feat: write agent output to a temporary file

[jawnsy]

How I tested this

Running the agent, the log data is written to a file as well (and truncated/re-created on subsequent starts):

$ go run ./cmd/coder/main.go agent start
2021-09-02 01:36:32.847 [INFO]  <agent.go:90>   starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 01:36:32.848 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=xxx"}
2021-09-02 01:36:32.928 [INFO]  <listen.go:136> broker connection established
^C2021-09-02 01:36:53.420 [INFO]        <agent.go:96>   closing wsnet listener
2021-09-02 01:36:53.421 [INFO]  <listen.go:451> listener closed

$ cat /tmp/coder-agent.log 
2021-09-02 15:22:25.006 [INFO]  <agent.go:92>   starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 15:22:25.007 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=xxx"}
2021-09-02 15:22:25.098 [INFO]  <listen.go:136> broker connection established
2021-09-02 15:22:26.690 [INFO]  <agent.go:98>   closing wsnet listener
2021-09-02 15:22:26.690 [INFO]  <listen.go:451> listener closed

If there's a permission error preventing the file frmo being truncated, a log message will be output to stderr (simulated by chowning the file to root):

$ sudo chown root:root /tmp/coder-agent.log 
$ go run ./cmd/coder/main.go agent start
2021-09-02 01:41:21.363 [INFO]  <agent.go:65>   failed to open agent log file   {"error": "open /tmp/coder-agent.log: permission denied"}
2021-09-02 01:41:21.365 [INFO]  <agent.go:93>   starting wsnet listener {"coder_access_url": "https://master.cdr.dev/"}
2021-09-02 01:41:21.365 [INFO]  <listen.go:114> connecting to broker    {"broker_url": "wss://master.cdr.dev/api/private/envagent/listen?service_token=xxx"}
2021-09-02 01:41:21.478 [INFO]  <listen.go:136> broker connection established
^C2021-09-02 01:41:23.116 [INFO]        <agent.go:99>   closing wsnet listener
2021-09-02 01:41:23.116 [INFO]  <listen.go:451> listener closed

[shortcut-integration]

This pull request has been linked to Clubhouse Story #16783: Modify the coder-cli agent to save to a log as well as stderr.

[coveralls]

Pull Request Test Coverage Report for Build 1194765666

• 0 of 13 (0.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 47.954%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/cmd/agent.go	0	13	0.0%

Files with Coverage Reduction	New Missed Lines	%
wsnet/dial.go	2	78.34%

Totals
Change from base Build 1163231010:	-0.04%
Covered Lines:	2789
Relevant Lines:	5816

---

💛 - Coveralls

[jawnsy]

it didn't seem like the file we write needs to be hidden, so I made it a not-dotfile

[deansheather]

Should be consistent for the other log files in that case

[jawnsy]

Which other log files do we have? I think just a code-server one right?

[deansheather]

code-server and envagent, they're in environment_stages.go

[deansheather]

slogjson is very hard to read, and we don't have automated ingestion of this log file into stackdriver so I'd rather stick with sloghuman for now. We can change this later with no consequences

[jawnsy]

We don't have tools for consuming slogjson output and converting to sloghuman output? The slogjson output seems to have more info (e.g. full paths to files) and being machine-readable does seem potentially useful.

I don't have strong feelings about it though, I'll change to sloghuman 🤷‍♂️

[deansheather]

Yeah that's the only difference between them, they have the same details otherwise. coder-cli doesn't have many files so I'm not too worried about not being able to find the files due to conflicts

[coadler]

Should this be an error log?

[jawnsy]

maybe, but I don't expect it to happen for coder workspaces and everything would be logged to our console anyways