FlashShare

High-speed LAN file transfer CLI tool for fast large file transfers, with resume support, multi-receiver fan-out, and relay chaining.

Build

Prerequisites

Ubuntu/Debian:

sudo apt install cmake build-essential libssl-dev

Fedora/RHEL:

sudo dnf install cmake gcc-c++ openssl-devel

Normal build

cd flashshare
mkdir -p build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release
make -j$(nproc)

The binary is at build/flashshare.

Static build (portable — runs on any Linux without dependencies)

cd flashshare
mkdir -p build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release \
         -DOPENSSL_USE_STATIC_LIBS=TRUE \
         -DCMAKE_EXE_LINKER_FLAGS="-static -lpthread -ldl"
make -j$(nproc)

Produces a ~7.5 MB binary with no external library dependencies. Copy it to any Linux machine and run.

Usage

FlashShare — High-speed LAN file transfer

USAGE:
  flashshare send <path> [<path>...] --to <ip[,ip...]> [options]
  flashshare recv [options]

COMMANDS:
  send <path> [<path>...]   Send one or more files and/or directories
  recv                      Listen for incoming transfers
  help                      Show this help message
  version                   Show version

OPTIONS:
  --to <ip[,ip...]>  Receiver IPv4 addresses, separated by commas
  --port <n>         Port number (default: 5117)
  --out <dir>        Output directory (default: current dir)
  --encrypt          Enable AES-256-GCM encryption
  --relay            Chain the --to receivers (S -> R1 -> R2 -> R3) instead
                     of fanning out to each of them from the sender
  --resume           Resume an interrupted transfer
  --accept-all       Auto-accept incoming transfers (no prompt)
  --verbose          Enable debug logging
  --log-file <f>     Mirror log output to file (default in --daemon mode:
                     /tmp/flashshare_receiver.log)
  -h, --help         Show help
  -v, --version      Show version

Examples

Basic file transfer

# Receiver (machine B):
flashshare recv --port 5117 --out ~/downloads --accept-all

# Sender (machine A):
flashshare send bigfile.iso --to 192.168.1.50 --port 5117

Send multiple files and directories

flashshare send a.txt b.txt ./project/ --to 192.168.1.50

Encrypted transfer

flashshare send secret.zip --to 192.168.1.50 --encrypt

Resume an interrupted transfer

flashshare send bigfile.iso --to 192.168.1.50 --resume

If the connection drops, the sender automatically retries with exponential backoff and resumes from the receiver's last checkpointed offset.

Multi-receiver fan-out

Send to multiple receivers simultaneously — each receiver gets a full copy:

flashshare send bigfile.iso --to 192.168.1.50,192.168.1.51,192.168.1.52 --resume

Relay chain

Chain receivers: S → R1 → R2 → R3. Each receiver forwards to the next:

flashshare send bigfile.iso --to 192.168.1.50,192.168.1.51,192.168.1.52 --relay

Next Direction

• Adapting it to low thread creation ovehead / epoll.
• Splice Tee instead of sendfile. And during recovery for aligning nodes to same offset first -> sendFile(). Then -> again Tee().
• Can possibly include io/uring to avoid kernel-userspace trap overhead(Maybe not needed for a small LAN).
• Testing one node in various connection/relay and design the sceanrio, if needed- implement then(Need to experiment whether io uring can actually help here).
• Currently no mechanism is done for slow reciver which hinders the overall file sharing. Can adapt to a hybrid chain rebuilding/recovery algorithm later.