chore: add support for native sha256() function (#881)

* chore: add support for native `sha256()` function

* Add documentation

docs/docs/jsonnet/native-functions.md

@@ -18,6 +18,32 @@ To use them in your code, you need to access them using `std.native` from the st
 
 `std.native` takes the native function's name as a `string` argument and returns a `function`, which is called using the second set of parentheses.
 
+## sha256
+
+### Signature
+
+```ts
+sha256(string str) string
+```
+
+`sha256` computes the SHA256 sum of the given string.
+
+### Examples
+
+```jsonnet
+{
+  sum: std.native('sha256')('Hello, World!'),
+}
+```
+
+Evaluating with Tanka results in the JSON:
+
+```json
+{
+  "sum": "dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f"
+}
+```
+
 ## parseJson
 
 ### Signature

pkg/jsonnet/native/funcs.go

@@ -2,7 +2,9 @@ package native
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"encoding/json"
+	"fmt"
 	"io"
 	"regexp"
 	"strings"
@@ -32,6 +34,9 @@ func Funcs() []*jsonnet.NativeFunction {
 		regexMatch(),
 		regexSubst(),
 
+		// Hash functions
+		hashSha256(),
+
 		helm.NativeFunc(helm.ExecHelm{}),
 		kustomize.NativeFunc(kustomize.ExecKustomize{}),
 	}
@@ -50,6 +55,18 @@ func parseJSON() *jsonnet.NativeFunction {
 	}
 }
 
+func hashSha256() *jsonnet.NativeFunction {
+	return &jsonnet.NativeFunction{
+		Name:   "sha256",
+		Params: ast.Identifiers{"str"},
+		Func: func(dataString []interface{}) (interface{}, error) {
+			h := sha256.New()
+			h.Write([]byte(dataString[0].(string)))
+			return fmt.Sprintf("%x", h.Sum(nil)), nil
+		},
+	}
+}
+
 // parseYAML wraps `yaml.Unmarshal` to convert a string of yaml document(s) into a (set of) dicts
 func parseYAML() *jsonnet.NativeFunction {
 	return &jsonnet.NativeFunction{

pkg/jsonnet/native/funcs_test.go

@@ -21,6 +21,14 @@ func callNative(name string, data []interface{}) (res interface{}, err error, ca
 	return nil, nil, fmt.Errorf("could not find native function %s", name)
 }
 
+func TestSha256(t *testing.T) {
+	ret, err, callerr := callNative("sha256", []interface{}{"foo"})
+
+	assert.Empty(t, callerr)
+	assert.Equal(t, "2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae", ret)
+	assert.Empty(t, err)
+}
+
 func TestParseJSONEmptyDict(t *testing.T) {
 	ret, err, callerr := callNative("parseJson", []interface{}{"{}"})