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: decodeheader.go
    path of file: ./repos/kubeedge/vendor/github.com/klauspost/compress/zstd
    
    the code of the file until where you have to start completion: // Copyright 2020+ Klaus Post. All rights reserved.
// License information can be found in the LICENSE file.

package zstd

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

// HeaderMaxSize is the maximum size of a Frame and Block Header.
// If less is sent to Header.Decode it *may* still contain enough information.
const HeaderMaxSize = 14 + 3

// Header contains information about the first frame and block within that.
type Header struct {
	// SingleSegment specifies whether the data is to be decompressed into a
	// single contiguous memory segment.
	// It implies that WindowSize is invalid and that FrameContentSize is valid.
	SingleSegment bool

	// WindowSize is the window of data to keep while decoding.
	// Will only be set if SingleSegment is false.
	WindowSize uint64

	// Dictionary ID.
	// If 0, no dictionary.
	DictionaryID uint32

	// HasFCS specifies whether FrameContentSize has a valid value.
	HasFCS bool

	// FrameContentSize is the expected uncompressed size of the entire frame.
	FrameContentSize uint64

	// Skippable will be true if the frame is meant to be skipped.
	// This implies that FirstBlock.OK is false.
	Skippable bool

	// SkippableID is the user-specific ID for the skippable frame.
	// Valid values are between 0 to 15, inclusive.
	SkippableID int

	// SkippableSize is the length of the user data to skip following
	// the header
    
func (h *Header) Decode(in []byte) error {
	*h = Header{}
	if len(in) < 4 {
		return io.ErrUnexpectedEOF
	}
	h.HeaderSize += 4
	b, in := in[:4], in[4:]
	if string(b) != frameMagic {
		if string(b[1:4]) != skippableFrameMagic || b[0]&0xf0 != 0x50 {
			return ErrMagicMismatch
		}
		if len(in) < 4 {
			return io.ErrUnexpectedEOF
		}
		h.HeaderSize += 4
		h.Skippable = true
		h.SkippableID = int(b[0] & 0xf)
		h.SkippableSize = binary.LittleEndian.Uint32(in)
		return nil
	}

	// Read Window_Descriptor
	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor
	if len(in) < 1 {
		return io.ErrUnexpectedEOF
	}
	fhd, in := in[0], in[1:]
	h.HeaderSize++
	h.SingleSegment = fhd&(1<<5) != 0
	h.HasCheckSum = fhd&(1<<2) != 0
	if fhd&(1<<3) != 0 {
		return errors.New("reserved bit set on frame header")
	}

	if !h.SingleSegment {
		if len(in) < 1 {
			return io.ErrUnexpectedEOF
		}
		var wd byte
		wd, in = in[0], in[1:]
		h.HeaderSize++
		windowLog := 10 + (wd >> 3)
		windowBase := uint64(1) << windowLog
		windowAdd := (windowBase / 8) * uint64(wd&0x7)
		h.WindowSize = windowBase + windowAdd
	}

	// Read Dictionary_ID
	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#dictionary_id
	if size := fhd & 3; size != 0 {
		if size == 3 {
			size = 4
		}
		if len(in) < int(size) {
			return io.ErrUnexpectedEOF
		}
		b, in = in[:size], in[size:]
		h.HeaderSize += int(size)
		switch len(b) {
		case 1:
			h.DictionaryID = uint32(b[0])
		case 2:
			h.DictionaryID = uint32(b[0]) | (uint32(b[1]) << 8)
		case 4:
			h.DictionaryID = uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
		}
	}

	// Read Frame_Content_Size
	// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#frame_content_size
	var fcsSize int
	v := fhd >> 6
	switch v {
	case 0:
		if h.SingleSegment {
			fcsSize = 1
		}
	default:
		fcsSize = 1 << v
	}

	if fcsSize > 0 {
		h.HasFCS = true
		if len(in) < fcsSize {
			return io.ErrUnexpectedEOF
		}
		b, in = in[:fcsSize], in[fcsSize:]
		h.HeaderSize += int(fcsSize)
		switch len(b) {
		case 1:
			h.FrameContentSize = uint64(b[0])
		case 2:
			// When FCS_Field_Size is 2, the offset of 256 is added.
			h.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) + 256
		case 4:
			h.FrameContentSize = uint64(b[0]) | (uint64(b[1]) << 8) | (uint64(b[2]) << 16) | (uint64(b[3]) << 24)
		case 8:
			d1 := uint32(b[0]) | (uint32(b[1]) << 8) | (uint32(b[2]) << 16) | (uint32(b[3]) << 24)
			d2 := uint32(b[4]) | (uint32(b[5]) << 8) | (uint32(b[6]) << 16) | (uint32(b[7]) << 24)
			h.FrameContentSize = uint64(d1) | (uint64(d2) << 32)
		}
	}

	// Frame Header done, we will not fail from now on.
	if len(in) < 3 {
		return nil
	}
	tmp := in[:3]
	bh := uint32(tmp[0]) | (uint32(tmp[1]) << 8) | (uint32(tmp[2]) << 16)
	h.FirstBlock.Last = bh&1 != 0
	blockType := blockType((bh >> 1) & 3)
	// find size.
	cSize := int(bh >> 3)
	switch blockType {
	case blockTypeReserved:
		return nil
	case blockTypeRLE:
		h.FirstBlock.Compressed = true
		h.FirstBlock.DecompressedSize = cSize
		h.FirstBlock.CompressedSize = 1
	case blockTypeCompressed:
		h.FirstBlock.Compressed = true
		h.FirstBlock.CompressedSize = cSize
	case blockTypeRaw:
		h.FirstBlock.DecompressedSize = cSize
		h.FirstBlock.CompressedSize = cSize
	default:
		panic("Invalid block type")
	}

	h.FirstBlock.OK = true
	return nil
}