Python中的base64解码问题

Question

Hello and thanks for reading. I am running into some issues decoding previously encoded files using base64. For example, suppose I want to encode a pdf file using base64. The result is a nice 80 char delimited series of strings. The code that does the encoding (cribbed from this board) is nice and easy:

    def encode_file_base64(bin_input):
      flag = 0
      try:
        with open(bin_input, 'rb') as fin, open('tmp.bin_hex', 'w') as fout:
        base64.encode(fin, fout)
      except:
        traceback.print_exc()
        flag = -1
      return flag 

Now the decoding function:

    def decode_file_base64(bin_output):
      flag = 0
      try:
        with open('tmp.bin_hex', 'rb') as fin, open(bin_output, 'w') as fout:
          base64.decode(fin, fout)
      except:
          traceback.print_exc()
          flag = -1
      return flag

It does the job, but when I try to open the output file, I am not able to and the file appears to be 'corrupt'. I have been struggling with this more than a fair amount and I'm about to give up. I suppose I could use other types of encodings but the BOSS insists on base64 (he must have heard that it's the best...).

Answer 1

I don't know if this is your problem (I don't even know what your problem is), but if you're on a platform/version/implementation where binary-mode makes a difference, you're doing it wrong:

with open('tmp.bin_hex', 'rb') as fin, open(bin_output, 'w') as fout:

You're opening the text file (the b64 file you wrote in text mode) in binary mode, and the binary file in text mode. Try this:

with open('tmp.bin_hex', 'r') as fin, open(bin_output, 'wb') as fout:

---

Meanwhile, for debugging purposes, you might want to try comparing a file to the result of encoding and decoding it. If, for example, you see that the new file is a little longer, and a hexdump shows that this is because every 0x0A byte has been replaced by two 0x0D 0x0A bytes, you know that the problem is that you're translating newlines, which in turn means that you're in text mode.