new file mode 100644
--- /dev/null
+++ b/src/http/modules/ngx_http_sub_filter_module.c
@@ -0,0 +1,794 @@
+
+/*
+ * Copyright (C) Igor Sysoev
+ */
+
+
+#include <ngx_config.h>
+#include <ngx_core.h>
+#include <ngx_http.h>
+
+
+typedef struct {
+    ngx_str_t      match;
+    ngx_str_t      sub;
+
+    ngx_array_t   *types;     /* array of ngx_str_t */
+
+    ngx_array_t   *sub_lengths;
+    ngx_array_t   *sub_values;
+
+    ngx_flag_t     once;
+} ngx_http_sub_loc_conf_t;
+
+
+typedef enum {
+    sub_start_state = 0,
+    sub_match_state,
+} ngx_http_sub_state_e;
+
+
+typedef struct {
+    ngx_str_t      match;
+
+    ngx_uint_t     once;   /* unsigned  once:1 */
+
+    ngx_buf_t     *buf;
+
+    u_char        *pos;
+    u_char        *copy_start;
+    u_char        *copy_end;
+
+    ngx_chain_t   *in;
+    ngx_chain_t   *out;
+    ngx_chain_t  **last_out;
+    ngx_chain_t   *busy;
+    ngx_chain_t   *free;
+
+    ngx_str_t      sub;
+
+    ngx_uint_t     state;
+    size_t         saved;
+    size_t         looked;
+} ngx_http_sub_ctx_t;
+
+
+static ngx_int_t ngx_http_sub_output(ngx_http_request_t *r,
+    ngx_http_sub_ctx_t *ctx);
+static ngx_int_t ngx_http_sub_parse(ngx_http_request_t *r,
+    ngx_http_sub_ctx_t *ctx);
+
+static char * ngx_http_sub_filter(ngx_conf_t *cf, ngx_command_t *cmd,
+    void *conf);
+static char *ngx_http_sub_types(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);
+static void *ngx_http_sub_create_conf(ngx_conf_t *cf);
+static char *ngx_http_sub_merge_conf(ngx_conf_t *cf,
+    void *parent, void *child);
+static ngx_int_t ngx_http_sub_filter_init(ngx_conf_t *cf);
+
+
+static ngx_command_t  ngx_http_sub_filter_commands[] = {
+
+    { ngx_string("sub_filter"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_TAKE2,
+      ngx_http_sub_filter,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      0,
+      NULL },
+
+    { ngx_string("sub_filter_types"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_1MORE,
+      ngx_http_sub_types,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      0,
+      NULL },
+
+    { ngx_string("sub_filter_once"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
+      ngx_conf_set_flag_slot,
+      NGX_HTTP_LOC_CONF_OFFSET,
+      offsetof(ngx_http_sub_loc_conf_t, once),
+      NULL },
+
+      ngx_null_command
+};
+
+
+static ngx_http_module_t  ngx_http_sub_filter_module_ctx = {
+    NULL,                                  /* preconfiguration */
+    ngx_http_sub_filter_init,              /* postconfiguration */
+
+    NULL,                                  /* create main configuration */
+    NULL,                                  /* init main configuration */
+
+    NULL,                                  /* create server configuration */
+    NULL,                                  /* merge server configuration */
+
+    ngx_http_sub_create_conf,              /* create location configuration */
+    ngx_http_sub_merge_conf                /* merge location configuration */
+};
+
+
+ngx_module_t  ngx_http_sub_filter_module = {
+    NGX_MODULE_V1,
+    &ngx_http_sub_filter_module_ctx,       /* module context */
+    ngx_http_sub_filter_commands,          /* module directives */
+    NGX_HTTP_MODULE,                       /* module type */
+    NULL,                                  /* init master */
+    NULL,                                  /* init module */
+    NULL,                                  /* init process */
+    NULL,                                  /* init thread */
+    NULL,                                  /* exit thread */
+    NULL,                                  /* exit process */
+    NULL,                                  /* exit master */
+    NGX_MODULE_V1_PADDING
+};
+
+
+static ngx_http_output_header_filter_pt  ngx_http_next_header_filter;
+static ngx_http_output_body_filter_pt    ngx_http_next_body_filter;
+
+
+static ngx_int_t
+ngx_http_sub_header_filter(ngx_http_request_t *r)
+{
+    ngx_str_t                *type;
+    ngx_uint_t                i;
+    ngx_http_sub_ctx_t        *ctx;
+    ngx_http_sub_loc_conf_t  *slcf;
+
