Incorrect use of OBJ_obj2txt

[federicovalenso]

Bug report

Bug description:

OBJ_obj2txt is used incorrectly. In man we can see this at Bugs section:

OBJ_obj2txt() is awkward and messy to use: it doesn't follow the convention of other OpenSSL functions where the buffer can be set to NULL to determine the amount of data that should be written. Instead buf must point to a valid buffer and buf_len should be set to a positive value. A buffer length of 80 should be more than enough to handle any OID encountered in practice.

CPython versions tested on:

3.11

Operating systems tested on:

No response

[encukou]

That's for an old OpenSSL version, 1.0.

Since 3.10, CPython only supports OpenSSL 1.1.1 and above, and the docs for that say:

Unless buf is NULL, the representation is written as a NUL-terminated string to buf, where at most buf_len bytes are written, truncating the result if necessary. In any case it returns the total string length, excluding the NUL character, required for non-truncated representation, or -1 on error.

3.9 can still be built with OpenSSL 1.0. But, it still uses an initial buffer of 256, so it should be OK in practice.

[federicovalenso]

@encukou, you're right about version 1.0, I think issue could be closed.