Remove usage of Arduino constant emptyString and use our own instead

examples/ChunkRetryResponse/ChunkRetryResponse.ino

@@ -177,7 +177,7 @@ void setup() {
         memcpy(buffer, answer.c_str(), answer.length());
 
         // finish!
-        triggerUART = emptyString;
+        triggerUART = asyncsrv::emptyString;
         key = -1;
 
         return answer.length();
@@ -218,6 +218,6 @@ void loop() {
     key = Serial.read();
     Serial.flush();
     // async_ws_log_d("UART input: %c", key);
-    triggerUART = emptyString;
+    triggerUART = asyncsrv::emptyString;
   }
 }

examples/RequestContinuation/RequestContinuation.ino

@@ -83,7 +83,7 @@ void loop() {
     Serial.setTimeout(10000);
     String response = Serial.readStringUntil('\n');  // waits for a key to be pressed
     Serial.println();
-    message = emptyString;
+    message = asyncsrv::emptyString;
     if (auto request = serialRequest.lock()) {
       request->send(200, "text/plain", "Answer: " + response);
     }

examples/Templates/Templates.ino

@@ -84,7 +84,7 @@ void setup() {
     if (var == "USER") {
       return String("Bob ") + millis();
     }
-    return emptyString;
+    return asyncsrv::emptyString;
   });
 
   // Serve a static template with a template processor
@@ -100,7 +100,7 @@ void setup() {
       if (var == "USER") {
         return "Bob";
       }
-      return emptyString;
+      return asyncsrv::emptyString;
     })
     .setLastModified("Sun, 28 Sep 2025 01:02:03 GMT");
 
@@ -115,7 +115,7 @@ void setup() {
     if (var == "USER") {
       return String("Bob ") + uptimeInMinutes + " minutes";
     }
-    return emptyString;
+    return asyncsrv::emptyString;
   });
 
   // Serve a template with dynamic content based on user request
@@ -132,7 +132,7 @@ void setup() {
           return param->value();
         }
       }
-      return emptyString;
+      return asyncsrv::emptyString;
     });
   });
 

src/AsyncEventSource.cpp

@@ -27,7 +27,7 @@ static String generateEventMessage(const char *message, const char *event, uint3
 
   if (!str.reserve(len)) {
     async_ws_log_e("Failed to allocate");
-    return emptyString;
+    return asyncsrv::emptyString;
   }
 
   if (reconnect) {

src/ESPAsyncWebServer.h

@@ -670,15 +670,17 @@ class AsyncWebServerRequest {
 
   AsyncWebServerResponse *
     beginResponse(FS &fs, const String &path, const char *contentType = asyncsrv::empty, bool download = false, AwsTemplateProcessor callback = nullptr);
-  AsyncWebServerResponse *
-    beginResponse(FS &fs, const String &path, const String &contentType = emptyString, bool download = false, AwsTemplateProcessor callback = nullptr) {
+  AsyncWebServerResponse *beginResponse(
+    FS &fs, const String &path, const String &contentType = asyncsrv::emptyString, bool download = false, AwsTemplateProcessor callback = nullptr
+  ) {
     return beginResponse(fs, path, contentType.c_str(), download, callback);
   }
 
   AsyncWebServerResponse *
     beginResponse(File content, const String &path, const char *contentType = asyncsrv::empty, bool download = false, AwsTemplateProcessor callback = nullptr);
-  AsyncWebServerResponse *
-    beginResponse(File content, const String &path, const String &contentType = emptyString, bool download = false, AwsTemplateProcessor callback = nullptr) {
+  AsyncWebServerResponse *beginResponse(
+    File content, const String &path, const String &contentType = asyncsrv::emptyString, bool download = false, AwsTemplateProcessor callback = nullptr
+  ) {
     return beginResponse(content, path, contentType.c_str(), download, callback);
   }
 
