Implement RFC rust-lang/rfcs#1123
Add str method str::split_at(mid: usize) -> (&str, &str).
Also a minor cleanup in the collections::str module. Remove redundant slicing of self.
As far as I was able to determine, it's currently *impossible* to allocate a C NUL-terminated string in Rust and then return it to C (transferring ownership), without leaking memory. There is support for passing the string to C (borrowing).
To complicate matters, it's not possible for the C code to just call `free` on the allocated string, due to the different allocators in use.
`CString` has no way to recreate itself from a pointer. This commit adds one. This is complicated a bit because Rust `Vec`s want the pointer, size, and capacity.
To deal with that, another method to shrink and "leak" the `CString` to a `char *` is also provided.
We can then use `strlen` to determine the length of the string, which must match the capacity.
**TODO**
- [x] Improve documentation
- [x] Add stability markers
- [x] Convert to `Box<[u8]>`
### Example code
With this example code:
```rust
#![feature(libc)]
#![feature(cstr_to_str)]
#![feature(c_str_memory)]
extern crate libc;
use std::ffi::{CStr,CString};
#[no_mangle]
pub extern fn reverse(s: *const libc::c_char) -> *const libc::c_char {
let s = unsafe { CStr::from_ptr(s) };
let s2 = s.to_str().unwrap();
let s3: String = s2.chars().rev().collect();
let s4 = CString::new(s3).unwrap();
s4.into_ptr()
}
#[no_mangle]
pub extern fn cleanup(s: *const libc::c_char) {
unsafe { CString::from_ptr(s) };
}
```
Compiled using `rustc --crate-type dylib str.rs`, I was able to link against it from C (`gcc -L. -l str str.c -o str`):
```c
#include <stdio.h>
extern char *reverse(char *);
extern void cleanup(char *);
int main() {
char *s = reverse("Hello, world!");
printf("%s\n", s);
cleanup(s);
}
```
As well as dynamically link via Ruby:
```ruby
require 'fiddle'
require 'fiddle/import'
module LibSum
extend Fiddle::Importer
dlload './libstr.dylib'
extern 'char* reverse(char *)'
extern 'void cleanup(char *)'
end
s = LibSum.reverse("hello, world!")
puts s
LibSum.cleanup(s)
```
Doc patch for #26120. Extra words here, because "value" is repeated.
I haven't read about whether/how it should go to stable (sorry), but I think it would help newcomers.
Thanks,
* Slate these features to be stable in 1.2 instead of 1.1 (not being backported)
* Have the `FromRawFd` implementations follow the contract of the `FromRawFd`
trait by taking ownership of the primitive specified.
* Refactor the implementations slightly to remove the `unreachable!` blocks as
well as separating the stdio representation of `std::process` from
`std::sys::process`.
This commit stabilizes the following APIs, slating them all to be cherry-picked
into the 1.1 release.
* fs::FileType (and transitively the derived trait implementations)
* fs::Metadata::file_type
* fs::FileType::is_dir
* fs::FileType::is_file
* fs::FileType::is_symlink
* fs::DirEntry::metadata
* fs::DirEntry::file_type
* fs::DirEntry::file_name
* fs::set_permissions
* fs::symlink_metadata
* os::raw::{self, *}
* os::{android, bitrig, linux, ...}::raw::{self, *}
* os::{android, bitrig, linux, ...}::fs::MetadataExt
* os::{android, bitrig, linux, ...}::fs::MetadataExt::as_raw_stat
* os::unix::fs::PermissionsExt
* os::unix::fs::PermissionsExt::mode
* os::unix::fs::PermissionsExt::set_mode
* os::unix::fs::PermissionsExt::from_mode
* os::unix::fs::OpenOptionsExt
* os::unix::fs::OpenOptionsExt::mode
* os::unix::fs::DirEntryExt
* os::unix::fs::DirEntryExt::ino
* os::windows::fs::MetadataExt
* os::windows::fs::MetadataExt::file_attributes
* os::windows::fs::MetadataExt::creation_time
* os::windows::fs::MetadataExt::last_access_time
* os::windows::fs::MetadataExt::last_write_time
* os::windows::fs::MetadataExt::file_size
The `os::unix::fs::Metadata` structure was also removed entirely, moving all of
its associated methods into the `os::unix::fs::MetadataExt` trait instead. The
methods are all marked as `#[stable]` still.
As some minor cleanup, some deprecated and unstable fs apis were also removed:
* File::path
* Metadata::accessed
* Metadata::modified
Features that were explicitly left unstable include:
* fs::WalkDir - the semantics of this were not considered in the recent fs
expansion RFC.
* fs::DirBuilder - it's still not 100% clear if the naming is right here and if
the set of functionality exposed is appropriate.
* fs::canonicalize - the implementation on Windows here is specifically in
question as it always returns a verbatim path. Additionally the Unix
implementation is susceptible to buffer overflows on long paths unfortunately.
* fs::PathExt - as this is just a convenience trait, it is not stabilized at
this time.
* fs::set_file_times - this funciton is still waiting on a time abstraction.
