Transceiver.cpp: use pointer arithmetics for CMD parsing

It looks like the author of control command parsing code was not
familar with simple pointer arithmetics, so excessive amount of
memory and useless memcopying was used to parse a single command.

Let's introduce two pointers, one of which will point to the
beginning of a command, another to the beginning of its arguments.
Also, let's simplify the command matching by using a separate
function called 'MATCH_CMD'.

Change-Id: I226ca0771e63228cf5e04ef9766057d4107fdd11

1 files changed, 64 insertions, 51 deletions

diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index 8f41c5e..4b4fefe 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -659,10 +659,40 @@ void Transceiver::reset()
 
 #define MAX_PACKET_LENGTH 100
 
+/**
+ * Matches a buffer with a command.
+ * @param  buf    a buffer to look command in
+ * @param  cmd    a command to look in buffer
+ * @param  params pointer to arguments, or NULL
+ * @return        true if command matches, otherwise false
+ */
+static bool match_cmd(char *buf,
+  const char *cmd, char **params)
+{
+  size_t cmd_len = strlen(cmd);
+
+  /* Check a command itself */
+  if (strncmp(buf, cmd, cmd_len))
+    return false;
+
+  /* A command has arguments */
+  if (params != NULL) {
+    /* Make sure there is a space */
+    if (buf[cmd_len] != ' ')
+      return false;
+
+    /* Update external pointer */
+    *params = buf + cmd_len + 1;
+  }
+
+  return true;
+}
+
 void Transceiver::driveControl(size_t chan)
 {
   char buffer[MAX_PACKET_LENGTH + 1];
   char response[MAX_PACKET_LENGTH + 1];
+  char *command, *params;
   int msgLen;
 
   /* Attempt to read from control socket */
@@ -673,22 +703,20 @@ void Transceiver::driveControl(size_t chan)
   /* Zero-terminate received string */
   buffer[msgLen] = '\0';
 
-  char cmdcheck[4];
-  char command[MAX_PACKET_LENGTH];
-
-  sscanf(buffer,"%3s %s",cmdcheck,command);
-
-  if (strcmp(cmdcheck,"CMD")!=0) {
+  /* Verify a command signature */
+  if (strncmp(buffer, "CMD ", 4)) {
     LOG(WARNING) << "bogus message on control interface";
     return;
   }
-  LOG(INFO) << "command is " << buffer;
 
