Resolver: retry sending queries on errors (ticket #1511). Errors when sending UDP datagrams can happen, e.g., when local IP address changes (see fa0e093b64d7), or an unavailable DNS server on the LAN can cause send() to fail with EHOSTDOWN on BSD systems. If this happens during initial query, retry sending immediately, to a different DNS server when possible. If this is not enough, allow normal resend to happen by ignoring the return code of the second ngx_resolver_send_query() call, much like we do in ngx_resolver_resend().

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


#ifndef _NGX_MD5_H_INCLUDED_
#define _NGX_MD5_H_INCLUDED_


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


typedef struct {
    uint64_t  bytes;
    uint32_t  a, b, c, d;
    u_char    buffer[64];
} ngx_md5_t;


void ngx_md5_init(ngx_md5_t *ctx);
void ngx_md5_update(ngx_md5_t *ctx, const void *data, size_t size);
void ngx_md5_final(u_char result[16], ngx_md5_t *ctx);


#endif /* _NGX_MD5_H_INCLUDED_ */