diff --git a/src/os/unix/ngx_darwin_sendfile_chain.c b/src/os/unix/ngx_darwin_sendfile_chain.c
index d28f6e1..d98fd74 100644
--- a/src/os/unix/ngx_darwin_sendfile_chain.c
+++ b/src/os/unix/ngx_darwin_sendfile_chain.c
@@ -31,17 +31,15 @@
 ngx_darwin_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
 {
     int              rc;
-    u_char          *prev;
     off_t            size, send, prev_send, aligned, sent, fprev;
-    off_t            header_size, file_size;
+    off_t            file_size;
     ngx_uint_t       eintr;
     ngx_err_t        err;
     ngx_buf_t       *file;
-    ngx_array_t      header, trailer;
     ngx_event_t     *wev;
     ngx_chain_t     *cl;
+    ngx_iovec_t      header, trailer;
     struct sf_hdtr   hdtr;
-    struct iovec    *iov;
     struct iovec     headers[NGX_IOVS_PREALLOCATE];
     struct iovec     trailers[NGX_IOVS_PREALLOCATE];
 
@@ -70,69 +68,27 @@
 
     send = 0;
 
-    header.elts = headers;
-    header.size = sizeof(struct iovec);
+    header.iovs = headers;
     header.nalloc = NGX_IOVS_PREALLOCATE;
-    header.pool = c->pool;
 
-    trailer.elts = trailers;
-    trailer.size = sizeof(struct iovec);
+    trailer.iovs = trailers;
     trailer.nalloc = NGX_IOVS_PREALLOCATE;
-    trailer.pool = c->pool;
 
     for ( ;; ) {
         file = NULL;
         file_size = 0;
-        header_size = 0;
         eintr = 0;
         prev_send = send;
 
-        header.nelts = 0;
-        trailer.nelts = 0;
-
         /* create the header iovec and coalesce the neighbouring bufs */
 
-        prev = NULL;
-        iov = NULL;
+        cl = ngx_output_chain_to_iovec(&header, in, limit - send, c->log);
 
-        for (cl = in; cl && send < limit; cl = cl->next) {
-
-            if (ngx_buf_special(cl->buf)) {
-                continue;
-            }
-
-            if (!ngx_buf_in_memory_only(cl->buf)) {
-                break;
-            }
-
-            size = cl->buf->last - cl->buf->pos;
-
-            if (send + size > limit) {
-                size = limit - send;
-            }
-
-            if (prev == cl->buf->pos) {
-                iov->iov_len += (size_t) size;
-
-            } else {
-                if (header.nelts >= IOV_MAX) {
-                    break;
-                }
-
-                iov = ngx_array_push(&header);
-                if (iov == NULL) {
-                    return NGX_CHAIN_ERROR;
-                }
-
-                iov->iov_base = (void *) cl->buf->pos;
-                iov->iov_len = (size_t) size;
-            }
-
-            prev = cl->buf->pos + (size_t) size;
-            header_size += size;
-            send += size;
+        if (cl == NGX_CHAIN_ERROR) {
+            return NGX_CHAIN_ERROR;
         }
 
+        send += header.size;
 
         if (cl && cl->buf->in_file && send < limit) {
             file = cl->buf;
@@ -165,51 +121,17 @@
                      && fprev == cl->buf->file_pos);
         }
 
-        if (file && header.nelts == 0) {
+        if (file && header.count == 0) {
 
             /* create the trailer iovec and coalesce the neighbouring bufs */
 
-            prev = NULL;
-            iov = NULL;
+            cl = ngx_output_chain_to_iovec(&trailer, cl, limit - send, c->log);
 
