Add DebugAPI client

DebugAPI implements the API interface and simply adds debug/trace logging to all calls made through it. This way we can get nice debug messages such as:

```
DEBU[2019-06-07T08:15:27-07:00] http://localhost:9090/api/v1/read             api=GetValue end="2019-06-07 08:11:33.855 -0700 PDT" matchers="[__name__=\"prometheus_api_remote_read_queries\"]" start="2019-06-07 07:06:33.855 -0700 PDT"
```

To avoid the performance overhead this layer is only added when the log level is >= debug.

Fixes #163

promclient/debug.go

@@ -0,0 +1,126 @@
+package promclient
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	v1 "github.com/prometheus/client_golang/api/prometheus/v1"
+	"github.com/prometheus/common/model"
+	"github.com/prometheus/prometheus/pkg/labels"
+	"github.com/sirupsen/logrus"
+)
+
+// DebugAPI simply logs debug lines for the given API with the given prefix
+type DebugAPI struct {
+	API
+	PrefixMessage string
+}
+
+// LabelValues performs a query for the values of the given label.
+func (d *DebugAPI) LabelValues(ctx context.Context, label string) (model.LabelValues, error) {
+	logrus.WithFields(logrus.Fields{
+		"api":   "LabelValues",
+		"label": label,
+	}).Debug(d.PrefixMessage)
+
+	v, err := d.API.LabelValues(ctx, label)
+
+	logrus.WithFields(logrus.Fields{
+		"api":   "LabelValues",
+		"label": label,
+		"value": v,
+		"error": err,
+	}).Trace(d.PrefixMessage)
+
+	return v, err
+}
+
+// Query performs a query for the given time.
+func (d *DebugAPI) Query(ctx context.Context, query string, ts time.Time) (model.Value, error) {
+	logrus.WithFields(logrus.Fields{
+		"api":   "Query",
+		"query": query,
+		"ts":    ts,
+	}).Debug(d.PrefixMessage)
+
+	v, err := d.API.Query(ctx, query, ts)
+
+	logrus.WithFields(logrus.Fields{
+		"api":   "Query",
+		"query": query,
+		"ts":    ts,
+		"value": v,
+		"error": err,
+	}).Trace(d.PrefixMessage)
+
+	return v, err
+}
+
+// QueryRange performs a query for the given range.
+func (d *DebugAPI) QueryRange(ctx context.Context, query string, r v1.Range) (model.Value, error) {
+	fmt.Println("what")
+	logrus.WithFields(logrus.Fields{
+		"api":   "QueryRange",
+		"query": query,
+		"r":     r,
+	}).Debug(d.PrefixMessage)
+
+	v, err := d.API.QueryRange(ctx, query, r)
+
+	logrus.WithFields(logrus.Fields{
+		"api":   "QueryRange",
+		"query": query,
+		"r":     r,
+		"value": v,
+		"error": err,
+	}).Trace(d.PrefixMessage)
+
+	return v, err
+}
+
+// Series finds series by label matchers.
+func (d *DebugAPI) Series(ctx context.Context, matches []string, startTime time.Time, endTime time.Time) ([]model.LabelSet, error) {
+	logrus.WithFields(logrus.Fields{
+		"api":       "Series",
+		"matches":   matches,
+		"startTime": startTime,
+		"endTime":   endTime,
+	}).Debug(d.PrefixMessage)
+
+	v, err := d.API.Series(ctx, matches, startTime, endTime)
+
+	logrus.WithFields(logrus.Fields{
+		"api":       "Series",
+		"matches":   matches,
+		"startTime": startTime,
+		"endTime":   endTime,
+		"value":     v,
+		"error":     err,
+	}).Trace(d.PrefixMessage)
+
+	return v, err
+}
+
+// GetValue loads the raw data for a given set of matchers in the time range
+func (d *DebugAPI) GetValue(ctx context.Context, start, end time.Time, matchers []*labels.Matcher) (model.Value, error) {
+	logrus.WithFields(logrus.Fields{
+		"api":      "GetValue",
+		"start":    start,
+		"end":      end,
+		"matchers": matchers,
+	}).Debug(d.PrefixMessage)
+
+	v, err := d.API.GetValue(ctx, start, end, matchers)
+
+	logrus.WithFields(logrus.Fields{
+		"api":      "GetValue",
+		"start":    start,
+		"end":      end,
+		"matchers": matchers,
+		"value":    v,
+		"error":    err,
+	}).Trace(d.PrefixMessage)
+
+	return v, err
+}

servergroup/servergroup.go

@@ -22,6 +22,7 @@ import (
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/relabel"
 	"github.com/prometheus/prometheus/storage/remote"
+	"github.com/sirupsen/logrus"
 
 	"github.com/jacksontj/promxy/promclient"
 
@@ -123,9 +124,9 @@ func (s *ServerGroup) Sync() {
 						panic(err) // TODO: shouldn't be possible? If this happens I guess we log and skip?
 					}
 
-					promAPIClient := &promclient.PromAPIV1{v1.NewAPI(client)}
-
 					var apiClient promclient.API
+					apiClient = &promclient.PromAPIV1{v1.NewAPI(client)}
+
 					if s.Cfg.RemoteRead {
 						u.Path = path.Join(u.Path, "api/v1/read")
 						cfg := &remote.ClientConfig{
@@ -138,9 +139,7 @@ func (s *ServerGroup) Sync() {
 							panic(err)
 						}
 
-						apiClient = &promclient.PromAPIRemoteRead{promAPIClient, remoteStorageClient}
-					} else {
-						apiClient = promAPIClient
+						apiClient = &promclient.PromAPIRemoteRead{apiClient, remoteStorageClient}
 					}
 
 					// Optionally add time range layers
@@ -169,7 +168,17 @@ func (s *ServerGroup) Sync() {
 						}
 					}
 
-					apiClients = append(apiClients, &promclient.AddLabelClient{apiClient, target.Merge(s.Cfg.Labels)})
+					// Add labels
+					apiClient = &promclient.AddLabelClient{apiClient, target.Merge(s.Cfg.Labels)}
+
+					// If debug logging is enabled, wrap the client with a debugAPI client
+					// Since these are called in the reverse order of what we add, we want
+					// to make sure that this is the last wrap of the client
+					if logrus.GetLevel() >= logrus.DebugLevel {
+						apiClient = &promclient.DebugAPI{apiClient, u.String()}
+					}
+
+					apiClients = append(apiClients, apiClient)
 				}
 			}
 		}