Retrieve a minimal substring of the actual signature (i.e. the "b=" tag
value) from a specified signature, of sufficient length to identify this
signature uniquely from others.
||dkim_getsig() is called after
dkim_eom() when dkim is a
verifying handle, i.e. one returned by an earlier call to
||Message-specific handle, returned by
||Signature-specific handle, retrieved by a prior call to
||Pointer to a buffer that should receive a minimal unique
substring of the digital signature portion of sig.
||The address of an integer that should contain the number of
bytes available at buf and will be updated to contain
the number of bytes needed to produce a minimal substring.
- No fewer than eight bytes will be requested. If two or more signatures
have the same initial byte sequences in "b=" tags, larger lengths will
be required, theoretically requiring as much as the entire signature.
- If the size of buf is too small to contain the minimal substring
of sig, DKIM_STAT_NORESOURCE is returned, buflen
will be updated to indicate the minimal number of bytes required,
and buf will be unchanged.
- The string written to buf will be NULL-terminated unless the
provided buffer is exactly the right size to contain the output.