more task functionality

lib/src/string.rs

@@ -0,0 +1,48 @@
+use std::ffi::{CStr, CString, NulError};
+
+// thinking:
+//  - TCString ownership always taken when passed in
+//  - TCString ownership always falls to C when passed out
+//  - accept that bytes must be copied to get owned string
+//  - Can we do this with an enum of some sort?
+
+/// TCString supports passing strings into and out of the TaskChampion API.
+pub struct TCString(CString);
+
+impl TCString {
+    /// Take a TCString from C as an argument.
+    pub(crate) fn from_arg(tcstring: *mut TCString) -> Self {
+        debug_assert!(!tcstring.is_null());
+        *(unsafe { Box::from_raw(tcstring) })
+    }
+
+    /// Get a regular Rust &str for this value.
+    pub(crate) fn as_str(&self) -> Result<&str, std::str::Utf8Error> {
+        self.0.as_c_str().to_str()
+    }
+
+    /// Construct a *mut TCString from a string for returning to C.
+    pub(crate) fn return_string(string: impl Into<Vec<u8>>) -> Result<*mut TCString, NulError> {
+        let tcstring = TCString(CString::new(string)?);
+        Ok(Box::into_raw(Box::new(tcstring)))
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn tc_string_new(cstr: *const libc::c_char) -> *mut TCString {
+    let cstring = unsafe { CStr::from_ptr(cstr) }.into();
+    Box::into_raw(Box::new(TCString(cstring)))
+}
+
+#[no_mangle]
+pub extern "C" fn tc_string_content(string: *mut TCString) -> *const libc::c_char {
+    debug_assert!(!string.is_null());
+    let string: &CString = unsafe { &(*string).0 };
+    string.as_ptr()
+}
+
+#[no_mangle]
+pub extern "C" fn tc_string_free(string: *mut TCString) {
+    debug_assert!(!string.is_null());
+    drop(unsafe { Box::from_raw(string) });
+}