Example body filter hangs when modified a little bit - request is not terminating.

ptcell nginx-forum at forum.nginx.org
Thu Jan 11 01:05:15 UTC 2018

I tried out this nginx example ngx_http_foo_body_filter body filter (here
) and got that to work just fine.  It inserts a "foo" string before each
incoming buffer.

I tried modifying a little bit so that it puts the foo string AFTER each
incoming buffer chain in the list.   The pages render correctly, but the
request never terminates and the browser just sits there spinning.   I don't
know what I'm doing wrong.   I'm pretty sure it is not module ordering
because the original version works ok.   I also set the content length to -1
in the header filter, etc.

In the debugger, the out linked chain looks right with no cycles or

I appreciate any help you can give.  Thank you.

Here is my version:

ngx_http_foo_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
    ngx_int_t                   rc;
    ngx_buf_t                  *b;
    ngx_chain_t                *cl, *tl, *out, **ll;
    ngx_http_foo_filter_ctx_t  *ctx;

    ctx = ngx_http_get_module_ctx(r, ngx_http_foo_filter_module);
    if (ctx == NULL) {
        return ngx_http_next_body_filter(r, in);

    /* create a new chain "out" from "in" with all the changes */

    ll = &out;

    for (cl = in; cl; cl = cl->next) {

        /* append the next incoming buffer */

        tl = ngx_alloc_chain_link(r->pool);
        if (tl == NULL) {
            return NGX_ERROR;

        tl->buf = cl->buf;
        *ll = tl;
        ll = &tl->next;

        /* append "foo" in a reused buffer if possible */

        tl = ngx_chain_get_free_buf(r->pool, &ctx->free);
        if (tl == NULL) {
            return NGX_ERROR;

        b = tl->buf;
        b->tag = (ngx_buf_tag_t) &ngx_http_foo_filter_module;
        b->memory = 1;
        b->pos = (u_char *) "foo";
        b->last = b->pos + 3;

        *ll = tl;
        ll = &tl->next;


    *ll = NULL;

    /* send the new chain */

    rc = ngx_http_next_body_filter(r, out);

    /* update "busy" and "free" chains for reuse */

    ngx_chain_update_chains(r->pool, &ctx->free, &ctx->busy, &out,
                            (ngx_buf_tag_t) &ngx_http_foo_filter_module);

    return rc;

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,278094,278094#msg-278094

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