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src/file.rs

@@ -0,0 +1,45 @@
+use std::{fs::File, task::Waker, io::Write, path::PathBuf};
+
+pub trait LiveWriter: Write {
+    fn add_waker(&mut self, waker: Waker);
+}
+
+/// A simple wrapper for a file that can be read while we're still appending data
+pub struct LiveFileWriter {
+    file: File,
+    /// Wake handles for contexts that are waiting for us to write more
+    wakers: Vec<Waker>,
+}
+
+impl LiveFileWriter {
+    pub fn new(path: &PathBuf) -> std::io::Result<Self> {
+        Ok(Self {
+            file: File::options().write(true).create_new(true).open(path)?,
+            wakers: Vec::new(),
+        })
+    }
+}
+
+impl LiveWriter for LiveFileWriter {
+    fn add_waker(&mut self, waker: Waker) {
+        self.wakers.push(waker);
+    }
+}
+
+impl Write for LiveFileWriter {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let result = self.file.write(buf);
+        if let Ok(n) = result {
+            if n > 0 {
+                for waker in self.wakers.drain(..) {
+                    waker.wake();
+                }
+            }
+        }
+        result
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        self.file.flush()
+    }
+}