Send logs from the backend to the Android log

Closes ankidroid#24

rslib-bridge/Cargo.toml

@@ -23,9 +23,12 @@ lexical-core = "0.7.5"
 
 # picked bundled - TODO: Is this correct?
 rusqlite = { version = "0.26.0", features = ["trace", "functions", "collation", "bundled"] }
+android_logger = "0.11.0"
+log = "0.4.17"
+slog = "2.7.0"
 
 [features]
 no-android = []
 
 [build-dependencies]
-prost-build = "0.9"
+prost-build = "0.9"

rslib-bridge/src/lib.rs

@@ -12,14 +12,18 @@ use prost::Message;
 use std::any::Any;
 use std::panic::{catch_unwind, AssertUnwindSafe};
 
+mod logging;
+
 #[no_mangle]
 pub unsafe extern "C" fn Java_net_ankiweb_rsdroid_NativeMethods_openBackend(
     env: JNIEnv,
     _: JClass,
     args: jbyteArray,
 ) -> jarray {
+    let logger = logging::setup_logging();
+
     let input = env.convert_byte_array(args).unwrap();
-    let result = init_backend(&input, None)
+    let result = init_backend(&input, Some(logger))
         .map(|backend| {
             let backend_ptr = Box::into_raw(Box::new(backend)) as i64;
             Int64 { val: backend_ptr }.encode_to_vec()

rslib-bridge/src/logging.rs

@@ -0,0 +1,44 @@
+//! A simple adaptor that takes log messages from the backend and sends them to
+//! the Android logs.
+
+use android_logger::Config;
+use log::Level;
+use slog::*;
+use std::{fmt, result};
+
+pub struct AndroidSerializer;
+
+impl Serializer for AndroidSerializer {
+    fn emit_arguments(&mut self, key: Key, val: &fmt::Arguments<'_>) -> Result {
+        log::debug!("{}={}", key, val);
+        Ok(())
+    }
+}
+
+pub struct AndroidDrain;
+
+impl Drain for AndroidDrain {
+    type Ok = ();
+    type Err = ();
+
+    fn log(
+        &self,
+        record: &Record<'_>,
+        values: &OwnedKVList,
+    ) -> result::Result<Self::Ok, Self::Err> {
+        log::debug!("{}", record.msg());
+
+        record
+            .kv()
+            .serialize(record, &mut AndroidSerializer)
+            .unwrap();
+        values.serialize(record, &mut AndroidSerializer).unwrap();
+
+        Ok(())
+    }
+}
+
+pub(crate) fn setup_logging() -> Logger {
+    android_logger::init_once(Config::default().with_min_level(Level::Debug));
+    Logger::root(AndroidDrain {}.fuse(), slog_o!())
+}