Listen directive example analysis in nginx

listen address[:port] [default_server] [setfib=number] [backlog=number] [rcvbuf=size] [sndbuf=size] [accept_filter=filter] [deferred] [bind] [ipv6only=on|off] [ssl] [so_keepalive=on|off|[keepidle]:[keepintvl]:[keepcnt]];

listen 127.0.0.1:8000;
listen 127.0.0.1 without adding port, default listening port is 80;
listen 8000
listen *:8000
listen localhost:8000

ngx_int_t
ngx_parse_url(ngx_pool_t *pool, ngx_url_t *u)
{
 u_char *p;
 size_t len;

 p = u->url.data;
 len = u->url.len;
 // Here is the protocol for parsing the Unix domain if (len >= 5 && ngx_strncasecmp(p, (u_char *) "unix:", 5) == 0) {
 return ngx_parse_unix_domain_url(pool, u);
 }
 // Parse IPV6 protocol if (len && p[0] == '[') {
 return ngx_parse_inet6_url(pool, u);
 }
 // Parse IPV4 protocol return ngx_parse_inet_url(pool, u);
}

// u.url = "80";
// u.listen = 1;
// u.default_port = 80;
static ngx_int_t
ngx_parse_inet_url(ngx_pool_t *pool, ngx_url_t *u)
{
 u_char *p, *host, *port, *last, *uri, *args;
 size_t len;
 ngx_int_t n;
 struct sockaddr_in *sin;
#if (NGX_HAVE_INET6)
 struct sockaddr_in6 *sin6;
#endif

 u->socklen = sizeof(struct sockaddr_in);
 sin = (struct sockaddr_in *) &u->sockaddr;
 sin->sin_family = AF_INET; //IPV4 type u->family = AF_INET; 

 host = u->url.data; // "80"

 last = host + u->url.len; // The position of the last character of host port = ngx_strlchr(host, last, ':'); // Find port, here is NULL

 uri = ngx_strlchr(host, last, '/'); // Find uri, here is NULL

 args = ngx_strlchr(host, last, '?'); // Find the parameter args, which is NULL here

 if (args) {
 if (uri == NULL || args < uri) {
 uri = args;
 }
 }

 if (uri) {
 if (u->listen || !u->uri_part) {
 u->err = "invalid host";
 return NGX_ERROR;
 }

 u->uri.len = last - uri;
 u->uri.data = uri;

 last = uri;

 if (uri < port) {
 port = NULL;
 }
 }

 if (port) {
 port++;

 len = last - port;

 n = ngx_atoi(port, len);

 if (n < 1 || n > 65535) {
 u->err = "invalid port";
 return NGX_ERROR;
 }

 u->port = (in_port_t) n;
 sin->sin_port = htons((in_port_t) n);

 u->port_text.len = len;
 u->port_text.data = port;

 last = port - 1;

 } else {
 if (uri == NULL) {

 if (u->listen) {

 /* test value as port only */

 n = ngx_atoi(host, last - host);

 if (n != NGX_ERROR) {

 if (n < 1 || n > 65535) {
 u->err = "invalid port";
 return NGX_ERROR;
 }

 u->port = (in_port_t) n;
 sin->sin_port = htons((in_port_t) n);

 u->port_text.len = last - host;
 u->port_text.data = host;

 u->wildcard = 1;

 return NGX_OK;
 }
 }
 }

 u->no_port = 1;
 u->port = u->default_port;
 sin->sin_port = htons(u->default_port);
 }

 len = last - host;

 if (len == 0) {
 u->err = "no host";
 return NGX_ERROR;
 }

 u->host.len = len;
 u->host.data = host;

 if (u->listen && len == 1 && *host == '*') {
 sin->sin_addr.s_addr = INADDR_ANY;
 u->wildcard = 1;
 return NGX_OK;
 }

 sin->sin_addr.s_addr = ngx_inet_addr(host, len);

 if (sin->sin_addr.s_addr != INADDR_NONE) {

 if (sin->sin_addr.s_addr == INADDR_ANY) {
 u->wildcard = 1;
 }

 u->naddrs = 1;

 u->addrs = ngx_pcalloc(pool, sizeof(ngx_addr_t));
 if (u->addrs == NULL) {
 return NGX_ERROR;
 }

 sin = ngx_pcalloc(pool, sizeof(struct sockaddr_in));
 if (sin == NULL) {
 return NGX_ERROR;
 }

 ngx_memcpy(sin, &u->sockaddr, sizeof(struct sockaddr_in));

 u->addrs[0].sockaddr = (struct sockaddr *) sin;
 u->addrs[0].socklen = sizeof(struct sockaddr_in);

 p = ngx_pnalloc(pool, u->host.len + sizeof(":65535") - 1);
 if (p == NULL) {
 return NGX_ERROR;
 }

 u->addrs[0].name.len = ngx_sprintf(p, "%V:%d",
  &u->host, u->port) - p;
 u->addrs[0].name.data = p;

