k8s.io/apiserver@v0.31.1/pkg/server/routes/flags.go (about)

     1  /*
     2  Copyright 2018 The Kubernetes Authors.
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package routes
    18  
    19  import (
    20  	"fmt"
    21  	"html/template"
    22  	"io/ioutil"
    23  	"net/http"
    24  	"path"
    25  	"sync"
    26  
    27  	"k8s.io/klog/v2"
    28  
    29  	"k8s.io/apiserver/pkg/server/mux"
    30  )
    31  
    32  var (
    33  	lock            = &sync.RWMutex{}
    34  	registeredFlags = map[string]debugFlag{}
    35  )
    36  
    37  // DebugFlags adds handlers for flags under /debug/flags.
    38  type DebugFlags struct {
    39  }
    40  
    41  // Install registers the APIServer's flags handler.
    42  func (f DebugFlags) Install(c *mux.PathRecorderMux, flag string, handler func(http.ResponseWriter, *http.Request)) {
    43  	c.UnlistedHandle("/debug/flags", http.HandlerFunc(f.Index))
    44  	c.UnlistedHandlePrefix("/debug/flags/", http.HandlerFunc(f.Index))
    45  
    46  	url := path.Join("/debug/flags", flag)
    47  	c.UnlistedHandleFunc(url, handler)
    48  
    49  	f.addFlag(flag)
    50  }
    51  
    52  // Index responds with the `/debug/flags` request.
    53  // For example, "/debug/flags/v" serves the "--v" flag.
    54  // Index responds to a request for "/debug/flags/" with an HTML page
    55  // listing the available flags.
    56  func (f DebugFlags) Index(w http.ResponseWriter, r *http.Request) {
    57  	lock.RLock()
    58  	defer lock.RUnlock()
    59  	if err := indexTmpl.Execute(w, registeredFlags); err != nil {
    60  		klog.Error(err)
    61  	}
    62  }
    63  
    64  var indexTmpl = template.Must(template.New("index").Parse(`<html>
    65  <head>
    66  <title>/debug/flags/</title>
    67  </head>
    68  <body>
    69  /debug/flags/<br>
    70  <br>
    71  flags:<br>
    72  <table>
    73  {{range .}}
    74  <tr>{{.Flag}}<br>
    75  {{end}}
    76  </table>
    77  <br>
    78  full flags configurable<br>
    79  </body>
    80  </html>
    81  `))
    82  
    83  type debugFlag struct {
    84  	Flag string
    85  }
    86  
    87  func (f DebugFlags) addFlag(flag string) {
    88  	lock.Lock()
    89  	defer lock.Unlock()
    90  	registeredFlags[flag] = debugFlag{flag}
    91  }
    92  
    93  // StringFlagSetterFunc is a func used for setting string type flag.
    94  type StringFlagSetterFunc func(string) (string, error)
    95  
    96  // StringFlagPutHandler wraps an http Handler to set string type flag.
    97  func StringFlagPutHandler(setter StringFlagSetterFunc) http.HandlerFunc {
    98  	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
    99  		switch {
   100  		case req.Method == "PUT":
   101  			body, err := ioutil.ReadAll(req.Body)
   102  			if err != nil {
   103  				writePlainText(http.StatusBadRequest, "error reading request body: "+err.Error(), w)
   104  				return
   105  			}
   106  			defer req.Body.Close()
   107  			response, err := setter(string(body))
   108  			if err != nil {
   109  				writePlainText(http.StatusBadRequest, err.Error(), w)
   110  				return
   111  			}
   112  			writePlainText(http.StatusOK, response, w)
   113  			return
   114  		default:
   115  			writePlainText(http.StatusNotAcceptable, "unsupported http method", w)
   116  			return
   117  		}
   118  	})
   119  }
   120  
   121  // writePlainText renders a simple string response.
   122  func writePlainText(statusCode int, text string, w http.ResponseWriter) {
   123  	w.Header().Set("Content-Type", "text/plain")
   124  	w.Header().Set("X-Content-Type-Options", "nosniff")
   125  	w.WriteHeader(statusCode)
   126  	fmt.Fprintln(w, text)
   127  }