Lake is a Go library that provides a unified interface for reading and writing collections of files across different storage backends: filesystem directories, ZIP archives, and single files. It is part of the itch.io ecosystem and primarily used by wharf.

A Pool gives indexed read/seek access to an ordered list of files. Pools are backed by different storage types but expose the same interface:

type Pool interface {
    GetSize(fileIndex int64) int64
    GetReader(fileIndex int64) (io.Reader, error)
    GetReadSeeker(fileIndex int64) (io.ReadSeeker, error)
    Close() error
}

WritablePool extends Pool with write access, and CaseFixerPool handles renaming on-disk files to match a container's expected casing (useful for case-insensitive filesystems).

The tlc.Container is a protobuf-based metadata format that captures a complete directory structure: files, directories, and symlinks with their sizes, permissions, and paths. Containers are produced by walking a directory or ZIP archive, and can be used to recreate that structure on disk.

wharf embeds Container structs serialized via protobuf in patch files (.pwr) and signature files to describe both the "old" and "new" versions of a build, paired with binary diffs of the actual file contents. butler is the CLI that drives wharf to produce and apply these patches for itch.io uploads.

Lake does not define the patch format itself, it provides the filesystem abstraction layer and directory manifest that wharf builds on top of.

Core interfaces: Pool, WritablePool, CaseFixerPool, and case-fix helpers.

Container type and filesystem operations:

• Walking: WalkDir, WalkZip, WalkAny (auto-detects), WalkSingle
• Preparing: Container.Prepare creates all directories, files, and symlinks from a container spec
• Validation: Container integrity checks
• Comparison: Diff containers to detect changes
• Permissions: Executable detection (ELF, Mach-O, shell scripts)
• Case handling: Cross-platform case-insensitive filesystem support
• Filtering: FilterFunc and built-in PresetFilter to ignore VCS metadata, OS junk files, etc.

Pool implementations for different backends:

import (
    "github.com/itchio/lake/tlc"
    "github.com/itchio/lake/pools/fspool"
)

// Walk a directory to get its container (file listing)
container, err := tlc.WalkDir("/path/to/dir", tlc.WalkOpts{
    Filter: tlc.PresetFilter,
})

// Open a filesystem pool for reading
pool := fspool.New(container, "/path/to/dir")
defer pool.Close()

reader, err := pool.GetReader(0) // read first file

MIT