-            while (cl && send < limit) {
-
-                if (ngx_buf_special(cl->buf)) {
-                    cl = cl->next;
-                    continue;
-                }
-
-                if (!ngx_buf_in_memory_only(cl->buf)) {
-                    break;
-                }
-
-                size = cl->buf->last - cl->buf->pos;
-
-                if (send + size > limit) {
-                    size = limit - send;
-                }
-
-                if (prev == cl->buf->pos) {
-                    iov->iov_len += (size_t) size;
-
-                } else {
-                    if (trailer.nelts >= IOV_MAX) {
-                        break;
-                    }
-
-                    iov = ngx_array_push(&trailer);
-                    if (iov == NULL) {
-                        return NGX_CHAIN_ERROR;
-                    }
-
-                    iov->iov_base = (void *) cl->buf->pos;
-                    iov->iov_len = (size_t) size;
-                }
-
-                prev = cl->buf->pos + (size_t) size;
-                send += size;
-                cl = cl->next;
+            if (cl == NGX_CHAIN_ERROR) {
+                return NGX_CHAIN_ERROR;
             }
+
+            send += trailer.size;
         }
 
         if (file) {
@@ -219,16 +141,16 @@
              * but corresponding pointer is not NULL
              */
 
-            hdtr.headers = header.nelts ? (struct iovec *) header.elts: NULL;
-            hdtr.hdr_cnt = header.nelts;
-            hdtr.trailers = trailer.nelts ? (struct iovec *) trailer.elts: NULL;
-            hdtr.trl_cnt = trailer.nelts;
+            hdtr.headers = header.count ? header.iovs : NULL;
+            hdtr.hdr_cnt = header.count;
+            hdtr.trailers = trailer.count ? trailer.iovs : NULL;
+            hdtr.trl_cnt = trailer.count;
 
-            sent = header_size + file_size;
+            sent = header.size + file_size;
 
             ngx_log_debug3(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                           "sendfile: @%O %O h:%O",
-                           file->file_pos, sent, header_size);
+                           "sendfile: @%O %O h:%uz",
+                           file->file_pos, sent, header.size);
 
             rc = sendfile(file->file->fd, c->fd, file->file_pos,
                           &sent, &hdtr, 0);
@@ -271,13 +193,13 @@
 
             ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
                            "sendfile: %d, @%O %O:%O",
-                           rc, file->file_pos, sent, file_size + header_size);
+                           rc, file->file_pos, sent, file_size + header.size);
 
         } else {
-            rc = writev(c->fd, header.elts, header.nelts);
+            rc = writev(c->fd, header.iovs, header.count);
 
             ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                           "writev: %d of %O", rc, header_size);
+                           "writev: %d of %uz", rc, header.size);
 
             if (rc == -1) {
                 err = ngx_errno;
diff --git a/src/os/unix/ngx_freebsd_sendfile_chain.c b/src/os/unix/ngx_freebsd_sendfile_chain.c
index 666e0c5..83e0f68 100644
--- a/src/os/unix/ngx_freebsd_sendfile_chain.c
+++ b/src/os/unix/ngx_freebsd_sendfile_chain.c
@@ -33,17 +33,15 @@
 ngx_freebsd_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
 {
     int              rc, flags;
-    u_char          *prev;
     off_t            size, send, prev_send, aligned, sent, fprev;
-    size_t           header_size, file_size;
+    size_t           file_size;
     ngx_uint_t       eintr, eagain;
     ngx_err_t        err;
     ngx_buf_t       *file;
-    ngx_array_t      header, trailer;
     ngx_event_t     *wev;
     ngx_chain_t     *cl;
+    ngx_iovec_t      header, trailer;
     struct sf_hdtr   hdtr;
-    struct iovec    *iov;
     struct iovec     headers[NGX_IOVS_PREALLOCATE];
     struct iovec     trailers[NGX_IOVS_PREALLOCATE];
 
@@ -74,69 +72,27 @@
     eagain = 0;
     flags = 0;
 
-    header.elts = headers;
-    header.size = sizeof(struct iovec);
+    header.iovs = headers;
     header.nalloc = NGX_IOVS_PREALLOCATE;
-    header.pool = c->pool;
 
