mirror of
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake.git
synced 2025-10-13 11:11:30 -04:00
Import Turbo Tunnel support code.
Copied and slightly modified from
https://gitweb.torproject.org/pluggable-transports/meek.git/log/?h=turbotunnel&id=7eb94209f857fc71c2155907b0462cc587fc76cc
https://github.com/net4people/bbs/issues/21
RedialPacketConn is adapted from clientPacketConn in
c64a61c6da/obfs4proxy/turbotunnel_client.go
https://github.com/net4people/bbs/issues/14#issuecomment-544747519
This commit is contained in:
David Fifield
parent
904af9cb8a
commit
222ab3d85a
7 changed files with 1050 additions and 0 deletions
194
common/encapsulation/encapsulation.go
Normal file
194
common/encapsulation/encapsulation.go
Normal file
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@ -0,0 +1,194 @@
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// Package encapsulation implements a way of encoding variable-size chunks of
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// data and padding into a byte stream.
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//
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// Each chunk of data or padding starts with a variable-size length prefix. One
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// bit ("d") in the first byte of the prefix indicates whether the chunk
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// represents data or padding (1=data, 0=padding). Another bit ("c" for
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// "continuation") is the indicates whether there are more bytes in the length
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// prefix. The remaining 6 bits ("x") encode part of the length value.
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// dcxxxxxx
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// If the continuation bit is set, then the next byte is also part of the length
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// prefix. It lacks the "d" bit, has its own "c" bit, and 7 value-carrying bits
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// ("y").
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// cyyyyyyy
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// The length is decoded by concatenating value-carrying bits, from left to
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// right, of all value-carrying bits, up to and including the first byte whose
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// "c" bit is 0. Although in principle this encoding would allow for length
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// prefixes of any size, length prefixes are arbitrarily limited to 3 bytes and
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// any attempt to read or write a longer one is an error. These are therefore
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// the only valid formats:
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// 00xxxxxx xxxxxx₂ bytes of padding
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// 10xxxxxx xxxxxx₂ bytes of data
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// 01xxxxxx 0yyyyyyy xxxxxxyyyyyyy₂ bytes of padding
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// 11xxxxxx 0yyyyyyy xxxxxxyyyyyyy₂ bytes of data
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// 01xxxxxx 1yyyyyyy 0zzzzzzz xxxxxxyyyyyyyzzzzzzz₂ bytes of padding
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// 11xxxxxx 1yyyyyyy 0zzzzzzz xxxxxxyyyyyyyzzzzzzz₂ bytes of data
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// The maximum encodable length is 11111111111111111111₂ = 0xfffff = 1048575.
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// There is no requirement to use a length prefix of minimum size; i.e. 00000100
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// and 01000000 00000100 are both valid encodings of the value 4.
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//
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// After the length prefix follow that many bytes of padding or data. There are
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// no restrictions on the value of bytes comprising padding.
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//
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// The idea for this encapsulation is sketched here:
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// https://github.com/net4people/bbs/issues/9#issuecomment-524095186
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package encapsulation
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import (
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"errors"
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"io"
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"io/ioutil"
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)
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// ErrTooLong is the error returned when an encoded length prefix is longer than
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// 3 bytes, or when ReadData receives an input whose length is too large to
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// encode in a 3-byte length prefix.
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var ErrTooLong = errors.New("length prefix is too long")
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// ReadData returns a new slice with the contents of the next available data
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// chunk, skipping over any padding chunks that may come first. The returned
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// error value is nil if and only if a data chunk was present and was read in
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// its entirety. The returned error is io.EOF only if r ended before the first
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// byte of a length prefix. If r ended in the middle of a length prefix or
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// data/padding, the returned error is io.ErrUnexpectedEOF.
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func ReadData(r io.Reader) ([]byte, error) {
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for {
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var b [1]byte
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_, err := r.Read(b[:])
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if err != nil {
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// This is the only place we may return a real io.EOF.
