x/build/cmd/relui: compute Google Groups URL of sent announcement email

[dmitshur]

A part of completing the task that sends a release announcement email (#47405) is being able to tell that the email has been received by Google Groups (and moderated as needed), and determining its URL. This URL serves as the canonical announcement URL, and is currently included in the release tweet (see ReleaseTweet.Announcement).

For example, the email announcing the release of Go 1.17.6 and Go 1.16.13 was sent on Jan 6. It was successfully received, moderated, and its URL became https://groups.google.com/g/golang-announce/c/95ZD3rKn4DI/m/93cyN8F1BAAJ.

We don't find out what the final URL will be on google groups as part of sending the email, this needs to be computed afterwards, so breaking it out as a smaller issue.

Since the announcement group is highly moderated, it's likely sufficient for us to match based on subject. If the subject matches, it must be the right email:

// Input:
"Go 1.17.6 and Go 1.16.13 are released"
// Output:
"https://groups.google.com/g/golang-announce/c/95ZD3rKn4DI/m/93cyN8F1BAAJ"
"https://groups.google.com/g/golang-announce/c/95ZD3rKn4DI"  // Alternative, also okay.

// Input:
"Go 1.17 Release Candidate 3 is released"
// Output:
os.ErrNotExist or context.DeadlineExceeded  // Accurate on 2022-01-27.

It's expected that emails don't travel instantaneously, so the code would need to run in a loop that tries (with a reasonable deadline) multiple times, and once the email is received by google groups, eventually succeeds.

Options:

• Extract the subject and URL from the HTML of Google Groups (https://groups.google.com/g/golang-announce).
• Use an API to find a matching thread, if such an API is available and using it is viable.

CC @golang/release.

[dmitshur]

I've explored the aforementioned options.

There may be an API we can use, but using it has some overhead in initial setup and maintenance. Based on what I've learned, I think we can defer considing/exploring it more until a later milestone.

Parsing the HTML appears to be a more attractive immediate solution to this (to unblock #47405). I've prototyped it locally and it seems to meet the needs of this task. Unless we learn of a reason it can't work well, I'll clean it up and send a CL.

[gopherbot]

Change https://go.dev/cl/411575 mentions this issue: cmd/relui, internal/task: add release announcement email task