SteamCache2

SteamCache2 is a blazing fast download cache for Steam, designed to reduce bandwidth usage and speed up game downloads.

Features

• High-speed caching for Steam downloads
• Tiered storage for getting the most out of your storage media
• Garbage Collected storage for limiting the size of RAM or Disk cache and will not go above what you choose or stop caching unlike others
• Reduces bandwidth usage
• Easy to set up and configure aside from dns stuff to trick Steam into using it
• Supports multiple clients
• NEW: YAML configuration system with automatic config generation
• NEW: Simple Makefile for development workflow
• Cross-platform builds (Linux, macOS, Windows)

Quick Start

First Time Setup

1. Clone and build:

   git clone <repository-url>
   cd steamcache2
   make  # This will run tests and build the application
   

2. Run the application (it will create a default config):

   ./steamcache2
   # or on Windows:
   steamcache2.exe
   

   The application will automatically create a config.yaml file with default settings and exit, allowing you to customize it.

3. Edit the configuration (config.yaml):

   listen_address: :80
   cache:
       memory:
           size: 1GB
           gc_algorithm: lru
       disk:
           size: 10GB
           path: ./disk
           gc_algorithm: hybrid
   upstream: "https://steam.cdn.com"  # Set your upstream server
   

4. Run the application again:

   make run  # or ./steamcache2
   

Development Workflow

Use make for the majority of common development tasks. The Makefile handles running tests, linting, hygiene checks, building, running the application, and other routine boilerplate work.

Run make help to see the full list of available commands.

This is the preferred approach for day-to-day development. Avoid running raw go test, go run, or golangci-lint commands directly for routine tasks.

Validating Full Functionality with external tools

steamcache2 provides a convenient small-cache configuration and helper targets so you can easily validate behavior using external tools such as SteamPrefill (tpill90/steam-lancache-prefill).

This gives you:

• Real Steam manifest + chunk traffic (no reinventing the wheel)
• Excellent benchmark setup / benchmark run workflow with warmup, randomization, and mixed chunk sizes
• The ability to validate a just-built binary end-to-end (caching, coalescing, Range support, memory+disk tiers, GC/eviction, metrics, special endpoints, startup validation, etc.)

Quick Start

# 1. Build the binary (this also runs short tests)
make build

# 2. Start a validation-oriented instance (small caches so disk tier + GC get exercised)
#    Uses port 80 by default; the script will automatically set the needed
#    capability on the binary via sudo setcap if it is missing.
./scripts/validate-with-prefill.sh

# 3. In another terminal (or on another machine), create a workload once if you haven't already,
#    then drive it through your local steamcache2.
#    Note: when using a non-80 port you may need to give SteamPrefill the full address.
./scripts/validate-with-prefill.sh   # (shows the exact commands with the correct port)

When the benchmark finishes, press Ctrl-C in the first terminal to cleanly stop the server.

Simple validation server (recommended for manual testing)

For easy validation with external tools (SteamPrefill, etc.), use:

make run-validation
# or
make validate

This starts steamcache2 on port 80 using a deliberately small memory + disk configuration (good for exercising the disk tier, GC, coalescing, promotions, etc.).

make run-validation (and make validate) will automatically ensure the cap_net_bind_service capability is set on the binary it just built (one sudo prompt the first time after each rebuild). This keeps the server running as your normal user so the disk cache directory stays owned by you.

If you want the capability on the binary for other workflows (e.g. make run, or running the binary directly on port 80), use the explicit target:

make setcap

When the server is running, point your external SteamPrefill (or other load generator) at it:

./SteamPrefill benchmark run ...

When finished, you can get a quick metrics summary with:

make validate-check

This is the recommended simple workflow. No automatic downloading or running of external tools.

Inspecting the Result

After a benchmark run you can ask for a quick report:

make validate-check
# or manually:
curl -s http://localhost/metrics

Look for:

• High cache hit rate after the warmup pass
• Non-zero coalesced and disk activity
• Zero unexpected errors

The Validation Config

The script uses docs/examples/validate-config.yaml. It enables both memory and disk tiers at modest sizes (128 MB / 512 MB) with conservative concurrency. Edit or copy it if you need larger caches for bigger workloads.

What Gets Validated

Running a realistic SteamPrefill benchmark workload through a built steamcache2 exercises the complete public surface that matters for production use:

• Steam User-Agent detection and depot/manifest/chunk URL patterns
• Full MISS → cache write → HIT (and HIT-COALESCED) paths
• Range request handling from cached full responses
• Request coalescing under concurrent load
• Memory tier + disk tier interaction (including async disk attach)
• Garbage collection and eviction under pressure
• Metrics and special endpoints (/, /lancache-heartbeat, /metrics)
• Per-client and global rate limiting (with trusted proxy handling)
• Startup configuration validation and upstream behavior
• Clean shutdown hygiene

This is the closest practical equivalent to "run the thing real clients will run and make sure nothing is broken."

