Certo Desktop Developer Reference

Spoofing a Network Stream

In this scenario, we mock a high-performance TCP telemetry stream on Port 1234.

Step 1: Target the Port

1. Create a new intercept target in Certo.
2. Set the target to Port 1234.

Step 2: The connect Hook

Certo automatically swaps the app’s socket with a virtual socketpair.

certo::logger "Intercepted connection attempt to Port 1234!"

Step 3: The recvfrom Hook

Feed the stream by generating payloads on the fly.

set buf_addr       [lindex $certo::arguments 1]
set requested_size [lindex $certo::arguments 2]

::certo::logger info "Feeding $requested_size bytes of telemetry."

# 1. Generate fake payload
set fake_packet "SENSOR_TEMP: 72F | STATUS: NOMINAL"

# 2. Pad to match requested size
set pad_length [expr {$requested_size - [string length $fake_packet]}]
if {$pad_length > 0} {
    append fake_packet [string repeat "\x00" $pad_length]
}

# 3. Inject into the application's buffer
::certo::write_memory $buf_addr $fake_packet
certo_set_return_value $requested_size

The Result

The application successfully connects even if the network is down, and its poll() loops run natively against your high-throughput virtual stream.