Add custom logger API.

docs/logging.md

@@ -47,3 +47,37 @@ If the `log` feature is not enabled, then `jack` will log info messages to
 ```rust
 jack::set_logger(jack::LoggerType::Stdio);
 ```
+
+## Custom
+
+`jack::LoggerType::Custom` can be used to set a custom logger. Here is
+stdout/stderr implemented as a custom logger:
+
+```rust
+fn main() {
+    jack::set_logger(jack::LoggerType::Custom{info: stdout_handler, error: stderr_handler});
+    ...
+}
+
+unsafe extern "C" fn stdout_handler(msg: *const libc::c_char) {
+    let res = std::panic::catch_unwind(|| match std::ffi::CStr::from_ptr(msg).to_str() {
+        Ok(msg) => println!("{}", msg),
+        Err(err) => println!("failed to log to JACK info: {:?}", err),
+    });
+    if let Err(err) = res {
+        eprintln!("{err:?}");
+        std::mem::forget(err); // Prevent from rethrowing panic.
+    }
+}
+
+unsafe extern "C" fn stderr_handler(msg: *const libc::c_char) {
+    let res = std::panic::catch_unwind(|| match std::ffi::CStr::from_ptr(msg).to_str() {
+        Ok(msg) => eprintln!("{}", msg),
+        Err(err) => eprintln!("failed to log to JACK error: {:?}", err),
+    });
+    if let Err(err) = res {
+        eprintln!("{err:?}");
+        std::mem::forget(err); // Prevent from rethrowing panic.
+    }
+}
+```

src/logging.rs

@@ -21,6 +21,13 @@ pub enum LoggerType {
     /// Use the info! and error! macro from the [log crate](https://crates.io/crates/log).
     #[cfg(feature = "log")]
     Log,
+    /// Use custom functions to handle logging.
+    Custom {
+        /// The function to call for info messages. Must not panic.
+        info: unsafe extern "C" fn(*const ::libc::c_char),
+        /// The function to call for error messages. Must not panic.
+        error: unsafe extern "C" fn(*const ::libc::c_char),
+    },
 }
 
 impl Default for LoggerType {
@@ -45,20 +52,23 @@ pub fn set_logger(logger: LoggerType) {
 }
 
 fn set_logger_impl(logger: LoggerType) {
-    match logger {
-        LoggerType::None => unsafe {
-            jack_sys::jack_set_error_function(Some(silent_handler));
-            jack_sys::jack_set_info_function(Some(silent_handler));
-        },
-        LoggerType::Stdio => unsafe {
-            jack_sys::jack_set_error_function(Some(stderr_handler));
-            jack_sys::jack_set_info_function(Some(stdout_handler));
-        },
+    let info_fn = match logger {
+        LoggerType::None => silent_handler,
+        LoggerType::Stdio => stdout_handler,
         #[cfg(feature = "log")]
-        LoggerType::Log => unsafe {
-            jack_sys::jack_set_error_function(Some(error_handler));
-            jack_sys::jack_set_info_function(Some(info_handler));
-        },
+        LoggerType::Log => info_handler,
+        LoggerType::Custom { info, .. } => info,
+    };
+    let error_fn = match logger {
+        LoggerType::None => silent_handler,
+        LoggerType::Stdio => stderr_handler,
+        #[cfg(feature = "log")]
+        LoggerType::Log => error_handler,
+        LoggerType::Custom { error, .. } => error,
+    };
+    unsafe {
+        jack_sys::jack_set_error_function(Some(error_fn));
+        jack_sys::jack_set_info_function(Some(info_fn));
     }
 }