Add Profiler Admin API (#6463)

Two handlers are added to admin API to enable profiling and disable
profiling of a server in a standalone mode, or all nodes in the
distributed mode.

/minio/admin/profiling/start/{cpu,block,mem}:
  - Start profiling and return starting JSON results, e.g. one
    node is offline.

/minio/admin/profiling/download:
  - Stop the on-going profiling task
  - Stream a zip file which contains all profiling files that can
    be later inspected by go tool pprof

cmd/local-admin-client.go

@@ -19,7 +19,11 @@ package cmd
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"os"
+
+	"io/ioutil"
 )
 
 // localAdminClient - represents admin operation to be executed locally.
@@ -80,3 +84,40 @@ func (lc localAdminClient) GetConfig() ([]byte, error) {
 
 	return json.Marshal(globalServerConfig)
 }
+
+// StartProfiling - starts profiling on the local server.
+func (lc localAdminClient) StartProfiling(profiler string) error {
+	if globalProfiler != nil {
+		globalProfiler.Stop()
+	}
+	prof, err := startProfiler(profiler, "")
+	if err != nil {
+		return err
+	}
+	globalProfiler = prof
+	return nil
+}
+
+// DownloadProfilingData - stops and returns profiling data of the local server.
+func (lc localAdminClient) DownloadProfilingData() ([]byte, error) {
+	if globalProfiler == nil {
+		return nil, errors.New("profiler not enabled")
+	}
+
+	profilerPath := globalProfiler.Path()
+
+	// Stop the profiler
+	globalProfiler.Stop()
+
+	profilerFile, err := os.Open(profilerPath)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := ioutil.ReadAll(profilerFile)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}