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return nil, err
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}
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isData := (b[0] & 0x80) != 0
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moreLength := (b[0] & 0x40) != 0
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n := int(b[0] & 0x3f)
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for i := 0; moreLength; i++ {
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if i >= 2 {
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return nil, ErrTooLong
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}
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_, err := r.Read(b[:])
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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if err != nil {
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return nil, err
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}
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moreLength = (b[0] & 0x80) != 0
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n = (n << 7) | int(b[0]&0x7f)
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}
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if isData {
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p := make([]byte, n)
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_, err := io.ReadFull(r, p)
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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if err != nil {
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return nil, err
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}
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return p, err
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} else {
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_, err := io.CopyN(ioutil.Discard, r, int64(n))
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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if err != nil {
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return nil, err
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}
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}
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}
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}
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// dataPrefixForLength returns a length prefix for the given length, with the
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// "d" bit set to 1.
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func dataPrefixForLength(n int) ([]byte, error) {
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switch {
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case (n>>0)&0x3f == (n >> 0):
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return []byte{0x80 | byte((n>>0)&0x3f)}, nil
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case (n>>7)&0x3f == (n >> 7):
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return []byte{0xc0 | byte((n>>7)&0x3f), byte((n >> 0) & 0x7f)}, nil
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case (n>>14)&0x3f == (n >> 14):
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return []byte{0xc0 | byte((n>>14)&0x3f), 0x80 | byte((n>>7)&0x7f), byte((n >> 0) & 0x7f)}, nil
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default:
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return nil, ErrTooLong
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}
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}
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// WriteData encodes a data chunk into w. It returns the total number of bytes
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// written; i.e., including the length prefix. The error is ErrTooLong if the
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// length of data cannot fit into a length prefix.
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func WriteData(w io.Writer, data []byte) (int, error) {
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prefix, err := dataPrefixForLength(len(data))
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if err != nil {
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return 0, err
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}
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total := 0
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n, err := w.Write(prefix)
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total += n
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if err != nil {
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return total, err
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}
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n, err = w.Write(data)
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total += n
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return total, err
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}
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var paddingBuffer = make([]byte, 1024)
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// WritePadding encodes padding chunks, whose total size (including their own
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// length prefixes) is n. Returns the total number of bytes written to w, which
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// will be exactly n unless there was an error. The error cannot be ErrTooLong
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// because this function will write multiple padding chunks if necessary to
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// reach the requested size. Panics if n is negative.
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func WritePadding(w io.Writer, n int) (int, error) {
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if n < 0 {
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panic("negative length")
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}
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total := 0
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for n > 0 {
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p := len(paddingBuffer)
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if p > n {
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p = n
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}
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n -= p
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var prefix []byte
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switch {
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case ((p-1)>>0)&0x3f == ((p - 1) >> 0):
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p = p - 1
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prefix = []byte{byte((p >> 0) & 0x3f)}
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case ((p-2)>>7)&0x3f == ((p - 2) >> 7):
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p = p - 2
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prefix = []byte{0x40 | byte((p>>7)&0x3f), byte((p >> 0) & 0x7f)}
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case ((p-3)>>14)&0x3f == ((p - 3) >> 14):
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p = p - 3
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prefix = []byte{0x40 | byte((p>>14)&0x3f), 0x80 | byte((p>>7)&0x3f), byte((p >> 0) & 0x7f)}
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}
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nn, err := w.Write(prefix)
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total += nn
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if err != nil {
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return total, err
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}
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nn, err = w.Write(paddingBuffer[:p])
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total += nn
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if err != nil {
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return total, err
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}
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}
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return total, nil
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}
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// MaxDataForSize returns the length of the longest slice that can pe passed to
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// WriteData, whose total encoded size (including length prefix) is no larger
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// than n. Call this to find out if a chunk of data will fit into a length
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// budget. Panics if n == 0.
