add basic example for compiling upkr to a c library

c_library/src/lib.rs

@@ -0,0 +1,42 @@
+use std::ffi::c_int;
+
+// the upkr config to use, this can be modified to use other configs
+fn config() -> upkr::Config {
+    upkr::Config::default()
+}
+
+#[no_mangle]
+pub extern "C" fn upkr_compress(
+    output_buffer: *mut u8,
+    output_buffer_size: usize,
+    input_buffer: *const u8,
+    input_size: usize,
+    compression_level: c_int,
+) -> usize {
+    let output_buffer = unsafe { std::slice::from_raw_parts_mut(output_buffer, output_buffer_size) };
+    let input_buffer = unsafe { std::slice::from_raw_parts(input_buffer, input_size) };
+
+    let packed_data = upkr::pack(input_buffer, compression_level.max(0).min(9) as u8, &config(), None);
+    let copy_size = packed_data.len().min(output_buffer.len());
+    output_buffer[..copy_size].copy_from_slice(&packed_data[..copy_size]);
+
+    packed_data.len()
+}
+
+#[no_mangle]
+pub extern "C" fn upkr_uncompress(output_buffer: *mut u8, output_buffer_size: usize, input_buffer: *const u8, input_size: usize) -> isize {
+    let output_buffer = unsafe { std::slice::from_raw_parts_mut(output_buffer, output_buffer_size)};
+    let input_buffer = unsafe { std::slice::from_raw_parts(input_buffer, input_size)};
+
+    match upkr::unpack(input_buffer, &config(), output_buffer.len()) {
+        Ok(unpacked_data) => {
+            output_buffer[..unpacked_data.len()].copy_from_slice(&unpacked_data);
+            unpacked_data.len() as isize
+        }
+        Err(upkr::UnpackError::OverSize { size, .. }) => size as isize,
+        Err(other) => {
+            eprintln!("[upkr] compressed data corrupt: {}", other);
+            -1
+        }
+    }
+}