Various String handling cleanups

Use the proper api (::clear(), isEmpty()) instead of doing
comparisons/assignments of empty strings. Also fix mixture
of tabs and spaces in the source code.

Author: dirkmueller

Diff for: cores/esp8266/WString.cpp

@@ -145,7 +145,7 @@ constructor:
 
 .. code:: cpp
 
-    String(const char *cstr = ""); // constructor from const char * 
+    String(const char *cstr = nullptr); // constructor from const char *
     String(const String &str); // copy constructor
     String(const __FlashStringHelper *str); // constructor for flash strings 
 

Diff for: doc/PROGMEM.rst

@@ -168,7 +168,7 @@ int ArduinoOTAClass::parseInt(){
 }
 
 String ArduinoOTAClass::readStringUntil(char end){
-  String res = "";
+  String res;
   int value;
   while(true){
     value = _udp_ota->read();

Diff for: libraries/ArduinoOTA/ArduinoOTA.cpp

@@ -119,7 +119,7 @@ void DNSServer::respondToRequest(uint8_t *buffer, size_t length)
 			  query, queryLength);
 
   // If we have no domain name configured, just return an error
-  if (_domainName == "")
+  if (_domainName.isEmpty())
     return replyWithError(dnsHeader, _errorReplyCode,
 			  query, queryLength);
 

Diff for: libraries/DNSServer/src/DNSServer.cpp

@@ -137,9 +137,9 @@ void HTTPClient::clear()
 {
     _returnCode = 0;
     _size = -1;
-    _headers = "";
+    _headers.clear();
+    _location.clear();
     _payload.reset();
-    _location = "";
 }
 
 
@@ -657,7 +657,7 @@ int HTTPClient::sendRequest(const char * type, const uint8_t * payload, size_t s
         // wipe out any existing headers from previous request
         for(size_t i = 0; i < _headerKeysCount; i++) {
             if (_currentHeaders[i].value.length() > 0) {
-                _currentHeaders[i].value = "";
+                _currentHeaders[i].value.clear();
             }
         }
 

Diff for: libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp

@@ -77,7 +77,7 @@ void ESP8266HTTPUpdateServerTemplate<ServerType>::setup(ESP8266WebServerTemplate
       HTTPUpload& upload = _server->upload();
 
       if(upload.status == UPLOAD_FILE_START){
-        _updaterError = String();
+        _updaterError.clear();
         if (_serial_output)
           Serial.setDebugOutput(true);
 

Diff for: libraries/ESP8266HTTPUpdateServer/src/ESP8266HTTPUpdateServer-impl.h

@@ -122,7 +122,7 @@ void handleFileUpload() {
     }
     DBG_OUTPUT_PORT.print("handleFileUpload Name: "); DBG_OUTPUT_PORT.println(filename);
     fsUploadFile = filesystem->open(filename, "w");
-    filename = String();
+    filename.clear();
   } else if (upload.status == UPLOAD_FILE_WRITE) {
     //DBG_OUTPUT_PORT.print("handleFileUpload Data: "); DBG_OUTPUT_PORT.println(upload.currentSize);
     if (fsUploadFile) {
@@ -150,7 +150,7 @@ void handleFileDelete() {
   }
   filesystem->remove(path);
   server.send(200, "text/plain", "");
-  path = String();
+  path.clear();
 }
 
 void handleFileCreate() {
@@ -172,7 +172,7 @@ void handleFileCreate() {
     return server.send(500, "text/plain", "CREATE FAILED");
   }
   server.send(200, "text/plain", "");
-  path = String();
+  path.clear();
 }
 
 void handleFileList() {
@@ -184,7 +184,7 @@ void handleFileList() {
   String path = server.arg("dir");
   DBG_OUTPUT_PORT.println("handleFileList: " + path);
   Dir dir = filesystem->openDir(path);
-  path = String();
+  path.clear();
 
   String output = "[";
   while (dir.next()) {
@@ -275,13 +275,13 @@ void setup(void) {
 
   //get heap status, analog input value and all GPIO statuses in one json call
   server.on("/all", HTTP_GET, []() {
-    String json = "{";
+    String json('{');
     json += "\"heap\":" + String(ESP.getFreeHeap());
     json += ", \"analog\":" + String(analogRead(A0));
     json += ", \"gpio\":" + String((uint32_t)(((GPI | GPO) & 0xFFFF) | ((GP16I & 0x01) << 16)));
     json += "}";
     server.send(200, "text/json", json);
-    json = String();
+    json.clear();
   });
   server.begin();
   DBG_OUTPUT_PORT.println("HTTP server started");

Diff for: libraries/ESP8266WebServer/examples/FSBrowser/FSBrowser.ino

@@ -209,7 +209,7 @@ void printDirectory() {
     return returnFail("BAD PATH");
   }
   File dir = SD.open((char *)path.c_str());
-  path = String();
+  path.clear();
   if (!dir.isDirectory()) {
     dir.close();
     return returnFail("NOT DIR");