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func MaxDataForSize(n int) int {
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if n == 0 {
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panic("zero length")
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}
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prefix, err := dataPrefixForLength(n)
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if err == ErrTooLong {
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return (1 << (6 + 7 + 7)) - 1 - 3
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} else if err != nil {
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panic(err)
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}
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return n - len(prefix)
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}
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330
common/encapsulation/encapsulation_test.go
Normal file
330
common/encapsulation/encapsulation_test.go
Normal file
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@ -0,0 +1,330 @@
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package encapsulation
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import (
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"bytes"
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"io"
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"math/rand"
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"testing"
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)
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// Return a byte slice with non-trivial contents.
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func pseudorandomBuffer(n int) []byte {
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source := rand.NewSource(0)
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p := make([]byte, n)
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for i := 0; i < len(p); i++ {
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p[i] = byte(source.Int63() & 0xff)
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}
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return p
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}
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func mustWriteData(w io.Writer, p []byte) int {
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n, err := WriteData(w, p)
|
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if err != nil {
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panic(err)
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}
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return n
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}
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func mustWritePadding(w io.Writer, n int) int {
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n, err := WritePadding(w, n)
|
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if err != nil {
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panic(err)
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}
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return n
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}
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// Test that ReadData(WriteData()) recovers the original data.
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func TestRoundtrip(t *testing.T) {
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// Test above and below interesting thresholds.
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for _, i := range []int{
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0x00, 0x01,
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0x3e, 0x3f, 0x40, 0x41,
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0xfe, 0xff, 0x100, 0x101,
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0x1ffe, 0x1fff, 0x2000, 0x2001,
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0xfffe, 0xffff, 0x10000, 0x10001,
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0xffffe, 0xfffff,
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} {
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original := pseudorandomBuffer(i)
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var enc bytes.Buffer
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n, err := WriteData(&enc, original)
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if err != nil {
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t.Fatalf("size %d, WriteData returned error %v", i, err)
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}
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if enc.Len() != n {
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t.Fatalf("size %d, returned length was %d, written length was %d",
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i, n, enc.Len())
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}
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inverse, err := ReadData(&enc)
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if err != nil {
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t.Fatalf("size %d, ReadData returned error %v", i, err)
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}
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if !bytes.Equal(inverse, original) {
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t.Fatalf("size %d, got <%x>, expected <%x>", i, inverse, original)
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}
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}
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}
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// Test that WritePadding writes exactly as much as requested.
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func TestPaddingLength(t *testing.T) {
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// Test above and below interesting thresholds. WritePadding also gets
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// values above 0xfffff, the maximum value of a single length prefix.
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for _, i := range []int{
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0x00, 0x01,
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0x3f, 0x40, 0x41, 0x42,
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0xff, 0x100, 0x101, 0x102,
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0x2000, 0x2001, 0x2002, 0x2003,
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0x10000, 0x10001, 0x10002, 0x10003,
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0x100001, 0x100002, 0x100003, 0x100004,
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} {
|
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var enc bytes.Buffer
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n, err := WritePadding(&enc, i)
|
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if err != nil {
|
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t.Fatalf("size %d, WritePadding returned error %v", i, err)
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}
|
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if n != i {
|
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t.Fatalf("requested %d bytes, returned %d", i, n)
|
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}
|
||||
if enc.Len() != n {
|
||||
t.Fatalf("requested %d bytes, wrote %d bytes", i, enc.Len())
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Test that ReadData skips over padding.
