seeking logic

1 files changed, 64 insertions, 0 deletions

diff --git a/remuxer/src/trim_writer.rs b/remuxer/src/trim_writer.rs
new file mode 100644
index 0000000..65d3589
--- /dev/null
+++ b/remuxer/src/trim_writer.rs
@@ -0,0 +1,64 @@
+use std::{
+    io::{Seek, Write},
+    ops::Range,
+};
+
+use anyhow::anyhow;
+use log::warn;
+
+pub struct TrimWriter<W> {
+    inner: W,
+    position: usize,
+    range: Range<usize>,
+}
+impl<W: Write> TrimWriter<W> {
+    pub fn new(inner: W, range: Range<usize>) -> Self {
+        Self {
+            inner,
+            range,
+            position: 0,
+        }
+    }
+}
+
+impl<W: Write> Write for TrimWriter<W> {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let start = self.range.start as isize - self.position as isize;
+        let end = self.range.end as isize - self.position as isize;
+
+        let start = start.clamp(0, buf.len() as isize) as usize;
+        let end = end.clamp(0, buf.len() as isize) as usize;
+
+        if self.position >= self.range.end {
+            return Err(std::io::Error::new(
+                std::io::ErrorKind::Other,
+                anyhow!("range ended"),
+            ));
+        }
+
+        let buf = &buf[start..end];
+        if !buf.is_empty() {
+            self.inner.write_all(buf)?;
+            self.position += buf.len()
+        }
+        Ok(buf.len())
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        self.inner.flush()
+    }
+}
+
+impl<W> Seek for TrimWriter<W> {
+    fn seek(&mut self, pos: std::io::SeekFrom) -> std::io::Result<u64> {
+        match pos {
+            std::io::SeekFrom::Start(s) => self.position = s as usize,
+            std::io::SeekFrom::End(_) => unimplemented!(),
+            std::io::SeekFrom::Current(s) => self.position += s as usize,
+        }
+        if self.position < self.range.end {
+            warn!("seeked beyond end")
+        }
+        Ok(self.position as u64)
+    }
+}