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Annotation of quake2/qcommon/net_chan.c, revision 1.1

1.1     ! root        1: 
        !             2: #include "qcommon.h"
        !             3: /*
        !             4: packet header
        !             5: -------------
        !             6: 31     sequence
        !             7: 1      does this message contain a reliable payload
        !             8: 31     acknowledge sequence
        !             9: 1      acknowledge receipt of even/odd message
        !            10: 16     qport
        !            11: The remote connection never knows if it missed a reliable message, the
        !            12: local side detects that it has been dropped by seeing a sequence acknowledge
        !            13: higher thatn the last reliable sequence, but without the correct evon/odd
        !            14: bit for the reliable set.
        !            15: If the sender notices that a reliable message has been dropped, it will be
        !            16: retransmitted.  It will not be retransmitted again until a message after
        !            17: the retransmit has been acknowledged and the reliable still failed to get there.
        !            18: if the sequence number is -1, the packet should be handled without a netcon
        !            19: The reliable message can be added to at any time by doing
        !            20: MSG_Write* (&netchan->message, <data>).
        !            21: If the message buffer is overflowed, either by a single message, or by
        !            22: multiple frames worth piling up while the last reliable transmit goes
        !            23: unacknowledged, the netchan signals a fatal error.
        !            24: Reliable messages are always placed first in a packet, then the unreliable
        !            25: message is included if there is sufficient room.
        !            26: To the receiver, there is no distinction between the reliable and unreliable
        !            27: parts of the message, they are just processed out as a single larger message.
        !            28: Illogical packet sequence numbers cause the packet to be dropped, but do
        !            29: not kill the connection.  This, combined with the tight window of valid
        !            30: reliable acknowledgement numbers provides protection against malicious
        !            31: address spoofing.
        !            32: 
        !            33: 
        !            34: The qport field is a workaround for bad address translating routers that
        !            35: sometimes remap the client's source port on a packet during gameplay.
        !            36: 
        !            37: If the base part of the net address matches and the qport matches, then the
        !            38: channel matches even if the IP port differs.  The IP port should be updated
        !            39: to the new value before sending out any replies.
        !            40: 
        !            41: 
        !            42: If there is no information that needs to be transfered on a given frame,
        !            43: such as during the connection stage while waiting for the client to load,
        !            44: then a packet only needs to be delivered if there is something in the
        !            45: unacknowledged reliable
        !            46: */
        !            47: cvar_t         *showpackets;
        !            48: cvar_t         *showdrop;
        !            49: cvar_t         *qport;
        !            50: netadr_t       net_from;
        !            51: sizebuf_t      net_message;
        !            52: byte           net_message_buffer[MAX_MSGLEN];
        !            53: /*
        !            54: ===============
        !            55: Netchan_Init
        !            56: ===============
        !            57: */
        !            58: void Netchan_Init (void)
        !            59: {
        !            60:        int             port;
        !            61: 
        !            62:        // pick a port value that should be nice and random
        !            63:        port = Sys_Milliseconds() & 0xffff;
        !            64:        showpackets = Cvar_Get ("showpackets", "0", 0);
        !            65:        showdrop = Cvar_Get ("showdrop", "0", 0);
        !            66:        qport = Cvar_Get ("qport", va("%i", port), CVAR_NOSET);
        !            67: }
        !            68: /*
        !            69: ===============
        !            70: Netchan_OutOfBand
        !            71: Sends an out-of-band datagram
        !            72: ================
        !            73: */
        !            74: void Netchan_OutOfBand (int net_socket, netadr_t adr, int length, byte *data)
        !            75: {
        !            76:        sizebuf_t       send;
        !            77:        byte            send_buf[MAX_MSGLEN];
        !            78: // write the packet header
        !            79:        SZ_Init (&send, send_buf, sizeof(send_buf));
        !            80:        
        !            81:        MSG_WriteLong (&send, -1);      // -1 sequence means out of band
        !            82:        SZ_Write (&send, data, length);
        !            83: // send the datagram
        !            84:        NET_SendPacket (net_socket, send.cursize, send.data, adr);
        !            85: }
        !            86: /*
        !            87: ===============
        !            88: Netchan_OutOfBandPrint
        !            89: Sends a text message in an out-of-band datagram
        !            90: ================
        !            91: */
        !            92: void Netchan_OutOfBandPrint (int net_socket, netadr_t adr, char *format, ...)
