From f17d2b6201bad85a12d7b4b2c54c0d30165af8c5 Mon Sep 17 00:00:00 2001
From: Ivan Smirnov <i.s.smirnov@gmail.com>
Date: Wed, 1 Dec 2021 16:01:58 +0000
Subject: [PATCH] Add decode::qoi_decode_header()

---
 src/decode.rs | 16 ++++++++++++++++
 src/lib.rs    |  2 +-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/decode.rs b/src/decode.rs
index 669599b..28a355e 100644
--- a/src/decode.rs
+++ b/src/decode.rs
@@ -178,3 +178,19 @@ pub fn qoi_decode_to_vec(data: impl AsRef<[u8]>, channels: u8) -> Result<(Header
         _ => Err(Error::InvalidChannels { channels }),
     }
 }
+
+#[inline]
+pub fn qoi_decode_header(data: impl AsRef<[u8]>) -> Result<Header> {
+    let data = data.as_ref();
+    if data.len() < QOI_HEADER_SIZE {
+        return Err(Error::InputBufferTooSmall { size: data.len(), required: QOI_HEADER_SIZE });
+    }
+    let header = unsafe {
+        // Safety: we have just checked the length above
+        Header::from_bytes(*(data.as_ptr() as *const _))
+    };
+    if header.magic != QOI_MAGIC {
+        return Err(Error::InvalidMagic { magic: header.magic });
+    }
+    Ok(header)
+}
diff --git a/src/lib.rs b/src/lib.rs
index 6221cd7..a2eef47 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,7 +10,7 @@ pub mod canonical;
 pub mod consts;
 
 pub use crate::colorspace::ColorSpace;
-pub use crate::decode::qoi_decode_to_vec;
+pub use crate::decode::{qoi_decode_header, qoi_decode_to_vec};
 pub use crate::encode::{encode_size_required, qoi_encode_to_buf, qoi_encode_to_vec};
 pub use crate::error::{Error, Result};
 pub use crate::header::Header;