How to get pieces value from .torrent file

Question

I am trying to build a .torrent file interpreter. The problem is that I can't seem to understand how to go about interpreting the pieces value. I am aware that the pieces key contains a concatenation of the SHA-1 hashes for each piece and that SHA-1 contains 20 bytes. A result of this is that the final output should be a multiple of 20 bytes. However, after counting the bytes from the pieces value as a string or in hexadecimal form it still does not satisfy this. How should I interpret the pieces key?

Answer 1

From looking at a real torrent file, I found that the SHA-1 hashes had to be taken from its hexadecimal string format, but I previously thought that it was wrong because the byte length of the hash was not a multiple of 20. Turns out I forgot to add a trailing 0 to hexadecimals that were only 1 character (e.g. a had to be changed to 0a)

Answer 2

Here we use bencode and bdecode, and the pieces value can get easily. I think you need to firstly read BEP for more details. What's more, you can see this and use it as an example.