add startup_poll_input config option

Add a `startup_poll_input` config option (default: true).   If set to false,
streampager will not poll input during the delayed or direct mode startup
phase.  This means input typed before the pager exits early for these modes
will remain in the terminal input buffer (e.g. for a subsequent command
passed to the shell).

Note that a side-effect of this is is that we also miss SIGWINCH events, as
they come from the termiz terminal on the same event stream.

Fixes #39.

Author: markbt

README.md

@@ -116,6 +116,7 @@ varies by platform; on Linux it is typically `~/.config`.
 interface_mode = "delayed"
 scroll_past_eof = true
 read_ahead_lines = 20000
+startup_poll_input = true
 wrapping_mode = "word"
 keymap = "mykeymap"
 ```

src/config.rs

@@ -164,6 +164,9 @@ pub struct Config {
     /// Specify how many lines to read ahead.
     pub read_ahead_lines: usize,
 
+    /// Specify whether to poll input during start-up (delayed or direct mode).
+    pub startup_poll_input: bool,
+
     /// Specify default wrapping move.
     pub wrapping_mode: WrappingMode,
 
@@ -177,6 +180,7 @@ impl Default for Config {
             interface_mode: Default::default(),
             scroll_past_eof: true,
             read_ahead_lines: crate::file::DEFAULT_NEEDED_LINES,
+            startup_poll_input: true,
             wrapping_mode: Default::default(),
             keymap: Default::default(),
         }

src/direct.rs

@@ -64,6 +64,7 @@ pub(crate) fn direct<T: Terminal>(
     progress: Option<&Progress>,
     events: &mut EventStream,
     mode: InterfaceMode,
+    poll_input: bool,
 ) -> Result<Outcome> {
     if mode == InterfaceMode::FullScreen {
         return Ok(Outcome::RenderNothing);
@@ -138,8 +139,18 @@ pub(crate) fn direct<T: Terminal>(
     let mut size = term.get_screen_size().map_err(Error::Termwiz)?;
     let mut loaded = BitSet::with_capacity(loading.capacity());
     let mut remaining = output_files.len() + error_files.len();
+    let interval = Duration::from_millis(10);
     while remaining > 0 {
-        match events.get(term, Some(Duration::from_millis(10)))? {
+        let maybe_event = if poll_input {
+            events.get(term, Some(interval))?
+        } else {
+            events.try_recv()?.or_else(|| {
+                // Sleep to avoid busy wait
+                std::thread::sleep(interval);
+                None
+            })
+        };
+        match maybe_event {
             Some(Event::Loaded(i)) => {
                 if loading.contains(i) && loaded.insert(i) {
                     remaining -= 1;

src/display.rs

@@ -185,6 +185,7 @@ pub(crate) fn start(
             progress.as_ref(),
             &mut events,
             config.interface_mode,
+            config.startup_poll_input,
         )?
     };
     match outcome {

src/event.rs

@@ -104,7 +104,7 @@ impl EventStream {
         ActionSender::new(self.sender())
     }
 
-    fn try_recv(&self) -> Result<Option<Event>, Error> {
+    pub(crate) fn try_recv(&self) -> Result<Option<Event>, Error> {
         match self.recv.try_recv() {
             Ok(Envelope::Normal(event)) => Ok(Some(event)),
             Ok(Envelope::Unique(event, unique)) => {

src/pager.rs

@@ -211,6 +211,11 @@ impl Pager {
         self.config.read_ahead_lines = lines;
     }
 
+    /// Set whether to poll input during start-up (delayed or direct mode).
+    pub fn set_startup_poll_input(&mut self, poll_input: bool) {
+        self.config.startup_poll_input = poll_input;
+    }
+
     /// Set default wrapping mode. See [`WrappingMode`] for details.
     pub fn set_wrapping_mode(&mut self, value: impl Into<WrappingMode>) {
         self.config.wrapping_mode = value.into();