add error logging in Rust

This allows errors to bubble up to the android log file, rather than
having to sift through a tombstone file on the device.

Cargo.lock

@@ -28,6 +28,21 @@ dependencies = [
  "stream-cipher 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "android_log-sys"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "android_logger"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "android_log-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "arrayvec"
 version = "0.4.7"
@@ -307,6 +322,14 @@ dependencies = [
  "cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "log-panics"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "lru-cache"
 version = "0.1.1"
@@ -582,7 +605,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "zcash-wallet-sdk-poc"
 version = "0.0.1"
 dependencies = [
+ "android_logger 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "jni 0.10.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log-panics 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "protobuf 2.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "protobuf-codegen-pure 2.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -644,6 +670,8 @@ dependencies = [
 "checksum aes 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e6fb1737cdc8da3db76e90ca817a194249a38fcb500c2e6ecec39b29448aa873"
 "checksum aes-soft 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "67cc03b0a090a05cb01e96998a01905d7ceedce1bc23b756c0bb7faa0682ccb1"
 "checksum aesni 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)" = "6810b7fb9f2bb4f76f05ac1c170b8dde285b6308955dc3afd89710268c958d9e"
+"checksum android_log-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "b8052e2d8aabbb8d556d6abbcce2a22b9590996c5f849b9c7ce4544a2e3b984e"
+"checksum android_logger 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "bad99185bc195e796e1591740c26716667b58ac9210a48731f71f803fc6ca43a"
 "checksum arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)" = "a1e964f9e24d588183fcb43503abda40d288c8657dfc27311516ce2f05675aef"
 "checksum ascii 0.9.1 (registry+https://github.com/rust-lang/crates.io-index)" = "a5fc969a8ce2c9c0c4b0429bb8431544f6658283c8326ba5ff8c762b75369335"
 "checksum backtrace 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "89a47830402e9981c5c41223151efcced65a0510c13097c769cede7efb34782a"
@@ -682,6 +710,7 @@ dependencies = [
 "checksum libsqlite3-sys 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)" = "742b695cbfb89e549dca6960a55e6802f67d352e33e97859ee46dee835211b0f"
 "checksum linked-hash-map 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7860ec297f7008ff7a1e3382d7f7e1dcd69efc94751a2284bafc3d013c2aa939"
 "checksum log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c84ec4b527950aa83a329754b01dbe3f58361d1c5efacd1f6d68c494d08a17c6"
+"checksum log-panics 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ae0136257df209261daa18d6c16394757c63e032e27aafd8b07788b051082bef"
 "checksum lru-cache 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "4d06ff7ff06f729ce5f4e227876cb88d10bc59cd4ae1e09fbb2bde15c850dc21"
 "checksum memchr 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0a3eb002f0535929f1199681417029ebea04aadc0c7a4224b46be99c7f5d6a16"
 "checksum nodrop 0.1.13 (registry+https://github.com/rust-lang/crates.io-index)" = "2f9667ddcc6cc8a43afc9b7917599d7216aa09c463919ea32c59ed6cac8bc945"

Cargo.toml

@@ -9,6 +9,7 @@ publish = false
 protobuf = "2"
 rand = "0.4"
 rusqlite = { version = "0.15", features = ["bundled"] }
+log = "0.4"
 
 [dependencies.zcash_client_backend]
 git = "https://github.com/str4d/librustzcash.git"
@@ -20,6 +21,8 @@ rev = "63ec78bb857a258a97d25a5a6e747389996e566a"
 
 [target.'cfg(target_os="android")'.dependencies]
 jni = { version = "0.10", default-features = false }
+android_logger = "0.6"
+log-panics = "2.0.0"
 
 [build-dependencies]
 protobuf-codegen-pure = "2"

src/main/rust/lib.rs

@@ -1,3 +1,6 @@
+#[macro_use]
+extern crate log;
+
 extern crate protobuf;
 extern crate rusqlite;
 extern crate zcash_client_backend;
@@ -75,16 +78,35 @@ fn scan_cached_blocks(
 #[cfg(target_os = "android")]
 #[allow(non_snake_case)]
 pub mod android {
+    extern crate android_logger;
     extern crate jni;
+    extern crate log_panics;
 
+    use log::Level;
     use protobuf::Message;
 
+    use self::android_logger::Filter;
     use self::jni::objects::{JClass, JString};
     use self::jni::sys::{jbyteArray, jint, jobjectArray, jsize, jstring};
     use self::jni::JNIEnv;
 
     use super::{address_from_extfvk, extfvk_from_seed, scan_cached_blocks};
 
+    #[no_mangle]
+    pub unsafe extern "C" fn Java_cash_z_wallet_sdk_jni_JniConverter_initLogs(
+        _env: JNIEnv,
+        _: JClass,
+    ) {
+        android_logger::init_once(
+            Filter::default().with_min_level(Level::Trace),
+            Some("cash.z.rust.logs"),
+        );
+
+        log_panics::init();
+
+        debug!("logs have been initialized successfully");
+    }
+
     #[no_mangle]
     pub unsafe extern "C" fn Java_cash_z_wallet_sdk_jni_JniConverter_getAddress(
         env: JNIEnv,