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rate_control.go
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rate_control.go
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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package rate contains functionality to deal with rates.
package rate
import (
"fmt"
"io/ioutil"
"net/http"
"strconv"
"strings"
"time"
"github.com/Arend-melissant/simhospital/pkg/logging"
)
var log = logging.ForCallerPackage()
// Controller is a rate controller.
type Controller struct {
rate float64
per time.Duration
rateChanged chan bool
}
// NewController creates a new Controller.
func NewController(rate float64, per time.Duration) *Controller {
return &Controller{
rate: rate,
per: per,
rateChanged: make(chan bool),
}
}
// ServeHTTP handles the requests made from the slider on the control dashboard.
func (c *Controller) ServeHTTP(w http.ResponseWriter, r *http.Request) {
switch r.Method {
case "GET":
s := strconv.FormatFloat(c.rate, 'f', -1, 64)
w.Write([]byte(s))
case "POST":
c.handlePost(w, r)
case "PUT", "DELETE":
http.Error(w, fmt.Sprintf("Method %q not implemented", r.Method), http.StatusInternalServerError)
default:
http.Error(w, fmt.Sprintf("Unknown method: %q", r.Method), http.StatusInternalServerError)
}
}
func (c *Controller) handlePost(w http.ResponseWriter, r *http.Request) {
defer r.Body.Close()
body, err := ioutil.ReadAll(r.Body)
errStr := "Failed to change the rate value"
if err != nil {
log.WithError(err).Warning(errStr)
http.Error(w, "Error reading request body", http.StatusInternalServerError)
return
}
sbody := string(body)
prefix := "value="
if !strings.HasPrefix(sbody, prefix) {
log.Warningf("%s: missing prefix %q in request body: %q", errStr, prefix, sbody)
http.Error(w, `Error extracting value: the request must be in the format "value=X"`, http.StatusInternalServerError)
return
}
svalue := strings.TrimPrefix(sbody, prefix)
f, err := strconv.ParseFloat(svalue, 64)
if err != nil {
log.WithError(err).Warning(errStr)
http.Error(w, "Error parsing value to float", http.StatusInternalServerError)
return
}
if f < 0 {
msg := fmt.Sprintf("Invalid value: rate per minute must be greater that zero, but was: %v", f)
log.Warningf("%s: %s", errStr, msg)
http.Error(w, msg, http.StatusInternalServerError)
return
}
// Sometimes we get a POST message even if the value didn't change.
if c.rate != f {
c.rate = f
c.rateChanged <- true
}
}
func (c *Controller) heartbeat() time.Duration {
return time.Duration(float64(c.per) / c.rate)
}
// Heartbeat returns a duration between two pathways based on rate and per values.
// If the rate is set to zero, returns the maximum duration value.
func (c *Controller) Heartbeat() time.Duration {
if c.rate == 0 {
log.Infof("Rate set to %v / %v. Not generating pathway", c.rate, c.per)
// Max Duration value.
return time.Duration(1<<63 - 1)
}
h := c.heartbeat()
log.Debugf("Rate set to %v / %v. Generating one pathway every %v", c.rate, c.per, h)
return h
}
// RateChanged returns a channel, where the changes of the rate are signaled.
func (c *Controller) RateChanged() <-chan bool {
return c.rateChanged
}
// InitialElapsed returns a value of the heartbeat, if the rate is not zero.
// Otherwise, returns zero.
func (c *Controller) InitialElapsed() time.Duration {
if c.rate > 0 {
return c.heartbeat()
}
return 0
}