Troubleshooting

• Low hit rate on first run: Normal. The first benchmark run is the warmup that populates the cache.
• Want to test real disk I/O (not RAM cache): Make sure your workload size (shown by benchmark setup) is larger than the total RAM on the machine running steamcache2.
• Server won't start or bind on port 80 as non-root: make run-validation and make validate automatically run setcap on the binary they just built. If it still fails, run make setcap explicitly and retry. The server always runs as your normal user (no root) so the disk cache directory ownership stays correct.
• SteamPrefill not found: Install it yourself from its GitHub releases. Then use make validate to start the server with small caches and point SteamPrefill at it manually.
• SteamPrefill won't use server as cache properly: SteamPrefill has some bad autodetectiong functions sometimes it works when the server is resolvable from localhost or 127.0.0.1 other times you have to fully override the dns for the proper dns name lancache.steamcontent.com to point to 127.0.0.1 i don't recommend doing it unless your okay with having to undo and redo it depending on if your running the server or not its a pain.

See also the SteamPrefill documentation for benchmark setup and benchmark run options.

Command Line Flags

While most configuration is done via the YAML file, some runtime options are still available as command-line flags:

# Use a custom config file
./steamcache2 --config /path/to/my-config.yaml

# Set logging level
./steamcache2 --log-level debug --log-format json

# Set number of worker threads
./steamcache2 --threads 8

# Show help
./steamcache2 --help

Configuration

SteamCache2 uses a YAML configuration file (config.yaml) for all settings. Here's a complete configuration example:

# Server configuration
listen_address: :80

# P1 hardening (see Security Hardening section)
max_object_size: "0"   # 0=unlimited; set e.g. "256MB" for response size DoS protection
trusted_proxies: []    # empty = safe (ignore XFF for rate limit); set CIDRs for trusted proxies

# Cache configuration
cache:
  # Memory cache settings
  memory:
    # Size of memory cache (e.g., "512MB", "1GB", "0" to disable)
    size: 1GB
    # Garbage collection algorithm
    gc_algorithm: lru

  # Disk cache settings
  disk:
    # Size of disk cache (e.g., "10GB", "50GB", "0" to disable)
    size: 10GB
    # Path to disk cache directory
    path: ./disk
    # Garbage collection algorithm
    gc_algorithm: hybrid

# Upstream server configuration
# The upstream server to proxy requests to
upstream: "https://steam.cdn.com"

Startup Validation

As of P0, steamcache2 performs strict validation on startup (after loading config + CLI overrides, before creating the cache). Invalid configs cause immediate clean failure (no default written, no panic):

• Negative max_concurrent_requests / max_requests_per_client: "negative concurrency not allowed"
• Invalid gc_algorithm (memory): "invalid memory gc algorithm: badvalue"
• Disk enabled (size non-zero/"") but no path: "disk cache enabled but no path specified"
• Invalid memory/disk size strings (via direct New): "invalid memory size: ..." / "invalid disk size: ..." (clean error return, no panic)

Example error on stderr + logs:

Error: Invalid configuration: invalid memory gc algorithm: foo. Please fix the config file and try again.

See config.Validate() and steamcache.New error paths. This ensures the LAN appliance fails fast on misconfig.

Security Hardening (P1)

• max_object_size (default "0" = unlimited): set e.g. "256MB" or "512MB" to reject oversized upstream responses with HTTP 413 before buffering/ReadAll. Prevents OOM DoS from large or malicious responses (P1-01). Large legitimate Steam files still served if under limit.
• trusted_proxies: CIDR list (default empty). When empty (safe default), X-Forwarded-For and client IP spoofing are ignored for rate limiting — always uses r.RemoteAddr only. When set (e.g. your reverse proxy CIDR), uses correct "rightmost untrusted" extraction. Prevents bypass of max_requests_per_client (P1-02). Documented for LAN proxy setups only.
• These + P0 validation make steamcache2 safe-by-default for LAN exposure.

Migration / Breaking Changes (P1)

• New() public signature gained 2 required trailing params (maxObjectSize, trustedProxies). Direct callers (rare; most use config or NewWithOptions) must update.
• Recommended: migrate to NewWithOptions(Options{...}) (non-breaking) or rely on YAML config + cmd/root.go.
• No behavior change for existing configs (defaults preserve prior semantics).

Large Cache Initialization (async DiskFS population)

• disk.New(root, capacity, evictFn) signature changed (now takes evict func from gc.GetGCAlgorithm, returns error for ctor hygiene). Callers updated internally; direct vfs/disk users must pass the evict (or nil for no startup guard).
• DiskFS initialization is now fully asynchronous for large caches (millions of files): New returns immediately without scanning. The first Size() (and many internal callers) blocks on an internal barrier until bg streaming population + any startup over-cap eviction (using the evictFn) completes. Subsequent Size() calls are instant.
• During the "proxy window" (while bg scan runs): disk-only configs (memory.size=0) have TieredCache Create returning ErrNotFound (no disk writes/caching occurs until attach); mem+disk configs serve from memory tier only. This keeps New fast and avoids heavy disk I/O/eviction during long scans on slow storage.
• The explicit startup guard (reduce size if pre-existing on-disk > cap) runs as the literal last step of bg init, before the barrier opens.
• Add a note for operators: very large disk caches (tens/hundreds GB with millions files) may show extended "memory-only or no-cache" behavior at startup (seconds to minutes depending on storage speed); this is by design for responsiveness.
• Godoc on disk.New and DiskFS.Size expanded with the barrier/attach behavior.

