Essentially, just don't try to set a status code and send any error
message in the body once metrics gathering has succeeded. At that
point, the most likely reason for errors is anyway that the client has
disconnected, in which sending an error is moot. The other possible
reason for an error is a problem during metrics encoding. This is
unlikely to happen (it's a coding error here in client_golang in any
case), and if it is happening, the odds are we have already sent
something to the ResponseWriter, which means we cannot set a status
code anymore. The doc comment for HTTPErrorOnError now describes these
circumstances explicitly and recommends to set a logger to report that
kind of error.
This should fix the reason for the infamous `superfluous
response.WriteHeader call` message.
Signed-off-by: beorn7 <beorn@grafana.com>
Fixes:
http.go:118: declaration of "part" shadows declaration at http.go:117
http_test.go:50: declaration of "respBody" shadows declaration at http_test.go:25
promhttp/http.go:305: declaration of "part" shadows declaration at promhttp/http.go:304
Signed-off-by: Karsten Weiss <knweiss@gmail.com>
To keep backwards compatibility while not creating circular import
chains, some code had to be duplicated. But all functions using it
have been declared deprecated hereby.
The new ways of instrumenting handlers will all go into the new
package, and ultimately, the prometheus package itself will be
completely igorant of HTTP.
beorn7