 return NGX_OK;
 }

 if (u->no_resolve) {
 return NGX_OK;
 }

 if (ngx_inet_resolve_host(pool, u) != NGX_OK) {
 return NGX_ERROR;
 }

 u->family = u->addrs[0].sockaddr->sa_family;
 u->socklen = u->addrs[0].socklen;
 ngx_memcpy(&u->sockaddr, u->addrs[0].sockaddr, u->addrs[0].socklen);

 switch (u->family) {

#if (NGX_HAVE_INET6)
 case AF_INET6:
 sin6 = (struct sockaddr_in6 *) &u->sockaddr;

 if (IN6_IS_ADDR_UNSPECIFIED(&sin6->sin6_addr)) {
 u->wildcard = 1;
 }

 break;
#endif

 default: /* AF_INET */
 sin = (struct sockaddr_in *) &u->sockaddr;

 if (sin->sin_addr.s_addr == INADDR_ANY) {
 u->wildcard = 1;
 }

 break;
 }

 return NGX_OK;
}

{ 
 ngx_string("listen"),
 NGX_HTTP_SRV_CONF|NGX_CONF_1MORE,
 ngx_http_core_listen,
 NGX_HTTP_SRV_CONF_OFFSET,
 0,
 NULL 
}

static char *
ngx_http_core_listen(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
 ngx_http_core_srv_conf_t *cscf = conf;

 ngx_str_t *value, size;
 ngx_url_t u;
 ngx_uint_t n;
 ngx_http_listen_opt_t lsopt;

 cscf->listen = 1;

 value = cf->args->elts;

 ngx_memzero(&u, sizeof(ngx_url_t));

 u.url = value[1];
 u.listen = 1;
 u.default_port = 80;

 if (ngx_parse_url(cf->pool, &u) != NGX_OK) {
 return NGX_CONF_ERROR;
 }

 ngx_memzero(&lsopt, sizeof(ngx_http_listen_opt_t));

 ngx_memcpy(&lsopt.sockaddr.sockaddr, &u.sockaddr, u.socklen);

 lsopt.socklen = u.socklen;
 lsopt.backlog = NGX_LISTEN_BACKLOG;
 lsopt.rcvbuf = -1;
 lsopt.sndbuf = -1;
#if (NGX_HAVE_SETFIB)
 lsopt.setfib = -1;
#endif
#if (NGX_HAVE_TCP_FASTOPEN)
 lsopt.fastopen = -1;
#endif
 lsopt.wildcard = u.wildcard;
#if (NGX_HAVE_INET6)
 lsopt.ipv6only = 1;
#endif

 (void) ngx_sock_ntop(&lsopt.sockaddr.sockaddr, lsopt.socklen, lsopt.addr,
  NGX_SOCKADDR_STRLEN, 1);

 for (n = 2; n < cf->args->nelts; n++) {

 if (ngx_strcmp(value[n].data, "default_server") == 0
 || ngx_strcmp(value[n].data, "default") == 0)
 {
 lsopt.default_server = 1;
 continue;
 }
 // The other codes here are all for processing various parameters of listen, which are useless for our analysis here}

 if (ngx_http_add_listen(cf, cscf, &lsopt) == NGX_OK) {
 return NGX_CONF_OK;
 }

 return NGX_CONF_ERROR;
}

// cf: configuration structure // cscf: configuration structure of the server where the listen directive is located // lsopt: listen option generated by ngx_http_core_listen()
ngx_int_t
ngx_http_add_listen(ngx_conf_t *cf, ngx_http_core_srv_conf_t *cscf,
 ngx_http_listen_opt_t *lsopt)
{
 in_port_t p;
 ngx_uint_t i;
 struct sockaddr *sa;
 ngx_http_conf_port_t *port;
 ngx_http_core_main_conf_t *cmcf;
 // Get the main_conf structure of the ngx_http_core_module module ngx_http_core_main_conf_t
 cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);
 // The ports field is an array if (cmcf->ports == NULL) {
  cmcf->ports = ngx_array_create(cf->temp_pool, 2,
          sizeof(ngx_http_conf_port_t));
  if (cmcf->ports == NULL) {
   return NGX_ERROR;
  }
 }

 sa = &lsopt->sockaddr.sockaddr;
 p = ngx_inet_get_port(sa);

 port = cmcf->ports->elts;
 for (i = 0; i < cmcf->ports->nelts; i++) {

  if (p != port[i].port || sa->sa_family != port[i].family) {
   continue;
  }

  /* a port is already in the port list */

  return ngx_http_add_addresses(cf, cscf, &port[i], lsopt);
 }

 /* add a port to the port list */

 port = ngx_array_push(cmcf->ports);
 if (port == NULL) {
  return NGX_ERROR;
 }

 port->family = sa->sa_family;
 port->port = p;
 port->addrs.elts = NULL;

 return ngx_http_add_address(cf, cscf, port, lsopt);
}