Prevent exception in HttpServer exporter when using custom root metrics path #1772
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it looks as though this is not backwards compatible - maybe add a setting to opt in? |
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What exactly do you think breaks the backwards compatibility? With Java 11 it should already behave exactly like this (replacing the previously registered default handler). And with a newer Java runtime the current implementation doesn't work at all. |
jaydeluca
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Jan 15, 2026
...orter-httpserver/src/test/java/io/prometheus/metrics/exporter/httpserver/HTTPServerTest.java
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Signed-off-by: David Sondermann <david.sondermann@hivemq.com>
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That registration would not work the first time What about this change? Index: prometheus-metrics-exporter-httpserver/src/main/java/io/prometheus/metrics/exporter/httpserver/HTTPServer.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/prometheus-metrics-exporter-httpserver/src/main/java/io/prometheus/metrics/exporter/httpserver/HTTPServer.java b/prometheus-metrics-exporter-httpserver/src/main/java/io/prometheus/metrics/exporter/httpserver/HTTPServer.java
--- a/prometheus-metrics-exporter-httpserver/src/main/java/io/prometheus/metrics/exporter/httpserver/HTTPServer.java (revision 7f93e015dc64160204b51d13aebf75c83044a364)
+++ b/prometheus-metrics-exporter-httpserver/src/main/java/io/prometheus/metrics/exporter/httpserver/HTTPServer.java (date 1768917816428)
@@ -9,6 +9,9 @@
import com.sun.net.httpserver.HttpsServer;
import io.prometheus.metrics.config.PrometheusProperties;
import io.prometheus.metrics.model.registry.PrometheusRegistry;
+
+import javax.annotation.Nullable;
+import javax.security.auth.Subject;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
@@ -21,8 +24,6 @@
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
-import javax.annotation.Nullable;
-import javax.security.auth.Subject;
/**
* Expose Prometheus metrics using a plain Java HttpServer.
@@ -66,11 +67,21 @@
this.server = httpServer;
this.executorService = executorService;
String metricsPath = getMetricsPath(metricsHandlerPath);
+ try {
+ server.removeContext("/");
+ } catch (IllegalArgumentException e) {
+ // context "/" not registered yet, ignore
+ }
registerHandler(
"/",
defaultHandler == null ? new DefaultHandler(metricsPath) : defaultHandler,
authenticator,
authenticatedSubjectAttributeName);
+ try {
+ server.removeContext(metricsPath);
+ } catch (IllegalArgumentException e) {
+ // context metricsPath not registered yet, ignore
+ }
registerHandler(
metricsPath,
new MetricsHandler(config, registry),
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The behavior of
HttpServer.createContext()was changed between Java 11 and 21. In the current JDKs the server doesn't allow to register multiple contexts with the same path. So if you configureyou get the following exception:
This PR fixes the issue by skipping the default handler registration in case the metrics are configured for the root path.
I also improved the unit test so we can properly assert
expectedStatusCodeandexpectedBody. With this improvement we can be sure that an endpoint actually returns the expected handler content, not just a matching status code.