001package io.prometheus.metrics.exporter.httpserver;
002
003import com.sun.net.httpserver.HttpExchange;
004import com.sun.net.httpserver.HttpHandler;
005import java.io.IOException;
006import java.nio.charset.StandardCharsets;
007
008/** Handler for the / endpoint */
009public class DefaultHandler implements HttpHandler {
010
011  private final byte[] responseBytes;
012  private final String contentType;
013
014  public DefaultHandler() {
015    String responseString =
016        "<html>\n"
017            + "<head><title>Prometheus Java Client</title></head>\n"
018            + "<body>\n"
019            + "<h1>Prometheus Java Client</h1>\n"
020            + "<h2>Metrics Path</h2>\n"
021            + "The metrics path is <a href=\"metrics\">/metrics</a>.\n"
022            + "<h2>Name Filter</h2>\n"
023            + "If you want to scrape only specific metrics, "
024            + "use the <tt>name[]</tt> parameter like this:\n"
025            + "<ul>\n"
026            + "<li><a href=\"metrics?name[]=my_metric\">/metrics?name[]=my_metric</a></li>\n"
027            + "</ul>\n"
028            + "You can also use multiple <tt>name[]</tt> parameters to query multiple metrics:\n"
029            + "<ul>\n"
030            + "<li><a href=\"metrics?name[]=my_metric_a&name=my_metrics_b\">"
031            + "/metrics?name[]=my_metric_a&amp;name=[]=my_metric_b</a></li>\n"
032            + "</ul>\n"
033            + "The <tt>name[]</tt> parameter can be used by the Prometheus server for scraping. "
034            + "Add the following snippet to your scrape job configuration in "
035            + "<tt>prometheus.yaml</tt>:\n"
036            + "<pre>\n"
037            + "params:\n"
038            + "    name[]:\n"
039            + "        - my_metric_a\n"
040            + "        - my_metric_b\n"
041            + "</pre>\n"
042            + "<h2>Debug Parameter</h2>\n"
043            + "The Prometheus Java metrics library supports multiple exposition formats.\n"
044            + "The Prometheus server sends the <tt>Accept</tt> header "
045            + "to indicate which format it accepts.\n"
046            + "By default, the Prometheus server accepts OpenMetrics text format, "
047            + "unless the Prometheus server is started with feature flag "
048            + "<tt>--enable-feature=native-histograms</tt>,\n"
049            + "in which case the default is Prometheus protobuf.\n"
050            + "The Prometheus Java metrics library supports a <tt>debug</tt> query parameter "
051            + "for viewing the different formats in a Web browser:\n"
052            + "<ul>\n"
053            + "<li><a href=\"metrics?debug=openmetrics\">/metrics?debug=openmetrics</a>: "
054            + "View OpenMetrics text format.</li>\n"
055            + "<li><a href=\"metrics?debug=text\">/metrics?debug=text</a>: "
056            + "View Prometheus text format (this is the default when accessing the "
057            + "<a href=\"metrics\">/metrics</a> endpoint with a Web browser).</li>\n"
058            + "<li><a href=\"metrics?debug=prometheus-protobuf\">"
059            + "/metrics?debug=prometheus-protobuf</a>: "
060            + "View a text representation of the Prometheus protobuf format.</li>\n"
061            + "</ul>\n"
062            + "Note that the <tt>debug</tt> parameter is only for viewing different formats in a "
063            + "Web browser, it should not be used by the Prometheus server for scraping. "
064            + "The Prometheus server uses the <tt>Accept</tt> "
065            + "header for indicating which format it accepts.\n"
066            + "</body>\n"
067            + "</html>\n";
068    this.responseBytes = responseString.getBytes(StandardCharsets.UTF_8);
069    this.contentType = "text/html; charset=utf-8";
070  }
071
072  @Override
073  public void handle(HttpExchange exchange) throws IOException {
074    try {
075      exchange.getResponseHeaders().set("Content-Type", contentType);
076      exchange.getResponseHeaders().set("Content-Length", Integer.toString(responseBytes.length));
077      exchange.sendResponseHeaders(200, responseBytes.length);
078      exchange.getResponseBody().write(responseBytes);
079    } finally {
080      exchange.close();
081    }
082  }
083}