Add availableForWrite handler

Author: earlephilhower

src/FatLib/FatFile.cpp

@@ -1495,5 +1495,26 @@ size_t FatFile::write(const void* buf, size_t nbyte) {
   return -1;
 }
 
+//-------------------------------------------------------
+// EFP3 - Match upstream Arduino hack
+int FatFile::availableSpaceForWrite() {
+  // error if not a normal file or is read-only
+  if (!isWritable() || m_vol->m_blockDev->isBusy()) {
+    return 0;
+  }
+  // seek to end of file if append flag
+  if ((m_flags & FILE_FLAG_APPEND)) {
+    if (!seekSet(m_fileSize)) {
+      return 0;
+    }
+  }
+  uint8_t sectorOfCluster = m_vol->sectorOfCluster(m_curPosition);
+  uint16_t sectorOffset = m_curPosition & m_vol->sectorMask();
+  if (sectorOfCluster == 0 && sectorOffset == 0) {
+    return 0;
+  }
+  return m_vol->bytesPerSector() - sectorOffset - 1;
+}
+//-------------------------------------------------------
 
 }; // namespace sdfat

src/FatLib/FatFile.h

@@ -937,6 +937,8 @@ class FatFile {
    *
    */
   size_t write(const void* buf, size_t count);
+
+  int availableSpaceForWrite();
 //------------------------------------------------------------------------------
 #if ENABLE_ARDUINO_SERIAL
   /** List directory contents.