+    slcf = ngx_http_get_module_loc_conf(r, ngx_http_sub_filter_module);
+
+    if (slcf->match.len == 0
+        || r->headers_out.content_type.len == 0
+        || r->headers_out.content_length_n == 0)
+    {
+        return ngx_http_next_header_filter(r);
+    }
+
+    type = slcf->types->elts;
+    for (i = 0; i < slcf->types->nelts; i++) {
+        if (r->headers_out.content_type.len >= type[i].len
+            && ngx_strncasecmp(r->headers_out.content_type.data,
+                               type[i].data, type[i].len) == 0)
+        {
+            goto found;
+        }
+    }
+
+    return ngx_http_next_header_filter(r);
+
+found:
+
+    ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_sub_ctx_t));
+    if (ctx == NULL) {
+        return NGX_ERROR;
+    }
+
+    ngx_http_set_ctx(r, ctx, ngx_http_sub_filter_module);
+
+    ctx->match = slcf->match;
+    ctx->last_out = &ctx->out;
+    ctx->sub = slcf->sub;
+
+    r->filter_need_in_memory = 1;
+
+    if (r == r->main) {
+        ngx_http_clear_content_length(r);
+        ngx_http_clear_last_modified(r);
+    }
+
+    return ngx_http_next_header_filter(r);
+}
+
+
+static ngx_int_t
+ngx_http_sub_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
+{
+    ngx_int_t                  rc;
+    ngx_buf_t                 *b;
+    ngx_chain_t               *cl;
+    ngx_http_sub_ctx_t        *ctx;
+    ngx_http_sub_loc_conf_t   *slcf;
+
+    ctx = ngx_http_get_module_ctx(r, ngx_http_sub_filter_module);
+
+    if (ctx == NULL) {
+        return ngx_http_next_body_filter(r, in);
+    }
+
+    if ((in == NULL
+         && ctx->buf == NULL
+         && ctx->in == NULL
+         && ctx->busy == NULL))
+    {
+        return ngx_http_next_body_filter(r, in);
+    }
+
+    if (ctx->once && (ctx->buf == NULL || ctx->in == NULL)) {
+
+        if (ctx->busy) {
+            if (ngx_http_sub_output(r, ctx) == NGX_ERROR) {
+                return NGX_ERROR;
+            }
+        }
+
+        return ngx_http_next_body_filter(r, in);
+    }
+
+    /* add the incoming chain to the chain ctx->in */
+
+    if (in) {
+        if (ngx_chain_add_copy(r->pool, &ctx->in, in) == NGX_ERROR) {
+            return NGX_ERROR;
+        }
+    }
+
+    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "http sub filter \"%V\"", &r->uri);
+
+    while (ctx->in || ctx->buf) {
+
+        if (ctx->buf == NULL ){
+            ctx->buf = ctx->in->buf;
+            ctx->in = ctx->in->next;
+            ctx->pos = ctx->buf->pos;
+        }
+
+        if (ctx->state == sub_start_state) {
+            ctx->copy_start = ctx->pos;
+            ctx->copy_end = ctx->pos;
+        }
+
+        b = NULL;
+
+        while (ctx->pos < ctx->buf->last) {
+
+            ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                           "saved: %d state: %d", ctx->saved, ctx->state);
+
+            rc = ngx_http_sub_parse(r, ctx);
+
+            ngx_log_debug4(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                           "parse: %d, looked: %d %p-%p",
+                           rc, ctx->looked, ctx->copy_start, ctx->copy_end);
+
+            if (rc == NGX_ERROR) {
+                return rc;
+            }
+
+            if (ctx->copy_start != ctx->copy_end) {
+
+                ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                               "saved: %d", ctx->saved);
+
+                if (ctx->saved) {
+
+                    if (ctx->free) {
+                        cl = ctx->free;
+                        ctx->free = ctx->free->next;
+                        b = cl->buf;
+                        ngx_memzero(b, sizeof(ngx_buf_t));
+
+                    } else {
+                        b = ngx_calloc_buf(r->pool);
+                        if (b == NULL) {
+                            return NGX_ERROR;
+                        }
+
+                        cl = ngx_alloc_chain_link(r->pool);
+                        if (cl == NULL) {
+                            return NGX_ERROR;
+                        }
+
+                        cl->buf = b;
+                    }
+
+                    b->memory = 1;
+                    b->pos = ctx->match.data;