-    trailer.elts = trailers;
-    trailer.size = sizeof(struct iovec);
+    trailer.iovs = trailers;
     trailer.nalloc = NGX_IOVS_PREALLOCATE;
-    trailer.pool = c->pool;
 
     for ( ;; ) {
         file = NULL;
         file_size = 0;
-        header_size = 0;
         eintr = 0;
         prev_send = send;
 
-        header.nelts = 0;
-        trailer.nelts = 0;
-
         /* create the header iovec and coalesce the neighbouring bufs */
 
-        prev = NULL;
-        iov = NULL;
+        cl = ngx_output_chain_to_iovec(&header, in, limit - send, c->log);
 
-        for (cl = in; cl && send < limit; cl = cl->next) {
-
-            if (ngx_buf_special(cl->buf)) {
-                continue;
-            }
-
-            if (!ngx_buf_in_memory_only(cl->buf)) {
-                break;
-            }
-
-            size = cl->buf->last - cl->buf->pos;
-
-            if (send + size > limit) {
-                size = limit - send;
-            }
-
-            if (prev == cl->buf->pos) {
-                iov->iov_len += (size_t) size;
-
-            } else {
-                if (header.nelts >= IOV_MAX){
-                    break;
-                }
-
-                iov = ngx_array_push(&header);
-                if (iov == NULL) {
-                    return NGX_CHAIN_ERROR;
-                }
-
-                iov->iov_base = (void *) cl->buf->pos;
-                iov->iov_len = (size_t) size;
-            }
-
-            prev = cl->buf->pos + (size_t) size;
-            header_size += (size_t) size;
-            send += size;
+        if (cl == NGX_CHAIN_ERROR) {
+            return NGX_CHAIN_ERROR;
         }
 
+        send += header.size;
 
         if (cl && cl->buf->in_file && send < limit) {
             file = cl->buf;
@@ -174,47 +130,13 @@
 
             /* create the trailer iovec and coalesce the neighbouring bufs */
 
-            prev = NULL;
-            iov = NULL;
+            cl = ngx_output_chain_to_iovec(&trailer, cl, limit - send, c->log);
 
-            while (cl && send < limit) {
-
-                if (ngx_buf_special(cl->buf)) {
-                    cl = cl->next;
-                    continue;
-                }
-
-                if (!ngx_buf_in_memory_only(cl->buf)) {
-                    break;
-                }
-
-                size = cl->buf->last - cl->buf->pos;
-
-                if (send + size > limit) {
-                    size = limit - send;
-                }
-
-                if (prev == cl->buf->pos) {
-                    iov->iov_len += (size_t) size;
-
-                } else {
-                    if (trailer.nelts >= IOV_MAX){
-                        break;
-                    }
-
-                    iov = ngx_array_push(&trailer);
-                    if (iov == NULL) {
-                        return NGX_CHAIN_ERROR;
-                    }
-
-                    iov->iov_base = (void *) cl->buf->pos;
-                    iov->iov_len = (size_t) size;
-                }
-
-                prev = cl->buf->pos + (size_t) size;
-                send += size;
-                cl = cl->next;
+            if (cl == NGX_CHAIN_ERROR) {
+                return NGX_CHAIN_ERROR;
             }
+
+            send += trailer.size;
         }
 
         if (file) {
@@ -250,10 +172,10 @@
              * but corresponding pointer is not NULL
              */
 
-            hdtr.headers = header.nelts ? (struct iovec *) header.elts: NULL;
-            hdtr.hdr_cnt = header.nelts;
-            hdtr.trailers = trailer.nelts ? (struct iovec *) trailer.elts: NULL;
-            hdtr.trl_cnt = trailer.nelts;
+            hdtr.headers = header.count ? header.iovs : NULL;
+            hdtr.hdr_cnt = header.count;
+            hdtr.trailers = trailer.count ? trailer.iovs : NULL;
+            hdtr.trl_cnt = trailer.count;
 
