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Thread: Reading Bytes from the Middle of a Character File

  1. #1
    Junior Member
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    Jul 2019
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    Default Reading Bytes from the Middle of a Character File

    Hey I could use some help.

    I'm extracting data from a file that uses Bencoding. Its a Metainfo .torrent file for a Torrent Client I'm working on. I'm reading it char by char using an InputStreamReader.

    The problem is in the middle of the concatenated string file there is a byte string I need to grab. The InputStreamReader only has methods for reading characters.

    Is there a way I can convert the character output of the InputStreamReader into the raw bytes from the file?

    From the documentation... it says that InputStreamReader will read a random number of bytes for each .read() statement as it tries to find characters. So I'm confused at how I might convert that back into raw bytes that might be outside of the range.

    Bellow is the part of the file I want to read.
    It's a short clip of the data becuase the forum doesn't like all the special characters the binary shows up as.
    pieces1100:' ...

    pieces is the name of the data and 1100 is the number of bytes to be read. It's supposed to be a concatenation of SHA-1 hashes for a file download.

    I'm reading each char from the file like this...
    int intch;
    intch = inputStreamReader.read();
    //char hold veriable
    char ch = (char) intch;

    I know I can reopen the file with a new reader that reads byte by byte. The problem is I would then have to write code to convert and then search the bytes for the location of the byte string in the middle of the file. With the InputStreamReader I have read up to it's location.

  2. #2
    Super Moderator Norm's Avatar
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    May 2010
    Eastern Florida
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    Default Re: Reading Bytes from the Middle of a Character File

    convert the character output of the InputStreamReader into the raw bytes from the file?
    You can get the bytes in a String by calling the String class's get bytes method.
    There might be a problem with that because of charset conversions done by some java I/O classes.

    Another way would be to read the bytes of the file into a byte array and scan that for the bytes that are in the String: pieces1100
    That would position you to the data you want and not get involved with charset conversion problems.
    If you don't understand my answer, don't ignore it, ask a question.

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