Implements seekDir and getNextFileName on FS Lib to improve performance (#7229)

* Implements seekDir and getNextFileName on FS lib to improve performance
* getNextFileName return String directly

libraries/FS/src/FS.cpp

@@ -187,6 +187,22 @@ File File::openNextFile(const char* mode)
     return _p->openNextFile(mode);
 }
 
+boolean File::seekDir(long position){
+    if(!_p){
+        return false;
+    }
+    return _p->seekDir(position);
+}
+
+String File::getNextFileName(void)
+{
+    if (!_p) {
+        return ""; 
+    }
+    return _p->getNextFileName();
+
+}
+
 void File::rewindDirectory(void)
 {
     if (!*this) {

libraries/FS/src/FS.h

@@ -78,7 +78,9 @@ public:
     const char* name() const;
 
     boolean isDirectory(void);
+    boolean seekDir(long position);
     File openNextFile(const char* mode = FILE_READ);
+    String getNextFileName(void);
     void rewindDirectory(void);
 
 protected:

libraries/FS/src/FSImpl.h

@@ -43,6 +43,8 @@ public:
     virtual const char* name() const = 0;
     virtual boolean isDirectory(void) = 0;
     virtual FileImplPtr openNextFile(const char* mode) = 0;
+    virtual boolean seekDir(long position);
+    virtual String getNextFileName(void);
     virtual void rewindDirectory(void) = 0;
     virtual operator bool() = 0;
 };

libraries/FS/src/vfs_api.cpp

@@ -476,6 +476,36 @@ FileImplPtr VFSFileImpl::openNextFile(const char* mode)
     return std::make_shared<VFSFileImpl>(_fs, name.c_str(), mode);
 }
 
+boolean VFSFileImpl::seekDir(long position){
+    if(!_d){
+        return false;
+    }
+    seekdir(_d, position);
+    return true;
+}
+
+
+String VFSFileImpl::getNextFileName()
+{
+    if (!_isDirectory || !_d) {
+        return "";
+    }
+    struct dirent *file = readdir(_d);
+    if (file == NULL) {
+        return "";
+    }
+    if (file->d_type != DT_REG && file->d_type != DT_DIR) {
+        return "";
+    }
+    String fname = String(file->d_name);
+    String name = String(_path);
+    if (!fname.startsWith("/") && !name.endsWith("/")) {
+        name += "/";
+    }
+    name += fname;
+    return name;
+}
+
 void VFSFileImpl::rewindDirectory(void)
 {
     if(!_isDirectory || !_d) {

libraries/FS/src/vfs_api.h

@@ -71,6 +71,8 @@ public:
     const char* name() const override;
     time_t      getLastWrite()  override;
     boolean     isDirectory(void) override;
+    boolean     seekDir(long position) override;
+    String      getNextFileName(void) override;
     FileImplPtr openNextFile(const char* mode) override;
     void        rewindDirectory(void) override;
     operator    bool();