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use std::{
ffi::{CStr, c_char},
ops::Deref,
};
use crate::duckdb_free;
pub struct DuckDbString {
// Invariant: ptr[0..len+1] is valid C string, i.e. ptr[len] is NUL byte.
ptr: core::ptr::NonNull<c_char>,
len: usize,
}
impl DuckDbString {
/// Creates a `DuckDbString` from a raw pointer to a C string.
///
/// # Safety
///
/// The caller must ensure that:
/// - `ptr` is non-null and points to a null-terminated C string.
/// - `ptr` was allocated by DuckDB and must be released with `duckdb_free`.
/// - Ownership of `ptr` transfers to the returned `DuckDbString`. The caller must not reuse or free it.
pub unsafe fn from_ptr(ptr: *const c_char) -> Self {
assert!(!ptr.is_null(), "DuckDbString::from_ptr requires a non-null pointer");
let len = unsafe { CStr::from_ptr(ptr) }.to_bytes().len();
unsafe { Self::from_raw_parts(ptr, len) }
}
/// Creates a `DuckDbString` from a nullable raw pointer to a C string.
///
/// Returns `None` if `ptr` is null.
///
/// # Safety
///
/// If `ptr` is non-null, the caller must ensure that:
/// - `ptr` points to a null-terminated C string.
/// - `ptr` was allocated by DuckDB and must be released with `duckdb_free`.
/// - Ownership of `ptr` transfers to the returned `DuckDbString`. The caller must not reuse or free it.
pub unsafe fn from_nullable_ptr(ptr: *const c_char) -> Option<Self> {
if ptr.is_null() {
None
} else {
Some(unsafe { Self::from_ptr(ptr) })
}
}
/// Creates a `DuckDbString` from raw parts.
///
/// # Safety
///
/// The caller must ensure that:
/// - `ptr` is non-null and points to a null-terminated C string.
/// - `len` accurately represents the length of the string (excluding the null terminator).
/// - `ptr` was allocated by DuckDB and must be released with `duckdb_free`.
/// - Ownership of `ptr` transfers to the returned `DuckDbString`. The caller must not reuse or free it.
/// - The string data is not mutated for the lifetime of the returned `DuckDbString`.
pub unsafe fn from_raw_parts(ptr: *const c_char, len: usize) -> Self {
let ptr = core::ptr::NonNull::new(ptr as *mut c_char)
.expect("DuckDbString::from_raw_parts requires a non-null pointer");
Self { ptr, len }
}
fn to_bytes_with_nul(&self) -> &[u8] {
let ptr = self.ptr.as_ptr() as *const u8;
unsafe { core::slice::from_raw_parts(ptr, self.len + 1) }
}
}
impl Deref for DuckDbString {
type Target = std::ffi::CStr;
fn deref(&self) -> &Self::Target {
let bytes = self.to_bytes_with_nul();
unsafe { CStr::from_bytes_with_nul_unchecked(bytes) }
}
}
impl Drop for DuckDbString {
fn drop(&mut self) {
let ptr = self.ptr.as_ptr() as *mut core::ffi::c_void;
unsafe { duckdb_free(ptr) };
}
}
#[cfg(test)]
mod tests {
use super::DuckDbString;
#[test]
fn from_nullable_ptr_returns_none_for_null() {
assert!(unsafe { DuckDbString::from_nullable_ptr(std::ptr::null()) }.is_none());
}
}