+                    b->last = ctx->match.data + ctx->saved;
+
+                    *ctx->last_out = cl;
+                    ctx->last_out = &cl->next;
+
+                    ctx->saved = 0;
+                }
+
+                if (ctx->free) {
+                    cl = ctx->free;
+                    ctx->free = ctx->free->next;
+                    b = cl->buf;
+
+                } else {
+                    b = ngx_alloc_buf(r->pool);
+                    if (b == NULL) {
+                        return NGX_ERROR;
+                    }
+
+                    cl = ngx_alloc_chain_link(r->pool);
+                    if (cl == NULL) {
+                        return NGX_ERROR;
+                    }
+
+                    cl->buf = b;
+                }
+
+                ngx_memcpy(b, ctx->buf, sizeof(ngx_buf_t));
+
+                b->pos = ctx->copy_start;
+                b->last = ctx->copy_end;
+                b->shadow = NULL;
+                b->last_buf = 0;
+                b->recycled = 0;
+
+                if (b->in_file) {
+                    b->file_last = b->file_pos + (b->last - b->start);
+                    b->file_pos += b->pos - b->start;
+                }
+
+                cl->next = NULL;
+                *ctx->last_out = cl;
+                ctx->last_out = &cl->next;
+            }
+
+            if (ctx->state == sub_start_state) {
+                ctx->copy_start = ctx->pos;
+                ctx->copy_end = ctx->pos;
+
+            } else {
+                ctx->copy_start = NULL;
+                ctx->copy_end = NULL;
+            }
+
+            if (rc == NGX_AGAIN) {
+                continue;
+            }
+
+
+            /* rc == NGX_OK */
+
+            b = ngx_calloc_buf(r->pool);
+            if (b == NULL) {
+                return NGX_ERROR;
+            }
+
+            cl = ngx_alloc_chain_link(r->pool);
+            if (cl == NULL) {
+                return NGX_ERROR;
+            }
+
+            slcf = ngx_http_get_module_loc_conf(r, ngx_http_sub_filter_module);
+
+            if (ctx->sub.data == NULL) {
+
+                if (ngx_http_script_run(r, &ctx->sub, slcf->sub_lengths->elts,
+                                        0, slcf->sub_values->elts)
+                    == NULL)
+                {
+                    return NGX_ERROR;
+                }
+            }
+
+            b->memory = 1;
+            b->pos = ctx->sub.data;
+            b->last = ctx->sub.data + ctx->sub.len;
+
+            cl->buf = b;
+            cl->next = NULL;
+            *ctx->last_out = cl;
+            ctx->last_out = &cl->next;
+
+            ctx->once = slcf->once;
+
+            continue;
+        }
+
+        if (ctx->buf->last_buf || ngx_buf_in_memory(ctx->buf)) {
+            if (b == NULL) {
+                if (ctx->free) {
+                    cl = ctx->free;
+                    ctx->free = ctx->free->next;
+                    b = cl->buf;
+                    ngx_memzero(b, sizeof(ngx_buf_t));
+
+                } else {
+                    b = ngx_calloc_buf(r->pool);
+                    if (b == NULL) {
+                        return NGX_ERROR;
+                    }
+
+                    cl = ngx_alloc_chain_link(r->pool);
+                    if (cl == NULL) {
+                        return NGX_ERROR;
+                    }
+
+                    cl->buf = b;
+                }
+
+                b->sync = 1;
+
+                cl->next = NULL;
+                *ctx->last_out = cl;
+                ctx->last_out = &cl->next;
+            }
+
+            b->last_buf = ctx->buf->last_buf;
+            b->shadow = ctx->buf;
+
+            b->recycled = ctx->buf->recycled;
+        }
+
+        ctx->buf = NULL;
+
+        ctx->saved = ctx->looked;
+    }
+
+    if (ctx->out == NULL && ctx->busy == NULL) {
+        return NGX_OK;
+    }
+
+    return ngx_http_sub_output(r, ctx);
+}
+
+
+static ngx_int_t
+ngx_http_sub_output(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
+{
+    ngx_int_t     rc;
+    ngx_buf_t    *b;
+    ngx_chain_t  *cl;
+
+#if 1
+    b = NULL;
