364 lines
8.9 KiB
Go
364 lines
8.9 KiB
Go
/*
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package netshovel/gapstring provides a GapString type,
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which represents a byte array with gaps: holes with no data.
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This is used by netshovel to represent
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captured data streams with drops.
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Gaps are represented efficiently,
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both in memory and in computation.
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Several convenience functions exist
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which operate on GapString data,
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while preserving the gaps.
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*/
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package gapstring
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"strings"
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"unicode/utf16"
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)
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// XXX: I think there's a clever way to do this with interfaces
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// XXX: But I'm too exhausted to figure it out.
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// XXX: I'll have to fix it later; it doesn't matter much for performance
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type chunk struct {
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gap int // This takes precedence over data
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data []byte
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}
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func (c chunk) length() int {
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if c.gap > 0 {
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return c.gap
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} else {
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return len(c.data)
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}
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}
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func (c chunk) missing() int {
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return c.gap
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}
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func (c chunk) slice(a, b int) chunk {
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if b > c.length() {
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panic("runtime error: index out of range")
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}
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if c.gap > 0 {
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return chunk{gap: b - a}
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} else {
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return chunk{data: c.data[a:b]}
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}
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}
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// A GapString is a string with gaps of no data in the middle
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type GapString struct {
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chunks []chunk
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}
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// Return a new zero-length GapString
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func New() GapString {
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return GapString{
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chunks: []chunk{},
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}
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}
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// Return a new GapString containing a gap
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func OfGap(gap int) GapString {
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return GapString{
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chunks: []chunk{{gap: gap}},
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}
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}
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// Return a new GapString containing some bytes
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func OfBytes(b []byte) GapString {
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return GapString{
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chunks: []chunk{{data: b}},
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}
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}
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// Return a new GapString containing a string
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func OfString(s string) GapString {
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return OfBytes([]byte(s))
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}
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// Return the length of a GapString
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//
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// This is the number of bytes you would have if the gaps were filled with some value.
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func (g GapString) Length() int {
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n := 0
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for _, c := range g.chunks {
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n += c.length()
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}
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return n
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}
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// Return the total size of all gaps
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func (g GapString) Missing() int {
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n := 0
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for _, c := range g.chunks {
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n += c.missing()
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}
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return n
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}
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// Return the current GapString with another GapString appended
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func (g GapString) Append(h GapString) GapString {
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if h.Length() > 0 {
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return GapString{
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chunks: append(g.chunks, h.chunks...),
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}
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} else {
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return g
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}
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}
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// Return the current GapString with a gap appended
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func (g GapString) AppendGap(gap int) GapString {
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return g.Append(OfGap(gap))
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}
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// Return the current GapString with some bytes appended
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func (g GapString) AppendBytes(b []byte) GapString {
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return g.Append(OfBytes(b))
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}
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// Return the current GapString with a string appended
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func (g GapString) AppendString(s string) GapString {
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return g.Append(OfString(s))
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}
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// Return a slice of this GapString
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//
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// This is what you would expect from g[start:end],
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// if g were a string or byte slice.
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func (g GapString) Slice(start, end int) GapString {
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outchunks := make([]chunk, 0, len(g.chunks))
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if end > g.Length() {
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panic("runtime error: slice bounds out of range")
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}
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for _, c := range g.chunks {
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chunklen := c.length()
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// Discard chunks that appear before the first
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if start > chunklen {
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start -= chunklen
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end -= chunklen
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continue
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}
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// Append chunks until we're done
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cend := chunklen
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if cend > end {
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cend = end
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}
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if start != cend {
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outchunks = append(outchunks, c.slice(start, cend))
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}
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start = 0
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end -= cend
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if end == 0 {
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break
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}
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}
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return GapString{chunks: outchunks}
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}
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// Return this GapString with the provided xor mask applied
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//
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// The mask is cycled for the length of the GapString.
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func (g GapString) Xor(mask ...byte) GapString {
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ret := GapString{}
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pos := 0
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for _, c := range g.chunks {
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ret = ret.AppendGap(c.gap)
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out := make([]byte, len(c.data))
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for i, b := range c.data {
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m := mask[(pos+i)%len(mask)]
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out[i] = b ^ m
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}
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ret = ret.AppendBytes(out)
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pos += c.length()
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}
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return ret
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}
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// Return this GapString with gaps filled in
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func (g GapString) Bytes(fill ...byte) []byte {
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ret := make([]byte, g.Length())
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pos := 0
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for _, c := range g.chunks {
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// Fill in gap
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if len(fill) > 0 {
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for i := 0; i < c.gap; i += 1 {
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ret[pos] = fill[pos%len(fill)]
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pos += 1
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}
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}
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// Fill in bytes
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for _, b := range c.data {
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ret[pos] = b
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pos += 1
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}
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}
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ret = ret[0:pos]
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return ret
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}
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// Returns the value at a specific position
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//
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// This returns the byte if one is present, or -1 if it's a gap
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func (g GapString) ValueAt(pos int) int {
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v := g.Slice(pos, pos+1)
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if v.chunks[0].gap > 0 {
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return -1
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} else {
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return int(v.chunks[0].data[0])
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}
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}
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// Return a string version of the GapString, with gaps filled in
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func (g GapString) String(fill string) string {
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return string(g.Bytes([]byte(fill)...))
