ndk-build: Use uid to limit logcat to the current application

This is a port of:
rust-mobile/xbuild#131
rust-mobile/xbuild#135

Having never really understood how Android Studio does it, I just
stumbled upon this very new [stackoverflow answer] that has a rather
beatiful solution to the current problems with `pidof`, without
drawbacks.  Pidof has always been flaky as it relies on the app to be
running, which may either take some time or never happen if the app
crashed before `pidof` is first run.  This results in silly workarounds
such as loops that induce extra delay and need to have an upper bound.
And this `pid` changes every time the app is restarted, making it a
tedious process that also doesn't react to manual app restarts on the
device.  Retrieving the `uid` via `pm list packages -U` on the other
hand, and passing that to `logcat --uid` has the following advantages:

- Always available immediately after the app has been installed, no need
  to check it in a loop (no extra delay);
- Doesn't change after the app is (re!)installed, unless the user fully
  deletes and installs the app again;
- Is resilient against app crashes because of that, and allows the user
  to see any error/crash related messages straight away;
- Still includes logs printed by other system components that run or are
  invoked within an app, as before.

The only downside is that `pm list package` possibly returns multiple
packages if there is a substring match; for this reason the code
searches for an explicit match in the output.

[stackoverflow answer]: https://stackoverflow.com/a/76551835

cargo-apk/src/apk.rs

@@ -313,16 +313,17 @@ impl<'a> ApkBuilder<'a> {
         let apk = self.build(artifact)?;
         apk.reverse_port_forwarding(self.device_serial.as_deref())?;
         apk.install(self.device_serial.as_deref())?;
-        let pid = apk.start(self.device_serial.as_deref())?;
+        apk.start(self.device_serial.as_deref())?;
+        let uid = apk.uidof(self.device_serial.as_deref())?;
 
         if !no_logcat {
             self.ndk
                 .adb(self.device_serial.as_deref())?
                 .arg("logcat")
                 .arg("-v")
                 .arg("color")
-                .arg("--pid")
-                .arg(pid.to_string())
+                .arg("--uid")
+                .arg(uid.to_string())
                 .status()?;
         }
 

ndk-build/CHANGELOG.md

@@ -1,7 +1,8 @@
 # Unreleased
 
 - Add `android:extractNativeLibs`, `android:usesCleartextTraffic` attributes to the manifest's `Application` element, and `android:alwaysRetainTaskState` to the `Activity` element. ([#15](https://github.com/rust-mobile/cargo-apk/pull/15))
-- Enable building from `android` host ([#29](https://github.com/rust-mobile/cargo-apk/pull/29))
+- Enable building from `android` host. ([#29](https://github.com/rust-mobile/cargo-apk/pull/29))
+- Use app `uid` instead of `pid` to limit `logcat` output to the current app. ([#33](https://github.com/rust-mobile/cargo-apk/pull/33))
 
 # 0.9.0 (2022-11-23)
 

ndk-build/src/apk.rs

@@ -292,37 +292,52 @@ impl Apk {
         Ok(())
     }
 
-    pub fn start(&self, device_serial: Option<&str>) -> Result<u32, NdkError> {
-        let mut am_start = self.ndk.adb(device_serial)?;
-        am_start
-            .arg("shell")
+    pub fn start(&self, device_serial: Option<&str>) -> Result<(), NdkError> {
+        let mut adb = self.ndk.adb(device_serial)?;
+        adb.arg("shell")
             .arg("am")
             .arg("start")
-            .arg("-W")
             .arg("-a")
             .arg("android.intent.action.MAIN")
             .arg("-n")
-            .arg(format!("{}/android.app.NativeActivity", &self.package_name));
-        if !am_start.status()?.success() {
-            return Err(NdkError::CmdFailed(am_start));
-        }
+            .arg(format!("{}/android.app.NativeActivity", self.package_name));
 
-        let pid_vec = self
-            .ndk
-            .adb(device_serial)?
-            .arg("shell")
-            .arg("pidof")
-            .arg(&self.package_name)
-            .output()?
-            .stdout;
+        if !adb.status()?.success() {
+            return Err(NdkError::CmdFailed(adb));
+        }
 
-        let pid = std::str::from_utf8(&pid_vec).unwrap().trim();
-        let pid: u32 = pid
-            .parse()
-            .map_err(|e| NdkError::NotAPid(e, pid.to_owned()))?;
+        Ok(())
+    }
 
-        println!("Launched with PID {}", pid);
+    pub fn uidof(&self, device_serial: Option<&str>) -> Result<u32, NdkError> {
+        let mut adb = self.ndk.adb(device_serial)?;
+        adb.arg("shell")
+            .arg("pm")
+            .arg("list")
+            .arg("package")
+            .arg("-U")
+            .arg(&self.package_name);
+        let output = adb.output()?;
+
+        if !output.status.success() {
+            return Err(NdkError::CmdFailed(adb));
+        }
 
-        Ok(pid)
+        let output = std::str::from_utf8(&output.stdout).unwrap();
+        let (_package, uid) = output
+            .lines()
+            .filter_map(|line| line.split_once(' '))
+            // `pm list package` uses the id as a substring filter; make sure
+            // we select the right package in case it returns multiple matches:
+            .find(|(package, _uid)| package.strip_prefix("package:") == Some(&self.package_name))
+            .ok_or(NdkError::PackageNotInOutput {
+                package: self.package_name.clone(),
+                output: output.to_owned(),
+            })?;
+        let uid = uid
+            .strip_prefix("uid:")
+            .ok_or(NdkError::UidNotInOutput(output.to_owned()))?;
+        uid.parse()
+            .map_err(|e| NdkError::NotAUid(e, uid.to_owned()))
     }
 }

ndk-build/src/error.rs

@@ -48,6 +48,10 @@ pub enum NdkError {
     CmdFailed(Command),
     #[error(transparent)]
     Serialize(#[from] quick_xml::de::DeError),
-    #[error("String `{1}` is not a PID")]
-    NotAPid(#[source] ParseIntError, String),
+    #[error("String `{1}` is not a UID")]
+    NotAUid(#[source] ParseIntError, String),
+    #[error("Could not find `package:{package}` in output `{output}`")]
+    PackageNotInOutput { package: String, output: String },
+    #[error("Could not find `uid:` in output `{0}`")]
+    UidNotInOutput(String),
 }