From 97ba8c745f40634d32fd6708e097bb2870f87787 Mon Sep 17 00:00:00 2001
From: Ryan Oldenburg <ryan@guzba.com>
Date: Sat, 11 Jun 2022 16:10:52 -0500
Subject: [PATCH] update png crc handling

---
 src/pixie/fileformats/png.nim | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/pixie/fileformats/png.nim b/src/pixie/fileformats/png.nim
index 79e3a14..7f2f717 100644
--- a/src/pixie/fileformats/png.nim
+++ b/src/pixie/fileformats/png.nim
@@ -21,8 +21,8 @@ type
 template failInvalid() =
   raise newException(PixieError, "Invalid PNG buffer, unable to load")
 
-# template failCRC() =
-#   raise newException(PixieError, "CRC check failed")
+template failCRC() =
+  raise newException(PixieError, "CRC check failed")
 
 when defined(release):
   {.push checks: off.}
@@ -400,8 +400,9 @@ proc decodePng*(data: pointer, len: int): Png {.raises: [PixieError].} =
   prevChunkType = "IHDR"
   inc(pos, 13)
 
-  # if crc32(data[pos - 17 ..< pos]) != read32be(data, pos):
-  #   failCRC()
+  let headerCrc = crc32(data[pos - 17].addr, 17)
+  if headerCrc != data.readUint32(pos).swap():
+    failCRC()
   inc(pos, 4) # CRC
 
   while true:
@@ -462,8 +463,9 @@ proc decodePng*(data: pointer, len: int): Png {.raises: [PixieError].} =
 
     inc(pos, chunkLen)
 
-    # if crc32(data[pos - chunkLen - 4 ..< pos]) != read32be(data, pos):
-    #   failCRC()
+    let chunkCrc = crc32(data[pos - chunkLen - 4].addr, chunkLen + 4)
+    if chunkCrc != data.readUint32(pos).swap():
+      failCRC()
     inc(pos, 4) # CRC
 
     prevChunkType = chunkType
@@ -523,7 +525,7 @@ proc encodePng*(
   result.add(0.char)
   result.add(0.char)
   result.add(0.char)
-  result.addUint32(crc32(result[result.len - 17 ..< result.len]).swap())
+  result.addUint32(crc32(result[result.len - 17].addr, 17).swap())
 
   # Add IDAT
   # Add room for 1 byte before each row for the filter type.
@@ -556,14 +558,15 @@ proc encodePng*(
   result.addUint32(compressed.len.uint32.swap())
   result.add("IDAT")
   result.add(compressed)
-  result.addUint32(
-    crc32(result[result.len - compressed.len - 4 ..< result.len]).swap()
-  )
+  result.addUint32(crc32(
+    result[result.len - compressed.len - 4].addr,
+    compressed.len + 4
+  ).swap())
 
   # Add IEND
   result.addUint32(0)
   result.add("IEND")
-  result.addUint32(crc32(result[result.len - 4 ..< result.len]).swap())
+  result.addUint32(crc32(result[result.len - 4].addr, 4).swap())
 
 proc encodePng*(png: Png): string {.raises: [PixieError].} =
   encodePng(png.width, png.height, 4, png.data[0].addr, png.data.len * 4)