truncate custom jmespath function (#2836)

* [feature] custom jmespath truncate function

Signed-off-by: Danny Kulchinsky <dkulchinsky@fastly.com>

* formatting

Signed-off-by: Danny Kulchinsky <dkulchinsky@fastly.com>

* simplify naming a bit

Signed-off-by: Danny Kulchinsky <dkulchinsky@fastly.com>

Co-authored-by: shuting <shutting06@gmail.com>

go.mod

@@ -54,6 +54,7 @@ require (
 )
 
 require (
+	github.com/aquilax/truncate v1.0.0 // indirect
 	github.com/opencontainers/image-spec v1.0.2 // indirect
 	gopkg.in/inf.v0 v0.9.1
 )

go.sum

@@ -222,6 +222,8 @@ github.com/apex/logs v0.0.4/go.mod h1:XzxuLZ5myVHDy9SAmYpamKKRNApGj54PfYLcFrXqDw
 github.com/aphistic/golf v0.0.0-20180712155816-02c07f170c5a/go.mod h1:3NqKYiepwy8kCu4PNA+aP7WUV72eXWJeP9/r3/K9aLE=
 github.com/aphistic/sweet v0.2.0/go.mod h1:fWDlIh/isSE9n6EPsRmC0det+whmX6dJid3stzu0Xys=
 github.com/appscode/jsonpatch v0.0.0-20190108182946-7c0e3b262f30/go.mod h1:4AJxUpXUhv4N+ziTvIcWWXgeorXpxPZOfk9HdEVr96M=
+github.com/aquilax/truncate v1.0.0 h1:UgIGS8U/aZ4JyOJ2h3xcF5cSQ06+gGBnjxH2RUHJe0U=
+github.com/aquilax/truncate v1.0.0/go.mod h1:BeMESIDMlvlS3bmg4BVvBbbZUNwWtS8uzYPAKXwwhLw=
 github.com/armon/circbuf v0.0.0-20150827004946-bbbad097214e/go.mod h1:3U/XgcO3hCbHZ8TKRvWD2dDTCfh9M9ya+I9JpbB7O8o=
 github.com/armon/consul-api v0.0.0-20180202201655-eb2c6b5be1b6/go.mod h1:grANhF5doyWs3UAsr3K4I6qtAmlQcZDesFNEHPZAzj8=
 github.com/armon/go-metrics v0.0.0-20180917152333-f0300d1749da/go.mod h1:Q73ZrmVTwzkszR9V5SSuryQ31EELlFMUz1kKyl939pY=

pkg/engine/jmespath/functions.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	trunc "github.com/aquilax/truncate"
 	gojmespath "github.com/jmespath/go-jmespath"
 	"github.com/minio/pkg/wildcard"
 )
@@ -53,6 +54,7 @@ var (
 	base64Encode           = "base64_encode"
 	timeSince              = "time_since"
 	pathCanonicalize       = "path_canonicalize"
+	truncate               = "truncate"
 )
 
 const errorPrefix = "JMESPath function '%s': "
@@ -242,6 +244,14 @@ func getFunctions() []*gojmespath.FunctionEntry {
 			},
 			Handler: jpPathCanonicalize,
 		},
+		{
+			Name: truncate,
+			Arguments: []ArgSpec{
+				{Types: []JpType{JpString}},
+				{Types: []JpType{JpNumber}},
+			},
+			Handler: jpTruncate,
+		},
 	}
 
 }
@@ -600,6 +610,20 @@ func jpPathCanonicalize(arguments []interface{}) (interface{}, error) {
 	return filepath.Join(str.String()), nil
 }
 
+func jpTruncate(arguments []interface{}) (interface{}, error) {
+	var err error
+	str, err := validateArg(truncate, arguments, 0, reflect.String)
+	if err != nil {
+		return nil, err
+	}
+	length, err := validateArg(truncate, arguments, 1, reflect.Float64)
+	if err != nil {
+		return nil, err
+	}
+
+	return trunc.Truncator(str.String(), int(length.Float()), trunc.CutStrategy{}), nil
+}
+
 // InterfaceToString casts an interface to a string type
 func ifaceToString(iface interface{}) (string, error) {
 	switch i := iface.(type) {

pkg/engine/jmespath/functions_test.go

@@ -972,3 +972,42 @@ func Test_PathCanonicalize(t *testing.T) {
 		})
 	}
 }
+
+func Test_Truncate(t *testing.T) {
+	// Can't use integer literals due to
+	// https://github.com/jmespath/go-jmespath/issues/27
+	//
+	// TODO: fix this in https://github.com/kyverno/go-jmespath
+
+	testCases := []struct {
+		jmesPath       string
+		expectedResult string
+	}{
+		{
+			jmesPath:       "truncate('Lorem ipsum dolor sit amet', `5`)",
+			expectedResult: "Lorem",
+		},
+		{
+			jmesPath:       "truncate('Lorem ipsum ipsum ipsum dolor sit amet', `11`)",
+			expectedResult: "Lorem ipsum",
+		},
+		{
+			jmesPath:       "truncate('Lorem ipsum ipsum ipsum dolor sit amet', `40`)",
+			expectedResult: "Lorem ipsum ipsum ipsum dolor sit amet",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.jmesPath, func(t *testing.T) {
+			jp, err := New(tc.jmesPath)
+			assert.NilError(t, err)
+
+			result, err := jp.Search("")
+			assert.NilError(t, err)
+
+			res, ok := result.(string)
+			assert.Assert(t, ok)
+			assert.Equal(t, res, tc.expectedResult)
+		})
+	}
+}