noop: allow specifying debug file in config JSON

Chaining sends different config JSON to each plugin, but the same
environment, and if we want to test multiple noop plugin runs in
the same chain we need a way of telling each run to use a different
debug file.

plugins/test/noop/main.go

@@ -22,19 +22,38 @@ the JSON encoding of a Debug.
 package main
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"strings"
 
 	"github.com/containernetworking/cni/pkg/skel"
+	"github.com/containernetworking/cni/pkg/types"
 	"github.com/containernetworking/cni/pkg/version"
 	noop_debug "github.com/containernetworking/cni/plugins/test/noop/debug"
 )
 
+type NetConf struct {
+	types.NetConf
+	DebugFile string `json:"debugFile"`
+}
+
+func loadConf(bytes []byte) (*NetConf, error) {
+	n := &NetConf{}
+	if err := json.Unmarshal(bytes, n); err != nil {
+		return nil, fmt.Errorf("failed to load netconf: %v", err)
+	}
+	return n, nil
+}
+
 // parse extra args i.e. FOO=BAR;ABC=123
 func parseExtraArgs(args string) (map[string]string, error) {
 	m := make(map[string]string)
+	if len(args) == 0 {
+		return m, nil
+	}
 
 	items := strings.Split(args, ";")
 	for _, item := range items {
@@ -47,16 +66,34 @@ func parseExtraArgs(args string) (map[string]string, error) {
 	return m, nil
 }
 
-func debugBehavior(args *skel.CmdArgs, command string) error {
-	extraArgs, err := parseExtraArgs(args.Args)
+func getDebugFilePath(stdinData []byte, args string) (string, error) {
+	netConf, err := loadConf(stdinData)
 	if err != nil {
-		return err
+		return "", err
+	}
+
+	extraArgs, err := parseExtraArgs(args)
+	if err != nil {
+		return "", err
 	}
 
 	debugFilePath, ok := extraArgs["DEBUG"]
 	if !ok {
+		debugFilePath = netConf.DebugFile
+	}
+
+	return debugFilePath, nil
+}
+
+func debugBehavior(args *skel.CmdArgs, command string) error {
+	debugFilePath, err := getDebugFilePath(args.StdinData, args.Args)
+	if err != nil {
+		return err
+	}
+
+	if debugFilePath == "" {
 		fmt.Printf(`{}`)
-		os.Stderr.WriteString("CNI_ARGS empty, no debug behavior\n")
+		os.Stderr.WriteString("CNI_ARGS or config empty, no debug behavior\n")
 		return nil
 	}
 
@@ -88,21 +125,16 @@ func debugBehavior(args *skel.CmdArgs, command string) error {
 	return nil
 }
 
-func debugGetSupportedVersions() []string {
+func debugGetSupportedVersions(stdinData []byte) []string {
 	vers := []string{"0.-42.0", "0.1.0", "0.2.0"}
 	cniArgs := os.Getenv("CNI_ARGS")
 	if cniArgs == "" {
 		return vers
 	}
 
-	extraArgs, err := parseExtraArgs(cniArgs)
+	debugFilePath, err := getDebugFilePath(stdinData, cniArgs)
 	if err != nil {
-		panic("test setup error: invalid CNI_ARGS format")
-	}
-
-	debugFilePath, ok := extraArgs["DEBUG"]
-	if !ok {
-		panic("test setup error: missing DEBUG in CNI_ARGS")
+		panic("test setup error: unable to get debug file path: " + err.Error())
 	}
 
 	debug, err := noop_debug.ReadDebug(debugFilePath)
@@ -123,7 +155,36 @@ func cmdDel(args *skel.CmdArgs) error {
 	return debugBehavior(args, "DEL")
 }
 
+func saveStdin() ([]byte, error) {
+	// Read original stdin
+	stdinData, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		return nil, err
+	}
+
+	// Make a new pipe for stdin, and write original stdin data to it
+	r, w, err := os.Pipe()
+	if err != nil {
+		return nil, err
+	}
+	if _, err := w.Write(stdinData); err != nil {
+		return nil, err
+	}
+	if err := w.Close(); err != nil {
+		return nil, err
+	}
+
+	os.Stdin = r
+	return stdinData, nil
+}
+
 func main() {
-	supportedVersions := debugGetSupportedVersions()
+	// Grab and read stdin before pkg/skel gets it
+	stdinData, err := saveStdin()
+	if err != nil {
+		panic("test setup error: unable to read stdin: " + err.Error())
+	}
+
+	supportedVersions := debugGetSupportedVersions(stdinData)
 	skel.PluginMain(cmdAdd, cmdDel, version.PluginSupports(supportedVersions...))
 }