[vlc-devel] [PATCH 6/7] mdns: Add basic ip address detection (Linux)

[Roland Bewick]

Hi Alexandre, thanks for the reply.

A heuristic sounds better :-) Do you have any resources you could link 
me to?

Currently I made it so the user can provide the http-host argument which 
will disable the ip address detection.

Example usage:

vlc --services-advertisement mdns --http-port 5028 --http-host 10.0.0.22 
--intf http

Roland

On 24/07/2019 10:56 PM, Alexandre Janniaux wrote:
> Hi,
>
> This can't work at all, on archlinux, debian, fedora, etc, it's not ethxx
> anymore since a long time and can't be guessed like that.
>
> You would have better heuristic with using the ip associated for the default
> route, but you might even want to choose the interface(s?) on which you're
> exposing the services.
>
> Greats,
>
> --
> Alexandre Janniaux
> VideoLabs
>
> On Wed, Jul 24, 2019 at 10:43:49PM +0700, Roland Bewick wrote:
>> ---
>>   modules/services_discovery/microdns.c | 62 +++++++++++++++++++++++++++++++++--
>>   1 file changed, 59 insertions(+), 3 deletions(-)
>>
>> diff --git a/modules/services_discovery/microdns.c b/modules/services_discovery/microdns.c
>> index c460126b58..fa34ffa8d8 100644
>> --- a/modules/services_discovery/microdns.c
>> +++ b/modules/services_discovery/microdns.c
>> @@ -28,6 +28,12 @@
>>   #include <stdatomic.h>
>>   #include <assert.h>
>>
>> +#if defined( _WIN32 )
>> +
>> +#else
>> +    #include <ifaddrs.h>
>> +#endif
>> +
>>   #include <vlc_common.h>
>>   #include <vlc_plugin.h>
>>   #include <vlc_modules.h>
>> @@ -868,9 +874,59 @@ CloseRD( vlc_object_t *p_this )
>>       CleanDiscoveryCommon( p_sys );
>>   }
>>
>> -static char * detect_ip_address()
>> +static char * detect_ip_address( vlc_object_t *p_obj )
>>   {
>> -    return strdup("127.0.0.1"); /* TODO: actually detect ip address */
>> +    char result[16] = "127.0.0.1";
>> +    bool found = false;
>> +#if defined( _WIN32 )
>> +
>> +#else
>> +    struct ifaddrs *id;
>> +    if( getifaddrs( &id ) == 0 )
>> +    {
>> +        int selected_priority = 0;
>> +
>> +        for( ; id != NULL; id = id->ifa_next )
>> +        {
>> +            if( id->ifa_addr->sa_family == AF_INET )
>> +            {
>> +                struct sockaddr_in *addr_in = (struct sockaddr_in *)id->ifa_addr;
>> +
>> +                char *ip_address = inet_ntoa( addr_in->sin_addr );
>> +
>> +                /* TODO: smarter priority function. */
>> +                int priority = 0;
>> +                if( strncmp( "eth0", id->ifa_name, strlen( "eth0" ) ) == 0 )
>> +                {
>> +                    priority = 1000;
>> +                }
>> +                else if( strncmp( "wifi0", id->ifa_name, strlen( "wifi0" ) ) == 0 )
>> +                {
>> +                    priority = 2000;
>> +                }
>> +
>> +                msg_Dbg( p_obj, "Assigned interface %s priority %d",
>> +                         id->ifa_name, priority);
>> +
>> +                if( priority > selected_priority )
>> +                {
>> +                    strcpy( result, ip_address );
>> +                    selected_priority = priority;
>> +                    found = true;
>> +                }
>> +            }
>> +        }
>> +    }
>> +    else
>> +    {
>> +        msg_Err( p_obj, "Couldn't get interface addresses");
>> +    }
>> +#endif
>> +
>> +    if ( !found )
>> +        msg_Err( p_obj, "No interface address found");
>> +
>> +    return strdup(result);
>>   }
>>
>>   static int
>> @@ -901,7 +957,7 @@ OpenSA( vlc_object_t *p_obj )
>>       if( !p_sys->psz_http_host )
>>       {
>>           msg_Dbg( p_obj, "http-host unset, detecting local IP address...");
>> -        p_sys->psz_http_host = detect_ip_address();
>> +        p_sys->psz_http_host = detect_ip_address( p_obj );
>>           msg_Dbg( p_obj, "chose local IP address: %s", p_sys->psz_http_host);
>>       }
>>
>> --
>> 2.11.0
>>
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