Moved reading of SD card data into a dedicated class DataSource.

src/data_sources.cpp

@@ -0,0 +1,35 @@
+#include "data_sources.h"
+
+////////////// SDDataSource //////////////
+SDDataSource::SDDataSource(String file) { _file = SD.open(file, "r"); }
+SDDataSource::~SDDataSource() { if (_file) _file.close(); }
+size_t SDDataSource::read(uint8_t* buf, size_t len) { return _file.read(buf, len); }
+uint8_t SDDataSource::read() { return _file.read(); }
+size_t SDDataSource::position() { return _file.position(); }
+void SDDataSource::seek(size_t position) { _file.seek(position); }
+size_t SDDataSource::size() { return _file.size(); }
+void SDDataSource::close() { _file.close(); }
+
+void SDDataSource::skip_id3_tag() {
+	uint32_t original_position = _file.position();
+	uint32_t offset = 0;
+	if (_file.read()=='I' && _file.read()=='D' && _file.read()=='3') {
+		DEBUG("ID3 tag found\n");
+		// Skip ID3 tag version
+		_file.read(); _file.read();
+		byte tags = _file.read();
+		bool footer_present = tags & 0x10;
+		DEBUG("ID3 footer found: %d\n", footer_present);
+		for (byte i=0; i<4; i++) {
+			offset <<= 7;
+			offset |= (0x7F & _file.read());
+		}
+		offset += 10;
+		if (footer_present) offset += 10;
+		DEBUG("ID3 tag length is %d bytes.\n", offset);
+		_file.seek(offset);
+	} else {
+		DEBUG("No ID3 tag found\n");
+		_file.seek(original_position);
+	}
+}