BASE64(3) Library Functions Manual BASE64(3)

Base64A simple base64 encoder/decoder with unpadded base64 support.

#include <Base64.h>


Base64DecodedSize(const char *, size_t);

char *
Base64Encode(const char *, size_t);

char *
Base64Decode(const char *, size_t);

Base64Unpad(char *, size_t);

Base64Pad(char **, size_t);

This is an efficient yet simple base64 encoding and decoding library that supports regular base64, as well as the Matrix specification's extension to base64, called "unpadded base64." provides the ability to convert between the two, instead of just implementing "unpadded base64."

() and () compute the amount of characters needed to store an encoded or decoded message, respectively. Both functions take the size of the message being encoded or decoded, but Base64DecodedSize() also takes a pointer to an encoded string, because a few bytes of the string need to be read in order to compute the size.

() and () do the actual work of encoding and decoding base64 data. They both take a string and its length.

() and () are used to implement Matrix unpadded base64. Base64Unpad() takes a valid base64 string and strips off the trailing equal signs, as per the specification. Base64Pad() does the opposite; it takes an unpadded base64 input string, and pads it with equal signs as necessary, so that it can be properly decoded with Base64Decode() if necessary. However, the Matrix specification envisons unpadded base64 as opaque; that is, once it's encoded, it never needs to be decoded. In practice, a homeserver might need to decode an unpadded base64 string.

Base64EncodedSize() and Base64DecodedSize() simply return unsigned integers representing a number of bytes generated from a simple computation.

Base64Encode() and Base64Decode() return pointers to new strings, allocated on the heap, or NULL if a heap allocation fails. These pointers must be free(3) -ed at some point when they are no longer needed.

Base64Unpad() modifies the passed string in-place. It thus has no return value, because it cannot fail. If the passed pointer is invalid, the behavior is undefined. Base64Pad() returns a boolean value indicating whether the pad operation was successful. In practice, this function will only fail if a bigger string is necessary, but could not be automatically allocated on the heap.

September 30, 2022 Telodendria Project