Allow clients to set a log callback.

This depends on mozilla/cubeb#802.

cubeb-core/src/log.rs

@@ -3,7 +3,9 @@
 // This program is made available under an ISC-style license.  See the
 // accompanying file LICENSE for details.
 
-use ffi;
+use std::ffi::{c_char, CStr};
+use std::sync::Mutex;
+use {ffi, Error, Result};
 
 /// Level (verbosity) of logging for a particular cubeb context.
 #[derive(PartialEq, Eq, Clone, Debug, Copy, PartialOrd, Ord)]
@@ -31,6 +33,33 @@ pub fn log_enabled() -> bool {
     unsafe { ffi::cubeb_log_get_level() != LogLevel::Disabled as _ }
 }
 
+static LOG_CALLBACK: Mutex<Option<fn(s: &CStr)>> = Mutex::new(None);
+
+unsafe extern "C" fn log_callback_wrapper(s: *const c_char) {
+    if let Ok(guard) = LOG_CALLBACK.lock() {
+        if let Some(f) = *guard {
+            f(CStr::from_ptr(s));
+        }
+        // Do nothing if there is no callback.
+    }
+    // Silently fail if lock cannot be acquired.
+}
+
+pub fn set_logging(level: LogLevel, f: Option<fn(s: &CStr)>) -> Result<()> {
+    match LOG_CALLBACK.lock() {
+        Ok(mut guard) => {
+            *guard = f;
+        }
+        Err(_) => return Err(Error::error()),
+    }
+    unsafe {
+        call!(ffi::cubeb_set_log_callback_string(
+            level as u32,
+            Some(log_callback_wrapper)
+        ))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

cubeb-sys/src/log.rs

@@ -14,13 +14,19 @@ cubeb_enum! {
 }
 
 pub type cubeb_log_callback = Option<unsafe extern "C" fn(*const c_char, ...)>;
+pub type cubeb_log_callback_string = Option<unsafe extern "C" fn(*const c_char)>;
 
 extern "C" {
     pub fn cubeb_set_log_callback(
         log_level: cubeb_log_level,
         log_callback: cubeb_log_callback,
     ) -> c_int;
 
+    pub fn cubeb_set_log_callback_string(
+        log_level: cubeb_log_level,
+        log_callback: cubeb_log_callback_string,
+    ) -> c_int;
+
     pub fn cubeb_log_get_callback() -> cubeb_log_callback;
     pub fn cubeb_log_get_level() -> cubeb_log_level;