Add debug url parameter to return debug logs.

diff --git a/README.md b/README.md
index dc6065cb11ac7ac47eedcf4b893618c1741e0f86..35159e6227d8da15d48ab1a965b7cbba294cbd74 100644 (file)
--- a/README.md
+++ b/README.md
@@ -15,7 +15,9 @@ HTTP, HTTPS, DNS, TCP and ICMP.
     ./blackbox_exporter <flags>
 
 Visiting [http://localhost:9115/probe?target=google.com&module=http_2xx](http://localhost:9115/probe?target=google.com&module=http_2xx)
-will return metrics for a HTTP probe against google.com. The `probe_success` metric indicates if the probe succeeded.
+will return metrics for a HTTP probe against google.com. The `probe_success`
+metric indicates if the probe succeeded. Adding a `debug=true` parameter
+will return debug information for that probe.
 
 ### Building with Docker
 

diff --git a/main.go b/main.go
index 044d9760b9c51f0e510ff484a84d590185b4a9ed..2495d98e53a8bb427f2a0e07203f5ba27abeafa7 100644 (file)
--- a/main.go
+++ b/main.go
@@ -14,6 +14,7 @@
 package main
 
 import (
+       "bytes"
        "context"
        "fmt"
        "net/http"
@@ -30,6 +31,7 @@ import (
 
        "github.com/prometheus/client_golang/prometheus"
        "github.com/prometheus/client_golang/prometheus/promhttp"
+       "github.com/prometheus/common/expfmt"
        "github.com/prometheus/common/promlog"
        "github.com/prometheus/common/promlog/flag"
        "github.com/prometheus/common/version"
@@ -108,19 +110,79 @@ func probeHandler(w http.ResponseWriter, r *http.Request, c *config.Config, logg
                return
        }
 
+       sl := newScrapeLogger(logger, moduleName, target)
+       level.Info(sl).Log("msg", "Beginning probe", "probe", module.Prober)
+
        start := time.Now()
        registry := prometheus.NewRegistry()
        registry.MustRegister(probeSuccessGauge)
        registry.MustRegister(probeDurationGauge)
-       success := prober(ctx, target, module, registry, logger)
+       success := prober(ctx, target, module, registry, sl)
        probeDurationGauge.Set(time.Since(start).Seconds())
        if success {
                probeSuccessGauge.Set(1)
+               level.Info(sl).Log("msg", "Probe succeeded")
+       } else {
+               level.Error(sl).Log("msg", "Probe failed")
+       }
+
+       debug := false
+       if r.URL.Query().Get("debug") == "true" {
+               debug = true
+       }
+
+       if debug {
+               w.Header().Set("Content-Type", "text/plain")
+               fmt.Fprintf(w, "Logs for the probe:\n")
+               sl.buffer.WriteTo(w)
+               fmt.Fprintf(w, "\n\n\nMetrics that would have been returned:\n")
+               mfs, err := registry.Gather()
+               if err != nil {
+                       fmt.Fprintf(w, "Error gathering metrics: %s\n", err)
+                       return
+               }
+               for _, mf := range mfs {
+                       expfmt.MetricFamilyToText(w, mf)
+               }
+               return
        }
+
        h := promhttp.HandlerFor(registry, promhttp.HandlerOpts{})
        h.ServeHTTP(w, r)
 }
 
+type scrapeLogger struct {
+       next         log.Logger
+       module       string
+       target       string
+       buffer       bytes.Buffer
+       bufferLogger log.Logger
+}
+
+func newScrapeLogger(logger log.Logger, module string, target string) *scrapeLogger {
+       logger = log.With(logger, "module", module, "target", target)
+       sl := &scrapeLogger{
+               next:   logger,
+               buffer: bytes.Buffer{},
+       }
+       bl := log.NewLogfmtLogger(&sl.buffer)
+       sl.bufferLogger = log.With(bl, "ts", log.DefaultTimestampUTC, "caller", log.Caller(6), "module", module, "target", target)
+       return sl
+}
+
+func (sl scrapeLogger) Log(keyvals ...interface{}) error {
+       sl.bufferLogger.Log(keyvals...)
+       kvs := make([]interface{}, len(keyvals))
+       copy(kvs, keyvals)
+       // Switch level to debug for application output.
+       for i := 0; i < len(kvs); i += 2 {
+               if kvs[i] == level.Key() {
+                       kvs[i+1] = level.DebugValue()
+               }
+       }
+       return sl.next.Log(kvs...)
+}
+
 func init() {
        prometheus.MustRegister(version.NewCollector("blackbox_exporter"))
 }
@@ -193,6 +255,7 @@ func main() {
     <body>
     <h1>Blackbox Exporter</h1>
     <p><a href="/probe?target=prometheus.io&module=http_2xx">Probe prometheus.io for http_2xx</a></p>
+    <p><a href="/probe?target=prometheus.io&module=http_2xx&debug=true">Debug probe prometheus.io for http_2xx</a></p>
     <p><a href="/metrics">Metrics</a></p>
     <p><a href="/config">Configuration</a></p>
     </body>