introduce the hold_max option for less jumpy Seek-implementing ProgressBarIters

src/iter.rs

@@ -62,6 +62,7 @@ where
 pub struct ProgressBarIter<T> {
     pub(crate) it: T,
     pub progress: ProgressBar,
+    pub(crate) hold_max: bool,
 }
 
 impl<T> ProgressBarIter<T> {
@@ -192,6 +193,11 @@ impl<R: io::BufRead> io::BufRead for ProgressBarIter<R> {
 impl<S: io::Seek> io::Seek for ProgressBarIter<S> {
     fn seek(&mut self, f: io::SeekFrom) -> io::Result<u64> {
         self.it.seek(f).map(|pos| {
+            let pos = if self.hold_max {
+                self.progress.position().max(pos)
+            } else {
+                pos
+            };
             self.progress.set_position(pos);
             pos
         })
@@ -203,6 +209,21 @@ impl<S: io::Seek> io::Seek for ProgressBarIter<S> {
     }
 }
 
+impl<S: io::Seek> ProgressBarIter<S> {
+    /// When random seeks are executed on the underlying io object the ProgressBar will jump harshly back and forth
+    /// setting hold_max to true keeps the progress to the maximum of the current and seeked-to position.
+    pub fn set_hold_max(&mut self, hold_max: bool) {
+        self.hold_max = hold_max
+    }
+    /// Builder-like function for holding the maximum reached position
+    ///
+    /// See [`ProgressBarIter::set_hold_max()`].
+    pub fn with_hold_max(mut self, hold_max: bool) -> Self {
+        self.hold_max = hold_max;
+        self
+    }
+}
+
 #[cfg(feature = "tokio")]
 #[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
 impl<W: tokio::io::AsyncWrite + Unpin> tokio::io::AsyncWrite for ProgressBarIter<W> {
@@ -323,7 +344,11 @@ impl<W: io::Write> io::Write for ProgressBarIter<W> {
 
 impl<S, T: Iterator<Item = S>> ProgressIterator for T {
     fn progress_with(self, progress: ProgressBar) -> ProgressBarIter<Self> {
-        ProgressBarIter { it: self, progress }
+        ProgressBarIter {
+            it: self,
+            progress,
+            hold_max: false,
+        }
     }
 }
 

src/progress_bar.rs

@@ -447,6 +447,7 @@ impl ProgressBar {
         ProgressBarIter {
             progress: self.clone(),
             it: read,
+            hold_max: false,
         }
     }
 
@@ -468,6 +469,7 @@ impl ProgressBar {
         ProgressBarIter {
             progress: self.clone(),
             it: write,
+            hold_max: false,
         }
     }
 
@@ -494,6 +496,7 @@ impl ProgressBar {
         ProgressBarIter {
             progress: self.clone(),
             it: write,
+            hold_max: false,
         }
     }
 
@@ -517,6 +520,7 @@ impl ProgressBar {
         ProgressBarIter {
             progress: self.clone(),
             it: read,
+            hold_max: false,
         }
     }
 
@@ -539,6 +543,7 @@ impl ProgressBar {
         ProgressBarIter {
             progress: self.clone(),
             it: stream,
+            hold_max: false,
         }
     }
 

src/rayon.rs

@@ -41,7 +41,11 @@ where
 
 impl<S: Send, T: ParallelIterator<Item = S>> ParallelProgressIterator for T {
     fn progress_with(self, progress: ProgressBar) -> ProgressBarIter<Self> {
-        ProgressBarIter { it: self, progress }
+        ProgressBarIter {
+            it: self,
+            progress,
+            hold_max: false,
+        }
     }
 }
 
@@ -99,6 +103,7 @@ impl<T, P: Producer<Item = T>> Producer for ProgressProducer<P> {
         ProgressBarIter {
             it: self.base.into_iter(),
             progress: self.progress,
+            hold_max: false,
         }
     }