Ascii85

Ascii85 encoder/decoder written in C.

Why?

There are many Ascii85 or Base85 implementations available. I needed something with three features:

• Complete and working implementation with unit tests
• Whitespace not ignored (so, non-standard)
• No memory allocation

The intended use is embedded microcontroller with limited memory and realtime constraints, for ASCII encoding binary data to be sent/received over serial interfaces. Whitespace is used for message framing, so cannot be ignored. Encoding/decoding is done from a complete input buffer to a complete output buffer.

There is a nice looking standard implementation at https://github.com/judsonx/base85 -- take a look at that one if you don't share my constraints. It supports a stateful stream processing approach as opposed to my complete input buffer to complete output buffer approach.

C API

/*!
 * @brief encode_ascii85: encode binary input into Ascii85
 * @param[in] inp pointer to a buffer of unsigned bytes 
 * @param[in] in_length the number of bytes at inp to encode
 * @param[in] outp pointer to a buffer for the encoded data
 * @param[in] out_max_length available space at outp in bytes; must be >=
 * ascii85_get_max_encoded_length(in_length)
 * @return number of bytes in the encoded value at outp if non-negative; error code from
 * ascii85_errs_e if negative
 * @par Possible errors include: ascii85_err_in_buf_too_large, ascii85_err_out_buf_too_small
 */
int32_t encode_ascii85 (const uint8_t *inp, int32_t in_length, uint8_t *outp, int32_t out_max_length);

/*!
 * @brief decode_ascii85: decode Ascii85 input to binary output
 * @param[in] inp pointer to a buffer of Ascii85 encoded unsigned bytes 
 * @param[in] in_length the number of bytes at inp to decode
 * @param[in] outp pointer to a buffer for the decoded data
 * @param[in] out_max_length available space at outp in bytes; must be >=
 * ascii85_get_max_decoded_length(in_length)
 * @return number of bytes in the decoded value at outp if non-negative; error code from
 * ascii85_errs_e if negative
 * @par Possible errors include: ascii85_err_in_buf_too_large, ascii85_err_out_buf_too_small, 
 * ascii85_err_bad_decode_char, ascii85_err_decode_overflow
 */
int32_t decode_ascii85 (const uint8_t *inp, int32_t in_length, uint8_t *outp, int32_t out_max_length);

/*!
 * @brief ascii85_get_max_encoded_length: get the maximum length a block of data will encode to
 * @param[in] in_length the number of data bytes to encode
 * @return maximum number of bytes the encoded buffer could be if non-negative; error code from
 * ascii85_errs_e if negative
 * @par Possible errors include: ascii85_err_in_buf_too_large
 */
int32_t ascii85_get_max_encoded_length (int32_t in_length);

/*!
 * @brief ascii85_get_max_encoded_length: get the maximum length a block of data will decode to
 * @param[in] in_length the number of encoded bytes to decode
 * @return maximum number of bytes the decoded buffer could be if non-negative; error code from
 * ascii85_errs_e if negative
 * @par Possible errors include: ascii85_err_in_buf_too_large
 */
int32_t ascii85_get_max_decoded_length (int32_t in_length);

Building

A Makefile is included that may work for you. But you really only need: ascii85.c and ascii85.h

The Makefile targets are: test and lint.

Tests

Run the unit tests with: ./test

CLI

The ./test program can be used to encode and decode data in a limited way.

Encode example:

  $ ./test -i hello
  <~BOu!rDZ~>

Decode example:

  $ ./test -o 'BOu!rDZ'
  ~Decoded: 68656c6c6f

Quick test example:

  $ ./test -i hello -o 'BOu!rDZ'
  ~Encode OK

License

MIT/X11