Use double quotes in JSON for non-numeric values (#929)

code/espurna/api.ino

@@ -102,7 +102,11 @@ ArRequestHandlerFunction _bindAPI(unsigned int apiID) {
         // Format response according to the Accept header
         if (_asJson(request)) {
             char buffer[64];
-            snprintf_P(buffer, sizeof(buffer), PSTR("{ \"%s\": %s }"), api.key, value);
+            if (isNumber(value)) {
+                snprintf_P(buffer, sizeof(buffer), PSTR("{ \"%s\": %s }"), api.key, value);
+            } else {
+                snprintf_P(buffer, sizeof(buffer), PSTR("{ \"%s\": \"%s\" }"), api.key, value);
+            }
             request->send(200, "application/json", buffer);
         } else {
             request->send(200, "text/plain", value);

code/espurna/utils.ino

@@ -589,3 +589,19 @@ void nice_delay(unsigned long ms) {
 int __get_adc_mode() {
     return (int) (ADC_MODE_VALUE);
 }
+
+bool isNumber(const char * s) {
+    unsigned char len = strlen(s);
+    bool decimal = false;
+    for (unsigned char i=0; i<len; i++) {
+        if (s[i] == '-') {
+            if (i>0) return false;
+        } else if (s[i] == '.') {
+            if (decimal) return false;
+            decimal = true;
+        } else if (!isdigit(s[i])) {
+            return false;
+        }
+    }
+    return true;
+}