Add some logging utilities to capture whisper.cpp output

src/whisper_sys_tracing.rs

@@ -0,0 +1,43 @@
+use std::sync::Once;
+use tracing::{debug, error, info, warn};
+use whisper_rs_sys::ggml_log_level;
+
+unsafe extern "C" fn whisper_cpp_tracing_trampoline(
+    level: ggml_log_level,
+    text: *const std::os::raw::c_char,
+    _: *mut std::os::raw::c_void, // user_data
+) {
+    if text.is_null() {
+        error!("whisper_cpp_tracing_trampoline: text is nullptr");
+    }
+
+    // SAFETY: we must trust whisper.cpp that it will not pass us a string that does not satisfy
+    // from_ptr's requirements.
+    let log_str = unsafe { std::ffi::CStr::from_ptr(text) }
+        .to_string_lossy()
+        .trim();
+
+    match level {
+        whisper_rs_sys::ggml_log_level_GGML_LOG_LEVEL_DEBUG => debug!("{}", log_str),
+        whisper_rs_sys::ggml_log_level_GGML_LOG_LEVEL_INFO => info!("{}", log_str),
+        whisper_rs_sys::ggml_log_level_GGML_LOG_LEVEL_WARN => warn!("{}", log_str),
+        whisper_rs_sys::ggml_log_level_GGML_LOG_LEVEL_ERROR => error!("{}", log_str),
+        _ => {
+            warn!(
+                "whisper_cpp_tracing_trampoline: unknown log level {}: message: {}",
+                level, log_str
+            )
+        }
+    }
+}
+
+/// Shortcut utility to redirect all whisper.cpp logging to the `tracing` crate.
+///
+/// Filter for logs from the `whisper-rs` crate to see all log output from whisper.cpp.
+///
+/// You should only call this once (subsequent calls have no effect).
+pub fn install_whisper_tracing_trampoline() {
+    crate::LOG_TRAMPOLINE_INSTALL.call_once(|| unsafe {
+        whisper_rs_sys::whisper_log_set(Some(whisper_cpp_tracing_trampoline), std::ptr::null_mut())
+    });
+}