             /*
              * the "nbytes bug" of the old sendfile() syscall:
@@ -261,7 +183,7 @@
              */
 
             if (!ngx_freebsd_sendfile_nbytes_bug) {
-                header_size = 0;
+                header.size = 0;
             }
 
             sent = 0;
@@ -271,7 +193,7 @@
 #endif
 
             rc = sendfile(file->file->fd, c->fd, file->file_pos,
-                          file_size + header_size, &hdtr, &sent, flags);
+                          file_size + header.size, &hdtr, &sent, flags);
 
             if (rc == -1) {
                 err = ngx_errno;
@@ -322,13 +244,13 @@
 
             ngx_log_debug4(NGX_LOG_DEBUG_EVENT, c->log, 0,
                            "sendfile: %d, @%O %O:%uz",
-                           rc, file->file_pos, sent, file_size + header_size);
+                           rc, file->file_pos, sent, file_size + header.size);
 
         } else {
-            rc = writev(c->fd, header.elts, header.nelts);
+            rc = writev(c->fd, header.iovs, header.count);
 
             ngx_log_debug2(NGX_LOG_DEBUG_EVENT, c->log, 0,
-                           "writev: %d of %uz", rc, header_size);
+                           "writev: %d of %uz", rc, header.size);
 
             if (rc == -1) {
                 err = ngx_errno;
diff --git a/src/os/unix/ngx_linux_sendfile_chain.c b/src/os/unix/ngx_linux_sendfile_chain.c
index 99d00bf..a84a134 100644
--- a/src/os/unix/ngx_linux_sendfile_chain.c
+++ b/src/os/unix/ngx_linux_sendfile_chain.c
@@ -32,15 +32,14 @@
 {
     int            rc, tcp_nodelay;
     off_t          size, send, prev_send, aligned, sent, fprev;
-    u_char        *prev;
     size_t         file_size;
     ngx_err_t      err;
     ngx_buf_t     *file;
     ngx_uint_t     eintr;
-    ngx_array_t    header;
     ngx_event_t   *wev;
     ngx_chain_t   *cl;
-    struct iovec  *iov, headers[NGX_IOVS_PREALLOCATE];
+    ngx_iovec_t    header;
+    struct iovec   headers[NGX_IOVS_PREALLOCATE];
 #if (NGX_HAVE_SENDFILE64)
     off_t          offset;
 #else
@@ -63,10 +62,8 @@
 
     send = 0;
 
-    header.elts = headers;
-    header.size = sizeof(struct iovec);
+    header.iovs = headers;
     header.nalloc = NGX_IOVS_PREALLOCATE;
-    header.pool = c->pool;
 
     for ( ;; ) {
         file = NULL;
@@ -74,75 +71,20 @@
         eintr = 0;
         prev_send = send;
 
-        header.nelts = 0;
-
-        prev = NULL;
-        iov = NULL;
-
         /* create the iovec and coalesce the neighbouring bufs */
 
-        for (cl = in; cl && send < limit; cl = cl->next) {
+        cl = ngx_output_chain_to_iovec(&header, in, limit - send, c->log);
 
-            if (ngx_buf_special(cl->buf)) {
-                continue;
-            }
-
-#if 1
-            if (!ngx_buf_in_memory(cl->buf) && !cl->buf->in_file) {
-                ngx_log_error(NGX_LOG_ALERT, c->log, 0,
-                              "zero size buf in sendfile "
-                              "t:%d r:%d f:%d %p %p-%p %p %O-%O",
-                              cl->buf->temporary,
-                              cl->buf->recycled,
-                              cl->buf->in_file,
-                              cl->buf->start,
-                              cl->buf->pos,
-                              cl->buf->last,
-                              cl->buf->file,
-                              cl->buf->file_pos,
-                              cl->buf->file_last);
-
-                ngx_debug_point();
-
-                return NGX_CHAIN_ERROR;
-            }
-#endif
-
-            if (!ngx_buf_in_memory_only(cl->buf)) {
-                break;
-            }
-
-            size = cl->buf->last - cl->buf->pos;
-
-            if (send + size > limit) {
-                size = limit - send;
-            }
-
-            if (prev == cl->buf->pos) {
-                iov->iov_len += (size_t) size;
-
-            } else {
-                if (header.nelts >= IOV_MAX) {
-                    break;
-                }
-
-                iov = ngx_array_push(&header);
-                if (iov == NULL) {
-                    return NGX_CHAIN_ERROR;
-                }
-
-                iov->iov_base = (void *) cl->buf->pos;
-                iov->iov_len = (size_t) size;
-            }
-
-            prev = cl->buf->pos + (size_t) size;
-            send += size;
+        if (cl == NGX_CHAIN_ERROR) {
+            return NGX_CHAIN_ERROR;
         }
 