-  if (strcmp(command,"POWEROFF")==0) {
+  /* Set command pointer */
+  command = buffer + 4;
+  LOG(INFO) << "command is " << command;
+
+  if (match_cmd(command, "POWEROFF", NULL)) {
     stop();
     sprintf(response,"RSP POWEROFF 0");
-  }
-  else if (strcmp(command,"POWERON")==0) {
+  } else if (match_cmd(command, "POWERON", NULL)) {
     if (!start()) {
       sprintf(response,"RSP POWERON 1");
     } else {
@@ -698,41 +726,35 @@ void Transceiver::driveControl(size_t chan)
           mHandover[i][j] = false;
       }
     }
-  }
-  else if (strcmp(command,"HANDOVER")==0){
+  } else if (match_cmd(command, "HANDOVER", &params)) {
     int ts=0,ss=0;
-    sscanf(buffer,"%3s %s %d %d",cmdcheck,command,&ts,&ss);
+    sscanf(params, "%d %d", &ts, &ss);
     mHandover[ts][ss] = true;
     sprintf(response,"RSP HANDOVER 0 %d %d",ts,ss);
-  }
-  else if (strcmp(command,"NOHANDOVER")==0){
+  } else if (match_cmd(command, "NOHANDOVER", &params)) {
     int ts=0,ss=0;
-    sscanf(buffer,"%3s %s %d %d",cmdcheck,command,&ts,&ss);
+    sscanf(params, "%d %d", &ts, &ss);
     mHandover[ts][ss] = false;
     sprintf(response,"RSP NOHANDOVER 0 %d %d",ts,ss);
-  }
-  else if (strcmp(command,"SETMAXDLY")==0) {
+  } else if (match_cmd(command, "SETMAXDLY", &params)) {
     //set expected maximum time-of-arrival
     int maxDelay;
-    sscanf(buffer,"%3s %s %d",cmdcheck,command,&maxDelay);
+    sscanf(params, "%d", &maxDelay);
     mMaxExpectedDelayAB = maxDelay; // 1 GSM symbol is approx. 1 km
     sprintf(response,"RSP SETMAXDLY 0 %d",maxDelay);
-  }
-  else if (strcmp(command,"SETMAXDLYNB")==0) {
+  } else if (match_cmd(command, "SETMAXDLYNB", &params)) {
     //set expected maximum time-of-arrival
     int maxDelay;
-    sscanf(buffer,"%3s %s %d",cmdcheck,command,&maxDelay);
+    sscanf(params, "%d", &maxDelay);
     mMaxExpectedDelayNB = maxDelay; // 1 GSM symbol is approx. 1 km
     sprintf(response,"RSP SETMAXDLYNB 0 %d",maxDelay);
-  }
-  else if (strcmp(command,"SETRXGAIN")==0) {
+  } else if (match_cmd(command, "SETRXGAIN", &params)) {
     //set expected maximum time-of-arrival
     int newGain;
-    sscanf(buffer,"%3s %s %d",cmdcheck,command,&newGain);
+    sscanf(params, "%d", &newGain);
     newGain = mRadioInterface->setRxGain(newGain, chan);
     sprintf(response,"RSP SETRXGAIN 0 %d",newGain);
-  }
-  else if (strcmp(command,"NOISELEV")==0) {
+  } else if (match_cmd(command, "NOISELEV", NULL)) {
     if (mOn) {
       float lev = mStates[chan].mNoiseLev;
       sprintf(response,"RSP NOISELEV 0 %d",
@@ -741,26 +763,23 @@ void Transceiver::driveControl(size_t chan)
     else {
       sprintf(response,"RSP NOISELEV 1  0");
     }
-  }
-  else if (!strcmp(command, "SETPOWER")) {
+  } else if (match_cmd(command, "SETPOWER", &params)) {
     int power;
-    sscanf(buffer, "%3s %s %d", cmdcheck, command, &power);
+    sscanf(params, "%d", &power);
     power = mRadioInterface->setPowerAttenuation(power, chan);
     mStates[chan].mPower = power;
     sprintf(response, "RSP SETPOWER 0 %d", power);
-  }
-  else if (!strcmp(command,"ADJPOWER")) {
+  } else if (match_cmd(command, "ADJPOWER", &params)) {
     int power, step;
-    sscanf(buffer, "%3s %s %d", cmdcheck, command, &step);
+    sscanf(params, "%d", &step);
     power = mStates[chan].mPower + step;
     power = mRadioInterface->setPowerAttenuation(power, chan);
     mStates[chan].mPower = power;
     sprintf(response, "RSP ADJPOWER 0 %d", power);
-  }
-  else if (strcmp(command,"RXTUNE")==0) {
+  } else if (match_cmd(command, "RXTUNE", &params)) {
     // tune receiver
     int freqKhz;
-    sscanf(buffer,"%3s %s %d",cmdcheck,command,&freqKhz);
+    sscanf(params, "%d", &freqKhz);
     mRxFreq = freqKhz * 1e3;
     if (!mRadioInterface->tuneRx(mRxFreq, chan)) {
        LOG(ALERT) << "RX failed to tune";
@@ -768,11 +787,10 @@ void Transceiver::driveControl(size_t chan)
     }
     else
        sprintf(response,"RSP RXTUNE 0 %d",freqKhz);
-  }
-  else if (strcmp(command,"TXTUNE")==0) {
+  } else if (match_cmd(command, "TXTUNE", &params)) {
     // tune txmtr
     int freqKhz;
-    sscanf(buffer,"%3s %s %d",cmdcheck,command,&freqKhz);
+    sscanf(params, "%d", &freqKhz);
     mTxFreq = freqKhz * 1e3;
     if (!mRadioInterface->tuneTx(mTxFreq, chan)) {
        LOG(ALERT) << "TX failed to tune";
@@ -780,11 +798,10 @@ void Transceiver::driveControl(size_t chan)
     }
     else
        sprintf(response,"RSP TXTUNE 0 %d",freqKhz);
-  }
-  else if (!strcmp(command,"SETTSC")) {
+  } else if (match_cmd(command, "SETTSC", &params)) {
     // set TSC
     unsigned TSC;
-    sscanf(buffer, "%3s %s %d", cmdcheck, command, &TSC);
+    sscanf(params, "%d", &TSC);
     if (TSC > 7) {
       sprintf(response, "RSP SETTSC 1 %d", TSC);
     } else {
@@ -792,12 +809,11 @@ void Transceiver::driveControl(size_t chan)
       mTSC = TSC;
       sprintf(response,"RSP SETTSC 0 %d", TSC);
     }
-  }
-  else if (strcmp(command,"SETSLOT")==0) {
+  } else if (match_cmd(command, "SETSLOT", &params)) {
     // set slot type
     int  corrCode;
     int  timeslot;
-    sscanf(buffer,"%3s %s %d %d",cmdcheck,command,&timeslot,&corrCode);
+    sscanf(params, "%d %d", &timeslot, &corrCode);
     if ((timeslot < 0) || (timeslot > 7)) {
       LOG(WARNING) << "bogus message on control interface";
       sprintf(response,"RSP SETSLOT 1 %d %d",timeslot,corrCode);
@@ -806,17 +822,14 @@ void Transceiver::driveControl(size_t chan)
     mStates[chan].chanType[timeslot] = (ChannelCombination) corrCode;
     setModulus(timeslot, chan);
     sprintf(response,"RSP SETSLOT 0 %d %d",timeslot,corrCode);
-
-  }
-  else if (strcmp(command,"_SETBURSTTODISKMASK")==0) {
+  } else if (match_cmd(command, "_SETBURSTTODISKMASK", &params)) {
     // debug command! may change or disapear without notice
     // set a mask which bursts to dump to disk
     int mask;
-    sscanf(buffer,"%3s %s %d",cmdcheck,command,&mask);
+    sscanf(params, "%d", &mask);
     mWriteBurstToDiskMask = mask;
     sprintf(response,"RSP _SETBURSTTODISKMASK 0 %d",mask);
-  }
-  else {
+  } else {
     LOG(WARNING) << "bogus command " << command << " on control interface.";
     sprintf(response,"RSP ERR 1");
   }