From 4fc7f3496a438d7c42064e583ffbf181b57d9143 Mon Sep 17 00:00:00 2001
From: Kornel <kornel@geekhood.net>
Date: Wed, 10 Jan 2024 17:01:45 +0000
Subject: [PATCH] Iterator interface

---
 src/reader/mod.rs  | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 tests/decode.rs    | 44 +++++++++++++++++++++++++++++++++++++++++++-
 tests/roundtrip.rs |  6 ++++++
 3 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/src/reader/mod.rs b/src/reader/mod.rs
index 32883e0..ee3dc95 100644
--- a/src/reader/mod.rs
+++ b/src/reader/mod.rs
@@ -108,6 +108,12 @@ pub struct DecodeOptions {
     allow_unknown_blocks: bool,
 }
 
+impl Default for DecodeOptions {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 impl DecodeOptions {
     /// Creates a new decoder builder
     #[must_use]
@@ -345,6 +351,8 @@ impl<R> Decoder<R> where R: Read {
     ///
     /// Do not call `Self::next_frame_info` beforehand.
     /// Deinterlaces the result.
+    ///
+    /// You can also call `.into_iter()` on the decoder to use it as a regular iterator.
     pub fn read_next_frame(&mut self) -> Result<Option<&Frame<'static>>, DecodingError> {
         if let Some(frame) = self.next_frame_info()? {
             let (width, height) = (frame.width, frame.height);
@@ -397,6 +405,14 @@ impl<R> Decoder<R> where R: Read {
         }
     }
 
+    /// This is private for iterator's use
+    fn take_current_frame(&mut self) -> Option<Frame<'static>> {
+        if self.current_frame.buffer.is_empty() {
+            return None;
+        }
+        Some(self.current_frame.take())
+    }
+
     /// Reads the data of the current frame into a pre-allocated buffer.
     ///
     /// `Self::next_frame_info` needs to be called beforehand.
@@ -516,7 +532,6 @@ impl<R> Decoder<R> where R: Read {
 
     /// Returns the color palette relevant for the frame that has been decoded
     pub fn palette(&self) -> Result<&[u8], DecodingError> {
-        // TODO prevent planic
         Ok(match self.current_frame.palette {
             Some(ref table) => table,
             None => self.global_palette.as_ref().ok_or(DecodingError::format(
@@ -559,6 +574,35 @@ impl<R> Decoder<R> where R: Read {
     }
 }
 
+impl<R: Read> IntoIterator for Decoder<R> {
+    type Item = Result<Frame<'static>, DecodingError>;
+    type IntoIter = DecoderIter<R>;
+
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        DecoderIter {
+            inner: self,
+        }
+    }
+}
+
+/// Use `decoder.into_iter()` to iterate over the frames
+pub struct DecoderIter<R: Read> {
+    inner: Decoder<R>,
+}
+
+impl<R: Read> Iterator for DecoderIter<R> {
+    type Item = Result<Frame<'static>, DecodingError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.inner.read_next_frame() {
+            Ok(Some(_)) => self.inner.take_current_frame().map(Ok),
+            Ok(None) => None,
+            Err(err) => Some(Err(err)),
+        }
+    }
+}
+
 struct InterlaceIterator {
     len: usize,
     next: usize,
diff --git a/tests/decode.rs b/tests/decode.rs
index 99d5069..4c09760 100644
--- a/tests/decode.rs
+++ b/tests/decode.rs
@@ -1,4 +1,4 @@
-use gif::{DecodeOptions, DisposalMethod, Encoder, Frame};
+use gif::{Decoder, DecodeOptions, DisposalMethod, Encoder, Frame};
 
 #[test]
 fn frame_consistency_is_configurable() {
@@ -83,6 +83,48 @@ fn check_for_end_code_is_configurable() {
     }
 }
 
+#[test]
+fn check_rebuild_without_reencode1() {
+    rebuild_without_reencode(include_bytes!("samples/gifplayer-muybridge.gif"));
+}
+
+#[test]
+fn check_rebuild_without_reencode2() {
+    rebuild_without_reencode(include_bytes!("samples/interlaced.gif"));
+}
+
+fn rebuild_without_reencode(image: &[u8]) {
+    let mut options = DecodeOptions::new();
+    options.skip_frame_decoding(true);
+    let mut decoder = options.read_info(&image[..]).unwrap();
+
+    let mut encoder = Encoder::new(Vec::new(), decoder.width(), decoder.height(), decoder.global_palette().unwrap_or_default()).unwrap();
+
+    let mut num_frames = 0;
+    while let Some(frame) = decoder.read_next_frame().unwrap() {
+        num_frames += 1;
+        encoder.write_lzw_pre_encoded_frame(&frame).unwrap();
+    }
+
+    let gif = encoder.into_inner().unwrap();
+    let rebuilt = Decoder::new(&gif[..]).unwrap();
+    let orig = Decoder::new(&image[..]).unwrap();
+
+    for (orig, rebuilt) in orig.into_iter().zip(rebuilt) {
+        num_frames -= 1;
+        let orig = orig.unwrap();
+        let rebuilt = rebuilt.unwrap();
+        assert_eq!(orig.delay, rebuilt.delay);
+        assert_eq!(orig.transparent, rebuilt.transparent);
+        assert_eq!(orig.palette, rebuilt.palette);
+        assert_eq!(orig.width, rebuilt.width);
+        assert_eq!(orig.height, rebuilt.height);
+        assert_eq!(orig.interlaced, rebuilt.interlaced);
+        assert_eq!(orig.buffer, rebuilt.buffer);
+    }
+    assert_eq!(num_frames, 0);
+}
+
 #[test]
 fn check_skip_frame_data() {
     let image: &[u8] = include_bytes!("samples/moon_impact.gif");
diff --git a/tests/roundtrip.rs b/tests/roundtrip.rs
index 953cf6d..2d56aa1 100644
--- a/tests/roundtrip.rs
+++ b/tests/roundtrip.rs
@@ -6,6 +6,12 @@ fn encode_roundtrip() {
     round_trip_from_image(ORIGINAL);
 }
 
+#[test]
+fn encode_roundtrip2() {
+    const ORIGINAL: &[u8] = include_bytes!("samples/interlaced.gif");
+    round_trip_from_image(ORIGINAL);
+}
+
 fn round_trip_from_image(original: &[u8]) {
     let (width, height, global_palette, repeat);
     let frames: Vec<_> = {