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https://github.com/mas-bandwidth/reliable

Packet acknowledgement system for UDP
https://github.com/mas-bandwidth/reliable

ack fragmentation game-development mtu protocol rtt udp

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Packet acknowledgement system for UDP

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README 

        
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# Introduction



**reliable** is a simple packet acknowledgement system for UDP-based protocols.



It's useful in situations where you need to know which UDP packets you sent were received by the other side.



![image](https://github.com/mas-bandwidth/reliable/assets/696656/c58edcde-8bff-4683-8bc9-36c562ee7570)



It has the following features:



1. Acknowledgement when packets are received

2. Packet fragmentation and reassembly

3. RTT, jitter and packet loss estimates



reliable is stable and production ready.



# Usage



Reliable is designed to operate with your own network socket library.



If you don't have one already, try [netcode](https://github.com/mas-bandwidth/netcode), it's designed to work well with reliable.



First, create an endpoint on each side of the connection:



```c

struct reliable_config_t config;



reliable_default_config( &config );



config.max_packet_size = 32 * 1024;

config.fragment_above = 1200;

config.max_fragments = 32;

config.fragment_size = 1024;

config.transmit_packet_function = transmit_packet;

config.process_packet_function = process_packet;



reliable_endpoint_t * endpoint = reliable_endpoint_create( &config, time );

if ( endpoint == NULL )

{

  printf( "error: could not create endpoint\n" );

  exit(1);

}

```



For example, in a client/server setup you would have one endpoint on each client, and n endpoints on the server, one for each client slot.



Next, create a function to transmit packets:



```c

static void transmit_packet( void * context, uint64_t id, uint16_t sequence, uint8_t * packet_data, int packet_bytes )

{

    // send packet using your own udp socket

}

```



And a function to process received packets:



```c

static int process_packet( void * context, uint64_t id, uint16_t sequence, uint8_t * packet_data, int packet_bytes )

{

    // read the packet here and process its contents, return 0 if the packet should not be acked

    return 1;

}

```



For each packet you receive from your udp socket, call this on the endpoint that should receive it:



```c

reliable_endpoint_receive_packet( endpoint, packet_data, packet_bytes );

```



Now you can send packets through the endpoint:



```c

reliable_endpoint_send_packet( endpoint, packet_data, packet_bytes );

```



And get acks like this:



```c

int num_acks;

uint16_t * acks = reliable_endpoint_get_acks( endpoint, &num_acks );

for ( int i = 0; i < num_acks; i++ )

{

    printf( "acked packet %d\n", acks[j] );

}

```



Once you process all acks, clear them:



```c

reliable_endpoint_clear_acks( endpoint );

```



Before you send a packet, you can ask reliable what sequence number the sent packet will have:



```c

uint16_t sequence = reliable_endpoint_next_packet_sequence( endpoint );

```



This way you can map acked sequence numbers to the contents of packets you sent, for example, resending unacked messages until a packet that included that message was acked.



Make sure to update each endpoint once per-frame. This keeps track of network stats like latency, jitter, packet loss and bandwidth:



```c

reliable_endpoint_update( endpoint, time );

```



You can then grab stats from the endpoint:



```c

    printf( rtt = %.1fms | jitter = %.1fms | packet loss = %.1f%%\n", 

        reliable_endpoint_rtt_min( endpoint ),

        reliable_endpoint_jitter_avg_vs_min_rtt( endpoint ),

        reliable_endpoint_packet_loss( endpoint ) ),

```



When you are finished with an endpoint, destroy it:



```c

reliable_endpoint_destroy( endpoint );

```



# Author



The author of this library is [Glenn Fiedler](https://www.linkedin.com/in/glenn-fiedler-11b735302/).



Open source libraries by the same author include: [netcode](https://github.com/mas-bandwidth/netcode), [serialize](https://github.com/mas-bandwidth/serialize),  and [yojimbo](https://github.com/mas-bandwidth/yojimbo)



If you find this software useful, [please consider sponsoring it](https://github.com/sponsors/mas-bandwidth). Thanks!



# License



[BSD 3-Clause license](https://opensource.org/licenses/BSD-3-Clause).