@@ -783,11 +785,11 @@ class AsyncWebServerRequest {
 #endif
   const String &arg(size_t i) const;  // get request argument value by number
   const String &arg(int i) const {
-    return i < 0 ? emptyString : arg((size_t)i);
+    return i < 0 ? asyncsrv::emptyString : arg((size_t)i);
   };
   const String &argName(size_t i) const;  // get request argument name by number
   const String &argName(int i) const {
-    return i < 0 ? emptyString : argName((size_t)i);
+    return i < 0 ? asyncsrv::emptyString : argName((size_t)i);
   };
   bool hasArg(const char *name) const;  // check if argument exists
   bool hasArg(const String &name) const {
@@ -800,14 +802,14 @@ class AsyncWebServerRequest {
 #ifdef ASYNCWEBSERVER_REGEX
   const String &pathArg(size_t i) const {
     if (i >= _pathParams.size()) {
-      return emptyString;
+      return asyncsrv::emptyString;
     }
     auto it = _pathParams.begin();
     std::advance(it, i);
     return *it;
   }
   const String &pathArg(int i) const {
-    return i < 0 ? emptyString : pathArg((size_t)i);
+    return i < 0 ? asyncsrv::emptyString : pathArg((size_t)i);
   }
 #else
   const String &pathArg(size_t i) const __attribute__((error("ERR: pathArg() requires -D ASYNCWEBSERVER_REGEX and only works on regex handlers")));
@@ -826,11 +828,11 @@ class AsyncWebServerRequest {
 
   const String &header(size_t i) const;  // get request header value by number
   const String &header(int i) const {
-    return i < 0 ? emptyString : header((size_t)i);
+    return i < 0 ? asyncsrv::emptyString : header((size_t)i);
   };
   const String &headerName(size_t i) const;  // get request header name by number
   const String &headerName(int i) const {
-    return i < 0 ? emptyString : headerName((size_t)i);
+    return i < 0 ? asyncsrv::emptyString : headerName((size_t)i);
   };
 
   size_t headers() const;  // get header count
@@ -888,7 +890,7 @@ class AsyncWebServerRequest {
     _attributes[name] = value;
   }
   void setAttribute(const char *name, bool value) {
-    _attributes[name] = value ? "1" : emptyString;
+    _attributes[name] = value ? "1" : asyncsrv::emptyString;
   }
   void setAttribute(const char *name, long value) {
     _attributes[name] = String(value);
@@ -904,7 +906,7 @@ class AsyncWebServerRequest {
     return _attributes.find(name) != _attributes.end();
   }
 
-  const String &getAttribute(const char *name, const String &defaultValue = emptyString) const;
+  const String &getAttribute(const char *name, const String &defaultValue = asyncsrv::emptyString) const;
   bool getAttribute(const char *name, bool defaultValue) const;
   long getAttribute(const char *name, long defaultValue) const;
   float getAttribute(const char *name, float defaultValue) const;

src/WebAuthentication.cpp

@@ -26,19 +26,19 @@ bool checkBasicAuthentication(const char *hash, const char *username, const char
 
 String generateBasicHash(const char *username, const char *password) {
   if (username == NULL || password == NULL) {
-    return emptyString;
+    return asyncsrv::emptyString;
   }
 
   size_t toencodeLen = strlen(username) + strlen(password) + 1;
 
   char *toencode = new char[toencodeLen + 1];
   if (toencode == NULL) {
-    return emptyString;
+    return asyncsrv::emptyString;
   }
   char *encoded = new char[base64_encode_expected_len(toencodeLen) + 1];
   if (encoded == NULL) {
     delete[] toencode;
-    return emptyString;
+    return asyncsrv::emptyString;
   }
   sprintf_P(toencode, PSTR("%s:%s"), username, password);
   if (base64_encode_chars(toencode, toencodeLen, encoded) > 0) {
@@ -49,7 +49,7 @@ String generateBasicHash(const char *username, const char *password) {
   }
   delete[] toencode;
   delete[] encoded;
-  return emptyString;
+  return asyncsrv::emptyString;
 }
 
