Dead-simple bencoding using the Io language

bencode.io

# See http://en.wikipedia.org/wiki/Bencode for reference


# encoding objects

Number asBencode := method(
    Sequence with("i", self asString, "e")
)

Sequence asBencode := method(
    Sequence with(self size asString, ":", self)
)

List asBencode := method(
    Sequence with("l", self map(value, value asBencode) join, "e")
)

Map asBencode := method(
    Sequence with("d", self keys sort map(key, key asBencode .. self at(key) asBencode) join, "e")
)


# decoding from string

Sequence fromBencode := method(
    offset    := 0

    endOfCollection := block(
        if (self at(offset) asCharacter == "e", offset = offset + 1)
    )

    decodeMap := block(
        map := Map clone
        while (true, 
            if (endOfCollection call, break)
            map atPut(decode call, decode call)
        )
        map
    )

    decodeList   := block(
        collection := List clone
        while (true,
            if (endOfCollection call, break)
            collection append(decode call)
        )
        collection
    )

    decodeNumber := block(delimiter, 
        delimiter ifNil(delimiter := "e")
        number := Sequence clone

        while ((digit := self at(offset) asCharacter) != delimiter, 
            number appendSeq(digit)
            offset = offset + 1
        )

        offset = offset + 1
        number asNumber
    )

    decodeString := block(
        offset = offset - 1
        stringSize := decodeNumber call(":")
        self exSlice(offset, (offset = offset + stringSize))
    )

    decodingMap := Map with(
        "d", decodeMap,
        "l", decodeList,
        "i", decodeNumber,
        "0", decodeString,
        "1", decodeString,
        "2", decodeString,
        "3", decodeString,
        "4", decodeString,
        "5", decodeString,
        "6", decodeString,
        "7", decodeString,
        "8", decodeString
    )

    decode := block(
        char := self at(offset) asCharacter
        offset = offset + 1
        decodingMap at(char)? call
    )

    decode call
)