
+            return ngx_event_pipe_drain_chains(p);
+        }
+
+        ngx_chain_update_chains(&p->free, &p->busy, &out, p->tag);
+
+        for (cl = p->free; cl; cl = cl->next) {
+
+            if (cl->buf->temp_file) {
+                if (p->cachable || !p->cyclic_temp_file) {
+                    continue;
+                }
+
+                /* reset p->temp_offset if all bufs had been sent */
+
+                if (cl->buf->file_last == p->temp_file->offset) {
+                    p->temp_file->offset = 0;
+                }
+            }
+
+            /* TODO: free buf if p->free_bufs && upstream done */
+
+            /* add the free shadow raw buf to p->free_raw_bufs */
+
+            if (cl->buf->last_shadow) {
+                b = cl->buf->shadow;
+                b->pos = b->last = b->start;
+                b->shadow = NULL;
+                ngx_alloc_link_and_set_buf(tl, b, p->pool, NGX_ABORT);
+                ngx_event_pipe_add_free_buf(&p->free_raw_bufs, tl);
+
+                cl->buf->last_shadow = 0;
+            }
+
+            cl->buf->shadow = NULL;
+        }
+    }
+
+    return NGX_OK;
+}
+
+
+static ngx_int_t ngx_event_pipe_write_chain_to_temp_file(ngx_event_pipe_t *p)
+{
+    ssize_t       size, bsize;
+    ngx_buf_t    *b;
+    ngx_chain_t  *cl, *tl, *next, *out, **ll, **last_free, fl;
+
+    if (p->buf_to_file) {
+        fl.buf = p->buf_to_file;
+        fl.next = p->in;
+        out = &fl;
+
+    } else {
+        out = p->in;
+    }
+
+    if (!p->cachable) {
+
+        size = 0;
+        cl = out;
+        ll = NULL;
+
+        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                       "pipe offset: %d", p->temp_file->offset);
+
+        do {
+            bsize = cl->buf->last - cl->buf->pos;
+
+            ngx_log_debug3(NGX_LOG_DEBUG_EVENT, p->log, 0,
+                           "pipe buf " PTR_FMT ", pos " PTR_FMT ", size: %d",
+                           cl->buf->start, cl->buf->pos, bsize);
+
+            if ((size + bsize > p->temp_file_write_size)
+               || (p->temp_file->offset + size + bsize > p->max_temp_file_size))
+            {
+                break;
+            }
+
+            size += bsize;
+            ll = &cl->next;
+            cl = cl->next;
+
+        } while (cl);
+
+        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0, "size: %d", size);
+
+        if (cl) {
+           p->in = cl;
+           *ll = NULL;
+
+        } else {
+           p->in = NULL;
+           p->last_in = &p->in;
+        }
+
+    } else {
+        p->in = NULL;
+        p->last_in = &p->in;
+    }
+
+    if (ngx_write_chain_to_temp_file(p->temp_file, out) == NGX_ERROR) {
+        return NGX_ABORT;
+    }
+
+    for (last_free = &p->free_raw_bufs;
+         *last_free != NULL;
+         last_free = &(*last_free)->next)
+    {
+        /* void */
+    }
+
+    if (p->buf_to_file) {
+        p->temp_file->offset = p->buf_to_file->last - p->buf_to_file->pos;
+        p->buf_to_file = NULL;
+        out = out->next;
+    }
+
+    for (cl = out; cl; cl = next) {
+        next = cl->next;
+        cl->next = NULL;
+
+        b = cl->buf;
+        b->file = &p->temp_file->file;
+        b->file_pos = p->temp_file->offset;
+        p->temp_file->offset += b->last - b->pos;
+        b->file_last = p->temp_file->offset;
+
+        b->in_file = 1;
+        b->temp_file = 1;
+
+        ngx_chain_add_link(p->out, p->last_out, cl);
+
+        if (b->last_shadow) {
+            b->shadow->last = b->shadow->pos = b->shadow->start;
