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Make caser a local varialbe, not a global one. #927

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merged 1 commit into from
Jun 17, 2022
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Make caser a local varialbe, not a global one. #927

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12 changes: 10 additions & 2 deletions prober/http.go
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Original file line number Diff line number Diff line change
Expand Up @@ -46,8 +46,6 @@ import (
"github.com/prometheus/blackbox_exporter/config"
)

var caser = cases.Title(language.Und)

func matchRegularExpressions(reader io.Reader, httpConfig config.HTTPProbe, logger log.Logger) bool {
body, err := ioutil.ReadAll(reader)
if err != nil {
Expand Down Expand Up @@ -342,6 +340,16 @@ func ProbeHTTP(ctx context.Context, target string, module config.Module, registr
return false
}

// Do not move the following variable to global scope. The cases.Caser returned by
// calling cases.Title *cannot* be shared among goroutines. This might happen when
// Prometheus tries to scrape multiple targets at the same time. From the docs:
//
// A Caser may be stateful and should therefore not be shared between goroutines.
//
// Issue: https://github.com/prometheus/blackbox_exporter/issues/922
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I don't think it is necessary to point to the gh issue here

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I felt it was necessary to keep the reference close to the code because the original version is what I would have written, too. The wording in the docs, "a Caser may", sounds like if that were the actual case, the individual Caser implementations would spell that out. Given that in this particular instance there no such note, I would have assumed that this Caser is not stateful.

Thanks for the review and merging this!


caser := cases.Title(language.Und)

httpClientConfig := module.HTTP.HTTPClientConfig
if len(httpClientConfig.TLSConfig.ServerName) == 0 {
// If there is no `server_name` in tls_config, use
Expand Down
3 changes: 3 additions & 0 deletions prober/http_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,8 @@ import (
"github.com/go-kit/log"
"github.com/prometheus/client_golang/prometheus"
pconfig "github.com/prometheus/common/config"
"golang.org/x/text/cases"
"golang.org/x/text/language"

"github.com/prometheus/blackbox_exporter/config"
)
Expand Down Expand Up @@ -1068,6 +1070,7 @@ func TestHTTPHeaders(t *testing.T) {
"Accept-Language": "en-US",
}
ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
caser := cases.Title(language.Und)
for key, value := range headers {
if caser.String(key) == "Host" {
if r.Host != value {
Expand Down