 static bool getMD5(uint8_t *data, uint16_t len, char *output) {  // 33 bytes or more
@@ -90,7 +90,7 @@ String genRandomMD5() {
   char *out = (char *)malloc(33);
   if (out == NULL || !getMD5((uint8_t *)(&r), 4, out)) {
     async_ws_log_e("Failed to allocate");
-    return emptyString;
+    return asyncsrv::emptyString;
   }
   String res = String(out);
   free(out);
@@ -101,7 +101,7 @@ static String stringMD5(const String &in) {
   char *out = (char *)malloc(33);
   if (out == NULL || !getMD5((uint8_t *)(in.c_str()), in.length(), out)) {
     async_ws_log_e("Failed to allocate");
-    return emptyString;
+    return asyncsrv::emptyString;
   }
   String res = String(out);
   free(out);
@@ -110,19 +110,19 @@ static String stringMD5(const String &in) {
 
 String generateDigestHash(const char *username, const char *password, const char *realm) {
   if (username == NULL || password == NULL || realm == NULL) {
-    return emptyString;
+    return asyncsrv::emptyString;
   }
   char *out = (char *)malloc(33);
   if (out == NULL) {
     async_ws_log_e("Failed to allocate");
-    return emptyString;
+    return asyncsrv::emptyString;
   }
 
   String in;
   if (!in.reserve(strlen(username) + strlen(realm) + strlen(password) + 2)) {
     async_ws_log_e("Failed to allocate");
     free(out);
-    return emptyString;
+    return asyncsrv::emptyString;
   }
 
   in.concat(username);
@@ -134,7 +134,7 @@ String generateDigestHash(const char *username, const char *password, const char
   if (!getMD5((uint8_t *)(in.c_str()), in.length(), out)) {
     async_ws_log_e("Failed to allocate");
     free(out);
-    return emptyString;
+    return asyncsrv::emptyString;
   }
 
   in = String(out);

src/WebHandlers.cpp

@@ -260,7 +260,7 @@ void AsyncStaticWebHandler::handleRequest(AsyncWebServerRequest *request) {
     request->_tempFile.close();
     response = new AsyncBasicResponse(304);  // Not modified
   } else {
-    response = new AsyncFileResponse(request->_tempFile, filename, emptyString, false, _callback);
+    response = new AsyncFileResponse(request->_tempFile, filename, asyncsrv::emptyString, false, _callback);
   }
 
   if (!response) {

src/WebRequest.cpp

@@ -298,7 +298,7 @@ void AsyncWebServerRequest::_addGetParams(const String &params) {
       equal = end;
     }
     String name = urlDecode(params.substring(start, equal));
-    String value = urlDecode(equal + 1 < end ? params.substring(equal + 1, end) : emptyString);
+    String value = urlDecode(equal + 1 < end ? params.substring(equal + 1, end) : asyncsrv::emptyString);
     if (name.length()) {
       _params.emplace_back(name, value);
     }
@@ -336,7 +336,7 @@ bool AsyncWebServerRequest::_parseReqHead() {
     _version = 1;
   }
 
-  _temp = emptyString;
+  _temp = asyncsrv::emptyString;
   return true;
 }
 
@@ -545,7 +545,7 @@ bool AsyncWebServerRequest::_parseReqHeader() {
   }
 #if defined(TARGET_RP2040) || defined(TARGET_RP2350) || defined(PICO_RP2040) || defined(PICO_RP2350) || defined(LIBRETINY)
   // Ancient PRI core does not have String::clear() method 8-()
-  _temp = emptyString;
+  _temp = asyncsrv::emptyString;
 #else
   _temp.clear();
 #endif
@@ -570,7 +570,7 @@ void AsyncWebServerRequest::_parsePlainPostChar(uint8_t data) {
 