|
||||
func TestSkipPadding(t *testing.T) {
|
||||
var data = [][]byte{{}, {}, []byte("hello"), {}, []byte("world")}
|
||||
var enc bytes.Buffer
|
||||
mustWritePadding(&enc, 10)
|
||||
mustWritePadding(&enc, 100)
|
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mustWriteData(&enc, data[0])
|
||||
mustWriteData(&enc, data[1])
|
||||
mustWritePadding(&enc, 10)
|
||||
mustWriteData(&enc, data[2])
|
||||
mustWriteData(&enc, data[3])
|
||||
mustWritePadding(&enc, 10)
|
||||
mustWriteData(&enc, data[4])
|
||||
mustWritePadding(&enc, 10)
|
||||
mustWritePadding(&enc, 10)
|
||||
for i, expected := range data {
|
||||
actual, err := ReadData(&enc)
|
||||
if err != nil {
|
||||
t.Fatalf("slice %d, got error %v, expected %v", i, err, nil)
|
||||
}
|
||||
if !bytes.Equal(actual, expected) {
|
||||
t.Fatalf("slice %d, got <%x>, expected <%x>", i, actual, expected)
|
||||
}
|
||||
}
|
||||
p, err := ReadData(&enc)
|
||||
if p != nil || err != io.EOF {
|
||||
t.Fatalf("got (<%x>, %v), expected (%v, %v)", p, err, nil, io.EOF)
|
||||
}
|
||||
}
|
||||
|
||||
// Test that EOF before a length prefix returns io.EOF.
|
||||
func TestEOF(t *testing.T) {
|
||||
p, err := ReadData(bytes.NewReader(nil))
|
||||
if p != nil || err != io.EOF {
|
||||
t.Fatalf("got (<%x>, %v), expected (%v, %v)", p, err, nil, io.EOF)
|
||||
}
|
||||
}
|
||||
|
||||
// Test that an EOF while reading a length prefix, or while reading the
|
||||
// subsequent data/padding, returns io.ErrUnexpectedEOF.
|
||||
func TestUnexpectedEOF(t *testing.T) {
|
||||
for _, test := range [][]byte{
|
||||
{0x40}, // expecting a second length byte
|
||||
{0xc0}, // expecting a second length byte
|
||||
{0x41, 0x80}, // expecting a third length byte
|
||||
{0xc1, 0x80}, // expecting a third length byte
|
||||
{0x02}, // expecting 2 bytes of padding
|
||||
{0x82}, // expecting 2 bytes of data
|
||||
{0x02, 'X'}, // expecting 1 byte of padding
|
||||
{0x82, 'X'}, // expecting 1 byte of data
|
||||
{0x41, 0x00}, // expecting 128 bytes of padding
|
||||
{0xc1, 0x00}, // expecting 128 bytes of data
|
||||
{0x41, 0x00, 'X'}, // expecting 127 bytes of padding
|
||||
{0xc1, 0x00, 'X'}, // expecting 127 bytes of data
|
||||
{0x41, 0x80, 0x00}, // expecting 32768 bytes of padding
|
||||
{0xc1, 0x80, 0x00}, // expecting 32768 bytes of data
|
||||
{0x41, 0x80, 0x00, 'X'}, // expecting 32767 bytes of padding
|
||||
{0xc1, 0x80, 0x00, 'X'}, // expecting 32767 bytes of data
|
||||
} {
|
||||
p, err := ReadData(bytes.NewReader(test))
|
||||
if p != nil || err != io.ErrUnexpectedEOF {
|
||||
t.Fatalf("<%x> got (<%x>, %v), expected (%v, %v)", test, p, err, nil, io.ErrUnexpectedEOF)
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Test that length encodings that are longer than they could be are still
|
||||
// interpreted.
|
||||
func TestNonMinimalLengthEncoding(t *testing.T) {
|
||||
for _, test := range []struct {
|
||||
enc []byte
|
||||
expected []byte
|
||||
}{
|
||||
{[]byte{0x81, 'X'}, []byte("X")},
|
||||
{[]byte{0xc0, 0x01, 'X'}, []byte("X")},
|
||||
{[]byte{0xc0, 0x80, 0x01, 'X'}, []byte("X")},
|
||||
} {
|
||||
p, err := ReadData(bytes.NewReader(test.enc))
|
||||
if err != nil {
|
||||
t.Fatalf("<%x> got error %v, expected %v", test.enc, err, nil)
|
||||
}
|
||||
if !bytes.Equal(p, test.expected) {
|
||||
t.Fatalf("<%x> got <%x>, expected <%x>", test.enc, p, test.expected)
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Test that ReadData only reads up to 3 bytes of length prefix.
