mp4/Parser.go

// Copyright 2024 Martin Riedl
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package gomp4

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
)

// Parser struct for mp4 container parsing
type Parser struct {
	reader              io.Reader
	childBoxDefinitions map[string]map[string]BoxDefinition
	Content             []any
}

// NewParser creates a new parser with byte data
func NewParser(reader io.Reader) *Parser {
	// prepare valid box type combinations
	types := make(map[string]map[string]BoxDefinition, 0)
	for _, definition := range BoxDefinitions {
		for _, parent := range definition.ParentTypes {
			if _, exists := types[parent]; !exists {
				types[parent] = make(map[string]BoxDefinition, 0)
			}
			types[parent][definition.Type] = definition
		}
	}

	return &Parser{reader: reader, childBoxDefinitions: types}
}

// Parse starts the file parsing
func (parser *Parser) Parse() error {
	var filePosition uint64 = 0
	for {
		box, endPosition, endOfFile, err := parseNextBox(parser, parser.reader, boxTypeParentFile, filePosition)
		if box != nil {
			parser.Content = append(parser.Content, box)
		}

		if endOfFile {
			return nil
		} else if err != nil {
			logger.Println("error at", endPosition)
			return err
		}
		filePosition = endPosition
	}
}

func parseNextBox(parser *Parser, reader io.Reader, currentBoxType string, filePosition uint64) (box any, endPosition uint64, endOfFile bool, err error) {
	// first 4 bytes are the size of the box
	sizeBytes := make([]byte, boxSizeLength)
	sizeBytesCount, err := reader.Read(sizeBytes)
	if err != nil {
		if err == io.EOF {
			return nil, filePosition, true, nil
		}
		return nil, filePosition, false, err
	}

	// check read bytes count
	if sizeBytesCount != len(sizeBytes) {
		return nil, filePosition, false, fmt.Errorf("unable to parse next box size")
	}

	// parse box size
	boxSize := binary.BigEndian.Uint32(sizeBytes)
	logger.Println("new box size", boxSize, "at", filePosition)

	// TODO: check large size box type

	// parse box type
	boxTypeBytes := make([]byte, boxTypeLength)
	boxTypeBytesCount, err := reader.Read(boxTypeBytes)
	if err != nil {
		return nil, filePosition, false, err
	}

	// check read bytes count
	if boxTypeBytesCount != len(boxTypeBytes) {
		return nil, filePosition, false, fmt.Errorf("unable to parse box type at %d", filePosition)
	}
	boxType := string(boxTypeBytes)
	logger.Println("new box type", boxType, "at", filePosition)

	// parse box data
	boxHeaderSize := boxSizeLength + boxTypeLength
	boxContentSize := boxSize - boxHeaderSize
	boxContentBytes := make([]byte, boxContentSize)
	boxContentBytesCount, err := reader.Read(boxContentBytes)
	if err != nil {
		return nil, filePosition, false, err
	}

	// check read bytes count
	if boxContentBytesCount != len(boxContentBytes) {
		return nil, filePosition, false, fmt.Errorf("unable to parse box content at %d", filePosition)
	}

	// parse struct of box type
	if boxTypeDefinition, found := parser.childBoxDefinitions[currentBoxType][boxType]; found {
		box, err = boxTypeDefinition.Parser(parser, filePosition, boxHeaderSize, boxContentBytes)
	} else {
		logger.Println("unknown box type", boxType, "at", filePosition, "in", currentBoxType)
		return nil, filePosition, false, errors.New("unknown box type " + boxType + " in " + currentBoxType)
	}

	// check for box errors
	if err != nil {
		return
	}

	// calculate end position
	endPosition = filePosition + uint64(boxSize)
	return
}

func (box *Box) parseChildBoxes(parser *Parser, currentBoxType string, filePosition uint64, content []byte) (subBoxes []any, e error) {
	byteReader := bytes.NewReader(content)
	endPosition := filePosition + uint64(box.HeaderSize) + uint64(len(content))
	var currentFilePosition = filePosition + uint64(box.HeaderSize)
	for {
		// parse next packet
		currentBox, currentEndPosition, _, err := parseNextBox(parser, byteReader, currentBoxType, currentFilePosition)
		if err != nil {
			e = err
			logger.Println("error at", currentEndPosition, err)
			return
		}
		currentFilePosition = currentEndPosition

		// store packet
		subBoxes = append(subBoxes, currentBox)

		// check for end of content
		if endPosition == currentEndPosition {
			return
		}
	}
}