haiku: improve C++ glue

.clang-format

@@ -1,7 +1,7 @@
 ---
 BasedOnStyle: Google
 IndentWidth: 4
-ColumnLimit: 100
+ColumnLimit: 120
 ---
 Language: Cpp
 SortIncludes: false

haiku/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "iana-time-zone-haiku"
 description = "iana-time-zone support crate for Haiku OS"
-version = "0.1.2"
+version = "0.1.3"
 authors = ["René Kijewski <crates.io@k6i.de>"]
 repository = "https://github.com/strawlab/iana-time-zone"
 license = "MIT OR Apache-2.0"

haiku/build.rs

@@ -5,7 +5,7 @@ fn main() {
         .warnings(false)
         .cpp(true)
         .file("src/implementation.cc")
-        .flag_if_supported("-std=c++11")
+        .flag_if_supported("-std=c++17")
         .compile("tz_haiku");
 
     println!("cargo:rerun-if-changed=src/lib.rs");

haiku/src/implementation.cc

@@ -9,59 +9,79 @@
 #include <String.h>
 #include <TimeZone.h>
 
-extern "C" {
+/**
+ * @brief Retrieves the IANA time zone identifier on Haiku.
+ *
+ * This function obtains the default time zone from the Haiku Locale Roster and writes its IANA
+ * time zone identifier into the provided buffer.
+ *
+ * @param buf Pointer to a character buffer where the time zone identifier will be stored.
+ * @param buf_size The size of the buffer pointed to by @a buf.
+ * @return The length of the time zone identifier written into @a buf (excluding the null terminator),
+ *         or 0 if an error occurs (e.g., invalid parameters, failure to retrieve the time zone,
+ *         or insufficient buffer size).
+ *
+ * @note If the buffer is large enough, the function guarantees that the output is null-terminated.
+ *
+ * @warning This function is marked as noexcept; it will not throw exceptions. In case of any
+ *          internal error, the function will simply return 0.
+ */
+extern "C" [[nodiscard]] auto iana_time_zone_haiku_get_tz(char* buf, const std::size_t buf_size) noexcept
+    -> std::size_t {
+    if (buf == nullptr || buf_size == 0) {
+        return 0;
+    }
 
-size_t iana_time_zone_haiku_get_tz(char *buf, size_t buf_size) {
     try {
-        static_assert(sizeof(char) == sizeof(uint8_t), "Illegal char size");
-
-        if (buf_size == 0) {
-            return 0;
-        }
-
-        // `BLocaleRoster::Default()` returns a reference to a statically allocated object.
-        // https://github.com/haiku/haiku/blob/8f16317/src/kits/locale/LocaleRoster.cpp#L143-L147
-        BLocaleRoster *locale_roster(BLocaleRoster::Default());
-        if (!locale_roster) {
+        // Retrieve the default locale roster (statically allocated object)
+        BLocaleRoster* locale_roster = BLocaleRoster::Default();
+        if (locale_roster == nullptr) {
             return 0;
         }
 
-        BTimeZone tz(NULL, NULL);
-        if (locale_roster->GetDefaultTimeZone(&tz) != B_OK) {
+        BTimeZone timezone(nullptr, nullptr);
+        if (locale_roster->GetDefaultTimeZone(&timezone) != B_OK) {
             return 0;
         }
 
-        BString bname(tz.ID());
-        int32_t ilength(bname.Length());
-        if (ilength <= 0) {
+        const BString bname = timezone.ID();
+        const auto raw_length = bname.Length();
+        if (raw_length <= 0) {
             return 0;
         }
 
-        size_t length(ilength);
-        if (length > buf_size) {
+        const auto length = static_cast<std::size_t>(raw_length);
+        // Ensure there is room for the null terminator without doing an addition that might overflow.
+        if (length >= buf_size) {
             return 0;
         }
 
-        // BString::String() returns a borrowed string.
-        // https://www.haiku-os.org/docs/api/classBString.html#ae4fe78b06c8e3310093b80305e14ba87
-        const char *sname(bname.String());
-        if (!sname) {
-            return 0;
-        }
-
-        std::memcpy(buf, sname, length);
+        bname.CopyInto(buf, 0, raw_length);
+        // Insert the null terminator.
+        buf[length] = '\0';
         return length;
+    } catch (const std::exception& /*e*/) {
+        return 0;
     } catch (...) {
         return 0;
     }
 }
-}  // extern "C"
 
 #else
 
-extern "C" {
-
-size_t iana_time_zone_haiku_get_tz(char *buf, size_t buf_size) { return 0; }
-}  // extern "C"
+/**
+ * @brief Dummy implementation for non-Haiku platforms.
+ *
+ * On non-Haiku platforms, this function does nothing and always returns 0.
+ *
+ * @param buf Pointer to a character buffer (unused).
+ * @param buf_size The size of the buffer (unused).
+ * @return Always returns 0.
+ */
+extern "C" [[nodiscard]] auto iana_time_zone_haiku_get_tz([[maybe_unused]] char* buf,
+                                                          [[maybe_unused]] const std::size_t buf_size) noexcept
+    -> std::size_t {
+    return 0;
+}
 
 #endif

haiku/src/lib.rs

@@ -23,6 +23,7 @@
 use std::os::raw::c_char;
 
 extern "C" {
+    #[must_use]
     fn iana_time_zone_haiku_get_tz(buf: *mut c_char, buf_size: usize) -> usize;
 }