+        send += header.size;
+
         /* set TCP_CORK if there is a header before a file */
 
         if (c->tcp_nopush == NGX_TCP_NOPUSH_UNSET
-            && header.nelts != 0
+            && header.count != 0
             && cl
             && cl->buf->in_file)
         {
@@ -206,7 +148,7 @@
 
         /* get the file buf */
 
-        if (header.nelts == 0 && cl && cl->buf->in_file && send < limit) {
+        if (header.count == 0 && cl && cl->buf->in_file && send < limit) {
             file = cl->buf;
 
             /* coalesce the neighbouring file bufs */
@@ -283,7 +225,7 @@
                            rc, file->file_pos, sent, file_size);
 
         } else {
-            rc = writev(c->fd, header.elts, header.nelts);
+            rc = writev(c->fd, header.iovs, header.count);
 
             if (rc == -1) {
                 err = ngx_errno;
diff --git a/src/os/unix/ngx_os.h b/src/os/unix/ngx_os.h
index a158642..fa6a6a6 100644
--- a/src/os/unix/ngx_os.h
+++ b/src/os/unix/ngx_os.h
@@ -64,6 +64,17 @@
 #endif
 
 
+typedef struct {
+    struct iovec  *iovs;
+    ngx_uint_t     count;
+    size_t         size;
+    ngx_uint_t     nalloc;
+} ngx_iovec_t;
+
+ngx_chain_t *ngx_output_chain_to_iovec(ngx_iovec_t *vec, ngx_chain_t *in,
+    size_t limit, ngx_log_t *log);
+
+
 extern ngx_os_io_t  ngx_os_io;
 extern ngx_int_t    ngx_ncpu;
 extern ngx_int_t    ngx_max_sockets;
diff --git a/src/os/unix/ngx_writev_chain.c b/src/os/unix/ngx_writev_chain.c
index 2f5b175..d9c94dd 100644
--- a/src/os/unix/ngx_writev_chain.c
+++ b/src/os/unix/ngx_writev_chain.c
@@ -13,15 +13,14 @@
 ngx_chain_t *
 ngx_writev_chain(ngx_connection_t *c, ngx_chain_t *in, off_t limit)
 {
-    u_char        *prev;
-    ssize_t        n, size, sent;
+    ssize_t        n, sent;
     off_t          send, prev_send;
     ngx_uint_t     eintr;
     ngx_err_t      err;
-    ngx_array_t    vec;
     ngx_chain_t   *cl;
     ngx_event_t   *wev;
-    struct iovec  *iov, iovs[NGX_IOVS_PREALLOCATE];
+    ngx_iovec_t    vec;
+    struct iovec   iovs[NGX_IOVS_PREALLOCATE];
 
     wev = c->write;
 
@@ -48,61 +47,43 @@
 
     send = 0;
 
-    vec.elts = iovs;
-    vec.size = sizeof(struct iovec);
+    vec.iovs = iovs;
     vec.nalloc = NGX_IOVS_PREALLOCATE;
-    vec.pool = c->pool;
 
     for ( ;; ) {
-        prev = NULL;
-        iov = NULL;
         eintr = 0;
         prev_send = send;
 
