The driver framework

A driver is a vendor personality. It owns the full interactive loop for one device: reading input, parsing commands, and writing responses. rcfg-sim ships five: cisco_ios, junos, ciena_tl1, infinera_tl1 and cisco_ons_tl1. Adding more is deliberately a one-file job.

The Driver interface

Every driver implements four methods:

type Driver interface {
    Name() string            // manifest `template` id, e.g. "cisco_ios"
    Commands() []string      // metric label values this driver can emit
    RequiresSSHAuth() bool    // does it authenticate at the SSH transport?
    Serve(ctx *sessionCtx)   // the full interactive loop
}

• Name() is the id used in the manifest template column and the registry key.
• Commands() is the closed set of command labels the driver may emit on rcfgsim_command_duration_seconds. The server unions these across all drivers and pre-registers them, so the metric’s cardinality is assembled from drivers rather than hardcoded — and stays bounded.
• RequiresSSHAuth() is consulted only under --ssh-auth=driver.
• Serve() runs the session.

How a driver is selected

At session start the server looks up the device’s manifest template value in the driver registry (driverFor). An empty value falls back to cisco_ios, so older manifests keep working unchanged.

new SSH session
   │
   ▼
manifest row ── template column ──▶ driver registry
                                        │
     ┌───────────┬───────────┬──────────┴───┬───────────────┬─────────────┐
 cisco_ios     junos     ciena_tl1    infinera_tl1    cisco_ons_tl1     empty
     │           │           │              │               │             │
     ▼           ▼           ▼              ▼               ▼             ▼
 ciscoIOS      junos     cienaTL1      infineraTL1     ciscoONSTL1    ciscoIOS
  .Serve      .Serve      .Serve         .Serve          .Serve      (fallback)

An unknown driver id is now a startup error

A non-empty template value that no driver is registered for stops the server before it binds:

rcfg-sim: manifest names unknown driver(s) in the template column: infinira_tl1

It used to fall back to cisco_ios, which meant a typo’d infinera_tl1 served a fleet that looked healthy and spoke the wrong protocol. Failing at startup is louder and cheaper.

Shared machinery

Drivers don’t reimplement timing, faults, or metrics. They route every response through two shared helpers on the session context:

• applyResponseDelay() — the single place a response sleep happens (base jitter plus the slow_response fault multiplier). See timing.
• emit() — writes the response, applies disconnect_mid / malformed faults to streamed config bytes, preserves the zero-copy path for the un-faulted case, and records the command-duration metric.

This is what guarantees that fault and metric behaviour is identical across vendors — a driver author gets all of it for free.

Registration

Each driver registers itself from an init() in its own file (driver_<vendor>.go), so nothing else in the hot path needs to know it exists:

func init() { registerDriver(ciscoIOS{}) }

The shipped drivers

• Cisco IOS (cisco_ios) — show commands, enable mode, prefix matching. Also serves Arista EOS devices, whose CLI is IOS-shaped; see EOS on cisco_ios.
• Juniper Junos (junos) — user@host> prompt, no enable mode, show configuration
• Ciena 6500 TL1 (ciena_tl1) — ACT-USER login, RTRV-NE-LIST neighbours
• Infinera DTN-X TL1 (infinera_tl1) — > prompt, paged RTRV-TIDMAP
• Cisco ONS 15454 TL1 (cisco_ons_tl1) — positional RTRV-MAP-NETWORK records

The three TL1 drivers share one core (internal/sshsrv/tl1.go) and differ where the hardware does. Those differences are the point, not an inconvenience:

	Ciena 6500	Infinera DTN-X	Cisco ONS 15454
Prompt	<	>	<
Neighbour command	RTRV-NE-LIST	RTRV-TIDMAP	RTRV-MAP-NETWORK
Record grammar	keyword, quoted	keyword, empty AID	positional
Response	one block	paged	one block
Header SID when routing	the addressed TID	its own system name	the addressed TID

cisco_ios and junos can also answer any command from a per-device file; see Command files.

Want to add your own? See Writing a new driver.