From 7d9ce36d6f8ec72696192c5e2a27e10ea41cd581 Mon Sep 17 00:00:00 2001
From: Matt Gaylor <magaylor@microsoft.com>
Date: Wed, 29 Oct 2025 16:28:42 -0700
Subject: [PATCH 1/2] Adding file logging to bindings

---
 Cargo.lock              | 12 +++++++++++
 c2pa_c_ffi/Cargo.toml   |  3 +++
 c2pa_c_ffi/src/c_api.rs | 45 ++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/Cargo.lock b/Cargo.lock
index b9ec38d6f..ccc613dc4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -541,6 +541,9 @@ version = "0.68.0"
 dependencies = [
  "c2pa",
  "cbindgen",
+ "chrono",
+ "fern",
+ "log",
  "scopeguard",
  "serde",
  "serde_json",
@@ -1375,6 +1378,15 @@ dependencies = [
  "simd-adler32",
 ]
 
+[[package]]
+name = "fern"
+version = "0.6.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d9f0c14694cbd524c8720dd69b0e3179344f04ebb5f90f2e4a440c6ea3b2f1ee"
+dependencies = [
+ "log",
+]
+
 [[package]]
 name = "ff"
 version = "0.13.1"
diff --git a/c2pa_c_ffi/Cargo.toml b/c2pa_c_ffi/Cargo.toml
index d251c5cfa..93dbfcb7e 100644
--- a/c2pa_c_ffi/Cargo.toml
+++ b/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"
diff --git a/c2pa_c_ffi/src/c_api.rs b/c2pa_c_ffi/src/c_api.rs
index c936fb11c..988c0fb45 100644
--- a/c2pa_c_ffi/src/c_api.rs
+++ b/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 +300,36 @@ 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);
+    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(fern::log_file(log_file).unwrap())
+        .apply();
+
+    if result.is_ok() {
+        0
+    } else {
+        -1
+    }
+}
+
 /// Returns the last error message.
 ///
 /// # Safety
@@ -1785,6 +1818,10 @@ 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 +1843,12 @@ 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]

From 5de8f9a1f2f3c91ac7e6f6cb8f47bf8a5aa3c347 Mon Sep 17 00:00:00 2001
From: Matt Gaylor <magaylor@microsoft.com>
Date: Tue, 11 Nov 2025 15:42:19 -0800
Subject: [PATCH 2/2] Adding better error handling for the file logger

---
 c2pa_c_ffi/src/c_api.rs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/c2pa_c_ffi/src/c_api.rs b/c2pa_c_ffi/src/c_api.rs
index 988c0fb45..0455df3ee 100644
--- a/c2pa_c_ffi/src/c_api.rs
+++ b/c2pa_c_ffi/src/c_api.rs
@@ -308,6 +308,13 @@ pub unsafe extern "C" fn c2pa_version() -> *mut c_char {
 #[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!(
@@ -320,7 +327,7 @@ pub unsafe extern "C" fn c2pa_init_file_logging(log_file: *const c_char) -> c_in
         .level(log::LevelFilter::Info)
         .chain(std::io::stdout())
         // Log to a file
-        .chain(fern::log_file(log_file).unwrap())
+        .chain(log_file_handle)
         .apply();
 
     if result.is_ok() {