You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mod.rs
    path of file: ./repos/Symphonia/symphonia-metadata/src/id3v2
    
    the code of the file until where you have to start completion: // Symphonia
// Copyright (c) 2019-2022 The Project Symphonia Developers.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

//! An ID3v2 metadata reader.

use symphonia_core::errors::{decode_error, unsupported_error, Result};
use symphonia_core::io::*;
use symphonia_core::meta::{MetadataBuilder, MetadataOptions, MetadataReader, MetadataRevision};
use symphonia_core::probe::{Descriptor, Instantiate, QueryDescriptor};
use symphonia_core::support_metadata;

use log::{info, trace, warn};

mod frames;
mod unsync;

use frames::*;
use unsync::{read_syncsafe_leq32, UnsyncStream};

#[derive(Debug)]
#[allow(clippy::enum_variant_names)]
enum TagSizeRestriction {
    Max128Frames1024KiB,
    Max64Frames128KiB,
    Max32Frames40KiB,
    Max32Frames4KiB,
}

#[derive(Debug)]
enum TextEncodingRestriction {
    None,
    Utf8OrIso88591,
}

#[derive(Debug)]
enum TextFieldSize {
    None,
    Max1024Characters,
    Max128Characters,
    Max30Characters,
}

#[derive(Debug)]
enum ImageEncodingRestriction {
    None,
    PngOrJpegOnly,
}

#[derive(Debug)]
enum ImageSizeRestriction {
    None,
    LessThan256x256,
    LessThan64x64,
    Exactly64x64,
}

#[derive(Debug)]
#[allow(dead_code)]
struct Header {
    major_version: u8,
    minor_version: u8,
    size: u32,
    unsynchronisation: bool,
    has_extended_header: bool,
    experimental: bool,
    has_footer: bool,
}

#[derive(Debug)]
#[allow(dead_code)]
struct Restrictions {
    tag_size: TagSizeRestriction,
    text_encoding: TextEncodingRestriction,
    text_field_size: TextFieldSize,
    image_encoding: ImageEncodingRestriction,
    image_size: ImageSizeRestriction,
}

#[derive(Debug)]
#[allow(dead_code)]
struct ExtendedHeader {
    /// ID3v2.3 only, the number of padding bytes.
    padding_size: Option<u32>,
    /// ID3v2.3+, a CRC32
    
fn read_id3v2_header<B: ReadBytes>(reader: &mut B) -> Result<Header> {
    let marker = reader.read_triple_bytes()?;

    if marker != *b"ID3" {
        return unsupported_error("id3v2: not an ID3v2 tag");
    }

    let major_version = reader.read_u8()?;
    let minor_version = reader.read_u8()?;
    let flags = reader.read_u8()?;
    let size = unsync::read_syncsafe_leq32(reader, 28)?;

    let mut header = Header {
        major_version,
        minor_version,
        size,
        unsynchronisation: false,
        has_extended_header: false,
        experimental: false,
        has_footer: false,
    };

    // Major and minor version numbers should never equal 0xff as per the specification.
    if major_version == 0xff || minor_version == 0xff {
        return decode_error("id3v2: invalid version number(s)");
    }

    // Only support versions 2.2.x (first version) to 2.4.x (latest version as of May 2019) of the
    // specification.
    if major_version < 2 || major_version > 4 {
        return unsupported_error("id3v2: unsupported ID3v2 version");
    }

    // Version 2.2 of the standard specifies a compression flag bit, but does not specify a
    // compression standard. Future versions of the standard remove this feature and repurpose this
    // bit for other features. Since there is no way to know how to handle the remaining tag data,
    // return an unsupported error.
    if major_version == 2 && (flags & 0x40) != 0 {
        return unsupported_error("id3v2: ID3v2.2 compression is not supported");
    }

    // With the exception of the compression flag in version 2.2, flags were added sequentially each
    // major version. Check each bit sequentially as they appear in each version.
    if major_version >= 2 {
        header.unsynchronisation = flags & 0x80 != 0;
    }

    if major_version >= 3 {
        header.has_extended_header = flags & 0x40 != 0;
        header.experimental = flags & 0x20 != 0;
    }

    if major_version >= 4 {
        header.has_footer = flags & 0x10 != 0;
    }

    Ok(header)
}