Diff for: libraries/ESP8266WebServer/examples/SDWebServer/SDWebServer.ino

@@ -89,7 +89,7 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
   String url = req.substring(addr_start + 1, addr_end);
   String versionEnd = req.substring(addr_end + 8);
   _currentVersion = atoi(versionEnd.c_str());
-  String searchStr = "";
+  String searchStr;
   int hasSearch = url.indexOf('?');
   if (hasSearch != -1){
     searchStr = url.substring(hasSearch + 1);
@@ -144,7 +144,7 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
     while(1){
       req = client.readStringUntil('\r');
       client.readStringUntil('\n');
-      if (req == "") break;//no moar headers
+      if (req.isEmpty()) break;//no moar headers
       int headerDiv = req.indexOf(':');
       if (headerDiv == -1){
         break;
@@ -222,7 +222,7 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
     while(1){
       req = client.readStringUntil('\r');
       client.readStringUntil('\n');
-      if (req == "") break;//no moar headers
+      if (req.isEmpty()) break;//no moar headers
       int headerDiv = req.indexOf(':');
       if (headerDiv == -1){
         break;
@@ -452,7 +452,7 @@ bool ESP8266WebServerTemplate<ServerType>::_parseForm(ClientType& client, const
               line = client.readStringUntil('\r');
               client.readStringUntil('\n');
               if (line.startsWith("--"+boundary)) break;
-              if (argValue.length() > 0) argValue += "\n";
+              if (argValue.length() > 0) argValue += '\n';
               argValue += line;
             }
 #ifdef DEBUG_ESP_HTTP_SERVER
@@ -600,7 +600,7 @@ bool ESP8266WebServerTemplate<ServerType>::_parseForm(ClientType& client, const
 template <typename ServerType>
 String ESP8266WebServerTemplate<ServerType>::urlDecode(const String& text)
 {
-  String decoded = "";
+  String decoded;
   char temp[] = "0x00";
   unsigned int len = text.length();
   unsigned int i = 0;

Diff for: libraries/ESP8266WebServer/src/Parsing-impl.h

@@ -31,7 +31,7 @@
 const IPAddress ESP8266WiFiMesh::emptyIP = IPAddress();
 const uint32_t ESP8266WiFiMesh::lwipVersion203Signature[3] {2,0,3};
 
-String ESP8266WiFiMesh::lastSSID = "";
+String ESP8266WiFiMesh::lastSSID;
 bool ESP8266WiFiMesh::staticIPActivated = false;
 
 // IP needs to be at the same subnet as server gateway (192.168.4 in this case). Station gateway ip must match ip for server.
@@ -55,7 +55,7 @@ ESP8266WiFiMesh::ESP8266WiFiMesh(ESP8266WiFiMesh::requestHandlerType requestHand
 {
   storeLwipVersion();
 
-  updateNetworkNames(meshName, (nodeID != "" ? nodeID : uint64ToString(ESP.getChipId())));
+  updateNetworkNames(meshName, (!nodeID.isEmpty() ? nodeID : uint64ToString(ESP.getChipId())));
   _requestHandler = requestHandler;
   _responseHandler = responseHandler;
   setWiFiChannel(meshWiFiChannel);
@@ -67,9 +67,9 @@ ESP8266WiFiMesh::ESP8266WiFiMesh(ESP8266WiFiMesh::requestHandlerType requestHand
 
 void ESP8266WiFiMesh::updateNetworkNames(const String &newMeshName, const String &newNodeID)
 {
-  if(newMeshName != "")
+  if(!newMeshName.isEmpty())
     _meshName = newMeshName;
-  if(newNodeID != "")
+  if(!newNodeID.isEmpty())
     _nodeID = newNodeID;
 
   String newSSID = _meshName + _nodeID;
@@ -453,7 +453,7 @@ void ESP8266WiFiMesh::initiateConnectionToAP(const String &targetSSID, int targe
  */
 transmission_status_t ESP8266WiFiMesh::connectToNode(const String &targetSSID, int targetChannel, uint8_t *targetBSSID)
 {
-  if(staticIPActivated && lastSSID != "" && lastSSID != targetSSID) // So we only do this once per connection, in case there is a performance impact.
+  if(staticIPActivated && !lastSSID.isEmpty() && lastSSID != targetSSID) // So we only do this once per connection, in case there is a performance impact.
   {
     #ifdef ENABLE_STATIC_IP_OPTIMIZATION
     if(atLeastLwipVersion(lwipVersion203Signature))
@@ -562,12 +562,12 @@ void ESP8266WiFiMesh::attemptTransmission(const String &message, bool concluding
       WiFi.disconnect();
       yield();
 
-      String currentSSID = "";
+      String currentSSID;
       int currentWiFiChannel = NETWORK_INFO_DEFAULT_INT;
       uint8_t *currentBSSID = NULL;
 
       // If an SSID has been assigned, it is prioritized over an assigned networkIndex since the networkIndex is more likely to change.
-      if(currentNetwork.SSID != "")
+      if(!currentNetwork.SSID.isEmpty())
       {
         currentSSID = currentNetwork.SSID;
         currentWiFiChannel = currentNetwork.wifiChannel;

Diff for: libraries/ESP8266WiFiMesh/src/ESP8266WiFiMesh.cpp

@@ -95,7 +95,7 @@ TEST_CASE("STA mode events are called both when using DHCP and static config", "
     delay(100);
 
     REQUIRE(events == "connected,got_ip,disconnected,");
-    events = String();
+    events.clear();
 
     // now run the same with static IP config saved above