Add a fuzz target for the decoder

fuzz/Cargo.toml

@@ -23,3 +23,9 @@ name = "qoi_encode"
 path = "fuzz_targets/qoi_encode.rs"
 test = false
 doc = false
+
+[[bin]]
+name = "qoi_decode"
+path = "fuzz_targets/qoi_decode.rs"
+test = false
+doc = false

fuzz/fuzz_targets/qoi_decode.rs

@@ -0,0 +1,37 @@
+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|input: (u16, u16, bool, &[u8])| {
+    let (w, h, is_4, data) = input;
+    let (w, h) = (w % 300, h % 300);
+    let channels = if is_4 { 4 } else { 3 };
+
+    let mut vec = vec![
+        b'q',
+        b'o',
+        b'i',
+        b'f',
+        0,
+        0,
+        (w >> 8) as u8,
+        (w & 0xff) as u8,
+        0,
+        0,
+        (h >> 8) as u8,
+        (h & 0xff) as u8,
+        channels,
+        0,
+    ];
+    vec.extend(&*data);
+    vec.extend(&[0, 0, 0, 0]);
+
+    let out = qoi_fast::qoi_decode_to_vec(&vec, channels);
+    if let Ok((header, out)) = out {
+        assert_eq!(header.magic, qoi_fast::consts::QOI_MAGIC);
+        assert_eq!(header.width, w as u32);
+        assert_eq!(header.height, h as u32);
+        assert_eq!(header.channels, channels);
+        assert_eq!(header.colorspace.to_u8(), 0);
+        assert_eq!(out.len(), w as usize * h as usize * channels as usize);
+    }
+});