+    for (cl = ctx->out; cl; cl = cl->next) {
+        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                       "sub out: %p %p", cl->buf, cl->buf->pos);
+        if (cl->buf == b) {
+            ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
+                          "the same buf was used in sub");
+            ngx_debug_point();
+            return NGX_ERROR;
+        }
+        b = cl->buf;
+    }
+#endif
+
+    rc = ngx_http_next_body_filter(r, ctx->out);
+
+    if (ctx->busy == NULL) {
+        ctx->busy = ctx->out;
+
+    } else {
+        for (cl = ctx->busy; cl->next; cl = cl->next) { /* void */ }
+        cl->next = ctx->out;
+    }
+
+    ctx->out = NULL;
+    ctx->last_out = &ctx->out;
+
+    while (ctx->busy) {
+
+        cl = ctx->busy;
+        b = cl->buf;
+
+        if (ngx_buf_size(b) != 0) {
+            break;
+        }
+
+#if (NGX_HAVE_WRITE_ZEROCOPY)
+        if (b->zerocopy_busy) {
+            break;
+        }
+#endif
+
+        if (b->shadow) {
+            b->shadow->pos = b->shadow->last;
+        }
+
+        ctx->busy = cl->next;
+
+        if (ngx_buf_in_memory(b) || b->in_file) {
+            /* add data bufs only to the free buf chain */
+
+            cl->next = ctx->free;
+            ctx->free = cl;
+        }
+    }
+
+    if (ctx->in || ctx->buf) {
+        r->buffered |= NGX_HTTP_SUB_BUFFERED;
+
+    } else {
+        r->buffered &= ~NGX_HTTP_SUB_BUFFERED;
+    }
+
+    return rc;
+}
+
+
+static ngx_int_t
+ngx_http_sub_parse(ngx_http_request_t *r, ngx_http_sub_ctx_t *ctx)
+{
+    u_char                *p, *last, *copy_end, ch, match;
+    size_t                 looked;
+    ngx_http_sub_state_e   state;
+
+    if (ctx->once) {
+        ctx->copy_start = ctx->pos;
+        ctx->copy_end = ctx->buf->last;
+        ctx->pos = ctx->buf->last;
+        ctx->looked = 0;
+
+        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0, "once");
+
+        return NGX_AGAIN;
+    }
+
+    state = ctx->state;
+    looked = ctx->looked;
+    last = ctx->buf->last;
+    copy_end = ctx->copy_end;
+
+    for (p = ctx->pos; p < last; p++) {
+
+        ch = *p;
+        ch = ngx_tolower(ch);
+
+        if (state == sub_start_state) {
+
+            /* the tight loop */
+
+            match = ctx->match.data[0];
+
+            for ( ;; ) {
+                if (ch == match) {
+                    copy_end = p;
+                    looked = 1;
+                    state = sub_match_state;
+
+                    goto match_started;
+                }
+
+                if (++p == last) {
+                    break;
+                }
+
+                ch = *p;
+                ch = ngx_tolower(ch);
+            }
+
+            ctx->pos = p;
+            ctx->looked = looked;
+            ctx->copy_end = p;
+
+            if (ctx->copy_start == NULL) {
+                ctx->copy_start = ctx->buf->pos;
+            }
+
+            return NGX_AGAIN;
+
+        match_started:
+
+            continue;
+        }
+
+        /* state == sub_match_state */
+
+        if (ch == ctx->match.data[looked]) {
+            looked++;
+
+            if (looked == ctx->match.len) {
+                ctx->state = sub_start_state;
+                ctx->pos = p + 1;
+                ctx->looked = looked;
+                ctx->copy_end = copy_end;
+
+                if (ctx->copy_start == NULL && copy_end) {
+                    ctx->copy_start = ctx->buf->pos;
+                }
+
+                return NGX_OK;
+            }
+
+        } else if (ch == ctx->match.data[0]) {
+            copy_end = p;
+            looked = 1;
+
+        } else {
+            copy_end = p;
+            looked = 0;
+            state = sub_start_state;
+        }
+    }
+
+    ctx->state = state;
+    ctx->pos = p;
+    ctx->looked = looked;
+
+    ctx->copy_end = (state == sub_start_state) ? p : copy_end;
+
+    if (ctx->copy_start == NULL && ctx->copy_end) {
+        ctx->copy_start = ctx->buf->pos;
+    }
+
+    return NGX_AGAIN;
+}
+
+
+static char *
+ngx_http_sub_filter(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ngx_http_sub_loc_conf_t *slcf = conf;
+
