correct impossibility to read value with HM10

#281 and make the code more flexible (deduct an offset from a key value instead of fixed offset)

OpenMQTTGateway.ino

@@ -881,6 +881,14 @@ void revert_hex_data(char * in, char * out, int l){
   out[l-1] = '\0';
 }
 
+int strpos(char *haystack, char *needle) //from @miere https://stackoverflow.com/users/548685/miere
+{
+   char *p = strstr(haystack, needle);
+   if (p)
+      return p - haystack;
+   return -1;
+}
+
 bool to_bool(String const& s) { // thanks Chris Jester-Young from stackoverflow
      return s != "0";
 }

ZgatewayBT.ino

@@ -112,13 +112,18 @@ Thanks to wolass https://github.com/wolass for suggesting me HM 10 and dinosd ht
 
                 if (strstr(serviceDataUUID.toString().c_str(),"fe95") != NULL){
                   trc("Processing BLE device data");
+                  int pos = -1;
+                  pos = strpos(service_data,"209800");
                   if (strstr(service_data,"209800") != NULL) {
                     trc("mi flora data reading");
-                    boolean result = process_data(-22,service_data,mac);
+                    
+                    boolean result = process_data(pos - 24,service_data,mac);
                   }
+                  pos = -1;
+                  pos = strpos(service_data,"20aa01");
                   if (strstr(service_data,"20aa01") != NULL){
                     trc("mi jia data reading");
-                    boolean result = process_data(-24,service_data,mac);
+                    boolean result = process_data(pos - 26,service_data,mac);
                   }
                 }
             }
@@ -257,16 +262,21 @@ boolean BTtoMQTT() {
                 trc(Service_data);
                 mactopic = subjectBTtoMQTT + String(d[0].extract) + subjectBTtoMQTTservicedata;
                 client.publish((char *)mactopic.c_str(),(char *)(Service_data).c_str());
-                if (strcmp(d[4].extract, "fe95") == 0) 
-                  if (strstr(d[5].extract,"209800") != NULL) {
-                    trc("mi flora data reading");
-                    boolean result = process_data(0,d[5].extract,d[0].extract);
-                  }
-                  if (strstr(d[5].extract,"20aa01") != NULL){
-                    trc("mi jia data reading");
-                    boolean result = process_data(-2,d[5].extract,d[0].extract);
-                  }
-                return true;
+                if (strcmp(d[4].extract, "fe95") == 0) {
+                    int pos = -1;
+                    pos = strpos(d[5].extract,"209800");
+                    if (pos != -1) {
+                      trc("mi flora data reading");
+                      boolean result = process_data(pos - 38,(char *)Service_data.c_str(),d[0].extract);
+                    }
+                    pos = -1;
+                    pos = strpos(d[5].extract,"20aa01");
+                    if (pos != -1){
+                      trc("mi jia data reading");
+                      boolean result = process_data(pos - 40,(char *)Service_data.c_str(),d[0].extract);
+                    }
+                  return true;
+                }
             }
           }
         }