Garbage Collection Algorithms

SteamCache2 supports different garbage collection algorithms for memory and disk caches, allowing you to optimize performance for each storage tier:

Available GC Algorithms:

• lru (default): Least Recently Used - evicts oldest accessed files
• lfu: Least Frequently Used (P1 real impl) - evicts by lowest AccessCount (tiebreak older ATime); uses existing FileInfo counters
• fifo: First In, First Out - evicts oldest created files (predictable)
• largest: Size-based - evicts largest files first (maximizes file count)
• smallest: Size-based - evicts smallest files first (maximizes cache hit rate)
• hybrid: Recency + frequency hybrid (P1 meaningful) - evicts by lowest time-decayed score (GetTimeDecayedScore combining ATime + AccessCount)

Recommended Algorithms by Cache Type:

For Memory Cache (Fast, Limited Size):

• lru - Best overall performance, good balance of speed and hit rate
• lfu - Excellent for gaming cafes where popular games stay cached
• hybrid - Optimal for mixed workloads with varying file sizes

For Disk Cache (Slow, Large Size):

• hybrid - Recommended for optimal performance, balances speed and storage efficiency
• largest - Good for maximizing number of cached files
• lru - Reliable default with good performance

Use Cases:

• Gaming Cafes: Use lfu for memory, hybrid for disk
• LAN Events: Use lfu for memory, hybrid for disk
• Home Use: Use lru for memory, hybrid for disk
• Testing: Use fifo for predictable behavior
• Large File Storage: Use largest for disk to maximize file count

DNS Configuration

Configure your DNS to direct Steam traffic to your SteamCache2 server:

• If you're on Windows and don't want a whole network implementation, see the Windows Hosts File Override section below.

Windows Hosts File Override

1. Open Notepad as Administrator:

   • Click on the Start menu, type Notepad, right-click on Notepad, and select Run as administrator.

2. Open the Hosts File:

   • In Notepad, go to File > Open.
   • Navigate to C:\Windows\System32\drivers\etc.
   • Select All Files from the dropdown menu to see the hosts file.
   • Open the hosts file.

3. Add the Override Entry:

   • At the end of the file, add a new line with the IP address of your SteamCache2 server followed by lancache.steamcontent.com. For example:

     192.168.1.100 lancache.steamcontent.com
     

     Replace 192.168.1.100 with the actual IP address of your SteamCache2 server.

4. Save the Hosts File:

   • Save the changes by going to File > Save.

5. Flush DNS Cache (optional but recommended):

   • Open Command Prompt as Administrator.
   • Run the following command to flush the DNS cache:

     ipconfig /flushdns
     

6. Restart

   • Restart Steam or Restart Your PC

This will direct any requests to lancache.steamcontent.com to your SteamCache2 server.

Building from Source

Prerequisites

• Go 1.19 or later
• Make (optional, but recommended)

Build Commands

# Clone the repository
git clone <repository-url>
cd SteamCache2

# Download dependencies
make deps

# Run tests
make test

# Build for current platform
go build -o steamcache2 .

# Build for specific platforms
GOOS=linux GOARCH=amd64 go build -o steamcache2-linux-amd64 .
GOOS=windows GOARCH=amd64 go build -o steamcache2-windows-amd64.exe .

Development

# Run in development mode with debug logging
make run-debug

# Run all tests and start the application
make

Troubleshooting

Common Issues

1. "Config file not found" on first run

   • This is expected! SteamCache2 will automatically create a default config.yaml file
   • Edit the generated config file with your desired settings
   • Run the application again

2. Permission denied when creating config

   • Make sure you have write permissions in the current directory
   • Try running with elevated privileges if necessary

3. Port already in use

   • Change the listen_address in config.yaml to a different port (e.g., :8080)
   • Or stop the service using the current port

4. High memory usage

   • Reduce the memory cache size in config.yaml
   • Consider using disk-only caching by setting memory.size: "0"

5. Slow disk performance

   • Use SSD storage for the disk cache
   • Consider using a different GC algorithm like hybrid
   • Adjust the disk cache size to match available storage

Getting Help

• Check the logs for detailed error messages
• Run with --log-level debug for more verbose output
• Ensure your upstream server is accessible
• Verify DNS configuration is working correctly

License

See the LICENSE file for details. But just for clarity this covers all files in this project unless stated in the individual file.

Acknowledgements

• Inspired by Lancache.net