This is not in "nm-glib.h", because it's not a complete replacement.
In glib before 2.62, it's not possible to implement g_ptr_array_copy()
as glib provides it, because the element_free_func is not accessible.
So, instead add our own implemented, which follows glib's version as
much as it can.
The output of nm_utils_format_variant_attributes() must be accepted by
nm_utils_parse_variant_attributes(), producing the initial attributes.
The latter has a special handling of some attributes, depending on the
input NMVariantAttributeSpec list. For example, if the
NMVariantAttributeSpec is a boolean with the 'no_value' flag, the
parser doesn't look for a value.
Pass the NMVariantAttributeSpec list to the format function so that it
can behave in the same way as the parse one.
We want to parse "/proc/cmdline". That is space separated with support
for quoting and escaping. Our implementation becomes part of stable
behavior, and we should interpret the kernel command line the same way
as the system does. That means, our implementation should match
systemd's.
Iterating hash tables gives an undefined order. Often we want to have
a stable order, for example when printing the content of a hash or
when converting it to a "a{sv}" variant.
How to achieve that best? I think we should only iterate the hash once,
and not require additional lookups. nm_utils_named_values_from_strdict()
achieves that by returning the key and the value together. Also, often
we only need the list for a short time, so we can avoid heap allocating
the list, if it is short enough. This works by allowing the caller to
provide a pre-allocated buffer (usually on the stack) and only as fallback
allocate a new list.
If the value pointer is const, it is commonly inconvenient and requires
a cast. Requiring casts on a common base does not increase type safety,
but is annoying.
When parsing user input if is often convenient to allow stripping whitespace.
Especially with escaped strings, the user could still escape the whitespace,
if the space should be taken literally.
Add support for that to nm_utils_buf_utf8safe_unescape().
Note that this is not the same as calling g_strstrip() before/after
unescape. That is, because nm_utils_buf_utf8safe_unescape() correctly
preserves escaped whitespace. If you call g_strstrip() before/after
the unescape, you don't know whether the whitespace is escaped.
We want to use the function to unescape (compress) secrets. As such, we want
to be sure that no secrets are leaked in memory due to growing the buffer with
realloc. In fact, reallocation should never happen. Assert for that.
As reallocation cannot happen, we could directly fill a buffer with
API like nm_utils_strbuf_*(). But NMStrBuf has low overhead even in this
case.
GPtrArray does not support NULL terminating the pointer array. That
makes it cumbersome to use it for tracking a strv array. Add a few
helper functions nm_strvarray_*() that help using a GArray instead.
Add nm_utils_invoke_on_timeout() beside nm_utils_invoke_on_idle().
They are fundamentally similar, except one schedules an idle handler
and the other a timeout.
Also, use the current g_main_context_get_thread_default() as context
instead of the singleton instance. That is a change in behavior, but
the only caller of nm_utils_invoke_on_idle() is the daemon, which
doesn't use different main contexts. Anyway, to avoid anybody being
tripped up by this also change the order of arguments. It anyway
seems nicer to first pass the cancellable, and the callback and user
data as last arguments. It's more in line with glib's asynchronous
methods.
Also, in the unlikely case that the cancellable is already cancelled
from the start, always schedule an idle action to complete fast.
When we have a buffer that we want to grow exponentially with
nm_utils_get_next_realloc_size(), then there are certain buffer
sizes that are better suited.
For example, if you have an empty NMStrBuf (len == 0), and you
want to allocate roughly one kilobyte, then 1024 is a bad choice,
because nm_utils_get_next_realloc_size() will give you 2024 bytes.
NM_UTILS_GET_NEXT_REALLOC_SIZE_1000 might be better in this case.
If you have a LIST with 7 elements, and you lookup a value that
is not in the (sorted) list and would lie before the first element,
the binary search will dig down to imin=0, imid=0, imax=0 and
strcmp will give positive cmp value (indicating that the searched
value is sorted before).
Then, we would do "imax = imid - 1;", which wrapped to G_MAXUINT,
and the following "if (G_UNLIKELY (imin > imax))" would not hit,
resulting in an out of bound access next.
The easy fix is to not used unsigned integers.
The binary search was adapted from nm_utils_array_find_binary_search()
and nm_utils_ptrarray_find_binary_search(), which already used signed
integers to avoid this problem.
Fixes: 17d9b852c8 ('shared: explicitly implement binary search in NM_UTILS_STRING_TABLE_LOOKUP_DEFINE*()')
Add flags to explicitly escape leading or trailing spaces. Note
that we were already escaping trailing spaces.
This will be used later when supporting backslash escapes for
option parameters for nmcli (vpn.data).
When growing a buffer by appending a previously unknown number
of elements, the often preferable strategy is growing it exponentially,
so that the amortized runtime and re-allocation costs scale linearly.
GString just always increases the buffer length to the next power of
two. That works.
I think there is value in trying to find an optimal next size. Because
while it doesn't matter in terms of asymptotic behavior, in practice
a better choice should make a difference. This is inspired by what QT
does ([1]), to take more care when growing the buffers:
- QString allocates 4 characters at a time until it reaches size 20.
- From 20 to 4084, it advances by doubling the size each time. More
precisely, it advances to the next power of two, minus 12. (Some memory
allocators perform worst when requested exact powers of two, because
they use a few bytes per block for book-keeping.)
- From 4084 on, it advances by blocks of 2048 characters (4096 bytes).
This makes sense because modern operating systems don't copy the entire
data when reallocating a buffer; the physical memory pages are simply
reordered, and only the data on the first and last pages actually needs
to be copied.
Note that a QT is talking about 12 characters, so we use 24 bytes
head room.
[1] https://doc.qt.io/qt-5/containers.html#growth-strategies
