Rust black magic, but this is considerably faster

src/main.rs

@@ -148,11 +148,9 @@ fn unfuck_color_type(color_type: &str) -> Result<ColorType> {
 }
 
 #[allow(clippy::too_many_lines)] // bruh
-fn decoder(inputfile: &str, outputfile: &str) -> Result<()> {
+fn decoder(inputfile: &str) -> Result<(u32, u32, ColorType, ArrayVec<String, 124_usize>, ArrayVec<String, 124_usize>, Vec<u8>)> {
     let infile = File::open(inputfile)?;
-    let outfile = File::create(outputfile)?;
     let mut lines = BufReader::new(infile).lines();
-    let rawriter = BufWriter::new(outfile);
 
     // "CIF: <flags>"
     if !lines.next().transpose()?.ok_or(InvalidHeaderError)?.starts_with("CIF:") {
@@ -204,14 +202,12 @@ fn decoder(inputfile: &str, outputfile: &str) -> Result<()> {
         return Err(NoDataError)
     }
 
-    let mut outpng = png::Encoder::new(rawriter, width, height);
-    outpng.set_color(format);
-    outpng.set_depth(BitDepth::Eight);
-
     let bytes_per_pixel = if format == ColorType::Rgb { 3 } else { 4 };
 
     let mut md_keylock = false;
     let mut md_key = ArrayString::<2048>::new();
+    let mut md_key_vec = ArrayVec::<String, 124>::new();
+    let mut md_val = ArrayVec::<String, 124>::new();
 
     let first = loop {
         if let Some(line) = lines_read_noempty(&mut lines)? {
@@ -221,7 +217,8 @@ fn decoder(inputfile: &str, outputfile: &str) -> Result<()> {
                 if split.len() != 2 {
                     continue
                 }
-                outpng.add_itxt_chunk(md_key.to_string(), split[1].trim_start().to_string())?;
+                md_key_vec.push(md_key.to_string());
+                md_val.push(split[1].trim_start().to_string());
                 md_keylock = false;
                 md_key.clear();
                 continue
@@ -233,12 +230,13 @@ fn decoder(inputfile: &str, outputfile: &str) -> Result<()> {
                     1 => {
                         md_key.try_push_str(&sline)?;
                         md_keylock = true;
-                    },
+                    }
                     _ => {
                         md_key.try_push_str(&sline)?;
-                        outpng.add_itxt_chunk(split[0].trim_start().to_string(), split[1].trim_start().to_string())?;
+                        md_key_vec.push(split[0].trim_start().to_string());
+                        md_val.push(split[1].trim_start().to_string());
                         md_key.clear();
-                    },
+                    }
                 }
                 continue
             }
@@ -247,8 +245,6 @@ fn decoder(inputfile: &str, outputfile: &str) -> Result<()> {
         return Err(NoDataError)
     };
 
-    let mut outpng = outpng.write_header()?;
-
     let mut pixmap = Vec::with_capacity((bytes_per_pixel * width * height) as usize);
 
     if !first.is_empty() {
@@ -271,8 +267,26 @@ fn decoder(inputfile: &str, outputfile: &str) -> Result<()> {
         }
     }
 
-    outpng.write_image_data(&pixmap)?;
+    Ok((width, height, format, md_key_vec, md_val, pixmap))
+}
 
+fn write_png(outfile: &str, width: u32, height: u32, format: ColorType, md_key: ArrayVec<String, 124>, md_val: ArrayVec<String, 124>, pixmap: Vec<u8>) -> Result<()> {
+    let outfile = File::create(outfile)?;
+    let rawriter = BufWriter::new(outfile);
+    let mut outpng = png::Encoder::new(rawriter, width, height);
+
+    for i in 0..md_key.len() {
+        if md_key[i].is_empty() {
+            break
+        }
+        outpng.add_itxt_chunk(md_key[i].clone(), md_val[i].clone())?;
+    }
+
+    outpng.set_color(format);
+    outpng.set_depth(BitDepth::Eight);
+
+    let mut outpng = outpng.write_header()?;
+    outpng.write_image_data(&pixmap)?;
     Ok(())
 }
 
@@ -282,8 +296,13 @@ fn main() {
         eprintln!("Invalid usage:\nUsage: zardzewialy-dekoder-cif <input cif file> <output bmp file>");
         process::exit(1);
     }
-    if let Err(e) = decoder(&argv[0], &argv[1]) {
-        eprintln!("Error: {}", e);
+    let data = decoder(&argv[0]);
+    if let Err(e) = data {
+        eprintln!("Error while parsing cif: {}", e);
         process::exit(1);
     }
+    let data = data.unwrap();
+    if let Err(e) = write_png(&argv[1], data.0, data.1, data.2, data.3, data.4, data.5) {
+        eprintln!("Error while writing image: {}", e);
+    }
 }