ESP8266lib/data/formats/mp3/ID3.h

#pragma once

#include <cstdint>
#include <vector>
#include <string>
#include <algorithm>

#include <string.h>

#include "../../../Debug.h"

/**
 * very basic ID3v2 reader
 * https://id3.org/id3v2.3.0#ID3v2_overview
 */
class ID3v2 {

	static constexpr const char* NAME = "ID3v2";

	/** 4 byte size, used to correct endianness */
	struct Size {
		uint8_t raw[4];
		operator uint32_t () const {return raw[3]<<0 | raw[2]<<8 | raw[1]<<16 | raw[0]<<24;}
	};

	/** ID3 header at the start of the file (if present) */
	struct Header {
		char ID3[3];			// "ID3" if present
		uint16_t version;
		uint8_t flags;
		uint8_t sizeBits[4];	// size of content, 4 bytes, the MSB of every byte is 0 -> 28 bits used
		uint32_t size() const {return sizeBits[0]<<21 | sizeBits[1]<<14 | sizeBits[2]<<7 | sizeBits[3]<<0;}
	} __attribute__((packed));

	/** header for every frame within the ID3 data */
	struct Frame {
		char name[4];			// tag name (e.g. TALB, APIC, ...)
		Size size;				// size of content
		uint16_t flags;
		bool operator == (const char* needle) const {return memcmp(name, needle, 4) == 0;}
		bool isPadding() const {return name[0] == 0x00 && size == 0;}
	} __attribute__((packed));

	static constexpr const uint8_t ENC_ISO8859 = 0x00;
	static constexpr const uint8_t ENC_UNICODE = 0x01;
	static constexpr const uint8_t ENC_UTF8 = 0x03;

	// maximum size for a frame to be read
	static constexpr const uint32_t MAX_FRM_SIZE = 65536;

public:

	struct Image {
		bool present = false;
		std::string mime;
		uint8_t type;
		std::string desc;
		uint32_t pos;		// the absolute position within the data where the image is
		uint32_t size;		// the length of the image in bytes
	};

	struct Data {
		bool ok = false;
		std::string artist;
		std::string title;
		std::string album;
		std::string year;
		Image img;
	};

public:

	ID3v2() {}

	template <typename DataSource> Data readTags(DataSource& src, bool readImages) {

		Data data;

		// start at beginning
		src.seekTo(0);

		// 10 byte ID3 header, file starts with "ID3" ?
		Header head;
		src.readType(head);
		if (memcmp(head.ID3, "ID3", 3) != 0) {return data;}

		// read all tags
		while(src.curPos() < head.size()) {

			Frame frm;
			src.readType(frm);
			uint32_t startOfData = src.curPos();

			if (frm.isPadding()) {
				break;	// only (empty) padding blocks will follow -> stop
			} else if (frm == "TALB") {
				data.album = readString(src, frm.size);
			} else if (frm == "TPE1") {
				data.artist = readString(src, frm.size);
			} else if (frm == "TIT2") {
				data.title = readString(src, frm.size);
			} else if (frm == "TYER") {
				data.year = readString(src, frm.size);
			} else if (frm == "APIC" && readImages) {
				data.img = parseImage(src, frm.size);
			}

			Log::addInfo(NAME, "%c%c%c%c:%d", frm.name[0],frm.name[1],frm.name[2],frm.name[3], (uint32_t)frm.size);

			// ensure we are positioned after the frame
			src.seekTo(startOfData + frm.size);

		}

		data.ok = true;
		return data;

	}

private:

	/** read a string with the given length, corrects encoding */
	template <typename DataSource> std::string readString(DataSource& src, uint32_t size) {

		// read no more than 120 chars
		uint8_t buf[128];
		size = std::min((uint32_t)120, size);
		src.read(size, buf);

		if (buf[0] == ENC_ISO8859 || buf[0] == ENC_UTF8) {
			return std::string((const char*) &buf[1]);

		} else if (buf[0] == ENC_UNICODE) {	// 16(!) bit unicode, starts with {0x01 0xFF 0xF4}
			uint32_t pos = 0;
			for (uint32_t i = 3; i < size; i += 2) {
				buf[pos++] = buf[i];
			}
			buf[pos] = 0;
			return std::string((const char*)buf);

		} else {
			return "ENCODING?";

		}

	}

	/** read a string with an unknown length, zero termined, corrects encoding, also returns the number of bytes read */
	template <typename DataSource> std::string readStringZeroTerm(DataSource& src, uint8_t encoding, uint32_t& bytesRead) {

		std::string res;
		bytesRead = 0;

		if (encoding == ENC_ISO8859 || encoding == ENC_UTF8) {
			char c;
			while(true) {
				src.readType(c);
				if (c == 0) {break;}
				res += c;
				++bytesRead;
			}

		} else if (encoding == ENC_UNICODE) {	// 16(!) bit unicode, starts with {0x01 0xFF 0xFE}
			char c[2];
			src.readType(c);	// skip 0xFF 0xFE
			while(true) {
				src.readType(c);
				if (c[0] == 0 && c[1] == 0) {break;}
				res += c[0];
				bytesRead += 2;
			}

		} else {
			return "ENCODING?";

		}

		return res;

	}

	/** read X bytes into a vector */
	template <typename DataSource> std::vector<uint8_t> readVector(DataSource& src, const uint32_t size) {
		std::vector<uint8_t> res;
		res.resize(size);
		src.read(size, res.data());
		return res;
	}

	/**
	 * parse an image tag
	 * image data is preceeded by mime type and description)
	 * the image is not actually read, but its offset within the data and its size are determined
	 */
	template <typename DataSource> Image parseImage(DataSource& src, const uint32_t size) {

		uint32_t read1, read2;
		Image img;

		uint8_t encoding;
		src.readType(encoding);

		img.mime = readStringZeroTerm(src, ENC_ISO8859, read1);
		src.readType(img.type);
		img.desc = readStringZeroTerm(src, encoding, read2);

		// determine the position and byte-size of the image
		img.pos = src.curPos();
		img.size = size - 1 - read1 - 1 - read2;
		img.present = true;

		return img;

	}

};