a.c

int write_to_ngx(void* req_ctx, void* buffer, size_t size) {
    ngx_http_request_t          *r;
    ngx_http_lua_ctx_t          *ctx;
    void                        *p;
    ngx_buf_t                   *b;
    ngx_chain_t                 *cl;
    ngx_int_t                    rc;

    if (0 == size) {
        WARN("0 size to write");
        return 0;
    }

    r = (ngx_http_request_t*) req_ctx;

    if (r == NULL) {
        return -9;
    }

    ctx = ngx_http_get_module_ctx(r, ngx_http_lua_module);

    if (ctx == NULL) {
        return -8;
    }

    /*
    ngx_http_cdata_check_context(ctx, NGX_HTTP_LUA_CONTEXT_REWRITE
                               | NGX_HTTP_LUA_CONTEXT_ACCESS
                               | NGX_HTTP_LUA_CONTEXT_CONTENT); */

    if (ctx->acquired_raw_req_socket) {
        //"raw request socket acquired";
        return -6;
    }

    if (r->header_only) {
        //"header only";
        return -5;
    }

    if (ctx->eof) {
        return -4;
    }

    cl = ngx_http_lua_chain_get_free_buf(r->connection->log, r->pool,
                                         &ctx->free_bufs, size);

    if (cl == NULL) {
        return -2;
    }

    b = cl->buf;

    p = buffer;

    b->last = ngx_copy(b->last, (u_char *) p, size);

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0, "lua write response");

    rc = ngx_http_lua_send_chain_link(r, ctx, cl);

    if (rc == NGX_ERROR || rc >= NGX_HTTP_SPECIAL_RESPONSE) {
        return -1;
    }

    dd("downstream write: %d, buf len: %d", (int) rc, (int) (b->last - b->pos));

    return 0;
}