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}
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// Return a hex representation of this GapString
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//
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// Each octet is space-separated, and gaps are represented with "--"
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func (g GapString) HexString() string {
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out := new(strings.Builder)
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glen := g.Length()
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for i := 0; i < glen; i += 1 {
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c := g.ValueAt(i)
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if c == -1 {
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out.WriteString("--")
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} else {
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// There's probably a faster way to do this. Do we care?
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fmt.Fprintf(out, "%02x", c)
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}
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if i+1 < glen {
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out.WriteRune(' ')
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if i%8 == 7 {
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out.WriteRune(' ')
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}
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}
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}
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return out.String()
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}
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var fluffych = []rune{
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'·', '☺', '☻', '♥', '♦', '♣', '♠', '•', '◘', '○', '◙', '♂', '♀', '♪', '♫', '☼',
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'►', '◄', '↕', '‼', '¶', '§', '▬', '↨', '↑', '↓', '→', '←', '∟', '↔', '▲', '▼',
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' ', '!', '"', '#', '$', '%', '&', '\'', '(', ')', '*', '+', ',', '-', '.', '/',
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', ':', ';', '<', '=', '>', '?',
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'@', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',
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'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', '[', '\\', ']', '^', '_',
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'`', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o',
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'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '{', '|', '}', '~', '⌂',
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'Ç', 'ü', 'é', 'â', 'ä', 'à', 'å', 'ç', 'ê', 'ë', 'è', 'ï', 'î', 'ì', 'Ä', 'Å',
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'É', 'æ', 'Æ', 'ô', 'ö', 'ò', 'û', 'ù', 'ÿ', 'Ö', 'Ü', '¢', '£', '¥', '₧', 'ƒ',
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'á', 'í', 'ó', 'ú', 'ñ', 'Ñ', 'ª', 'º', '¿', '⌐', '¬', '½', '¼', '¡', '«', '»',
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'░', '▒', '▓', '│', '┤', '╡', '╢', '╖', '╕', '╣', '║', '╗', '╝', '╜', '╛', '┐',
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'└', '┴', '┬', '├', '─', '┼', '╞', '╟', '╚', '╔', '╩', '╦', '╠', '═', '╬', '╧',
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'╨', '╤', '╥', '╙', '╘', '╒', '╓', '╫', '╪', '┘', '┌', '█', '▄', '▌', '▐', '▀',
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'α', 'ß', 'Γ', 'π', 'Σ', 'σ', 'µ', 'τ', 'Φ', 'Θ', 'Ω', 'δ', '∞', 'φ', 'ε', '∩',
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'≡', '±', '≥', '≤', '⌠', '⌡', '÷', '≈', '°', '∀', '∃', '√', 'ⁿ', '²', '■', '¤',
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}
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// Return a rune representation of this GapString
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//
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// This uses the glyph set from the Fluffy toolkit
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// (https://dirtbags.github.io/fluffy/).
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// Gaps are represented with the rune '<27>'
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func (g GapString) Runes() string {
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out := new(strings.Builder)
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glen := g.Length()
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for i := 0; i < glen; i += 1 {
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c := g.ValueAt(i)
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if c == -1 {
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out.WriteRune('<27>')
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} else {
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out.WriteRune(fluffych[c])
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}
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}
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return out.String()
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}
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// Return a hex dump of this GapString
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func (g GapString) Hexdump() string {
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out := new(strings.Builder)
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skipping := false
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glen := g.Length()
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pos := 0
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prev := []byte{}
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for pos < glen {
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// Check for repeats
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end := pos + 16
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if end > glen {
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end = glen
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}
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cur := g.Slice(pos, end)
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curBytes := cur.Bytes()
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if 0 == bytes.Compare(prev, curBytes) {
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if !skipping {
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fmt.Fprintln(out, "*")
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skipping = true
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}
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continue
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}
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fmt.Fprintf(out, "%08x ", pos)
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fmt.Fprintf(out, "%-50s", cur.HexString())
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fmt.Fprintln(out, cur.Runes())
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pos += cur.Length()
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}
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fmt.Fprintf(out, "%08x\n", pos)
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return out.String()
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}
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// Return a uint32, little-endian, taken from the front of this GapString
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//
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// The rest of the GapString is returned as the second argument.
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func (g GapString) Uint32LE() (uint32, GapString) {
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return binary.LittleEndian.Uint32(g.Slice(0, 4).Bytes(0)), g.Slice(4, g.Length())
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}
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// Return a uint16, little-endian, taken from the front of this GapString
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//
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// The rest of the GapString is returned as the second argument.
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func (g GapString) Uint16LE() (uint16, GapString) {
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return binary.LittleEndian.Uint16(g.Slice(0, 2).Bytes(0)), g.Slice(2, g.Length())
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}
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// Return this GapString decoded as UTF-16
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func (g GapString) Utf16(order binary.ByteOrder, fill string) string {
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in := g.Bytes([]byte(fill)...)
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ints := make([]uint16, len(in)/2)
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for i := 0; i < len(in); i += 2 {
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ints[i/2] = order.Uint16(in[i:])
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}
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return string(utf16.Decode(ints))
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}
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// Return this GapString decoded as UTF-16 Little Endian
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//
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// This format is used extensively in Microsoft Windows.
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func (g GapString) Utf16LE(gap string) string {
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return g.Utf16(binary.LittleEndian, gap)
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}
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// Return this GapString decoded as UTF-16 Big Endian
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func (g GapString) Utf16BE(gap string) string {
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return g.Utf16(binary.BigEndian, gap)
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}
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