Corrections of Stream.Find, FindUntil and added FindMulti - like AVR-Core Libraries (#3442)

* Corrections of Find, FindUntil and FindMulti

Find has some bug that is not working with Ethernet.find() so, I copied code from Stream.h and Stream.cpp in AVR-CORE library and now it's working perfectly.
I don't know where was the error, but an Ethernet.find compiled to MEGA2560 was working but not working when compiled to esp32, after corrections of code (copy of AVR-Core libraries) it's working perfect.
So probably has some error on original ESP32-Core library.

Below is part of code that was working with MEGA2560 and not with ESP32 libraries.
client.find never return TRUE with ESP32 original library and with AVR it's works.

boolean esp32_fw_update(EthernetClient &client, DecodedHeader &header, const String &field_filename, const String &field_crc) {

  char bound[header.boundary.length()+3];
  char term[]="\r\n";
  
  strcpy(bound,header.boundary.c_str());
  strcat(bound,term);
  while (client.find(bound)) { 
    String line=client.readStringUntil('\r');

* Update Stream.h

* Update Stream.cpp
Co-authored-by: Me No Dev <me-no-dev@users.noreply.github.com>

cores/esp32/Stream.cpp

@@ -89,7 +89,7 @@ unsigned long Stream::getTimeout(void) {
 // find returns true if the target string is found
 bool  Stream::find(const char *target)
 {
-    return findUntil(target, (char*) "");
+  return findUntil(target, strlen(target), NULL, 0);
 }
 
 // reads data from the stream until the target string of given length is found
@@ -110,35 +110,78 @@ bool Stream::findUntil(const char *target, const char *terminator)
 // returns true if target string is found, false if terminated or timed out
 bool Stream::findUntil(const char *target, size_t targetLen, const char *terminator, size_t termLen)
 {
-    size_t index = 0;  // maximum target string length is 64k bytes!
-    size_t termIndex = 0;
-    int c;
+  if (terminator == NULL) {
+    MultiTarget t[1] = {{target, targetLen, 0}};
+    return findMulti(t, 1) == 0 ? true : false;
+  } else {
+    MultiTarget t[2] = {{target, targetLen, 0}, {terminator, termLen, 0}};
+    return findMulti(t, 2) == 0 ? true : false;
+  }
+}
 
-    if(*target == 0) {
-        return true;    // return true if target is a null string
+int Stream::findMulti( struct Stream::MultiTarget *targets, int tCount) {
+  // any zero length target string automatically matches and would make
+  // a mess of the rest of the algorithm.
+  for (struct MultiTarget *t = targets; t < targets+tCount; ++t) {
+    if (t->len <= 0)
+      return t - targets;
   }
-    while((c = timedRead()) > 0) {
 
-        if(c != target[index]) {
-            index = 0;    // reset index if any char does not match
+  while (1) {
+    int c = timedRead();
+    if (c < 0)
+      return -1;
+
+    for (struct MultiTarget *t = targets; t < targets+tCount; ++t) {
+      // the simple case is if we match, deal with that first.
+      if (c == t->str[t->index]) {
+        if (++t->index == t->len)
+          return t - targets;
+        else
+          continue;
       }
 
-        if(c == target[index]) {
-            //////Serial.print("found "); Serial.write(c); Serial.print("index now"); Serial.println(index+1);
-            if(++index >= targetLen) { // return true if all chars in the target match
-                return true;
+      // if not we need to walk back and see if we could have matched further
+      // down the stream (ie '1112' doesn't match the first position in '11112'
+      // but it will match the second position so we can't just reset the current
+      // index to 0 when we find a mismatch.
+      if (t->index == 0)
+        continue;
+
+      int origIndex = t->index;
+      do {
+        --t->index;
+        // first check if current char works against the new current index
+        if (c != t->str[t->index])
+          continue;
+
+        // if it's the only char then we're good, nothing more to check
+        if (t->index == 0) {
+          t->index++;
+          break;
         }
+
+        // otherwise we need to check the rest of the found string
+        int diff = origIndex - t->index;
+        size_t i;
+        for (i = 0; i < t->index; ++i) {
+          if (t->str[i] != t->str[i + diff])
+            break;
         }
 
-        if(termLen > 0 && c == terminator[termIndex]) {
-            if(++termIndex >= termLen) {
-                return false;    // return false if terminate string found before target string
+        // if we successfully got through the previous loop then our current
+        // index is good.
+        if (i == t->index) {
+          t->index++;
+          break;
         }
-        } else {
-            termIndex = 0;
+
+        // otherwise we just try the next index
+      } while (t->index);
     }
   }
-    return false;
+  // unreachable
+  return -1;
 }
 
 // returns the first valid (long) integer value from the current position.

cores/esp32/Stream.h

@@ -60,6 +60,7 @@ public:
 
     void setTimeout(unsigned long timeout);  // sets maximum milliseconds to wait for stream data, default is 1 second
     unsigned long getTimeout(void);
+      
     bool find(const char *target);   // reads data from the stream until the target string is found
     bool find(uint8_t *target)
     {
@@ -123,6 +124,17 @@ protected:
     // this allows format characters (typically commas) in values to be ignored
 
     float parseFloat(char skipChar);  // as above but the given skipChar is ignored
+  
+    struct MultiTarget {
+      const char *str;  // string you're searching for
+      size_t len;       // length of string you're searching for
+      size_t index;     // index used by the search routine.
+    };
+
+  // This allows you to search for an arbitrary number of strings.
+  // Returns index of the target that is found first or -1 if timeout occurs.
+  int findMulti(struct MultiTarget *targets, int tCount);
+
 };
 
 #endif