Zazama / node-id3

import { getTags } from "./frames-reader"

import { Options } from "./types/Options"

import { WriteTags } from "./types/Tags"

import { decodeSize, encodeSize } from "./util-size"

export const Header = {

    identifier: "ID3",

    size: 10,

    offset: {

        identifier: 0,  // 3 bytes

        version: 3,     // major version: 1 byte

        revision: 4,    // 1 byte

        flags: 5,       // 1 byte

        size: 6         // 4 bytes

    }

} as const

/**

 * ID3v2 Header

 */

type TagHeader = {

    /**

     * The sum of the header size and the tag data size.

     */

    tagSize: number

    /**

     * Version format is v2.major.revision

     */

    version: {

        /**

         * Major versions are not backwards compatible.

         */

        major: number

        /**

         * Revisions are backwards compatible.

         */

        revision: number

    }

    flags: TagHeaderFlags

}

type TagHeaderFlags = {

    /**

     * Indicates whether or not unsynchronisation is applied on all frames

     * (see section 6.1 for details); true indicates usage.

     */

    unsynchronisation: boolean

    /**

     * Indicates whether or not the header is followed by an extended

     * header. The extended header is described in section 3.2.

     * True indicates the presence of an extended header.

     */

    extendedHeader: boolean

    /**

     * This flag SHALL always be set when the tag is in an experimental stage.

     */

    experimentalIndicator: boolean

    /**

     * A footer (section 3.4) is present at the very end of the tag.

     * True indicates the presence of a footer.

     */

    footerPresent?: boolean

}

const subarray = (buffer: Buffer, offset: number, size: number) =>

    buffer.subarray(offset, offset + size)

export function createId3Tag(tags: WriteTags) {

    const frames = buildFramesBuffer(tags)

    return embedFramesInId3Tag(frames)

}

export function embedFramesInId3Tag(frames: Buffer) {

    const header = Buffer.alloc(Header.size)

    header.fill(0)

    header.write(Header.identifier, Header.offset.identifier)

    header.writeUInt16BE(0x0300, Header.offset.version)

    header.writeUInt16BE(0x0000, Header.offset.flags)

    encodeSize(frames.length).copy(header, Header.offset.size)

    return Buffer.concat([header, frames])

}

/**

 * Remove already written ID3-Frames from a buffer

 */

export function removeId3Tag(data: Buffer) {

    const tagPosition = findId3TagPosition(data)

    if (tagPosition === -1) {

        return data

    }

    const encodedSize = subarray(data, tagPosition + Header.offset.size, 4)

    if (!isValidEncodedSize(encodedSize)) {

        return false

    }

    if (data.length >= tagPosition + Header.size) {

        const size = decodeSize(encodedSize)

        return Buffer.concat([

            data.subarray(0, tagPosition),

            data.subarray(tagPosition + size + Header.size)

        ])

    }

    return data

}

export function getTagsFromId3Tag(buffer: Buffer, options: Options) {

    const tagBody = getId3TagBody(buffer)

    return getTags(tagBody, options)

}

export function getId3TagSize(buffer: Buffer): number {

    const encodedSize = subarray(buffer, Header.offset.size, 4)

    return Header.size + decodeSize(encodedSize)

}

function getId3TagBody(buffer: Buffer) {

    const tagPosition = findId3TagPosition(buffer)

    if (tagPosition === -1) {

        return undefined

    }

    const tagBuffer = buffer.subarray(tagPosition)

    const tagHeader = decodeId3TagHeader(tagBuffer)

    const totalHeaderSize =

        Header.size + getExtendedHeaderSize(tagHeader, tagBuffer)

    const bodySize = tagHeader.tagSize - totalHeaderSize

    // Copy for now, it might not be necessary, but we are not really sure for

    // now, will be re-assessed if we can avoid the copy.

    const body = Buffer.alloc(bodySize)

    tagBuffer.copy(body, 0, totalHeaderSize)

    return {

        version: tagHeader.version.major,

        buffer: body

    }

}

/**

 * @param tagBuffer A buffer starting with a valid id3 tag header.

 * @returns The size of the extended header.

 */

function getExtendedHeaderSize(header: TagHeader, tagBuffer: Buffer) {

    if (header.flags.extendedHeader) {

        if (header.version.major === 3) {

            return 4 + tagBuffer.readUInt32BE(Header.size)

        }

        if (header.version.major === 4) {

            return decodeSize(subarray(tagBuffer, Header.size, 4))

        }

    }

    return 0

}

}

/**

 * @param tagBuffer A buffer starting with a valid id3 tag header.

 * @returns The size of tag including the header.

 */

function decodeId3TagSize(tagBuffer: Buffer) {

    const encodedSize = subarray(tagBuffer, Header.offset.size, 4)

    return Header.size + decodeSize(encodedSize)

}

function parseTagHeaderFlags(header: Buffer): TagHeaderFlags {

    const version = header[Header.offset.version]

    const flagsByte = header[Header.offset.flags]

    if (version === 3) {

        return {

            unsynchronisation: !!(flagsByte & 128),

            extendedHeader: !!(flagsByte & 64),

            experimentalIndicator: !!(flagsByte & 32)

        }

    }

    if (version === 4) {

        return {

            unsynchronisation: !!(flagsByte & 128),

            extendedHeader: !!(flagsByte & 64),

            experimentalIndicator: !!(flagsByte & 32),

            footerPresent: !!(flagsByte & 16)

        }

    }

    return {

        unsynchronisation: false,

        extendedHeader: false,

        experimentalIndicator: false

    }

}

/**

 * Returns the position of the first valid tag found or -1 if no tag was found.

 */

export function findId3TagPosition(buffer: Buffer) {

    // Search Buffer for valid ID3 frame

    let position = -1

    do {

        position = buffer.indexOf(Header.identifier, position + 1)

        if (position !== -1) {

            // It's possible that there is a "ID3" sequence without being an

            // ID3 Frame, so we need to check for validity of the next 10 bytes.

            if (isValidId3Header(buffer.subarray(position))) {

                return position

            }

        }

    } while (position !== -1)

    return -1

}

function isValidId3Header(buffer: Buffer) {

    // From id3.org:

    // An ID3v2 tag can be detected with the following pattern:

    // $49 44 33 yy yy xx zz zz zz zz

    // Where yy is less than $FF, xx is the 'flags' byte and zz is less than

    // $80.

    if (buffer.length < Header.size) {

        return false

    }

    const identifier = buffer.readUIntBE(Header.offset.identifier, 3)

    if (identifier !== 0x494433) {

        return false

    }

    const majorVersion = buffer[Header.offset.version]

    const revision = buffer[Header.offset.revision]

    if (majorVersion === 0xFF || revision === 0xFF) {

        return false

    }

    // This library currently only handle these versions.

    if ([0x02, 0x03, 0x04].indexOf(majorVersion) === -1) {

        return false

    }

    return isValidEncodedSize(subarray(buffer, Header.offset.size, 4))

}

function isValidEncodedSize(encodedSize: Buffer) {

    // The size must not have the bit 7 set

    return ((

        encodedSize[0] |

        encodedSize[1] |

        encodedSize[2] |

        encodedSize[3]

    ) & 128) === 0

}