class

BakedFileSystem::BakedFile

Inherits IO < Reference < Object

BakedFile represents a virtual file in a BakedFileSystem.

BakedFile is a read-only IO wrapper around files embedded at compile-time. Write operations will raise ReadOnlyError since embedded files cannot be modified at runtime.

Architecture

Files are stored compressed in the binary's read-only data section as byte slices. On first access, BakedFile creates:

  1. Memory IO: Wraps the compressed byte slice
  2. Gzip Reader: Wraps the memory IO for transparent decompression
  3. Wrapped IO: Either the memory IO (for .gz files) or gzip reader

This lazy-loading approach minimizes memory usage:

  • Compressed data stays in read-only binary section
  • Decompression happens on-demand during read
  • No heap allocation unless content is explicitly stored

Streaming Behavior

BakedFile is a forward-only stream by default:

  • Read operations consume the stream
  • Call rewind to return to the beginning
  • Each rewind recreates the decompression reader (see #rewind for details)

Thread Safety

Each call to get() or get?() returns a new BakedFile instance with independent state, making concurrent access safe.

Usage

file = MyFileSystem.get("hello-world.txt")
file.path        # => "hello-world.txt"
file.size        # => 12
file.gets_to_end # => "Hello World\n"
file.compressed? # => false

Constructors

new(path : String, size : Int32, compressed : Bool, slice : Bytes)

Instance methods

close

Closes the file and releases resources. Can be called multiple times safely. After closing, read operations will raise IO::Error.

closed?

Returns true if the file has been closed.

compressed?

Returns whether this file is compressed. If not, it is decompressed on read.

compressed_size

Returns the compressed size of this virtual file.

See #size for the real size of the (uncompressed) file.

finalize

Ensures resources are freed when the object is garbage collected.

path

Returns the path in the virtual file system.

read(slice : Bytes)

Reads at most slice.size bytes from this IO into slice. Returns the number of bytes read, which is 0 if and only if there is no more data to read (so checking for 0 is the way to detect end of file).

io = IO::Memory.new "hello"
slice = Bytes.new(4)
io.read(slice) # => 4
slice          # => Bytes[104, 101, 108, 108]
io.read(slice) # => 1
slice          # => Bytes[111, 101, 108, 108]
io.read(slice) # => 0
read

Return the data for this file as a String.

DEPRECATED: BakedFile can be used as an IO directly. Use gets_to_end instead

rewind

Rewinds the file to the beginning for re-reading.

Implementation Note

This method recreates the gzip decompression reader instead of rewinding it because Compress::Gzip::Reader is a forward-only stream that doesn't support seeking backward. This is intentional and necessary for correct behavior.

Why Recreation is Required

  • Compress::Gzip::Reader maintains internal state during decompression
  • This state cannot be reset to return to the beginning
  • Creating a new reader over the rewound underlying stream is the only way to re-read

Performance Implications

  • Creating a new reader is fast (no decompression happens yet)
  • Decompression happens on-demand during read operations
  • Memory usage is minimal (same underlying byte slice is reused)
  • This is the standard approach for streaming decompression

Alternatives Considered

Cache decompressed content:

  • Pro: True rewind without recreation
  • Con: Significant memory overhead (defeats purpose of streaming)
  • Con: Not suitable for large files
  • Decision: Rejected

Add seeking to Gzip::Reader:

  • Pro: More intuitive API
  • Con: Requires changes to Crystal standard library
  • Con: Decompression algorithms are inherently forward-only
  • Decision: Not feasible
size

Returns the size of this virtual file.

to_encoded(compressed = true)

Return the data for this file as a URL-safe Base64-encoded String.

DEPRECATED: BakedFile can be used as an IO directly.

to_slice(compressed)

Return the file's data as a Slice(UInt8)

DEPRECATED: BakedFile can be used as an IO directly.

to_slice

Returns a Bytes holding the (compressed) content of this virtual file. This data needs to be extracted using a Compress::Gzip::Reader unless #compressed? is true.

write(slice : Bytes) : Nil

Writes the contents of slice into this IO.

io = IO::Memory.new
slice = Bytes.new(4) { |i| ('a'.ord + i).to_u8 }
io.write(slice)
io.to_s # => "abcd"
write_to_io(io, compressed = true)

Write the file's data to the given IO, minimizing any memory copies or unnecessary conversions.

DEPRECATED: BakedFile can be used as an IO directly.