Avoid startup stall with non-fatal startup preflight and cached betterdisplaycli resolution

README.md

@@ -124,6 +124,22 @@ Restart the agent after changing config:
 launchctl kickstart -k "gui/$(id -u)/com.github.hacksore.betterdisplay-kvm"
 ```
 
+Stop the LaunchAgent when you want to run the daemon manually:
+
+```bash
+launchctl bootout "gui/$(id -u)/com.github.hacksore.betterdisplay-kvm"
+betterdisplay-kvm --status
+cargo run -- --launch
+```
+
+Start the LaunchAgent again when you are done:
+
+```bash
+launchctl bootstrap "gui/$(id -u)" "$HOME/Library/LaunchAgents/com.github.hacksore.betterdisplay-kvm.plist"
+launchctl enable "gui/$(id -u)/com.github.hacksore.betterdisplay-kvm"
+launchctl kickstart -k "gui/$(id -u)/com.github.hacksore.betterdisplay-kvm"
+```
+
 The generated plist lives at:
 
 ```text

src/app.rs

@@ -1,4 +1,4 @@
-use crate::utils::{ResolvedConfig, get_betterdisplay_path, load_config, setup_logger};
+use crate::utils::{ResolvedConfig, load_config, prime_betterdisplay_path_cache, setup_logger};
 use log::{debug, error, info};
 use std::panic;
 
@@ -20,13 +20,11 @@ impl App {
 
     info!("betterdisplay-kvm starting...");
 
-    let betterdisplay_path = get_betterdisplay_path();
-    debug!("Found betterdisplaycli at: {:?}", betterdisplay_path);
-
     // Set up panic hook to capture panics and log them
     Self::setup_panic_hook();
 
     debug!("Starting betterdisplay-kvm with config: {:?}", config);
+    prime_betterdisplay_path_cache();
 
     Ok(Self { config })
   }

src/utils.rs

@@ -11,12 +11,15 @@ use std::{
   io::{self, IsTerminal},
   os::unix::fs::PermissionsExt,
   path::{Path, PathBuf},
-  process::{self, Command, Output},
+  process::Command,
+  process::{self, Output},
+  sync::OnceLock,
 };
 
 pub const DEFAULT_DEVICE_ID: &str = "046d:c547";
 pub const LAUNCH_AGENT_LABEL: &str = "com.github.hacksore.betterdisplay-kvm";
 const BIN_NAME: &str = "betterdisplay-kvm";
+static BETTERDISPLAY_PATH_CACHE: OnceLock<Result<PathBuf, String>> = OnceLock::new();
 
 #[derive(Debug, Serialize, Deserialize)]
 pub struct AppConfig {
@@ -55,44 +58,60 @@ pub struct ResolvedConfig {
   pub ddc_alt: bool,
 }
 
-pub fn get_betterdisplay_path() -> PathBuf {
-  if let Ok(override_path) = std::env::var("BETTERDISPLAYCLI_PATH") {
-    let p = PathBuf::from(override_path);
-    if p.exists() {
-      return p;
+fn resolve_betterdisplay_path(
+  override_path: Option<PathBuf>,
+  candidates: &[PathBuf],
+) -> anyhow::Result<PathBuf> {
+  if let Some(path) = override_path {
+    if path.is_file() {
+      return Ok(path);
     }
+    return Err(anyhow::anyhow!(
+      "BETTERDISPLAYCLI_PATH is set but does not point to a file: {}",
+      path.display()
+    ));
   }
 
-  let common_candidates = [
-    "/opt/homebrew/bin/betterdisplaycli",
-    "/usr/local/bin/betterdisplaycli",
-    "/usr/bin/betterdisplaycli",
-    "/bin/betterdisplaycli",
-  ];
-  for candidate in common_candidates {
-    let p = Path::new(candidate);
-    if p.exists() {
-      return p.to_path_buf();
+  for candidate in candidates {
+    if candidate.is_file() {
+      return Ok(candidate.clone());
     }
   }
 
-  if let Some(path_var) = std::env::var_os("PATH") {
-    for dir in std::env::split_paths(&path_var) {
-      let p = dir.join("betterdisplaycli");
-      if p.exists() {
-        return p;
-      }
-    }
+  Err(anyhow::anyhow!(
+    "Could not locate 'betterdisplaycli'. Set BETTERDISPLAYCLI_PATH or install to /opt/homebrew/bin or /usr/local/bin."
+  ))
+}
+
+fn detect_betterdisplay_path() -> anyhow::Result<PathBuf> {
+  let override_path = std::env::var_os("BETTERDISPLAYCLI_PATH").map(PathBuf::from);
+  let common_candidates = [
+    Path::new("/opt/homebrew/bin/betterdisplaycli").to_path_buf(),
+    Path::new("/usr/local/bin/betterdisplaycli").to_path_buf(),
+    Path::new("/usr/bin/betterdisplaycli").to_path_buf(),
+    Path::new("/bin/betterdisplaycli").to_path_buf(),
+  ];
+
+  resolve_betterdisplay_path(override_path, &common_candidates)
+}
+
+pub fn get_betterdisplay_path() -> anyhow::Result<PathBuf> {
+  match BETTERDISPLAY_PATH_CACHE
+    .get_or_init(|| detect_betterdisplay_path().map_err(|err| err.to_string()))
+  {
+    Ok(path) => Ok(path.clone()),
+    Err(err) => Err(anyhow::anyhow!("{}", err)),
   }
+}
 
-  error!(
-    "Could not locate 'betterdisplaycli'. Set BETTERDISPLAYCLI_PATH or install to /opt/homebrew/bin or /usr/local/bin."
-  );
-  process::exit(1);
+pub fn prime_betterdisplay_path_cache() {
+  if let Err(err) = get_betterdisplay_path() {
+    debug!("betterdisplaycli path preflight failed: {}", err);
+  }
 }
 
 pub fn set_input(input_code: u16, use_ddc_alt: bool) -> anyhow::Result<()> {
-  let betterdisplay_path = get_betterdisplay_path();
+  let betterdisplay_path = get_betterdisplay_path()?;
 
   // TODO: figure out how to make this path dynamic or configurable
   let mut cmd = Command::new(betterdisplay_path);