Stream: relaxed next upstream condition (ticket #1317). When switching to a next upstream, some buffers could be stuck in the middle of the filter chain. A condition existed that raised an error when this happened. As it turned out, this condition prevented switching to a next upstream if ssl preread was used with the TCP protocol (see the ticket). In fact, the condition does not make sense for TCP, since after successful connection to an upstream switching to another upstream never happens. As for UDP, the issue with stuck buffers is unlikely to happen, but is still possible. Specifically, if a filter delays sending data to upstream. The condition can be relaxed to only check the "buffered" bitmask of the upstream connection. The new condition is simpler and fixes the ticket issue as well. Additionally, the upstream_out chain is now reset for UDP prior to connecting to a new upstream to prevent repeating the client data twice.

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_CHANNEL_H_INCLUDED_
#define _NGX_CHANNEL_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>


typedef struct {
    ngx_uint_t  command;
    ngx_pid_t   pid;
    ngx_int_t   slot;
    ngx_fd_t    fd;
} ngx_channel_t;


ngx_int_t ngx_write_channel(ngx_socket_t s, ngx_channel_t *ch, size_t size,
    ngx_log_t *log);
ngx_int_t ngx_read_channel(ngx_socket_t s, ngx_channel_t *ch, size_t size,
    ngx_log_t *log);
ngx_int_t ngx_add_channel_event(ngx_cycle_t *cycle, ngx_fd_t fd,
    ngx_int_t event, ngx_event_handler_pt handler);
void ngx_close_channel(ngx_fd_t *fd, ngx_log_t *log);


#endif /* _NGX_CHANNEL_H_INCLUDED_ */