Diff: main.cpp

Revision:

35:e7068df4d971

Parent:

34:8a6fbc73a7f1

Child:

36:2a9b457f8276

diff -r 8a6fbc73a7f1 -r e7068df4d971 main.cpp
--- a/main.cpp	Thu Jan 05 04:14:35 2017 +0000
+++ b/main.cpp	Thu Jan 05 08:16:50 2017 +0000
@@ -81,7 +81,7 @@
     ppp.pkt.len=0;
     ppp.ident=0;
     ppp.sync=0;
-    ppp.seq=77;
+    ppp.seq=1000;
     ppp.ledState=0;
 }
 
@@ -494,15 +494,15 @@
     char * checksumtcp   = s + 16; // 2 bytes
 
     int tcpSize = packetLength - headerSizeIP;
-    int tcpHeaderLen = ((offset[0]>>4)&0x0f)*4; // size of tcp header only
-    int dataLen = tcpSize - tcpHeaderLen; // data is what's left after the header
+    int headerSizeTCP = ((offset[0]>>4)&0x0f)*4; // size of tcp header only
 
     unsigned int seq = (seqtcp[0]<<24)|(seqtcp[1]<<16)|(seqtcp[2]<<8)|(seqtcp[3]);
     unsigned int ack = (acktcp[0]<<24)|(acktcp[1]<<16)|(acktcp[2]<<8)|(acktcp[3]);
 
-    char * dataStart = s + tcpHeaderLen; // start of data
+    int flagsTCP = ((flagbitstcp[0]&1)<<8)|flagbitstcp[1];
 
-    int flagsTCP = ((flagbitstcp[0]&1)<<8)|flagbitstcp[1];
+    char * dataStart = ppp.pkt.buf + 4 + headerSizeIP + headerSizeTCP; // start of data block after TCP header
+    int incomingLen = tcpSize - headerSizeTCP; // size of data block after TCP header
 
 #define TCP_FLAG_ACK (1<<4)
 #define TCP_FLAG_SYN (1<<1)
@@ -512,50 +512,26 @@
 
     // A sparse TCP flag interpreter that implements basic TCP connections from a single source
 
-    int incomingLen = dataLen; // remember length of incoming packet
-    dataLen = 0; // most of our responses will have zero TCP data, only a header
-    
-    if ( ((flagsTCP & TCP_FLAG_FIN) != 0) && ((flagsTCP & TCP_FLAG_ACK) != 0) ) {
-            if (ack <= ppp.seq) return; // their idea of our sequence is larger
-            int temp = ack; // remember what they thought
-            ack = seq + incomingLen; // ack their sequence
-            ppp.seq = temp; // adopt their calculation of our sequence
-   } else if ( ((flagsTCP & ~TCP_FLAG_ACK) == 0) && ((flagsTCP & TCP_FLAG_ACK) != 0) ) {
-        if (incomingLen > 0) {  // they sent data in the ack
-            ack = seq + incomingLen; // acknowledge the number of bytes they sent
-            seq = ppp.seq; // confirm our current sequence position
-        } else {
-            if (ack <= ppp.seq) return; // their idea of our sequence is larger
-            int temp = ack; // remember what they thought
-            ack = seq; // ack their sequence
-            ppp.seq = temp; // adopt their calculation of our sequence
-            seq = ppp.seq;
-        }
+    int dataLen = 0; // most of our responses will have zero TCP data, only a header
+    int teardown = 0; // see if we must tear down the link
+
+    if ( ((flagsTCP & ~TCP_FLAG_ACK) == 0) && ((flagsTCP & TCP_FLAG_ACK) != 0) ) {
+       if (incomingLen == 0) return; // no new data
     } else if ( (flagsTCP & TCP_FLAG_FIN) != 0 ) { // got FIN
-        flagbitstcp[1] |= TCP_FLAG_ACK; // do a fin-ack
-        ack = seq;
-        seq = ppp.seq;
+        flagbitstcp[1] = TCP_FLAG_ACK; // do an ack
+        teardown=1;
     } else if ( (flagsTCP & TCP_FLAG_SYN) != 0 ) { // got SYN
         flagbitstcp[1] |= TCP_FLAG_ACK; // do a syn-ack
-        ack = seq + 1; // when you see SYN you increment their sequence
-        seq = ppp.seq-1; // we cheat - our sequence will be one higher hereafter
+        seq++;
     } else if ( (flagsTCP & TCP_FLAG_PSH) != 0 ) { // they are pushing data
-
-        // Ok, we are done with figuring out the flags. Now we start preparing to respond
-
-        int temp = ack;
-        ack = seq + incomingLen; // acknowledge the number of bytes they sent by adding it to seq
-        ppp.seq = temp; // adopt their calculation of our sequence number
-        seq = ppp.seq;
-        
-        // let's check incoming text for an HTTP home page GET request
+        // It's a push - let's check the data for an HTTP home page GET request
         if ( strncmp(dataStart, "GET / HTTP/1.1", 14) == 0) {
-            flagbitstcp[1] = TCP_FLAG_ACK | TCP_FLAG_FIN; // close connection after delivering page
+            flagbitstcp[1] = TCP_FLAG_ACK; // | TCP_FLAG_FIN; // close connection after delivering page
             dataLen = 15*32; // this block has to hold the web page below, but keep it under 1k
             memset(dataStart,'x', dataLen ); // initialize the block
-            int n=0; // number of bytes we have printed so far
+            int n=1; // number of bytes we have printed so far
             n=n+sprintf(n+dataStart,"HTTP/1.1 200 OK\r\nServer: PPP-Blinky\r\n"); // http header
-            n=n+sprintf(n+dataStart,"Content-Length: 377\r\n"); // http header
+            n=n+sprintf(n+dataStart,"Content-Length: 376\r\n"); // http header
             n=n+sprintf(n+dataStart,"Content-Type: text/html; charset=us-ascii\r\n\r\n"); // http header
             int nHeader=n; // byte total of all headers
             n=n+sprintf(n+dataStart,"<html><head><title>mbed-PPP-Blinky</title><script>window.onload=function()"); // html
@@ -566,10 +542,10 @@
             int contentLength = dataLen-nHeader; // this is how to calculate Content-Length, but using curl -v is easier
             contentLength = contentLength+0; // get around unreferenced variable warning
             if (v0) {
-                debug(("HTTP GET dataLen %d*32=%d Header %d Content-Length %d Total %d Margin %d\n",dataLen/32,dataLen,nHeader,contentLength,n,dataLen-n-1));
+                debug(("HTTP GET dataLen %d*32=%d Header %d Content-Length %d Total %d Margin %d\n",dataLen/32,dataLen,nHeader,contentLength,n,dataLen-n));
             }
         } else if ( strncmp(dataStart, "GET /", 4) == 0) { // all other files get 404 not found
-            flagbitstcp[1] = TCP_FLAG_ACK | TCP_FLAG_FIN; // close connection after delivering page
+            flagbitstcp[1] = TCP_FLAG_ACK;// | TCP_FLAG_FIN; // close connection after delivering page
             dataLen = 5*32; // this block has to hold the web page below, but keep it under 1k
             memset(dataStart,'x', dataLen ); // initialize the block
             int n=0;
@@ -582,18 +558,28 @@
             int contentLength = dataLen-nHeader; // this is how to calculate Content-Length, but using curl -v is easier
             contentLength = contentLength+0; // get around unreferenced variable warning
             if (v0) {
-                debug(("HTTP GET dataLen %d*32=%d Header %d Content-Length %d Total %d Margin %d\n",dataLen/32,dataLen,nHeader,contentLength,n,dataLen-n-1));
+                debug(("HTTP GET dataLen %d*32=%d Header %d Content-Length %d Total %d Margin %d\n",dataLen/32,dataLen,nHeader,contentLength,n,dataLen-n));
             }
+        } else {
+            flagbitstcp[1] = TCP_FLAG_ACK; // we have nothing to say, just ack
+            dataLen=0;
         }
     }
 