|
||||
func TestReadLimits(t *testing.T) {
|
||||
// Test the maximum length that's possible with 3 bytes of length
|
||||
// prefix.
|
||||
maxLength := (0x3f << 14) | (0x7f << 7) | 0x7f
|
||||
data := bytes.Repeat([]byte{'X'}, maxLength)
|
||||
prefix := []byte{0xff, 0xff, 0x7f} // encodes 0xfffff
|
||||
p, err := ReadData(bytes.NewReader(append(prefix, data...)))
|
||||
if err != nil {
|
||||
t.Fatalf("got error %v, expected %v", err, nil)
|
||||
}
|
||||
if !bytes.Equal(p, data) {
|
||||
t.Fatalf("got %d bytes unequal to %d bytes", len(p), len(data))
|
||||
}
|
||||
// Test a 4-byte prefix.
|
||||
prefix = []byte{0xc0, 0xc0, 0x80, 0x80} // encodes 0x100000
|
||||
data = bytes.Repeat([]byte{'X'}, maxLength+1)
|
||||
p, err = ReadData(bytes.NewReader(append(prefix, data...)))
|
||||
if p != nil || err != ErrTooLong {
|
||||
t.Fatalf("got (<%x>, %v), expected (%v, %v)", p, err, nil, ErrTooLong)
|
||||
}
|
||||
// Test that 4 bytes don't work, even when they encode an integer that
|
||||
// would fix in 3 bytes.
|
||||
prefix = []byte{0xc0, 0x80, 0x80, 0x80} // encodes 0x0
|
||||
data = []byte{}
|
||||
p, err = ReadData(bytes.NewReader(append(prefix, data...)))
|
||||
if p != nil || err != ErrTooLong {
|
||||
t.Fatalf("got (<%x>, %v), expected (%v, %v)", p, err, nil, ErrTooLong)
|
||||
}
|
||||
|
||||
// Do the same tests with padding lengths.
|
||||
data = []byte("hello")
|
||||
prefix = []byte{0x7f, 0xff, 0x7f} // encodes 0xfffff
|
||||
padding := bytes.Repeat([]byte{'X'}, maxLength)
|
||||
enc := bytes.NewBuffer(append(prefix, padding...))
|
||||
mustWriteData(enc, data)
|
||||
p, err = ReadData(enc)
|
||||
if err != nil {
|
||||
t.Fatalf("got error %v, expected %v", err, nil)
|
||||
}
|
||||
if !bytes.Equal(p, data) {
|
||||
t.Fatalf("got <%x>, expected <%x>", p, data)
|
||||
}
|
||||
prefix = []byte{0x40, 0xc0, 0x80, 0x80} // encodes 0x100000
|
||||
padding = bytes.Repeat([]byte{'X'}, maxLength+1)
|
||||
enc = bytes.NewBuffer(append(prefix, padding...))
|
||||
mustWriteData(enc, data)
|
||||
p, err = ReadData(enc)
|
||||
if p != nil || err != ErrTooLong {
|
||||
t.Fatalf("got (<%x>, %v), expected (%v, %v)", p, err, nil, ErrTooLong)
|
||||
}
|
||||
prefix = []byte{0x40, 0x80, 0x80, 0x80} // encodes 0x0
|
||||
padding = []byte{}
|
||||
enc = bytes.NewBuffer(append(prefix, padding...))
|
||||
mustWriteData(enc, data)
|
||||
p, err = ReadData(enc)
|
||||
if p != nil || err != ErrTooLong {
|
||||
t.Fatalf("got (<%x>, %v), expected (%v, %v)", p, err, nil, ErrTooLong)
|
||||
}
|
||||
}
|
||||
|
||||
// Test that WriteData and WritePadding only accept lengths that can be encoded
|
||||
// in up to 3 bytes of length prefix.
