// makeTreeFromTreeFile takes in a file in the same format TREE.writeToFile()
// puts out, and remakes a HuffTree from it.
func makeTreeFromTreeFile(file *os.File) (t *huffNode, err error) {
bytes := make([]byte, 1)
_, err = file.Read(bytes)
if err != nil {
return nil, err
}
length := int(bytes[0] + 1)
// Now we read in all the characters and their associated bit strings,
// and make a tree out of them
root := huffNode{char: 1}
for i := 0; i < length; i++ {
_, err = file.Read(bytes)
if err != nil {
return nil, err
}
char := bytes[0]
_, err = file.Read(bytes)
if err != nil {
return nil, err
}
numBits := int(bytes[0])
br, err := bitIO.NewReaderOnFile(file)
if err != nil {
return nil, err
}
current := &root
for j := 0; j < numBits; j++ {
bit, err := br.ReadBit()
if err != nil {
return nil, err
}
if bit == 0 {
if current.left == nil {
current.left = &huffNode{char: 1}
}
current = current.left
} else {
if current.right == nil {
current.right = &huffNode{char: 1}
}
current = current.right
}
}
current.char = char
}
return &root, nil
}
// writeDecodedText decompresses the bits in the passed file, and puts the decompressed
// text into a new file described by toFile. If toFile exists before this is called,
// it will be truncated. Returns a nil error on success, non-nil error otherwise.
func (t *huffNode) writeDecodedText(fromFile *os.File,
toFile string, length uint64) (err error) {
// Set up a BitReader on the file to decodes
reader, err := bitIO.NewReaderOnFile(fromFile)
if err != nil {
return err
}
// Decode our bits
toWrite := []byte{}
current := t
// until we've written as many bytes as are encoded...
for uint64(len(toWrite)) < length {
bit, err := reader.ReadBit()
// Check for errors
if err != nil {
return err
}
if bit == 0 {
current = current.left
} else if bit == 1 {
current = current.right
} else {
// Should never happen
return errors.New("Got invalid bit")
}
if current.left == nil && current.right == nil {
// We're at a leaf node, write out its character
toWrite = append(toWrite, current.char)
current = t
}
}
// We've terminated, write it all out
return ioutil.WriteFile(toFile, toWrite, 0644)
}