feat(sdk): Introduce new API for file logging in the bindings

c2pa_c_ffi/Cargo.toml

@@ -34,6 +34,9 @@ serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 thiserror = "1.0.64"
 tokio = { version = "1.36", features = ["rt-multi-thread", "rt"] }
+log = "0.4"
+fern = "0.6"
+chrono = "0.4"   # For timestamps
 
 [dev-dependencies]
 tempfile = "3.7.0"

c2pa_c_ffi/src/c_api.rs

@@ -17,6 +17,9 @@ use std::{
     ptr,
 };
 
+use chrono::Local;
+use fern::Dispatch;
+
 /// Validates that a buffer size is within safe bounds and doesn't cause integer overflow
 /// when used with pointer arithmetic.
 ///
@@ -65,7 +68,7 @@ unsafe fn safe_slice_from_raw_parts(
 
     if !is_safe_buffer_size(len, ptr) {
         return Err(Error::Other(format!(
-            "Buffer size {len} is invalid for parameter '{param_name}'",
+            "Buffer size {len} is invalid for parameter '{param_name}'"
         )));
     }
 
@@ -297,6 +300,43 @@ pub unsafe extern "C" fn c2pa_version() -> *mut c_char {
     to_c_string(version)
 }
 
+/// Sets up file logging.
+/// The logger will append any logged text to the end of the log_file provided.
+///
+/// # Safety
+/// Reads from NULL-terminated C strings.
+#[no_mangle]
+pub unsafe extern "C" fn c2pa_init_file_logging(log_file: *const c_char) -> c_int {
+    let log_file = from_cstr_or_return_int!(log_file);
+
+    // Attempt to open the log file, return -1 if it fails (e.g., parent directory doesn't exist)
+    let log_file_handle = match fern::log_file(log_file) {
+        Ok(handle) => handle,
+        Err(_) => return -1,
+    };
+
+    let result = Dispatch::new()
+        .format(|out, message, record| {
+            out.finish(format_args!(
+                "[{}][{}] {}",
+                Local::now().format("%Y-%m-%d %H:%M:%S"),
+                record.level(),
+                message
+            ))
+        })
+        .level(log::LevelFilter::Info)
+        .chain(std::io::stdout())
+        // Log to a file
+        .chain(log_file_handle)
+        .apply();
+
+    if result.is_ok() {
+        0
+    } else {
+        -1
+    }
+}
+
 /// Returns the last error message.
 ///
 /// # Safety
@@ -1785,6 +1825,10 @@ mod tests {
     #[test]
     #[cfg(feature = "file_io")]
     fn test_c2pa_sign_file_null_source_path() {
+        let log_path_str = "c2pa_test.log";
+        let log_path = CString::new(log_path_str).unwrap();
+        unsafe { c2pa_init_file_logging(log_path.as_ptr()) };
+
         let dest_path = CString::new("/tmp/output.jpg").unwrap();
         let manifest = CString::new("{}").unwrap();
         let signer_info = C2paSignerInfo {
@@ -1806,6 +1850,12 @@ mod tests {
         let error = unsafe { c2pa_error() };
         let error_str = unsafe { CString::from_raw(error) };
         assert_eq!(error_str.to_str().unwrap(), "NullParameter: source_path");
+
+        use std::fs;
+        let content = fs::read(log_path_str);
+        assert!(content.is_ok());
+        assert!(content.unwrap().is_empty());
+        let _ = fs::remove_file(log_path_str);
     }
 
     #[test]