* Use a custom user-agent when previewing links
Many websites block requests made with Go's default user-agent. We had
previous special-cased Twitter links to use a nonstandard user-agent.
This makes that behavior apply everywhere and also customizes the
user-agent to belong specifically to Mattermost.
* Correctly use custom transport for link previews
This allows us to use the custom user-agent defined in
services/httpservice/client.go.
* Stop leaking server version in custom user-agent
Since the custom user-agent is now used when previewing links, exposing
the server version could provide a vector for a malicious actor to
gather information about private deployments. To avoid this, we switch
to a generic string.
* Remove extraneous Transport creation
MakeClient already creates a transport for us, so this is unnecessary.
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
* Consistent license message for all the go files
* Fixing the last set of unconsistencies with the license headers
* Addressing PR review comments
* Fixing busy.go and busy_test.go license header
Previously, mattermost-server would always request with the default
user-agent of Go's net/http package that is `Go-http-client/1.1` or
something similar.
This has several disadvantages, one is that the default user-agent
made it pretty hard to distinguish mattermost requests from other
service requests in a network log for example.
Now a user-agent of the form `mattermost-<current-version>` is set in
the client.
- [x] Added or updated unit tests (required for all new features)
