> proxy.golang.org does not save all modules forever. There are a number of reasons for this, but one reason is if proxy.golang.org is not able to detect a suitable license.
If you're vendoring something without an appropriate license, you're skating on thin ice legally.
> Why did a previously available module become unavailable in the mirror? > > proxy.golang.org does not save all modules forever. There are a number of reasons for this…
(I am a googler, but don't work on the go team – my opinions that projects should vendor and actually review their dependencies are my own)