|
||||
func TestWriteLimits(t *testing.T) {
|
||||
maxLength := (0x3f << 14) | (0x7f << 7) | 0x7f
|
||||
var enc bytes.Buffer
|
||||
n, err := WriteData(&enc, bytes.Repeat([]byte{'X'}, maxLength))
|
||||
if n != maxLength+3 || err != nil {
|
||||
t.Fatalf("got (%d, %v), expected (%d, %v)", n, err, maxLength, nil)
|
||||
}
|
||||
enc.Reset()
|
||||
n, err = WriteData(&enc, bytes.Repeat([]byte{'X'}, maxLength+1))
|
||||
if n != 0 || err != ErrTooLong {
|
||||
t.Fatalf("got (%d, %v), expected (%d, %v)", n, err, 0, ErrTooLong)
|
||||
}
|
||||
|
||||
// Padding gets an extra 3 bytes because the prefix is counted as part
|
||||
// of the length.
|
||||
enc.Reset()
|
||||
n, err = WritePadding(&enc, maxLength+3)
|
||||
if n != maxLength+3 || err != nil {
|
||||
t.Fatalf("got (%d, %v), expected (%d, %v)", n, err, maxLength+3, nil)
|
||||
}
|
||||
// Writing a too-long padding is okay because WritePadding will break it
|
||||
// into smaller chunks.
|
||||
enc.Reset()
|
||||
n, err = WritePadding(&enc, maxLength+4)
|
||||
if n != maxLength+4 || err != nil {
|
||||
t.Fatalf("got (%d, %v), expected (%d, %v)", n, err, maxLength+4, nil)
|
||||
}
|
||||
}
|
||||
|
||||
// Test that WritePadding panics when given a negative length.
|
||||
func TestNegativeLength(t *testing.T) {
|
||||
for _, n := range []int{-1, ^0} {
|
||||
var enc bytes.Buffer
|
||||
panicked, nn, err := testNegativeLengthSub(t, &enc, n)
|
||||
if !panicked {
|
||||
t.Fatalf("WritePadding(%d) returned (%d, %v) instead of panicking", n, nn, err)
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Calls WritePadding(w, n) and augments the return value with a flag indicating
|
||||
// whether the call panicked.
|
||||
func testNegativeLengthSub(t *testing.T, w io.Writer, n int) (panicked bool, nn int, err error) {
|
||||
defer func() {
|
||||
if r := recover(); r != nil {
|
||||
panicked = true
|
||||
}
|
||||
}()
|
||||
t.Helper()
|
||||
nn, err = WritePadding(w, n)
|
||||
return false, n, err
|
||||
}
|
||||
|
||||
// Test that MaxDataForSize panics when given a 0 length.
|
||||
func TestMaxDataForSizeZero(t *testing.T) {
|
||||
defer func() {
|
||||
if r := recover(); r == nil {
|
||||
t.Fatal("didn't panic")
|
||||
}
|
||||
}()
|
||||
MaxDataForSize(0)
|
||||
}
|
||||
|
||||
// Test thresholds of available sizes for MaxDataForSize.
|
||||
func TestMaxDataForSize(t *testing.T) {
|
||||
for _, test := range []struct {
|
||||
size int
|
||||
expected int
|
||||
}{
|
||||
{0x01, 0x00},
|
||||
{0x02, 0x01},
|
||||
{0x3f, 0x3e},
|
||||
{0x40, 0x3e},
|
||||
{0x41, 0x3f},
|
||||
{0x1fff, 0x1ffd},
|
||||
{0x2000, 0x1ffd},
|
||||
{0x2001, 0x1ffe},
|
||||
{0xfffff, 0xffffc},
|
||||
{0x100000, 0xffffc},
|
||||
{0x100001, 0xffffc},
|
||||
{0x7fffffff, 0xffffc},
|
||||
} {
|
||||
max := MaxDataForSize(test.size)
|
||||
if max != test.expected {
|
||||
t.Fatalf("size %d, got %d, expected %d", test.size, max, test.expected)
|
||||
}
|
||||
}
|
||||
}
|
||||
Loading…
Add table
Add a link
Reference in a new issue