 #if defined(TARGET_RP2040) || defined(TARGET_RP2350) || defined(PICO_RP2040) || defined(PICO_RP2350) || defined(LIBRETINY)
     // Ancient PRI core does not have String::clear() method 8-()
-    _temp = emptyString;
+    _temp = asyncsrv::emptyString;
 #else
     _temp.clear();
 #endif
@@ -615,10 +615,10 @@ void AsyncWebServerRequest::_parseMultipartPostByte(uint8_t data, bool last) {
 
   if (!_parsedLength) {
     _multiParseState = EXPECT_BOUNDARY;
-    _temp = emptyString;
-    _itemName = emptyString;
-    _itemFilename = emptyString;
-    _itemType = emptyString;
+    _temp = asyncsrv::emptyString;
+    _itemName = asyncsrv::emptyString;
+    _itemFilename = asyncsrv::emptyString;
+    _itemType = asyncsrv::emptyString;
   }
 
   if (_multiParseState == WAIT_FOR_RETURN1) {
@@ -686,13 +686,13 @@ void AsyncWebServerRequest::_parseMultipartPostByte(uint8_t data, bool last) {
             _params.emplace_back(T_filename, _itemFilename, true, true);
           }
         }
-        _temp = emptyString;
+        _temp = asyncsrv::emptyString;
       } else {
         _multiParseState = WAIT_FOR_RETURN1;
         // value starts from here
         _itemSize = 0;
         _itemStartIndex = _parsedLength;
-        _itemValue = emptyString;
+        _itemValue = asyncsrv::emptyString;
         if (_itemIsFile) {
           if (_itemBuffer) {
             free(_itemBuffer);
@@ -1219,7 +1219,7 @@ const String &AsyncWebServerRequest::arg(const char *name) const {
       return arg.value();
     }
   }
-  return emptyString;
+  return asyncsrv::emptyString;
 }
 
 #ifdef ESP8266
@@ -1238,7 +1238,7 @@ const String &AsyncWebServerRequest::argName(size_t i) const {
 
 const String &AsyncWebServerRequest::header(const char *name) const {
   const AsyncWebHeader *h = getHeader(name);
-  return h ? h->value() : emptyString;
+  return h ? h->value() : asyncsrv::emptyString;
 }
 
 #ifdef ESP8266
@@ -1249,12 +1249,12 @@ const String &AsyncWebServerRequest::header(const __FlashStringHelper *data) con
 
 const String &AsyncWebServerRequest::header(size_t i) const {
   const AsyncWebHeader *h = getHeader(i);
-  return h ? h->value() : emptyString;
+  return h ? h->value() : asyncsrv::emptyString;
 }
 
 const String &AsyncWebServerRequest::headerName(size_t i) const {
   const AsyncWebHeader *h = getHeader(i);
-  return h ? h->name() : emptyString;
+  return h ? h->name() : asyncsrv::emptyString;
 }
 
 String AsyncWebServerRequest::urlDecode(const String &text) const {
@@ -1265,7 +1265,7 @@ String AsyncWebServerRequest::urlDecode(const String &text) const {
   // Allocate the string internal buffer - never longer from source text
   if (!decoded.reserve(len)) {
     async_ws_log_e("Failed to allocate");
-    return emptyString;
+    return asyncsrv::emptyString;
   }
   while (i < len) {
     char decodedChar;

src/WebResponseImpl.h

@@ -37,7 +37,7 @@ class AsyncBasicResponse : public AsyncWebServerResponse {
 
 public:
   explicit AsyncBasicResponse(int code, const char *contentType = asyncsrv::empty, const char *content = asyncsrv::empty);
-  AsyncBasicResponse(int code, const String &contentType, const String &content = emptyString)
+  AsyncBasicResponse(int code, const String &contentType, const String &content = asyncsrv::emptyString)
     : AsyncBasicResponse(code, contentType.c_str(), content.c_str()) {}
   void _respond(AsyncWebServerRequest *request) final;
   size_t _ack(AsyncWebServerRequest *request, size_t len, uint32_t time) final {

src/literals.h

@@ -24,6 +24,12 @@
 
 namespace asyncsrv {
 
+#ifdef ARDUINO
+using ::emptyString;
+#else
+inline const String emptyString{};
+#endif
+
 static constexpr const char empty[] = "";
 
 static constexpr const char T__opaque[] = "\", opaque=\"";