+            ngx_alloc_link_and_set_buf(tl, b->shadow, p->pool, NGX_ABORT);
+            *last_free = tl;
+            last_free = &tl->next;
+        }
+    }
+
+    return NGX_OK;
+}
+
+
+/* the copy input filter */
+
+ngx_int_t ngx_event_pipe_copy_input_filter(ngx_event_pipe_t *p, ngx_buf_t *buf)
+{
+    ngx_buf_t    *b;
+    ngx_chain_t  *cl;
+
+    if (buf->pos == buf->last) {
+        return NGX_OK;
+    }
+
+    if (p->free) {
+        b = p->free->buf;
+        p->free = p->free->next;
+
+    } else {
+        if (!(b = ngx_alloc_buf(p->pool))) {
+            return NGX_ERROR;
+        }
+    }
+
+    ngx_memcpy(b, buf, sizeof(ngx_buf_t));
+    b->shadow = buf;
+    b->tag = p->tag;
+    b->last_shadow = 1;
+    b->recycled = 1;
+    buf->shadow = b;
+
+    ngx_alloc_link_and_set_buf(cl, b, p->pool, NGX_ERROR);
+
+    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, p->log, 0, "buf #%d", b->num);
+
+    ngx_chain_add_link(p->in, p->last_in, cl);
+
+    return NGX_OK;
+}
+
+
+ngx_inline static void ngx_event_pipe_remove_shadow_links(ngx_buf_t *buf)
+{
+    ngx_buf_t  *b, *next;
+
+    if (buf->shadow == NULL) {
+        return;
+    }
+
+    b = buf->shadow;
+
+    while (!b->last_shadow) {
+        next = b->shadow;
+
+        b->in_file = 0;
+        b->temp_file = 0;
+        b->flush = 0;
+        b->zerocopy_busy = 0;
+
+        b->shadow = NULL;
+        b = next;
+    }
+
+    b->in_file = 0;
+    b->temp_file = 0;
+    b->flush = 0;
+    b->zerocopy_busy = 0;
+    b->last_shadow = 0;
+
+    b->shadow = NULL;
+
+    buf->shadow = NULL;
+}
+
+
+ngx_inline static void ngx_event_pipe_free_shadow_raw_buf(ngx_chain_t **free,
+                                                          ngx_buf_t *buf)
+{
+    ngx_buf_t    *s;
+    ngx_chain_t  *cl, **ll;
+
+    if (buf->shadow == NULL) {
+        return;
+    }
+
+    for (s = buf->shadow; !s->last_shadow; s = s->shadow) { /* void */ }
+
+    ll = free;
+
+    for (cl = *free ; cl; cl = cl->next) {
+        if (cl->buf == s) {
+            *ll = cl->next;
+            break;
+        }
+
+        if (cl->buf->shadow) {
+            break;
+        }
+
+        ll = &cl->next;
+    }
+}
+
+
+ngx_inline static void ngx_event_pipe_add_free_buf(ngx_chain_t **chain,
+                                                   ngx_chain_t *cl)
+{
+    if (*chain == NULL) {
+        *chain = cl;
+        return;
+    }
+
+    if ((*chain)->buf->pos != (*chain)->buf->last) {
+        cl->next = (*chain)->next;
+        (*chain)->next = cl;
+
+    } else {
+        cl->next = (*chain);
+        (*chain) = cl;
+    }
+}
+
+
+static ngx_int_t ngx_event_pipe_drain_chains(ngx_event_pipe_t *p)
+{
+    ngx_buf_t    *b;
+    ngx_chain_t  *cl, *tl;
+
+    for ( ;; ) {
+        if (p->busy) {
+            cl = p->busy;
+            p->busy = NULL;
+
+        } else if (p->out) {
+            cl = p->out;
+            p->out = NULL;
+
+        } else if (p->in) {
+            cl = p->in;
+            p->in = NULL;
+
+        } else {
+            return NGX_OK;
+        }
+
+        while (cl) {
+            if (cl->buf->last_shadow) {
+                b = cl->buf->shadow;
+                b->pos = b->last = b->start;
+                b->shadow = NULL;
+                ngx_alloc_link_and_set_buf(tl, b, p->pool, NGX_ABORT);
+                ngx_event_pipe_add_free_buf(&p->free_raw_bufs, tl);
+
+                cl->buf->last_shadow = 0;
+            }
+
+            cl->buf->shadow = NULL;
+            tl = cl->next;
+            cl->next = p->free;
+            p->free = cl;
+            cl = tl;
+        }
+    }
+}