Separate ASCII from binary in a socket transmission

Question

I have to decode a socket transmission which contains pieces of a file:

data %filekey% [3:%piece3% 5:%piece5% 7:%piece7% 8:%piece8% 9:%piece9%]

• %pieceN% contains the N-th binary piece of the file
• Pieces' lengths are known
• %filekey% is known
• Indexes are known (but maybe not in the right order)
• Everything but the pieces is ASCII
• This message ends with a carriage return (\n).
• This "protocol" can't be changed.

I'm facing two problems:

• I can extract the line from my InputStream, looking for \n. But what if a byte from %pieceN% also contains a carriage return ?
• To split each pieces and its corresponding index, I have to find N:. Just like my previous question: what if %pieceN% contains a : ?

Answer 1

Since you know the lengths of every part of data %filekey% [3:%piece3% 5:%piece5% 7:%piece7% 8:%piece8% 9:%piece9%] — you know the number of spaces, you know what %filekey% is, you know the lengths of each %pieceN%, etc. — this means you know the full length of data %filekey% [3:%piece3% 5:%piece5% 7:%piece7% 8:%piece8% 9:%piece9%], so you can just use java.io.InputStream.read(byte[]) or .read(byte[], int, int) to read the exact number of bytes you need. (N.B. those methods both return an int to indicate the number of bytes they actually read. You may need to call them in a loop to ensure that you fill your byte-array.) Don't worry about searching for \n.