        !            93: {
        !            94:        va_list         argptr;
        !            95:        static char             string[MAX_MSGLEN - 4];
        !            96:        
        !            97:        va_start (argptr, format);
        !            98:        vsprintf (string, format,argptr);
        !            99:        va_end (argptr);
        !           100:        Netchan_OutOfBand (net_socket, adr, strlen(string), (byte *)string);
        !           101: }
        !           102: /*
        !           103: ==============
        !           104: Netchan_Setup
        !           105: called to open a channel to a remote system
        !           106: ==============
        !           107: */
        !           108: void Netchan_Setup (netsrc_t sock, netchan_t *chan, netadr_t adr, int qport)
        !           109: {
        !           110:        memset (chan, 0, sizeof(*chan));
        !           111:        
        !           112:        chan->sock = sock;
        !           113:        chan->remote_address = adr;
        !           114:        chan->qport = qport;
        !           115:        chan->last_received = curtime;
        !           116:        chan->incoming_sequence = 0;
        !           117:        chan->outgoing_sequence = 1;
        !           118:        SZ_Init (&chan->message, chan->message_buf, sizeof(chan->message_buf));
        !           119:        chan->message.allowoverflow = true;
        !           120: }
        !           121: /*
        !           122: ===============
        !           123: Netchan_CanReliable
        !           124: Returns true if the last reliable message has acked
        !           125: ================
        !           126: */
        !           127: qboolean Netchan_CanReliable (netchan_t *chan)
        !           128: {
        !           129:        if (chan->reliable_length)
        !           130:                return false;                   // waiting for ack
        !           131:        return true;
        !           132: }
        !           133: 
        !           134: qboolean Netchan_NeedReliable (netchan_t *chan)
        !           135: {
        !           136:        qboolean        send_reliable;
        !           137: 
        !           138: // if the remote side dropped the last reliable message, resend it
        !           139:        send_reliable = false;
        !           140: 
        !           141:        if (chan->incoming_acknowledged > chan->last_reliable_sequence
        !           142:        && chan->incoming_reliable_acknowledged != chan->reliable_sequence)
        !           143:                send_reliable = true;
        !           144: 
        !           145: // if the reliable transmit buffer is empty, copy the current message out
        !           146:        if (!chan->reliable_length && chan->message.cursize)
        !           147:        {
        !           148:                send_reliable = true;
        !           149:        }
        !           150: 
        !           151:        return send_reliable;
        !           152: }
        !           153: /*
        !           154: ===============
        !           155: Netchan_Transmit
        !           156: tries to send an unreliable message to a connection, and handles the
        !           157: transmition / retransmition of the reliable messages.
        !           158: A 0 length will still generate a packet and deal with the reliable messages.
        !           159: ================
        !           160: */
        !           161: void Netchan_Transmit (netchan_t *chan, int length, byte *data)
        !           162: {
        !           163:        sizebuf_t       send;
        !           164:        byte            send_buf[MAX_MSGLEN];
        !           165:        qboolean        send_reliable;
        !           166:        unsigned        w1, w2;
        !           167: // check for message overflow
        !           168:        if (chan->message.overflowed)
        !           169:        {
        !           170:                chan->fatal_error = true;
        !           171:                Com_Printf ("%s:Outgoing message overflow\n"
        !           172:                        , NET_AdrToString (chan->remote_address));
        !           173:                return;
        !           174:        }
        !           175: 
        !           176:        send_reliable = Netchan_NeedReliable (chan);
        !           177: 
        !           178:        if (!chan->reliable_length && chan->message.cursize)
        !           179:        {
        !           180:                memcpy (chan->reliable_buf, chan->message_buf, chan->message.cursize);
        !           181:                chan->reliable_length = chan->message.cursize;
        !           182:                chan->message.cursize = 0;
        !           183:                chan->reliable_sequence ^= 1;
        !           184:        }
        !           185: // write the packet header
        !           186:        SZ_Init (&send, send_buf, sizeof(send_buf));
        !           187:        w1 = ( chan->outgoing_sequence & ~(1<<31) ) | (send_reliable<<31);
        !           188:        w2 = ( chan->incoming_sequence & ~(1<<31) ) | (chan->incoming_reliable_sequence<<31);
        !           189:        chan->outgoing_sequence++;
        !           190:        chan->last_sent = curtime;
        !           191:        MSG_WriteLong (&send, w1);
        !           192:        MSG_WriteLong (&send, w2);
        !           193: 
        !           194:        // send the qport if we are a client
        !           195:        if (chan->sock == NS_CLIENT)
        !           196:                MSG_WriteShort (&send, qport->value);
        !           197: // copy the reliable message to the packet first
        !           198:        if (send_reliable)
        !           199:        {
        !           200:                SZ_Write (&send, chan->reliable_buf, chan->reliable_length);
        !           201:                chan->last_reliable_sequence = chan->outgoing_sequence;
        !           202:        }
        !           203:        
        !           204: // add the unreliable part if space is available
        !           205:        if (send.maxsize - send.cursize >= length)
        !           206:                SZ_Write (&send, data, length);
        !           207:        else
        !           208:                Com_Printf ("Netchan_Transmit: dumped unreliable\n");