+    ngx_str_t                  *value;
+    ngx_int_t                   n;
+    ngx_uint_t                  i;
+    ngx_http_script_compile_t   sc;
+
+    if (slcf->match.len) {
+        return "is duplicate";
+    }
+
+    value = cf->args->elts;
+
+    slcf->match = value[1];
+
+    for (i = 0; i < value[1].len; i++) {
+        value[1].data[i] = ngx_tolower(value[1].data[i]);
+    }
+
+    n = ngx_http_script_variables_count(&value[2]);
+
+    if (n == 0) {
+        slcf->sub = value[2];
+        return NGX_CONF_OK;
+    }
+
+    ngx_memzero(&sc, sizeof(ngx_http_script_compile_t));
+
+    sc.cf = cf;
+    sc.source = &value[2];
+    sc.lengths = &slcf->sub_lengths;
+    sc.values = &slcf->sub_values;
+    sc.variables = n;
+    sc.complete_lengths = 1;
+    sc.complete_values = 1;
+
+    if (ngx_http_script_compile(&sc) != NGX_OK) {
+        return NGX_CONF_ERROR;
+    }
+
+    return NGX_CONF_OK;
+}
+
+
+static char *
+ngx_http_sub_types(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
+{
+    ngx_http_sub_loc_conf_t *slcf = conf;
+
+    ngx_str_t   *value, *type;
+    ngx_uint_t   i;
+
+    if (slcf->types == NULL) {
+        slcf->types = ngx_array_create(cf->pool, 4, sizeof(ngx_str_t));
+        if (slcf->types == NULL) {
+            return NGX_CONF_ERROR;
+        }
+
+        type = ngx_array_push(slcf->types);
+        if (type == NULL) {
+            return NGX_CONF_ERROR;
+        }
+
+        type->len = sizeof("text/html") - 1;
+        type->data = (u_char *) "text/html";
+    }
+
+    value = cf->args->elts;
+
+    for (i = 1; i < cf->args->nelts; i++) {
+
+        if (ngx_strcmp(value[i].data, "text/html") == 0) {
+            continue;
+        }
+
+        type = ngx_array_push(slcf->types);
+        if (type == NULL) {
+            return NGX_CONF_ERROR;
+        }
+
+        type->len = value[i].len;
+
+        type->data = ngx_palloc(cf->pool, type->len + 1);
+        if (type->data == NULL) {
+            return NGX_CONF_ERROR;
+        }
+
+        ngx_cpystrn(type->data, value[i].data, type->len + 1);
+    }
+
+    return NGX_CONF_OK;
+}
+
+
+static void *
+ngx_http_sub_create_conf(ngx_conf_t *cf)
+{
+    ngx_http_sub_loc_conf_t  *slcf;
+
+    slcf = ngx_pcalloc(cf->pool, sizeof(ngx_http_sub_loc_conf_t));
+    if (slcf == NULL) {
+        return NGX_CONF_ERROR;
+    }
+
+    /*
+     * set by ngx_pcalloc():
+     *
+     *     conf->match.len = 0;
+     *     conf->match.data = NULL;
+     *     conf->sub.len = 0;
+     *     conf->sub.data = NULL;
+     *     conf->sub_lengths = NULL;
+     *     conf->sub_values = NULL;
+     *     conf->types = NULL;
+     */
+
+    slcf->once = NGX_CONF_UNSET;
+
+    return slcf;
+}
+
+
+static char *
+ngx_http_sub_merge_conf(ngx_conf_t *cf, void *parent, void *child)
+{
+    ngx_http_sub_loc_conf_t *prev = parent;
+    ngx_http_sub_loc_conf_t *conf = child;
+
+    ngx_str_t  *type;
+
+    ngx_conf_merge_value(conf->once, prev->once, 1);
+    ngx_conf_merge_str_value(conf->match, prev->match, "");
+
+    if (conf->sub.data == NULL && conf->sub_lengths == NULL) {
+        conf->sub = prev->sub;
+        conf->sub_lengths = prev->sub_lengths;
+        conf->sub_values = prev->sub_values;
+    }
+
+    if (conf->types == NULL) {
+        if (prev->types == NULL) {
+            conf->types = ngx_array_create(cf->pool, 1, sizeof(ngx_str_t));
+            if (conf->types == NULL) {
+                return NGX_CONF_ERROR;
+            }
+
+            type = ngx_array_push(conf->types);
+            if (type == NULL) {
+                return NGX_CONF_ERROR;
+            }
+
+            type->len = sizeof("text/html") - 1;
+            type->data = (u_char *) "text/html";
+
+        } else {
+            conf->types = prev->types;
+        }
+    }
+
+    return NGX_CONF_OK;
+}
+
+
+static ngx_int_t
+ngx_http_sub_filter_init(ngx_conf_t *cf)
+{
+    ngx_http_next_header_filter = ngx_http_top_header_filter;
+    ngx_http_top_header_filter = ngx_http_sub_header_filter;
+
+    ngx_http_next_body_filter = ngx_http_top_body_filter;
+    ngx_http_top_body_filter = ngx_http_sub_body_filter;
+
+    return NGX_OK;
+}