-    // now we have to recalculate all the header sizes
+    // All the flag checking is now donw
+
+    // Now we have to recalculate all the header sizes
 
-    int newPacketSize = headerSizeIP + tcpHeaderLen + dataLen;
+    ack = seq + incomingLen; // acknowledge the number of bytes they sent by adding it to seq
+    seq = ppp.seq;
+    
+teardownEntry:
+
+    int newPacketSize = headerSizeIP + headerSizeTCP + dataLen;
     pktLen[0] = (newPacketSize>>8);
     pktLen[1]=newPacketSize; // ip total packet size
     ppp.pkt.len = newPacketSize+6; // ppp packet length
-    tcpSize = tcpHeaderLen + dataLen; // tcp packet size
+    tcpSize = headerSizeTCP + dataLen; // tcp packet size
 
     // redo all the header stuff
 
@@ -639,19 +625,26 @@
     checksumtcp[1]=sum;
     memcpy( s-12, temp, 12); // overwrite the pseudoheader
     sendFrame(); // return the TCP packet
+    ppp.seq = ppp.seq + dataLen; // increase OUR sequence by outgoing data length - for the next round
+    if (teardown) {
+        teardown=0; // clear the teardown flag
+        flagbitstcp[1] = TCP_FLAG_FIN; // we want to end the link
+        dataLen=0; // no data needed
+        goto teardownEntry;
+    }
 }
 
 void dumpDataTCP()
 {
     int ipPktLen     = (ppp.pkt.buf[6]<<8)|ppp.pkt.buf[7]; // overall length of ip packet
     int ipHeaderLen  = (ppp.pkt.buf[4]&0xf)*4; // length of ip header
-    int tcpHeaderLen = ((ppp.pkt.buf[4+ipHeaderLen+12]>>4)&0xf)*4;; // length of tcp header
-    int dataLen = ipPktLen - ipHeaderLen - tcpHeaderLen; // data is what's left after the two headers
+    int headerSizeTCP = ((ppp.pkt.buf[4+ipHeaderLen+12]>>4)&0xf)*4;; // length of tcp header
+    int dataLen = ipPktLen - ipHeaderLen - headerSizeTCP; // data is what's left after the two headers
     if (v1) {
-        debug(("TCP %d ipHeader %d tcpHeader %d Data %d\n", ipPktLen, ipHeaderLen, tcpHeaderLen, dataLen));    // 1 for more verbose
+        debug(("TCP %d ipHeader %d tcpHeader %d Data %d\n", ipPktLen, ipHeaderLen, headerSizeTCP, dataLen));    // 1 for more verbose
     }
     if (dataLen > 0) {
-        debug(("%s\n",ppp.pkt.buf+4+ipHeaderLen+tcpHeaderLen));    // show the data
+        debug(("%s\n",ppp.pkt.buf+4+ipHeaderLen+headerSizeTCP));    // show the data
     }
 }