It's possible to have `if_indextoname` and `if_nametoindex` without `if_nameindex`, but socket doesn't expose that

[A5rocks]

Bug report

Bug description:

I may be misreading the code, but it seems like if_indextoname is conditionally defined only if if_nameindex is (

cpython/Modules/socketmodule.c

Lines 7315 to 7459 in fe3a26f

	#if defined(HAVE_IF_NAMEINDEX) || defined(MS_WINDOWS)
	/* Python API for getting interface indices and names */
	/*[clinic input]
	_socket.if_nameindex
	Return a list of network interface information (index, name) tuples.
	[clinic start generated code]*/
	static PyObject *
	_socket_if_nameindex_impl(PyObject *module)
	/*[clinic end generated code: output=93c863a6262059c4 input=d6438bb556de2100]*/
	{
	PyObject *list = PyList_New(0);
	if (list == NULL) {
	return NULL;
	}
	#ifdef MS_WINDOWS
	PMIB_IF_TABLE2 tbl;
	int ret;
	if ((ret = GetIfTable2Ex(MibIfTableRaw, &tbl)) != NO_ERROR) {
	Py_DECREF(list);
	// ret is used instead of GetLastError()
	return PyErr_SetFromWindowsErr(ret);
	}
	for (ULONG i = 0; i < tbl->NumEntries; ++i) {
	MIB_IF_ROW2 r = tbl->Table[i];
	WCHAR buf[NDIS_IF_MAX_STRING_SIZE + 1];
	if ((ret = ConvertInterfaceLuidToNameW(&r.InterfaceLuid, buf,
	Py_ARRAY_LENGTH(buf)))) {
	Py_DECREF(list);
	FreeMibTable(tbl);
	// ret is used instead of GetLastError()
	return PyErr_SetFromWindowsErr(ret);
	}
	PyObject *tuple = Py_BuildValue("Iu", r.InterfaceIndex, buf);
	if (tuple == NULL || PyList_Append(list, tuple) == -1) {
	Py_XDECREF(tuple);
	Py_DECREF(list);
	FreeMibTable(tbl);
	return NULL;
	}
	Py_DECREF(tuple);
	}
	FreeMibTable(tbl);
	return list;
	#else
	int i;
	struct if_nameindex *ni;
	ni = if_nameindex();
	if (ni == NULL) {
	PyErr_SetFromErrno(PyExc_OSError);
	Py_DECREF(list);
	return NULL;
	}
	#ifdef _Py_MEMORY_SANITIZER
	__msan_unpoison(ni, sizeof(ni));
	__msan_unpoison(&ni[0], sizeof(ni[0]));
	#endif
	for (i = 0; ni[i].if_index != 0 && i < INT_MAX; i++) {
	#ifdef _Py_MEMORY_SANITIZER
	/* This one isn't the end sentinel, the next one must exist. */
	__msan_unpoison(&ni[i+1], sizeof(ni[0]));
	/* Otherwise Py_BuildValue internals are flagged by MSan when
	they access the not-msan-tracked if_name string data. */
	{
	char *to_sanitize = ni[i].if_name;
	do {
	__msan_unpoison(to_sanitize, 1);
	} while (*to_sanitize++ != '\0');
	}
	#endif
	PyObject *ni_tuple = Py_BuildValue("IO&",
	ni[i].if_index, unicode_fsdecode, ni[i].if_name);
	if (ni_tuple == NULL || PyList_Append(list, ni_tuple) == -1) {
	Py_XDECREF(ni_tuple);
	Py_DECREF(list);
	if_freenameindex(ni);
	return NULL;
	}
	Py_DECREF(ni_tuple);
	}
	if_freenameindex(ni);
	return list;
	#endif
	}
	/*[clinic input]
	_socket.if_nametoindex
	oname: unicode_fs_encoded
	/
	Returns the interface index corresponding to the interface name if_name.
	[clinic start generated code]*/
	static PyObject *
	_socket_if_nametoindex_impl(PyObject *module, PyObject *oname)
	/*[clinic end generated code: output=289a411614f30244 input=6125dc20683560cf]*/
	{
	#ifdef MS_WINDOWS
	NET_IFINDEX index;
	#else
	unsigned long index;
	#endif
	errno = ENODEV; // in case 'if_nametoindex' does not set errno
	index = if_nametoindex(PyBytes_AS_STRING(oname));
	if (index == 0) {
	PyErr_SetFromErrno(PyExc_OSError);
	return NULL;
	}
	return PyLong_FromUnsignedLong(index);
	}
	/*[clinic input]
	@permit_long_summary
	_socket.if_indextoname
	if_index as index: NET_IFINDEX
	/
	Returns the interface name corresponding to the interface index if_index.
	[clinic start generated code]*/
	static PyObject *
	_socket_if_indextoname_impl(PyObject *module, NET_IFINDEX index)
	/*[clinic end generated code: output=e48bc324993052e0 input=2a0026b271cd43ae]*/
	{
	errno = ENXIO; // in case 'if_indextoname' does not set errno
	char name[IF_NAMESIZE + 1];
	if (if_indextoname(index, name) == NULL) {
	PyErr_SetFromErrno(PyExc_OSError);
	return NULL;
	}
	return PyUnicode_DecodeFSDefault(name);
	}
	#endif // defined(HAVE_IF_NAMEINDEX) || defined(MS_WINDOWS)

). This is an issue on e.g. Android, where (I believe) if_indextoname is available on many API versions but if_nameindex is only available on API 24+.

I haven't actually tested anything since I don't have access to an Android emulator, but based on some source code reading I think I'm right?

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response