metrics: Fix hidden panic while observing with bad exemplars (#3733)

* metrics: Fixing panic while observing with bad exemplars

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

* Minor cleanup

The server is already added to the context. So, we can simply use that
to get the server name, which is a field on the server.

* Add integration test for auto HTTP->HTTPS redirects

A test like this would have caught the problem in the first place

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/caddytest/integration/autohttps_test.go b/caddytest/integration/autohttps_test.go
new file mode 100644
index 0000000..62f172d
--- /dev/null
+++ b/caddytest/integration/autohttps_test.go
@@ -0,0 +1,22 @@
+package integration
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2/caddytest"
+)
+
+func TestAutoHTTPtoHTTPSRedirects(t *testing.T) {
+	tester := caddytest.NewTester(t)
+	tester.InitServer(`
+	{
+		http_port     9080
+		https_port    9443
+	}
+	localhost:9443
+	respond "Yahaha! You found me!"
+  `, "caddyfile")
+
+	tester.AssertRedirect("http://localhost:9080/", "https://localhost/", http.StatusPermanentRedirect)
+}