[Dashboard] Use less resources when serving dashboard.esp

No need to load the entire dashboard.esp file in memory.
Just replace the things that can be replaced per line and serve it directly to the client.

src/src/WebServer/CustomPage.cpp

@@ -23,8 +23,7 @@
 // ********************************************************************************
 // Web Interface custom page handler
 // ********************************************************************************
-boolean handle_custom(String path) {
-  // path is a deepcopy, since it will be changed.
+bool handle_custom(const String& path) {
   #ifndef BUILD_NO_RAM_TRACKER
   checkRAM(F("handle_custom"));
   #endif
@@ -33,7 +32,7 @@ boolean handle_custom(String path) {
 
   // create a dynamic custom page, parsing task values into [<taskname>#<taskvalue>] placeholders and parsing %xx% system variables
   fs::File   dataFile      = tryOpenFile(path.c_str(), "r");
-  const bool dashboardPage = path.startsWith(F("dashboard"));
+  const bool dashboardPage = path.startsWith(F("dashboard")) || path.startsWith(F("/dashboard"));
 
   if (!dataFile && !dashboardPage) {
     return false;    // unknown file that does not exist...
@@ -137,14 +136,35 @@ boolean handle_custom(String path) {
 
   if (dataFile)
   {
-    String page;
-    page.reserve(dataFile.size());
-
-    while (dataFile.available()) {
-      page += ((char)dataFile.read());
+    // Read the file per line and serve per line to reduce amount of memory needed.
+    int available = dataFile.available();
+    String line;
+    line.reserve(128);
+    while (available > 0) {
+      uint32_t chunksize = 64;
+      if (available < chunksize) {
+        chunksize = available;
+      }
+      uint8_t buf[64] = {0};
+      const size_t read = dataFile.read(buf, chunksize);
+      if (read == chunksize) {
+        for (uint32_t i = 0; i < chunksize; ++i) {
+          const char c = (char)buf[i];
+          line += c;
+          if (c == '\n') {
+            addHtml(parseTemplate(line));
+            line.clear();
+            line.reserve(128);
+          }
+        }
+        available = dataFile.available();
+      } else {
+        available = 0;
+      }
+    }
+    if (!line.isEmpty()) {
+      addHtml(parseTemplate(line));
     }
-
-    addHtml(parseTemplate(page));
     dataFile.close();
   }
   else // if the requestef file does not exist, create a default action in case the page is named "dashboard*"

src/src/WebServer/CustomPage.h

@@ -7,7 +7,7 @@
 // ********************************************************************************
 // Web Interface custom page handler
 // ********************************************************************************
-boolean handle_custom(String path);
+bool handle_custom(const String& path);
 #endif
 
 #endif

src/src/WebServer/LoadFromFS.cpp

@@ -56,7 +56,7 @@ bool loadFromFS(String path) {
 
   statusLED(true);
 
-  String dataType             = F("text/plain");
+  const __FlashStringHelper* dataType = F("text/plain");
   bool   mustCheckCredentials = false;
 
   path = fileFromUrl(path);