qsend

A file transfer tool built over QUIC. Streams data directly from disk to the network socket with zero in-memory buffering, making it suitable for large file transfers without causing memory pressure on the host.

How it works

The client opens a QUIC stream to the server and sends a fixed binary header, followed by the raw file payload. The server reads the header, determines whether the client wants to upload or download, and acts accordingly. All file I/O goes through io.Reader/io.Writer interfaces piped directly into io.Copy , no intermediate buffers.

Upload: The client hashes the file with SHA-256 before sending, embeds the checksum in the header, and streams the file. The server writes the incoming bytes to disk, re-hashes the result, and compares against the header checksum. A mismatch returns a Hash mismatch response.

Download: The server opens the requested file and streams it to the client. Integrity verification on downloads is not implemented at the application layer , QUIC's transport frames handle packet-level integrity only.

A live throughput display prints MB/s to stdout every second during transfer.

Binary protocol

[ 1 byte  ]  Action      ,  'U' (upload) or 'D' (download)
[ 1 byte  ]  NameLen     ,  length of the filename in bytes
[ N bytes ]  Filename    ,  UTF-8 filename string
[ 32 bytes]  Hash        ,  SHA-256 of the file payload (uploads only; zeroed for downloads)
[ ...     ]  Payload     ,  raw file bytes, streamed until EOF

Build

git clone https://github.com/so1icitx/qsend.git
cd qsend
go build -o qsend-server ./cmd/server
go build -o qsend-client ./cmd/client

Usage

Start the server:

./qsend-server

The server generates a self-signed TLS certificate in memory at startup. No certificate files are required. The client connects with certificate verification disabled (InsecureSkipVerify). For production use, export the certificate from the server and configure the client to verify it , the relevant code is present in both files, commented out.

Upload a file:

./qsend-client U ./video.mp4

Download a file:

./qsend-client D video.mp4

The server listens on localhost:1447.

Known limitations

• Download path has no application-layer integrity check
• No retransmission or retry logic if the server reports a hash mismatch
• Single stream per connection; no concurrent transfers
• Filename is capped at 255 bytes (uint8 length field)