ROM download SHA256 testing (#568)

scripts/download_unpack_roms.sh

@@ -5,13 +5,35 @@ base_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" &> /dev/null && pwd)/.."
 unpack_dir="${base_dir}/unpack_dir"
 target_dir="${base_dir}/src/ale/python/roms"
 
+file_url="https://gist.githubusercontent.com/jjshoots/61b22aefce4456920ba99f2c36906eda/raw/00046ac3403768bfe45857610a3d333b8e35e026/Roms.tar.gz.b64"
+expected_checksum="02ca777c16476a72fa36680a2ba78f24c3ac31b2155033549a5f37a0653117de"
+temp_file="Roms.tar.gz.b64"
+
 # make the directory where we will do the unpacking
 mkdir $unpack_dir
 
-# download the ROMs from the git gist, decode it, then unpack it
-curl "https://gist.githubusercontent.com/jjshoots/61b22aefce4456920ba99f2c36906eda/raw/00046ac3403768bfe45857610a3d333b8e35e026/Roms.tar.gz.b64" \
-  | base64 --decode \
-  | tar -xzf - -C $unpack_dir
+# Download the ROMs
+curl -o "$temp_file" "$file_url"
+
+# Compute the SHA256 checksum of the ROMs file and compare with the expected checksum
+if [[ "$(uname)" == "Darwin" ]]; then
+    computed_checksum=$(shasum -a 256 "$temp_file" | awk '{ print $1 }')
+else
+    computed_checksum=$(sha256sum "$temp_file" | awk '{ print $1 }')
+fi
+
+if [ "$computed_checksum" == "$expected_checksum" ]; then
+    # Decode the base64 file and extract the tar.gz content
+    cat "$temp_file" \
+      | base64 --decode \
+      | tar -xzf - -C "$unpack_dir"
+
+    # Clean up the temporary file
+    rm -f "$temp_file"
+else
+    echo "Checksum verification failed! Exiting."
+    exit 1  # Stop the script on checksum failure
+fi
 
 # move the ROMs out into a roms folder
 mv ${unpack_dir}/ROM/*/*.bin $target_dir