From ef0c23fe69688241df05f1125bea0659e691ea43 Mon Sep 17 00:00:00 2001
From: Andrew <andrew@digerati.co.nz>
Date: Tue, 23 May 2023 17:19:57 +1200
Subject: [PATCH] Allow APNG with reductions disabled

---
 src/headers.rs |  4 +++-
 src/lib.rs     | 18 ++++++++++++++++--
 src/png/mod.rs | 28 +++++++++++++++++++++-------
 tests/lib.rs   |  6 +++---
 4 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/src/headers.rs b/src/headers.rs
index 274173d7..8a70a85e 100644
--- a/src/headers.rs
+++ b/src/headers.rs
@@ -86,7 +86,9 @@ pub enum StripChunks {
 
 impl StripChunks {
     /// List of chunks that will be kept when using the `Safe` option
-    pub const KEEP_SAFE: [[u8; 4]; 4] = [*b"cICP", *b"iCCP", *b"sRGB", *b"pHYs"];
+    pub const KEEP_SAFE: [[u8; 4]; 7] = [
+        *b"cICP", *b"iCCP", *b"sRGB", *b"pHYs", *b"acTL", *b"fcTL", *b"fdAT",
+    ];
 
     pub(crate) fn keep(&self, name: &[u8; 4]) -> bool {
         match &self {
diff --git a/src/lib.rs b/src/lib.rs
index 46886f33..ddf71c1d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -32,6 +32,7 @@ use crate::png::PngImage;
 use crate::reduction::*;
 use log::{debug, info, trace, warn};
 use rayon::prelude::*;
+use std::borrow::Cow;
 use std::fmt;
 use std::fs::{copy, File, Metadata};
 use std::io::{stdin, stdout, BufWriter, Read, Write};
@@ -559,17 +560,30 @@ fn optimize_png(
     debug!("    IDAT size = {} bytes", idat_original_size);
     debug!("    File size = {} bytes", file_original_size);
 
+    // Check for APNG by presence of acTL chunk
+    let opts = if png.aux_chunks.iter().any(|c| &c.name == b"acTL") {
+        warn!("APNG detected, disabling all reductions");
+        let mut opts = opts.to_owned();
+        opts.interlace = None;
+        opts.bit_depth_reduction = false;
+        opts.color_type_reduction = false;
+        opts.palette_reduction = false;
+        opts.grayscale_reduction = false;
+        Cow::Owned(opts)
+    } else {
+        Cow::Borrowed(opts)
+    };
     let max_size = if opts.force {
         None
     } else {
         Some(png.estimated_output_size())
     };
-    if let Some(new_png) = optimize_raw(raw.clone(), opts, deadline, max_size) {
+    if let Some(new_png) = optimize_raw(raw.clone(), &opts, deadline, max_size) {
         png.raw = new_png.raw;
         png.idat_data = new_png.idat_data;
     }
 
-    postprocess_chunks(png, opts, &raw.ihdr);
+    postprocess_chunks(png, &opts, &raw.ihdr);
 
     let output = png.output();
 
diff --git a/src/png/mod.rs b/src/png/mod.rs
index 49f7a89d..c2008098 100644
--- a/src/png/mod.rs
+++ b/src/png/mod.rs
@@ -93,8 +93,16 @@ impl PngData {
         let mut aux_chunks: Vec<Chunk> = Vec::new();
         while let Some(chunk) = parse_next_chunk(byte_data, &mut byte_offset, opts.fix_errors)? {
             match &chunk.name {
-                b"IDAT" => idat_data.extend_from_slice(chunk.data),
-                b"acTL" => return Err(PngError::APNGNotSupported),
+                b"IDAT" => {
+                    if idat_data.is_empty() {
+                        // Keep track of where the first IDAT sits relative to other chunks
+                        aux_chunks.push(Chunk {
+                            name: chunk.name,
+                            data: Vec::new(),
+                        })
+                    }
+                    idat_data.extend_from_slice(chunk.data);
+                }
                 b"IHDR" | b"PLTE" | b"tRNS" => {
                     key_chunks.insert(chunk.name, chunk.data.to_owned());
                 }
@@ -165,9 +173,10 @@ impl PngData {
         ihdr_data.write_all(&[0]).ok(); // Filter method -- 5-way adaptive filtering
         ihdr_data.write_all(&[self.raw.ihdr.interlaced as u8]).ok();
         write_png_block(b"IHDR", &ihdr_data, &mut output);
-        // Ancillary chunks
-        for chunk in self
-            .aux_chunks
+        // Ancillary chunks - split into those that come before IDAT and those that come after
+        let mut aux_split = self.aux_chunks.split(|c| &c.name == b"IDAT");
+        let aux_pre = aux_split.next().unwrap();
+        for chunk in aux_pre
             .iter()
             .filter(|c| !(&c.name == b"bKGD" || &c.name == b"hIST" || &c.name == b"tRNS"))
         {
@@ -202,8 +211,7 @@ impl PngData {
             _ => {}
         }
         // Special ancillary chunks that need to come after PLTE but before IDAT
-        for chunk in self
-            .aux_chunks
+        for chunk in aux_pre
             .iter()
             .filter(|c| &c.name == b"bKGD" || &c.name == b"hIST" || &c.name == b"tRNS")
         {
@@ -211,6 +219,12 @@ impl PngData {
         }
         // IDAT data
         write_png_block(b"IDAT", &self.idat_data, &mut output);
+        // Ancillary chunks that come after IDAT
+        for aux_post in aux_split {
+            for chunk in aux_post {
+                write_png_block(&chunk.name, &chunk.data, &mut output);
+            }
+        }
         // Stream end
         write_png_block(b"IEND", &[], &mut output);
 
diff --git a/tests/lib.rs b/tests/lib.rs
index a32de8b1..3c27f8be 100644
--- a/tests/lib.rs
+++ b/tests/lib.rs
@@ -30,7 +30,7 @@ fn optimize_from_memory_apng() {
     in_file.read_to_end(&mut in_file_buf).unwrap();
 
     let result = oxipng::optimize_from_memory(&in_file_buf, &Options::default());
-    assert!(result.is_err());
+    assert!(result.is_ok());
 }
 
 #[test]
@@ -58,9 +58,9 @@ fn optimize_apng() {
     let result = oxipng::optimize(
         &"tests/files/apng_file.png".into(),
         &OutFile::Path(None),
-        &Options::default(),
+        &Options::from_preset(0),
     );
-    assert!(result.is_err());
+    assert!(result.is_ok());
 }
 
 #[test]