DeprecatedString (formerly String) has been with us since the start,
and it has served us well. However, it has a number of shortcomings
that I'd like to address.
Some of these issues are hard if not impossible to solve incrementally
inside of DeprecatedString, so instead of doing that, let's build a new
String class and then incrementally move over to it instead.
Problems in DeprecatedString:
- It assumes string allocation never fails. This makes it impossible
to use in allocation-sensitive contexts, and is the reason we had to
ban DeprecatedString from the kernel entirely.
- The awkward null state. DeprecatedString can be null. It's different
from the empty state, although null strings are considered empty.
All code is immediately nicer when using Optional<DeprecatedString>
but DeprecatedString came before Optional, which is how we ended up
like this.
- The encoding of the underlying data is ambiguous. For the most part,
we use it as if it's always UTF-8, but there have been cases where
we pass around strings in other encodings (e.g ISO8859-1)
- operator[] and length() are used to iterate over DeprecatedString one
byte at a time. This is done all over the codebase, and will *not*
give the right results unless the string is all ASCII.
How we solve these issues in the new String:
- Functions that may allocate now return ErrorOr<String> so that ENOMEM
errors can be passed to the caller.
- String has no null state. Use Optional<String> when needed.
- String is always UTF-8. This is validated when constructing a String.
We may need to add a bypass for this in the future, for cases where
you have a known-good string, but for now: validate all the things!
- There is no operator[] or length(). You can get the underlying data
with bytes(), but for iterating over code points, you should be using
an UTF-8 iterator.
Furthermore, it has two nifty new features:
- String implements a small string optimization (SSO) for strings that
can fit entirely within a pointer. This means up to 3 bytes on 32-bit
platforms, and 7 bytes on 64-bit platforms. Such small strings will
not be heap-allocated.
- String can create substrings without making a deep copy of the
substring. Instead, the superstring gets +1 refcount from the
substring, and it acts like a view into the superstring. To make
substrings like this, use the substring_with_shared_superstring() API.
One caveat:
- String does not guarantee that the underlying data is null-terminated
like DeprecatedString does today. While this was nifty in a handful of
places where we were calling C functions, it did stand in the way of
shared-superstring substrings.
This will make it easier to support both string types at the same time
while we convert code, and tracking down remaining uses.
One big exception is Value::to_string() in LibJS, where the name is
dictated by the ToString AO.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
These are guarded with #ifndef KERNEL, since doubles (and floats) are
not allowed in KERNEL mode.
In StringUtils there is convert_to_floating_point which does have a
template parameter incase you have a templated type.
By appending individual bytes as code points, we were "breaking apart"
multi-byte UTF-8 code points. This now behaves the same way as the
invert_case() helper in StringUtils.
If the entire string you want to right-trim consists of characters you
want to remove, we previously would incorrectly leave the first
character there.
For example: `trim("aaaaa", "a")` would return "a" instead of "".
We can't use `i >= 0` in the loop since that would fail to detect
underflow, so instead we keep `i` in the range `size .. 1` and then
subtract 1 from it when reading the character.
Added some trim() tests while I was at it. (And to confirm that this was
the issue.)
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).
No functional changes.
This commit has no behavior changes.
In particular, this does not fix any of the wrong uses of the previous
default parameter (which used to be 'false', meaning "only replace the
first occurence in the string"). It simply replaces the default uses by
String::replace(..., ReplaceMode::FirstOnly), leaving them incorrect.
Previously, case-insensitively searching the haystack "Go Go Back" for
the needle "Go Back" would return false:
1. Match the first three characters. "Go ".
2. Notice that 'G' and 'B' don't match.
3. Skip ahead 3 characters, plus 1 for the outer for-loop.
4. Now, the haystack is effectively "o Back", so the match fails.
Reducing the skip by 1 fixes this issue. I'm not 100% convinced this
fixes all cases, but I haven't been able to find any cases where it
doesn't work now. :^)
This change also applys to to_uint
On i686 u64 == long long but on x86_64 u64 == long. Therefor on either
arch, one of the instantiations is missed. This change makes sure that
all integer types have an instantiation.
We already know the length of these substrings, so there's no need to
check their lengths using strlen in the StringView(char*) constructor.
This patch also removes an accidental 1-byte OOB read that was left over
from when this method received null-terminated char pointers instead of
string views, as well removes the unnecessary lambda call (two of the
checks were impossible, and this was only called in one place, so we can
just inline it)
This removes the awkward String::replace API which was the only String
API which mutated the String and replaces it with a new immutable
version that returns a new String with the replacements applied. This
also fixes a couple of UAFs that were caused by the use of this API.
As an optimization an equivalent StringView::replace API was also added
to remove an unnecessary String allocations in the format of:
`String { view }.replace(...);`
This was needlessly copying StringView arguments, and was also using
strstr internally, which meant it was doing a bunch of unnecessary
strlen calls on it. This also moves the implementation to StringUtils
to allow API consistency between String and StringView.
Problem:
- New `all_of` implementation takes the entire container so the user
does not need to pass explicit begin/end iterators. This is unused
except is in tests.
Solution:
- Make use of the new and more user-friendly version where possible.
This implements StringUtils::find_any_of() and uses it in
String::find_any_of() and StringView::find_any_of(). All uses of
find_{first,last}_of have been replaced with find_any_of(), find() or
find_last(). find_{first,last}_of have subsequently been removed.
This implements the StringView::find_all() method by re-implemeting the
current method existing for String in StringUtils, and using that
implementation for both String and StringView.
The rewrite uses memmem() instead of strstr(), so the String::find_all()
argument type has been changed from String to StringView, as the null
byte is no longer required.
This patch reimplements the StringView::find methods in StringUtils, so
they can also be used by String. The methods now also take an optional
start parameter, which moves their API in line with String's respective
methods.
This also implements a StringView::find_ast(char) method, which is
currently functionally equivalent to find_last_of(char). This is because
find_last_of(char) will be removed in a further commit.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
We had an unusual optimization in AK::StringView where constructing
a StringView from a String would cause it to remember the internal
StringImpl pointer of the String.
This was used to make constructing a String from a StringView fast
and copy-free.
I tried removing this optimization and indeed we started seeing a
ton of allocation traffic. However, all of it was due to a silly
pattern where functions would take a StringView and then go on
to create a String from it.
I've gone through most of the code and updated those functions to
simply take a String directly instead, which now makes this
optimization unnecessary, and indeed a source of bloat instead.
So, let's get rid of it and make StringView a little smaller. :^)
Previously this would create new to_lowercase()'d strings from the
needle and the haystack. This generated a huge amount of malloc
traffic in some programs.
This is basically just for consistency, it's quite strange to see
multiple AK container types next to each other, some with and some
without the namespace prefix - we're 'using AK::Foo;' a lot and should
leverage that. :^)
This is an improved version of WrapperGenerator's snake_name(), which
seems like the kind of thing that could be useful elsewhere but would
end up getting duplicated - so let's add this to AK::String instead,
like to_{lowercase,uppercase}().
Personally I found this unintuitive at first, but it is in line with
strtol(), Python's int() or JavaScript's parseInt(), so I guess it makes
sense.
Fixes#4097.
Get rid of the weird old signature:
- int StringType::to_int(bool& ok) const
And replace it with sensible new signature:
- Optional<int> StringType::to_int() const
FileSystemPath::has_extension was jumping through hoops and allocating
memory to do a case insensitive comparison needlessly. Extend the
existing String::ends_with method to allow the caller to specify the
case sensitivity required.
