ADDED   src/0dev.org/commands/short/main.go
Index: src/0dev.org/commands/short/main.go
==================================================================
--- src/0dev.org/commands/short/main.go
+++ src/0dev.org/commands/short/main.go
@@ -0,0 +1,269 @@
+package main
+
+import (
+	iou "0dev.org/ioutil"
+	"fmt"
+	"io"
+	// "io/ioutil"
+	"bytes"
+	"os"
+	"sort"
+)
+
+func main() {
+	f, err := os.Open(os.Args[1])
+	if err != nil {
+		os.Stderr.WriteString("Unable to open input file. " + err.Error())
+		os.Exit(1)
+	}
+
+	pairs, symbols := analyze(f)
+	_, err = f.Seek(0, 0)
+	if err != nil {
+		os.Stderr.WriteString("Unable to reset input file position. " + err.Error())
+		os.Exit(1)
+	}
+
+	rec := recommend(pairs, symbols)
+
+	reader, err := apply(rec, f)
+	if err != nil {
+		os.Stderr.WriteString("Error while constructing application reader. " + err.Error())
+		os.Exit(1)
+	}
+
+	var buf bytes.Buffer
+	_, err = io.Copy(&buf, reader)
+	if err != nil {
+		os.Stderr.WriteString("Error while applying recommendations. " + err.Error())
+		os.Exit(1)
+	}
+
+	var in *bytes.Reader = bytes.NewReader(buf.Bytes())
+	rev, err := apply(rec.reverse(), in)
+	if err != nil {
+		os.Stderr.WriteString("Error while constructing application reader. " + err.Error())
+		os.Exit(1)
+	}
+
+	_, err = io.Copy(os.Stdout, rev)
+	if err != nil {
+		os.Stderr.WriteString("Error while applying recommendations. " + err.Error())
+		os.Exit(1)
+	}
+}
+
+type recommendation struct {
+	p2s map[uint16]byte
+	s2p map[byte]uint16
+}
+
+// Produces a reversed recommendation struct
+func (r *recommendation) reverse() *recommendation {
+	var rec recommendation
+	rec.p2s = make(map[uint16]byte)
+	for k, v := range r.s2p {
+		rec.p2s[v] = k
+	}
+	rec.s2p = make(map[byte]uint16)
+	for k, v := range r.p2s {
+		rec.s2p[v] = k
+	}
+	return &rec
+}
+
+// Returns an io.Reader that reads from the underlying one while applying the given recommendations
+func apply(rec *recommendation, reader io.Reader) (io.Reader, error) {
+	// The symbol reader replaces symbols with pairs according to the s2p mapping
+	symbolReader := iou.SizedReader(iou.ReaderFunc(func(output []byte) (int, error) {
+		var (
+			i   int = 0
+			err error
+		)
+		for ; i < len(output)-1 && err == nil; i++ {
+			// Read a byte from the underlying reader
+			count, err := reader.Read(output[i : i+1])
+
+			// If we can't read anything else - return immediatelly
+			if count == 0 {
+				return i, err
+			}
+
+			// Convert the byte to a pair if there is a mapping for it
+			if p, ok := rec.s2p[output[i]]; ok {
+				output[i] = byte(p >> 8) // extract the high byte from the pair
+				i++
+				output[i] = byte(p) // leave only the low byte from the pair
+			}
+		}
+		return i, nil
+	}), 2)
+
+	currentByte, err := iou.ReadByte(symbolReader)
+	if err != nil {
+		return nil, err
+	}
+
+	// The pair reader replaces pairs with symbols according to the p2s mapping
+	pairReader := iou.ReaderFunc(func(output []byte) (int, error) {
+		var (
+			total int
+			err   error
+		)
+	start:
+		if len(output) <= 1 || err != nil {
+			return total, err
+		}
+
+		nextByte, err := iou.ReadByte(symbolReader)
+		if s, ok := rec.p2s[(uint16(currentByte)<<8 | uint16(nextByte))]; ok {
+			output[0] = s
+			currentByte, err = iou.ReadByte(symbolReader)
+		} else {
+			output[0] = currentByte
+			currentByte = nextByte
+		}
+
+		output, total = output[1:], total+1
+		goto start
+	})
+
+	return pairReader, nil
+}
+
+func recommend(pairs pairSlice, symbols symbolSlice) *recommendation {
+	var rec recommendation
+	rec.p2s = make(map[uint16]byte) // Store pair to symbol mappings
+	rec.s2p = make(map[byte]uint16) // Store symbol to pair mappings
+
+	for i, pairsLength := 0, len(pairs); i < pairsLength; i++ {
+		currentPair := pairs[i]
+
+		// Termination condition for when we are out of symbols
+		if len(symbols) == 1 { // TODO drop to zero ?
+			break
+		}
+
+		gain := currentPair.count - 4 // 4 bytes for the default header
+		currentSymbol := symbols[0]
+
+		if currentSymbol.count == 0 {
+			// Termination condition for possitive compression effect
+			if gain <= 0 {
+				break
+			}
+
+			// Mark the recommendation
+			rec.p2s[currentPair.value] = currentSymbol.value
+		} else { // if the current symbol is present in the data
+			// Decrease the gain by a symbol -> p`, p -> symbol replacement
+			gain = gain - 2 - currentSymbol.count // 2 more bytes for header + replacement cost
+
+			// Termination condition for possitive compression effect
+			if gain <= 0 {
+				break
+			}
+
+			// Mark this symbol for replacement by the last unused pair
+			rec.s2p[currentSymbol.value] = pairs[pairsLength-1].value
+			pairsLength--
+
+			// Mark the current pair for replacement by the current symbol
+			rec.p2s[currentPair.value] = currentSymbol.value
+		}
+		symbols = symbols[1:]
+	}
+	return &rec
+}
+
+// Reads the provided input and returns information about the available byte pair and used symbols
+func analyze(reader io.Reader) (pairSlice, symbolSlice) {
+	var (
+		current uint16   // Stores a pair of bytes in it's high and low bits
+		buffer  []byte   = make([]byte, 1)
+		pairs   []uint64 = make([]uint64, 65536) // all possible pairs, 512kb
+		symbols []uint64 = make([]uint64, 256)   // all possible characters, 2kb
+	)
+
+	// Read the first byte and store in the low bits of the current pair
+	if c, err := reader.Read(buffer); err != nil || c != 1 {
+		os.Stderr.WriteString("Error reading input.")
+		os.Exit(1)
+	}
+	current = uint16(buffer[0])
+
+	// Read all of the data and note the counts of bytes and byte pairs
+	io.Copy(iou.WriterFunc(func(data []byte) (int, error) {
+		for _, value := range data {
+			// Store pairs frequency
+			current <<= 8            // Shift the previous byte from low to high
+			current |= uint16(value) // Add the current byte to low
+			pairs[current]++
+
+			// Store bytes frequency
+			symbols[value]++
+		}
+		return len(data), nil
+	}), reader)
+
+	// Extract and sort all byte pairs
+	availablePairs := make(pairSlice, 0)
+	for index, value := range pairs {
+		availablePairs = append(availablePairs, pair{value: uint16(index), count: value})
+	}
+	sort.Sort(availablePairs)
+
+	// Extract and sort all symbols (including the ones with zero counts)
+	allSymbols := make(symbolSlice, 0)
+	for index, value := range symbols {
+		allSymbols = append(allSymbols, symbol{value: byte(index), count: value})
+	}
+	sort.Sort(allSymbols)
+
+	return availablePairs, allSymbols
+}
+
+type pair struct {
+	value uint16
+	count uint64
+}
+
+type symbol struct {
+	value byte
+	count uint64
+}
+
+// Implements fmt.Stringer, used for debugging
+func (p pair) String() string {
+	return fmt.Sprintf("[ %d %d (%d) ]", (p.value >> 8), ((p.value << 8) >> 8), p.count)
+}
+
+type pairSlice []pair
+
+func (s pairSlice) Len() int {
+	return len(s)
+}
+
+func (s pairSlice) Less(i, j int) bool {
+	// Sort in descending order
+	return s[i].count > s[j].count
+}
+
+func (s pairSlice) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}
+
+type symbolSlice []symbol
+
+func (s symbolSlice) Len() int {
+	return len(s)
+}
+
+func (s symbolSlice) Less(i, j int) bool {
+	// Sort in ascending order
+	return s[i].count < s[j].count
+}
+
+func (s symbolSlice) Swap(i, j int) {
+	s[i], s[j] = s[j], s[i]
+}

