etcdctl/check: create new check command for memory usage

Create a new command similar to check perf that can check the memory
consumption for putting different workloads on a given endpoint. If no endpoint
is provided, localhost will be used. Return user with a message that whether
there are enough memory for a given workload with pass or fail.

Fixed #9121

etcdctl/ctlv3/command/util.go

@@ -18,7 +18,11 @@ import (
 	"context"
 	"encoding/hex"
 	"fmt"
+	"io/ioutil"
+	"net/http"
 	"regexp"
+	"strconv"
+	"strings"
 
 	pb "github.com/coreos/etcd/internal/mvcc/mvccpb"
 
@@ -75,3 +79,42 @@ func commandCtx(cmd *cobra.Command) (context.Context, context.CancelFunc) {
 	}
 	return context.WithTimeout(context.Background(), timeOut)
 }
+
+// get the process_resident_memory_bytes from <server:2379>/metrics
+func endpointMemoryMetrics(host string) float64 {
+	residentMemoryKey := "process_resident_memory_bytes"
+	var residentMemoryValue string
+	if !strings.HasPrefix(host, `http://`) {
+		host = "http://" + host
+	}
+	url := host + "/metrics"
+	resp, err := http.Get(url)
+	if err != nil {
+		fmt.Println(fmt.Sprintf("fetch error: %v", err))
+		return 0.0
+	}
+	byts, readerr := ioutil.ReadAll(resp.Body)
+	resp.Body.Close()
+	if readerr != nil {
+		fmt.Println(fmt.Sprintf("fetch error: reading %s: %v", url, readerr))
+		return 0.0
+	}
+
+	for _, line := range strings.Split(string(byts), "\n") {
+		if strings.HasPrefix(line, residentMemoryKey) {
+			residentMemoryValue = strings.TrimSpace(strings.TrimPrefix(line, residentMemoryKey))
+			break
+		}
+	}
+	if residentMemoryValue == "" {
+		fmt.Println(fmt.Sprintf("could not find: %v", residentMemoryKey))
+		return 0.0
+	}
+	residentMemoryBytes, parseErr := strconv.ParseFloat(residentMemoryValue, 64)
+	if parseErr != nil {
+		fmt.Println(fmt.Sprintf("parse error: %v", parseErr))
+		return 0.0
+	}
+
+	return residentMemoryBytes
+}