-        vec.nelts = 0;
-
         /* create the iovec and coalesce the neighbouring bufs */
 
-        for (cl = in; cl && send < limit; cl = cl->next) {
+        cl = ngx_output_chain_to_iovec(&vec, in, limit - send, c->log);
 
-            if (ngx_buf_special(cl->buf)) {
-                continue;
-            }
-
-#if 1
-            if (!ngx_buf_in_memory(cl->buf)) {
-                ngx_debug_point();
-            }
-#endif
-
-            size = cl->buf->last - cl->buf->pos;
-
-            if (send + size > limit) {
-                size = (ssize_t) (limit - send);
-            }
-
-            if (prev == cl->buf->pos) {
-                iov->iov_len += size;
-
-            } else {
-                if (vec.nelts >= IOV_MAX) {
-                    break;
-                }
-
-                iov = ngx_array_push(&vec);
-                if (iov == NULL) {
-                    return NGX_CHAIN_ERROR;
-                }
-
-                iov->iov_base = (void *) cl->buf->pos;
-                iov->iov_len = size;
-            }
-
-            prev = cl->buf->pos + size;
-            send += size;
+        if (cl == NGX_CHAIN_ERROR) {
+            return NGX_CHAIN_ERROR;
         }
 
-        n = writev(c->fd, vec.elts, vec.nelts);
+        if (cl && cl->buf->in_file) {
+            ngx_log_error(NGX_LOG_ALERT, c->log, 0,
+                          "file buf in writev "
+                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
+                          cl->buf->temporary,
+                          cl->buf->recycled,
+                          cl->buf->in_file,
+                          cl->buf->start,
+                          cl->buf->pos,
+                          cl->buf->last,
+                          cl->buf->file,
+                          cl->buf->file_pos,
+                          cl->buf->file_last);
+
+            ngx_debug_point();
+
+            return NGX_CHAIN_ERROR;
+        }
+
+        send += vec.size;
+
+        n = writev(c->fd, vec.iovs, vec.count);
 
         if (n == -1) {
             err = ngx_errno;
@@ -148,3 +129,77 @@
         }
     }
 }
+
+
+ngx_chain_t *
+ngx_output_chain_to_iovec(ngx_iovec_t *vec, ngx_chain_t *in, size_t limit,
+    ngx_log_t *log)
+{
+    size_t         total, size;
+    u_char        *prev;
+    ngx_uint_t     n;
+    struct iovec  *iov;
+
+    iov = NULL;
+    prev = NULL;
+    total = 0;
+    n = 0;
+
+    for ( /* void */ ; in && total < limit; in = in->next) {
+
+        if (ngx_buf_special(in->buf)) {
+            continue;
+        }
+
+        if (in->buf->in_file) {
+            break;
+        }
+
+        if (!ngx_buf_in_memory(in->buf)) {
+            ngx_log_error(NGX_LOG_ALERT, log, 0,
+                          "bad buf in output chain "
+                          "t:%d r:%d f:%d %p %p-%p %p %O-%O",
+                          in->buf->temporary,
+                          in->buf->recycled,
+                          in->buf->in_file,
+                          in->buf->start,
+                          in->buf->pos,
+                          in->buf->last,
+                          in->buf->file,
+                          in->buf->file_pos,
+                          in->buf->file_last);
+
+            ngx_debug_point();
+
+            return NGX_CHAIN_ERROR;
+        }
+
+        size = in->buf->last - in->buf->pos;
+
+        if (size > limit - total) {
+            size = limit - total;
+        }
+
+        if (prev == in->buf->pos) {
+            iov->iov_len += size;
+
+        } else {
+            if (n == vec->nalloc) {
+                break;
+            }
+
+            iov = &vec->iovs[n++];
+
+            iov->iov_base = (void *) in->buf->pos;
+            iov->iov_len = size;
+        }
+
+        prev = in->buf->pos + size;
+        total += size;
+    }
+
+    vec->count = n;
+    vec->size = total;
+
+    return in;
+}