Support filtering connections using expr in report connz

Signed-off-by: R.I.Pienaar <[email protected]>

cli/cheats/server.md

@@ -14,6 +14,9 @@ nats server report connz --account WEATHER
 nats server report connz --sort in-msgs
 nats server report connz --top 10 --sort in-msgs
 
+# To limit connections report to surveyor connections and all from a specific IP using https://expr.medv.io/docs/Language-Definition
+nats server report connz --filter 'lower(conns.name) matches "surveyor" || conns.ip == "46.101.44.80"'
+
 # To report on accounts
 nats server report accounts
 nats server report accounts --account WEATHER --sort in-msgs --top 10

cli/server_report_command.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"sort"
 
+	"github.com/antonmedv/expr"
 	"github.com/choria-io/fisk"
 	"github.com/dustin/go-humanize"
 	"github.com/fatih/color"
@@ -28,16 +29,17 @@ import (
 type SrvReportCmd struct {
 	json bool
 
-	account string
-	waitFor int
-	sort    string
-	topk    int
-	reverse bool
-	compact bool
-	subject string
-	server  string
-	cluster string
-	tags    []string
+	filterExpression string
+	account          string
+	waitFor          int
+	sort             string
+	topk             int
+	reverse          bool
+	compact          bool
+	subject          string
+	server           string
+	cluster          string
+	tags             []string
 }
 
 type srvReportAccountInfo struct {
@@ -72,6 +74,7 @@ func configureServerReportCommand(srv *fisk.CmdClause) {
 	conns.Flag("top", "Limit results to the top results").Default("1000").IntVar(&c.topk)
 	conns.Flag("subject", "Limits responses only to those connections with matching subscription interest").StringVar(&c.subject)
 	conns.Flag("json", "Produce JSON output").Short('j').UnNegatableBoolVar(&c.json)
+	conns.Flag("filter", "Expression based filter for connections").StringVar(&c.filterExpression)
 
 	acct := report.Command("accounts", "Report on account activity").Alias("acct").Action(c.reportAccount)
 	acct.Arg("account", "Account to produce a report for").StringVar(&c.account)
@@ -492,7 +495,7 @@ func (c *SrvReportCmd) reportConnections(_ *fisk.ParseContext) error {
 		return fmt.Errorf("did not get results from any servers")
 	}
 
-	conns := connz.flatConnInfo()
+	conns := connz.flatConnInfo(c.filterExpression)
 
 	if c.json {
 		printJSON(conns)
@@ -624,10 +627,39 @@ func (c *SrvReportCmd) renderConnections(report []connInfo) {
 
 type connzList []*server.ServerAPIConnzResponse
 
-func (c connzList) flatConnInfo() []connInfo {
+func (c connzList) flatConnInfo(filter string) []connInfo {
 	var conns []connInfo
 	for _, conn := range c {
+		srv := structWithoutOmitEmpty(*conn.Server)
+
 		for _, c := range conn.Data.Conns {
+			if filter != "" {
+				ci := structWithoutOmitEmpty(*c)
+				env := map[string]any{
+					"server": srv,
+					"Server": conn.Server,
+					"conns":  ci,
+					"Conns":  c,
+				}
+
+				program, err := expr.Compile(filter, expr.Env(env), expr.AsBool())
+				fisk.FatalIfError(err, "Invalid expression: %v", err)
+
+				out, err := expr.Run(program, env)
+				if err != nil {
+					fisk.FatalIfError(err, "Invalid expression: %v", err)
+				}
+
+				should, ok := out.(bool)
+				if !ok {
+					fisk.FatalIfError(err, "expression did not return a boolean")
+				}
+
+				if !should {
+					continue
+				}
+			}
+
 			conns = append(conns, connInfo{c, conn.Server})
 		}
 	}

cli/util.go

@@ -27,6 +27,7 @@ import (
 	"net/textproto"
 	"os"
 	"os/exec"
+	"reflect"
 	"regexp"
 	"sort"
 	"strconv"
@@ -1324,3 +1325,38 @@ func filterDataThroughCmd(data []byte, filter, subject, stream string) ([]byte,
 	// maybe we want to do something on error?
 	return runner.CombinedOutput()
 }
+
+// given a non pointer instance of a type with a lot of omitempty json tags will return a new instance without those
+//
+// does not handle nested values
+func structWithoutOmitEmpty(s any) any {
+	st := reflect.TypeOf(s)
+
+	// It's a pointer struct, convert to the value that it points to.
+	if st.Kind() == reflect.Ptr {
+		st = st.Elem()
+	}
+
+	fs := []reflect.StructField{}
+	for i := 0; i < st.NumField(); i++ {
+		field := st.Field(i)
+		field.Tag = reflect.StructTag(strings.ReplaceAll(string(field.Tag), ",omitempty", ""))
+		fs = append(fs, field)
+	}
+
+	st2 := reflect.StructOf(fs)
+	v := reflect.ValueOf(s)
+
+	j, err := json.Marshal(v.Convert(st2).Interface())
+	if err != nil {
+		panic(err)
+	}
+
+	var res any
+	err = json.Unmarshal(j, &res)
+	if err != nil {
+		panic(err)
+	}
+
+	return res
+}

go.mod

@@ -47,6 +47,7 @@ require (
 	github.com/prometheus/client_model v0.4.0 // indirect
 	github.com/prometheus/procfs v0.11.1 // indirect
 	github.com/rivo/uniseg v0.4.4 // indirect
+	github.com/sevlyar/retag v0.0.0-20190429052747-c3f10e304082 // indirect
 	golang.org/x/net v0.15.0 // indirect
 	golang.org/x/sys v0.12.0 // indirect
 	golang.org/x/text v0.13.0 // indirect

go.sum

@@ -112,6 +112,8 @@ github.com/rivo/uniseg v0.4.4/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUc
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/santhosh-tekuri/jsonschema/v5 v5.3.1 h1:lZUw3E0/J3roVtGQ+SCrUrg3ON6NgVqpn3+iol9aGu4=
 github.com/santhosh-tekuri/jsonschema/v5 v5.3.1/go.mod h1:uToXkOrWAZ6/Oc07xWQrPOhJotwFIyu2bBVN41fcDUY=
+github.com/sevlyar/retag v0.0.0-20190429052747-c3f10e304082 h1:fj05fHX+p6w6xqPfvEjFtdu95JwguF0Kg1cz/sht8+U=
+github.com/sevlyar/retag v0.0.0-20190429052747-c3f10e304082/go.mod h1:mOWh3Kdot9kBKCLbKcJTzIBBEPKRJAq2lk03eVVDmco=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
 github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=