Using Bindgen

The bindgen tool can auto-generate bindings from a C header file.

First create a small C library:

interoperability/bindgen/libbirthday.h:

1. typedef struct card {
2. const char* name;
3. int years;
4. } card;

6. void print_card(const card* card);

interoperability/bindgen/libbirthday.c:

1. #include <stdio.h>
2. #include "libbirthday.h"

4. void print_card(const card* card) {
5. printf("+--------------\n");
6. printf("| Happy Birthday %s!\n", card->name);
7. printf("| Congratulations with the %i years!\n", card->years);
8. printf("+--------------\n");
9. }

Add this to your Android.bp file:

interoperability/bindgen/Android.bp:

1. cc_library {
2. name: "libbirthday",
3. srcs: ["libbirthday.c"],
4. }

Create a wrapper header file for the library (not strictly needed in this example):

interoperability/bindgen/libbirthday_wrapper.h:

1. #include "libbirthday.h"

You can now auto-generate the bindings:

interoperability/bindgen/Android.bp:

1. rust_bindgen {
2. name: "libbirthday_bindgen",
3. crate_name: "birthday_bindgen",
4. wrapper_src: "libbirthday_wrapper.h",
5. source_stem: "bindings",
6. static_libs: ["libbirthday"],
7. }

Finally, we can use the bindings in our Rust program:

interoperability/bindgen/Android.bp:

1. rust_binary {
2. name: "print_birthday_card",
3. srcs: ["main.rs"],
4. rustlibs: ["libbirthday_bindgen"],
5. }

interoperability/bindgen/main.rs:

1. ```
   //! Bindgen demo.
   ```

3. ```
   use birthday_bindgen::{card, print_card};
   ```

5. ```
   fn main() {
   ```
6. ```
       let name = std::ffi::CString::new("Peter").unwrap();
   ```
7. ```
       let card = card { name: name.as_ptr(), years: 42 };
   ```
8. ```
       // SAFETY: The pointer we pass is valid because it came from a Rust
   ```
9. ```
       // reference, and the `name` it contains refers to `name` above which also
   ```
10. ```
        // remains valid. `print_card` doesn't store either pointer to use later
    ```
11. ```
        // after it returns.
    ```
12. ```
        unsafe {
    ```
13. ```
            print_card(&card as *const card);
    ```
14. ```
        }
    ```
15. ```
    }
    ```

Build, push, and run the binary on your device:

1. m print_birthday_card
2. adb push "$ANDROID_PRODUCT_OUT/system/bin/print_birthday_card" /data/local/tmp
3. adb shell /data/local/tmp/print_birthday_card

Finally, we can run auto-generated tests to ensure the bindings work:

interoperability/bindgen/Android.bp:

1. rust_test {
2. name: "libbirthday_bindgen_test",
3. srcs: [":libbirthday_bindgen"],
4. crate_name: "libbirthday_bindgen_test",
5. test_suites: ["general-tests"],
6. auto_gen_config: true,
7. clippy_lints: "none", // Generated file, skip linting
8. lints: "none",
9. }

1. atest libbirthday_bindgen_test