        !           209: // send the datagram
        !           210:        NET_SendPacket (chan->sock, send.cursize, send.data, chan->remote_address);
        !           211:        if (showpackets->value)
        !           212:        {
        !           213:                if (send_reliable)
        !           214:                        Com_Printf ("send %4i : s=%i reliable=%i ack=%i rack=%i\n"
        !           215:                                , send.cursize
        !           216:                                , chan->outgoing_sequence - 1
        !           217:                                , chan->reliable_sequence
        !           218:                                , chan->incoming_sequence
        !           219:                                , chan->incoming_reliable_sequence);
        !           220:                else
        !           221:                        Com_Printf ("send %4i : s=%i ack=%i rack=%i\n"
        !           222:                                , send.cursize
        !           223:                                , chan->outgoing_sequence - 1
        !           224:                                , chan->incoming_sequence
        !           225:                                , chan->incoming_reliable_sequence);
        !           226:        }
        !           227: }
        !           228: /*
        !           229: =================
        !           230: Netchan_Process
        !           231: called when the current net_message is from remote_address
        !           232: modifies net_message so that it points to the packet payload
        !           233: =================
        !           234: */
        !           235: qboolean Netchan_Process (netchan_t *chan, sizebuf_t *msg)
        !           236: {
        !           237:        unsigned        sequence, sequence_ack;
        !           238:        unsigned        reliable_ack, reliable_message;
        !           239:        int                     qport;
        !           240: // get sequence numbers                
        !           241:        MSG_BeginReading (msg);
        !           242:        sequence = MSG_ReadLong (msg);
        !           243:        sequence_ack = MSG_ReadLong (msg);
        !           244: 
        !           245:        // read the qport if we are a server
        !           246:        if (chan->sock == NS_SERVER)
        !           247:                qport = MSG_ReadShort (msg);
        !           248:        reliable_message = sequence >> 31;
        !           249:        reliable_ack = sequence_ack >> 31;
        !           250:        sequence &= ~(1<<31);
        !           251:        sequence_ack &= ~(1<<31);       
        !           252:        if (showpackets->value)
        !           253:        {
        !           254:                if (reliable_message)
        !           255:                        Com_Printf ("recv %4i : s=%i reliable=%i ack=%i rack=%i\n"
        !           256:                                , msg->cursize
        !           257:                                , sequence
        !           258:                                , chan->incoming_reliable_sequence ^ 1
        !           259:                                , sequence_ack
        !           260:                                , reliable_ack);
        !           261:                else
        !           262:                        Com_Printf ("recv %4i : s=%i ack=%i rack=%i\n"
        !           263:                                , msg->cursize
        !           264:                                , sequence
        !           265:                                , sequence_ack
        !           266:                                , reliable_ack);
        !           267:        }
        !           268: //
        !           269: // discard stale or duplicated packets
        !           270: //
        !           271:        if (sequence <= chan->incoming_sequence)
        !           272:        {
        !           273:                if (showdrop->value)
        !           274:                        Com_Printf ("%s:Out of order packet %i at %i\n"
        !           275:                                , NET_AdrToString (chan->remote_address)
        !           276:                                ,  sequence
        !           277:                                , chan->incoming_sequence);
        !           278:                return false;
        !           279:        }
        !           280: //
        !           281: // dropped packets don't keep the message from being used
        !           282: //
        !           283:        chan->dropped = sequence - (chan->incoming_sequence+1);
        !           284:        if (chan->dropped > 0)
        !           285:        {
        !           286:                if (showdrop->value)
        !           287:                        Com_Printf ("%s:Dropped %i packets at %i\n"
        !           288:                        , NET_AdrToString (chan->remote_address)
        !           289:                        , chan->dropped
        !           290:                        , sequence);
        !           291:        }
        !           292: //
        !           293: // if the current outgoing reliable message has been acknowledged
        !           294: // clear the buffer to make way for the next
        !           295: //
        !           296:        if (reliable_ack == chan->reliable_sequence)
        !           297:                chan->reliable_length = 0;      // it has been received
        !           298:        
        !           299: //
        !           300: // if this message contains a reliable message, bump incoming_reliable_sequence 
        !           301: //
        !           302:        chan->incoming_sequence = sequence;
        !           303:        chan->incoming_acknowledged = sequence_ack;
        !           304:        chan->incoming_reliable_acknowledged = reliable_ack;
        !           305:        if (reliable_message)
        !           306:        {
        !           307:                chan->incoming_reliable_sequence ^= 1;
        !           308:        }
        !           309: //
        !           310: // the message can now be read from the current message pointer
        !           311: //
        !           312:        chan->last_received = curtime;
        !           313:        return true;
        !           314: }

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