Expect for Go
A simple expect library for Go.
Highlights
- Simple API. Multi-pattern expect() statements are not supported, however this limitation is generally not an issue. See the examples for details.
- Efficient - At the expense of guaranteeing non-greedy matches, the matching algorithm should be efficient and handle large amounts of output well.
- Observation API - Sniff the conversation for debugging / logging purposes.
- Bundled command logging and mocking tool.
Quick Example
For real examples, see examples.
This example ignores some important things, like error checking.
// Spawn an expect process
ssh, err := expect.Spawn("ssh", "remote_host")
ssh.SetTimeout(10 * time.Second)
const PROMPT = `(?m)[^$]*$`
// Login
ssh.Expect(`[Pp]assword:`)
ssh.SendMasked("bad password") // SendMasked hides from logging
ssh.Send("\n")
ssh.Expect(PROMPT) // Wait for prompt
// Run a command
ssh.SendLn("ls -lh")
match, err := ssh.Expect(PROMPT) // Wait for prompt
fmt.Println("ls -lh output:", match.Before)
// Hit a timeout
ssh.SendLn("sleep 60") // This will cause a timeout
match, err := ssh.Expect(PROMPT) // This will timeout
if err == expect.ErrTimeout {
fmt.Println("Session timed out. Like we were expecting.\n")
}
// Wait for EOF
ssh.SendLn("exit")
ssh.ExpectEOF()Observing the session and logging
Expect has the ability to let the user observe I/O and API calls. This is mostly useful for logging the session.
ssh.AddObserver(expect.LoggingObserver("ssh.log"))Mocking tests
Tools that make use of Expect libraries are notoriously hard to test. We provide tools to record sessions and subsequently mock that device/session with a TCL-Expect script that's generated by this recorder.
Optimally, it'll eventually implement the replay functionality purely in Go, but I made my head spin too much doing that one night. So, for now we're hacking together TCL-Expect to emulate how an ssh host would respond.
mocker := expect.CreateMocker()
ssh.AddObserver(mocker.ObservationChannel())
// Do stuff with SSH
ssh.SendLn("blah")
ssh.Expect(`blah`)
...
// Store
expectScript := mocker.TCLExpectScript()
ioutil.WriteFile("ssh_mock", expectScript, 0700)Now you can use that mocked data for further unit tests. It's not perfect by any means, but we'll see how it works in practice.