how to transfer file between two RPI over Wi-fi?

Question

Hello I received two Pi 4 for Christmas. It is the first time I use RPI, I have succeeded to turn them on and to connect them to my local wifi !

I am a a beginner and I wanted to start with a simple project : connecting 2 RPI together and send data( file of 60 Mo) through Wi-fi between them.

After startup, an automatic connection is set up between the RPI[1] and the RPI[2], RPI[1] sends a set of data to the RPI[2].

The idea would be that RPI [1] should send a "presence" signal only every 30 min approximatively (configurable)

The RPI[2] would be in permanent listening, and as soon as it receives the signal of presence of the RPI[1], it opens a communication protocol with the RPI[2] of the type : "I know that RPI[1] is there, RPI[1] confirms that it is sending me data, I receive the data, I check the integrity of the data (how ..?), I confirm receipt to RPI[1], I close the communication". "If the integrity of the data is not good, I ask for the data to be sent back from RPI[1] following the same process as before".

I was wondering :

• the simpliest way to send file through Wi-fi ?
• Which protocol to choose ? TCP or MQTT ( seemed better than http)
• which languages to choose ? Python or C ?
• Any good ressources to help me started or similar projects ?
• This is a good "scenario" ?

Thank you in advance for your help,
Antoine

Answer 1

To answer your last point

• This is a good "scenario" ?

and with the announcement

I am a a beginner and I wanted to start with a simple project : connecting 2 RPI together and send data( file of 60 Mo) through Wi-fi between them.

I would say "No".

To transfer a file form RPi1 to RP2 just use:

rpi ~$ scp /path/to/file pi@rpi2:/path/to/file

To repeat this automatically after a time, create a systemd service with a timer:

rpi ~$ sudo systemctl edit --force --full transfer-file.service

In the empty editor insert these statements, save them and quit the editor:

[Unit]
Description=Transfer file
[Service]
Type=oneshot
ExecStart=/usr/bin/scp /path/to/file pi@rpi2:/path/to/file

rpi ~$ sudo systemctl edit --force --full transfer-file.timer

In the empty editor insert these statements, save them and quit the editor:

[Timer]
OnActiveSec=30min

Enable and manage this with

rpi ~$ sudo systemctl enable --now transfer-file.timer
rpi ~$ sudo systemctl status transfer-file.timer
rpi ~$ sudo systemctl edit --full transfer-file.timer

This will transfer a file every 30 minutes. All error handling and handshake is done by the operating system, the scp program and the TCP network protocol.

Answer 2

If this file transfer is to be an ongoing effort, you may wish to consider rsync. If you're using the RPi OS, rsync is pre-installed, and you can learn about its use by perusing man rsync.

You have at least two choices for running rsync across two RPis:

1. set up an SSH connection

2. set up a Samba server(s) on one or both RPis & mount the shared drives

If you use the SSH connection, you may find it convenient to set up a public-private key pair as that will avoid userid+password authentication which can be messy and insecure.

All of the information you need to do this is available online for the cost of an Internet search. Please take a few minutes to read some of these search results. If you have specific questions, please post those as separate questions.