verbose zip headers

Author: milahu

builder.sh

@@ -16,20 +16,71 @@ mkdir -p "$out"/bin
 cp $runtimeScript "$out"/bin/nix-portable.zip
 chmod +w "$out"/bin/nix-portable.zip
 
+file_name=runtimeScript.sh
+file_name_size_hex=$(printf "%04x" ${#file_name} | tac -rs ..)
+file_name_hex=$(echo -n "$file_name" | xxd -p)
+
+# note: zip fails to extract the file because the local file header comes after the file contents
+
 # Local file header
-sizeA=$(printf "%08x" $(stat -c "%s" "$out"/bin/nix-portable.zip) | tac -rs ..)
-echo 504b 0304 0000 0000 0000 0000 0000 0000 | xxd -r -p >> "$out"/bin/nix-portable.zip
-echo 0000 0000 0000 0000 0000 0200 0000 4242 | xxd -r -p >> "$out"/bin/nix-portable.zip
+local_file_header_offset_hex=$(printf "%08x" $(stat -c "%s" "$out"/bin/nix-portable.zip) | tac -rs ..)
+{
+  echo 50 4b 03 04 # Local file header signature
+  echo 00 00 # Version needed to extract (minimum)
+  echo 00 00 # General purpose bit flag
+  echo 00 00 # Compression method
+  echo 00 00 # File last modification time
+  echo 00 00 # File last modification date
+  echo 00 00 00 00 # CRC-32 of uncompressed data
+  echo 00 00 00 00 # Compressed size
+  echo 00 00 00 00 # Uncompressed size
+  echo $file_name_size_hex # File name length (n)
+  echo 00 00 # Extra field length (m)
+  echo $file_name_hex # File name
+  # Extra field
+} | xxd -r -p >> "$out"/bin/nix-portable.zip
 
 # Central directory file header
-sizeB=$(printf "%08x" $(stat -c "%s" "$out"/bin/nix-portable.zip) | tac -rs ..)
-echo 504b 0102 0000 0000 0000 0000 0000 0000 | xxd -r -p >> "$out"/bin/nix-portable.zip
-echo 0000 0000 0000 0000 0000 0000 0200 0000 | xxd -r -p >> "$out"/bin/nix-portable.zip
-echo 0000 0000 0000 0000 0000 "$sizeA" 4242 | xxd -r -p >> "$out"/bin/nix-portable.zip
+central_directory_file_header_offset_hex=$(printf "%08x" $(stat -c "%s" "$out"/bin/nix-portable.zip) | tac -rs ..)
+{
+  echo 50 4b 01 02 # Central directory file header signature
+  echo 00 00 # Version made by
+  echo 00 00 # Version needed to extract (minimum)
+  echo 00 00 # General purpose bit flag
+  echo 00 00 # Compression method
+  echo 00 00 # File last modification time
+  echo 00 00 # File last modification date
+  echo 00 00 00 00 # CRC-32 of uncompressed data
+  echo 00 00 00 00 # Compressed size
+  echo 00 00 00 00 # Uncompressed size
+  echo $file_name_size_hex # File name length (n)
+  echo 00 00 # Extra field length (m)
+  echo 00 00 # File comment length (k)
+  echo 00 00 # Disk number where file starts (or 0xffff for ZIP64)
+  echo 00 00 # Internal file attributes
+  echo 00 00 00 00 # External file attributes
+  echo "$local_file_header_offset_hex" # Relative offset of local file header
+  echo $file_name_hex # File name
+  # Extra field
+  # File comment
+} | xxd -r -p >> "$out"/bin/nix-portable.zip
+
+# 62 -> 3e 00 00 00
+central_directory_size_hex=$(printf "%08x" $((46 + ${#file_name})) | tac -rs ..)
 
 # End of central directory record
-echo 504b 0506 0000 0000 0000 0100 3000 0000 | xxd -r -p >> "$out"/bin/nix-portable.zip
-echo "$sizeB" 0000 0000 0000 0000 0000 0000 | xxd -r -p >> "$out"/bin/nix-portable.zip
+{
+  echo 50 4b 05 06 # End of central directory signature
+  echo 00 00 # Number of this disk
+  echo 00 00 # Disk where central directory starts
+  echo 00 00 # Number of central directory records on this disk
+  echo 01 00 # Total number of central directory records
+  echo $central_directory_size_hex # Size of central directory (bytes)
+  echo "$central_directory_file_header_offset_hex" # Offset of start of central directory, relative to start of archive
+  echo 00 00 # Comment length
+  # Comment
+  echo 00 00 00 00 00 00 00 00 00 00 # 10 null bytes (?)
+} | xxd -r -p >> "$out"/bin/nix-portable.zip
 
 unzip -vl "$out"/bin/nix-portable.zip