Index: src/0dev.org/ioutil/ioutil.go
==================================================================
--- src/0dev.org/ioutil/ioutil.go
+++ src/0dev.org/ioutil/ioutil.go
@@ -18,10 +18,20 @@
 
 // Delegates the call to the WriterFunc while implementing io.Reader.
 func (r ReaderFunc) Read(b []byte) (int, error) {
 	return r(b)
 }
+
+// Reads a single byte from the provided io.Reader
+func ReadByte(reader io.Reader) (byte, error) {
+	var (
+		arr [1]byte
+		err error
+	)
+	_, err = reader.Read(arr[:])
+	return arr[0], err
+}
 
 // Returns a writer that delegates calls to Write(...) while ensuring
 // that it is never called with less bytes than the specified amount.
 //
 // Calls with fewer bytes are buffered while a call with a nil slice

Index: src/0dev.org/ioutil/ioutil_test.go
==================================================================
--- src/0dev.org/ioutil/ioutil_test.go
+++ src/0dev.org/ioutil/ioutil_test.go
@@ -45,10 +45,30 @@
 		func(i, j int) bool { return input[i] == output[j] }})
 	if len(delta.Added) > 0 || len(delta.Removed) > 0 {
 		t.Error("Differences detected ", delta)
 	}
 }
+
+func TestReadByte(t *testing.T) {
+	var (
+		input  []byte        = []byte{255}
+		reader *bytes.Reader = bytes.NewReader(input)
+	)
+
+	result, err := ReadByte(reader)
+	if result != input[0] {
+		t.Error("Unexpected read result from ReadByte", result)
+	}
+	if err != nil {
+		t.Error("Unexpected error from ReadByte", err)
+	}
+
+	result, err = ReadByte(reader)
+	if err != io.EOF {
+		t.Error("Unexpected nil error from ReadByte, read value:", result)
+	}
+}
 
 func TestSizedWriter(t *testing.T) {
 	var (
 		buffer bytes.Buffer
 		writer io.Writer = SizedWriter(&buffer, 4)