DroidDeck/tools/xbox/droiddeck-credential-fallback.patch

diff --git a/crates/xodus/src/tokens/backend/keychain.rs b/crates/xodus/src/tokens/backend/keychain.rs
index 1903638..19480da 100644
--- a/crates/xodus/src/tokens/backend/keychain.rs
+++ b/crates/xodus/src/tokens/backend/keychain.rs
@@ -1,20 +1,45 @@
 use crate::tokens::store::{TokenBackend, TokenStoreError};
 use serde_json::{Value, json};
 use std::io::{BufRead, Read, Write};
+use std::net::{Ipv4Addr, SocketAddrV4, TcpStream};
 use std::os::linux::net::SocketAddrExt;
 use std::os::unix::net::{SocketAddr, UnixStream};
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::time::Duration;
 
 pub struct KeychainBackend;
 
-fn request(value: Value) -> Result<Value, TokenStoreError> {
-    let name = std::env::var("DROIDDECK_XBOX_CREDENTIAL_SOCKET")
-        .map_err(|_| std::io::Error::other("Android credential host is unavailable"))?;
-    let address = SocketAddr::from_abstract_name(name)?;
-    let mut stream = UnixStream::connect_addr(&address)?;
-    stream.set_read_timeout(Some(Duration::from_secs(10)))?;
-    stream.set_write_timeout(Some(Duration::from_secs(10)))?;
-    serde_json::to_writer(&mut stream, &value)?;
+// keyed loopback port the app also listens on is used for the rest of the process.
+static LOOPBACK: AtomicBool = AtomicBool::new(false);
+static REPORTED: AtomicBool = AtomicBool::new(false);
+
+/// Letters and dashes only: the app passes `NEXUS_CREDENTIAL_ERROR_V1 [a-z-]{1,48}` lines to its log.
+fn reason(error: &std::io::Error) -> &'static str {
+    match error.raw_os_error() {
+        Some(111) => "refused",
+        Some(13) => "denied",
+        Some(1) => "not-permitted",
+        Some(2) => "missing",
+        Some(110) => "timed-out",
+        Some(38) => "unsupported",
+        Some(97) => "family-unsupported",
+        Some(22) => "invalid",
+        Some(104) => "reset",
+        Some(32) => "broken-pipe",
+        _ => match error.kind() {
+            std::io::ErrorKind::TimedOut | std::io::ErrorKind::WouldBlock => "timed-out",
+            std::io::ErrorKind::UnexpectedEof => "closed",
+            _ => "other",
+        },
+    }
+}
+
+fn exchange<S: Read + Write>(mut stream: S, prefix: Option<&str>, value: &Value) -> Result<Value, TokenStoreError> {
+    if let Some(key) = prefix {
+        stream.write_all(key.as_bytes())?;
+        stream.write_all(b"\n")?;
+    }
+    serde_json::to_writer(&mut stream, value)?;
     stream.write_all(b"\n")?;
     let mut bytes = Vec::new();
     std::io::BufReader::new(stream).take(2_097_153).read_until(b'\n', &mut bytes)?;
@@ -22,10 +47,52 @@ fn request(value: Value) -> Result<Value, TokenStoreError> {
         return Err(std::io::Error::other("Invalid Android credential response").into());
     }
     let response: Value = serde_json::from_slice(&bytes)?;
-    if response["ok"] != true { return Err(std::io::Error::other("Android credential storage unavailable").into()); }
+    if response["ok"] != true {
+        eprintln!("NEXUS_CREDENTIAL_ERROR_V1 host-refused");
+        return Err(std::io::Error::other("Android credential storage unavailable").into());
+    }
     Ok(response)
 }
 
+fn loopback(value: &Value) -> Result<Value, TokenStoreError> {
+    let port: u16 = std::env::var("DROIDDECK_XBOX_CREDENTIAL_PORT").ok().and_then(|v| v.parse().ok())
+        .ok_or_else(|| std::io::Error::other("Android credential port is unavailable"))?;
+    let key = std::env::var("DROIDDECK_XBOX_CREDENTIAL_KEY")
+        .map_err(|_| std::io::Error::other("Android credential key is unavailable"))?;
+    let address = SocketAddrV4::new(Ipv4Addr::LOCALHOST, port).into();
+    let stream = TcpStream::connect_timeout(&address, Duration::from_secs(5)).inspect_err(|error| {
+        eprintln!("NEXUS_CREDENTIAL_ERROR_V1 loopback-{}", reason(error));
+    })?;
+    stream.set_read_timeout(Some(Duration::from_secs(10)))?;
+    stream.set_write_timeout(Some(Duration::from_secs(10)))?;
+    exchange(stream, Some(&key), value)
+}
+
+fn request(value: Value) -> Result<Value, TokenStoreError> {
+    if LOOPBACK.load(Ordering::Relaxed) { return loopback(&value); }
+    let name = std::env::var("DROIDDECK_XBOX_CREDENTIAL_SOCKET")
+        .map_err(|_| std::io::Error::other("Android credential host is unavailable"))?;
+    let address = SocketAddr::from_abstract_name(name)?;
+    match UnixStream::connect_addr(&address) {
+        Ok(stream) => {
+            stream.set_read_timeout(Some(Duration::from_secs(10)))?;
+            stream.set_write_timeout(Some(Duration::from_secs(10)))?;
+            exchange(stream, None, &value)
+        }
+        Err(error) => {
+            if !REPORTED.swap(true, Ordering::Relaxed) {
+                eprintln!("NEXUS_CREDENTIAL_ERROR_V1 socket-{}", reason(&error));
+            }
+            let result = loopback(&value);
+            if result.is_ok() {
+                LOOPBACK.store(true, Ordering::Relaxed);
+                eprintln!("NEXUS_CREDENTIAL_ERROR_V1 loopback-in-use");
+            }
+            result
+        }
+    }
+}
+
 impl TokenBackend for KeychainBackend {
     fn get(&self, key: &str) -> Result<Option<Vec<u8>>, TokenStoreError> {
         let response = request(json!({"op":"get", "key":key}))?;