mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-12-04 22:36:34 +00:00
262 lines
7.8 KiB
Go
262 lines
7.8 KiB
Go
|
// 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.
|
||
|
SkippableSize uint32
|
||
|
|
||
|
// HeaderSize is the raw size of the frame header.
|
||
|
//
|
||
|
// For normal frames, it includes the size of the magic number and
|
||
|
// the size of the header (per section 3.1.1.1).
|
||
|
// It does not include the size for any data blocks (section 3.1.1.2) nor
|
||
|
// the size for the trailing content checksum.
|
||
|
//
|
||
|
// For skippable frames, this counts the size of the magic number
|
||
|
// along with the size of the size field of the payload.
|
||
|
// It does not include the size of the skippable payload itself.
|
||
|
// The total frame size is the HeaderSize plus the SkippableSize.
|
||
|
HeaderSize int
|
||
|
|
||
|
// First block information.
|
||
|
FirstBlock struct {
|
||
|
// OK will be set if first block could be decoded.
|
||
|
OK bool
|
||
|
|
||
|
// Is this the last block of a frame?
|
||
|
Last bool
|
||
|
|
||
|
// Is the data compressed?
|
||
|
// If true CompressedSize will be populated.
|
||
|
// Unfortunately DecompressedSize cannot be determined
|
||
|
// without decoding the blocks.
|
||
|
Compressed bool
|
||
|
|
||
|
// DecompressedSize is the expected decompressed size of the block.
|
||
|
// Will be 0 if it cannot be determined.
|
||
|
DecompressedSize int
|
||
|
|
||
|
// CompressedSize of the data in the block.
|
||
|
// Does not include the block header.
|
||
|
// Will be equal to DecompressedSize if not Compressed.
|
||
|
CompressedSize int
|
||
|
}
|
||
|
|
||
|
// If set there is a checksum present for the block content.
|
||
|
// The checksum field at the end is always 4 bytes long.
|
||
|
HasCheckSum bool
|
||
|
}
|
||
|
|
||
|
// Decode the header from the beginning of the stream.
|
||
|
// This will decode the frame header and the first block header if enough bytes are provided.
|
||
|
// It is recommended to provide at least HeaderMaxSize bytes.
|
||
|
// If the frame header cannot be read an error will be returned.
|
||
|
// If there isn't enough input, io.ErrUnexpectedEOF is returned.
|
||
|
// The FirstBlock.OK will indicate if enough information was available to decode the first block header.
|
||
|
func (h *Header) Decode(in []byte) error {
|
||
|
_, err := h.DecodeAndStrip(in)
|
||
|
return err
|
||
|
}
|
||
|
|
||
|
// DecodeAndStrip will decode the header from the beginning of the stream
|
||
|
// and on success return the remaining bytes.
|
||
|
// This will decode the frame header and the first block header if enough bytes are provided.
|
||
|
// It is recommended to provide at least HeaderMaxSize bytes.
|
||
|
// If the frame header cannot be read an error will be returned.
|
||
|
// If there isn't enough input, io.ErrUnexpectedEOF is returned.
|
||
|
// The FirstBlock.OK will indicate if enough information was available to decode the first block header.
|
||
|
func (h *Header) DecodeAndStrip(in []byte) (remain []byte, err error) {
|
||
|
*h = Header{}
|
||
|
if len(in) < 4 {
|
||
|
return nil, 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 nil, ErrMagicMismatch
|
||
|
}
|
||
|
if len(in) < 4 {
|
||
|
return nil, io.ErrUnexpectedEOF
|
||
|
}
|
||
|
h.HeaderSize += 4
|
||
|
h.Skippable = true
|
||
|
h.SkippableID = int(b[0] & 0xf)
|
||
|
h.SkippableSize = binary.LittleEndian.Uint32(in)
|
||
|
return in[4:], nil
|
||
|
}
|
||
|
|
||
|
// Read Window_Descriptor
|
||
|
// https://github.com/facebook/zstd/blob/dev/doc/zstd_compression_format.md#window_descriptor
|
||
|
if len(in) < 1 {
|
||
|
return nil, 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 nil, errors.New("reserved bit set on frame header")
|
||
|
}
|
||
|
|
||
|
if !h.SingleSegment {
|
||
|
if len(in) < 1 {
|
||
|
return nil, 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 nil, 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 nil, 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 in, 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 in, 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 in, nil
|
||
|
}
|
||
|
|
||
|
// AppendTo will append the encoded header to the dst slice.
|
||
|
// There is no error checking performed on the header values.
|
||
|
func (h *Header) AppendTo(dst []byte) ([]byte, error) {
|
||
|
if h.Skippable {
|
||
|
magic := [4]byte{0x50, 0x2a, 0x4d, 0x18}
|
||
|
magic[0] |= byte(h.SkippableID & 0xf)
|
||
|
dst = append(dst, magic[:]...)
|
||
|
f := h.SkippableSize
|
||
|
return append(dst, uint8(f), uint8(f>>8), uint8(f>>16), uint8(f>>24)), nil
|
||
|
}
|
||
|
f := frameHeader{
|
||
|
ContentSize: h.FrameContentSize,
|
||
|
WindowSize: uint32(h.WindowSize),
|
||
|
SingleSegment: h.SingleSegment,
|
||
|
Checksum: h.HasCheckSum,
|
||
|
DictID: h.DictionaryID,
|
||
|
}
|
||
|
return f.appendTo(dst), nil
|
||
|
}
|