Implementation of the Starlark run_local() function

This patch implements the Go code for starlark builtin function run_local(). This
function allows Crashd script to run arbitrary command  from on the local machine.

This patch does the followings:
- Adds Go function to support starlark builtin func for run_local
- Adds and updates tests for run_local

Signed-off-by: Vladimir Vivien <vivienv@vmware.com>

starlark/run_local.go

@@ -0,0 +1,32 @@
+// Copyright (c) 2020 VMware, Inc. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package starlark
+
+import (
+	"fmt"
+
+	"github.com/vladimirvivien/echo"
+	"go.starlark.net/starlark"
+)
+
+// runLocalFunc is a built-in starlark function that runs a provided command on the local machine.
+// It returns the result of the command as struct containing information about the executed command.
+// Starlark format: run_local(<command string>)
+func runLocalFunc(thread *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	var cmdStr string
+	if args != nil && args.Len() == 1 {
+		cmd, ok := args.Index(0).(starlark.String)
+		if !ok {
+			return starlark.None, fmt.Errorf("%s: command must be a string", identifiers.runLocal)
+		}
+		cmdStr = string(cmd)
+	}
+
+	p := echo.New().RunProc(cmdStr)
+	if p.Err() != nil {
+		return starlark.None, fmt.Errorf("%s: %s", identifiers.runLocal, p.Err())
+	}
+
+	return starlark.String(p.Result()), nil
+}

starlark/run_local_test.go

@@ -0,0 +1,84 @@
+// Copyright (c) 2020 VMware, Inc. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package starlark
+
+import (
+	"strings"
+	"testing"
+
+	"go.starlark.net/starlark"
+)
+
+func TestRunLocalFunc(t *testing.T) {
+	tests := []struct {
+		name string
+		args func(t *testing.T) starlark.Tuple
+		eval func(t *testing.T, args starlark.Tuple)
+	}{
+		{
+			name: "simple command",
+			args: func(t *testing.T) starlark.Tuple { return starlark.Tuple{starlark.String("echo 'Hello World!'")} },
+			eval: func(t *testing.T, args starlark.Tuple) {
+				val, err := runLocalFunc(newTestThreadLocal(t), nil, args, nil)
+				if err != nil {
+					t.Fatal(err)
+				}
+				result := ""
+				if r, ok := val.(starlark.String); ok {
+					result = string(r)
+				}
+				if result != "Hello World!" {
+					t.Errorf("unexpected result: %s", result)
+				}
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			test.eval(t, test.args(t))
+		})
+	}
+}
+
+func TestRunLocalScript(t *testing.T) {
+	tests := []struct {
+		name   string
+		script string
+		eval   func(t *testing.T, script string)
+	}{
+		{
+			name: "run local",
+			script: `
+result = run_local("""echo 'Hello World!'""")
+`,
+			eval: func(t *testing.T, script string) {
+				exe := New()
+				if err := exe.Exec("test.star", strings.NewReader(script)); err != nil {
+					t.Fatal(err)
+				}
+
+				resultVal := exe.result["result"]
+				if resultVal == nil {
+					t.Fatal("run_local() should be assigned to a variable for test")
+				}
+				result, ok := resultVal.(starlark.String)
+				if !ok {
+					t.Fatal("run_local() should return a string")
+				}
+
+				if string(result) != "Hello World!" {
+					t.Fatalf("uneexpected result %s", result)
+				}
+
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			test.eval(t, test.script)
+		})
+	}
+}

starlark/starlark_exec.go

@@ -75,6 +75,7 @@ func newPredeclareds() starlark.StringDict {
 		identifiers.hostListProvider: starlark.NewBuiltin(identifiers.hostListProvider, hostListProvider),
 		identifiers.resources:        starlark.NewBuiltin(identifiers.resources, resourcesFunc),
 		identifiers.run:              starlark.NewBuiltin(identifiers.run, runFunc),
+		identifiers.runLocal:         starlark.NewBuiltin(identifiers.runLocal, runLocalFunc),
 		identifiers.capture:          starlark.NewBuiltin(identifiers.capture, captureFunc),
 		identifiers.copyFrom:         starlark.NewBuiltin(identifiers.copyFrom, copyFromFunc),
 		identifiers.kubeCfg:          starlark.NewBuiltin(identifiers.kubeCfg, kubeConfigFn),

starlark/support.go

@@ -34,6 +34,7 @@ var (
 		hostResource     string
 		resources        string
 		run              string
+		runLocal         string
 		capture          string
 		copyFrom         string
 
@@ -55,6 +56,7 @@ var (
 		hostResource:     "host_resource",
 		resources:        "resources",
 		run:              "run",
+		runLocal:         "run_local",
 		capture:          "capture",
 		copyFrom:         "copy_from",