cmd/clef, signer: refresh tutorial, fix noticed issues (#19774)

* cmd/clef, signer: refresh tutorial, fix noticed issues

* cmd/clef, signer: support removing stored keys (delpw + rules)

* cmd/clef: polishes + Geth integration in the tutorial

signer/storage/aes_gcm_storage.go

@@ -53,7 +53,7 @@ func NewAESEncryptedStorage(filename string, key []byte) *AESEncryptedStorage {
 	}
 }
 
-// Put stores a value by key. 0-length keys results in no-op
+// Put stores a value by key. 0-length keys results in noop.
 func (s *AESEncryptedStorage) Put(key, value string) {
 	if len(key) == 0 {
 		return
@@ -75,27 +75,41 @@ func (s *AESEncryptedStorage) Put(key, value string) {
 	}
 }
 
-// Get returns the previously stored value, or the empty string if it does not exist or key is of 0-length
-func (s *AESEncryptedStorage) Get(key string) string {
+// Get returns the previously stored value, or an error if it does not exist or
+// key is of 0-length.
+func (s *AESEncryptedStorage) Get(key string) (string, error) {
 	if len(key) == 0 {
-		return ""
+		return "", ErrZeroKey
 	}
 	data, err := s.readEncryptedStorage()
 	if err != nil {
 		log.Warn("Failed to read encrypted storage", "err", err, "file", s.filename)
-		return ""
+		return "", err
 	}
 	encrypted, exist := data[key]
 	if !exist {
 		log.Warn("Key does not exist", "key", key)
-		return ""
+		return "", ErrNotFound
 	}
 	entry, err := decrypt(s.key, encrypted.Iv, encrypted.CipherText, []byte(key))
 	if err != nil {
 		log.Warn("Failed to decrypt key", "key", key)
-		return ""
+		return "", err
+	}
+	return string(entry), nil
+}
+
+// Del removes a key-value pair. If the key doesn't exist, the method is a noop.
+func (s *AESEncryptedStorage) Del(key string) {
+	data, err := s.readEncryptedStorage()
+	if err != nil {
+		log.Warn("Failed to read encrypted storage", "err", err, "file", s.filename)
+		return
+	}
+	delete(data, key)
+	if err = s.writeEncryptedStorage(data); err != nil {
+		log.Warn("Failed to write entry", "err", err)
 	}
-	return string(entry)
 }
 
 // readEncryptedStorage reads the file with encrypted creds

signer/storage/aes_gcm_storage_test.go

@@ -110,8 +110,8 @@ func TestEnd2End(t *testing.T) {
 	}
 
 	s1.Put("bazonk", "foobar")
-	if v := s2.Get("bazonk"); v != "foobar" {
-		t.Errorf("Expected bazonk->foobar, got '%v'", v)
+	if v, err := s2.Get("bazonk"); v != "foobar" || err != nil {
+		t.Errorf("Expected bazonk->foobar (nil error), got '%v' (%v error)", v, err)
 	}
 }
 
@@ -154,11 +154,11 @@ func TestSwappedKeys(t *testing.T) {
 		}
 	}
 	swap()
-	if v := s1.Get("k1"); v != "" {
+	if v, _ := s1.Get("k1"); v != "" {
 		t.Errorf("swapped value should return empty")
 	}
 	swap()
-	if v := s1.Get("k1"); v != "v1" {
+	if v, _ := s1.Get("k1"); v != "v1" {
 		t.Errorf("double-swapped value should work fine")
 	}
 }

signer/storage/storage.go

@@ -17,11 +17,26 @@
 
 package storage
 
+import "errors"
+
+var (
+	// ErrZeroKey is returned if an attempt was made to inset a 0-length key.
+	ErrZeroKey = errors.New("0-length key")
+
+	// ErrNotFound is returned if an unknown key is attempted to be retrieved.
+	ErrNotFound = errors.New("not found")
+)
+
 type Storage interface {
-	// Put stores a value by key. 0-length keys results in no-op
+	// Put stores a value by key. 0-length keys results in noop.
 	Put(key, value string)
-	// Get returns the previously stored value, or the empty string if it does not exist or key is of 0-length
-	Get(key string) string
+
+	// Get returns the previously stored value, or an error if the key is 0-length
+	// or unknown.
+	Get(key string) (string, error)
+
+	// Del removes a key-value pair. If the key doesn't exist, the method is a noop.
+	Del(key string)
 }
 
 // EphemeralStorage is an in-memory storage that does
@@ -31,23 +46,29 @@ type EphemeralStorage struct {
 	namespace string
 }
 
+// Put stores a value by key. 0-length keys results in noop.
 func (s *EphemeralStorage) Put(key, value string) {
 	if len(key) == 0 {
 		return
 	}
-	//fmt.Printf("storage: put %v -> %v\n", key, value)
 	s.data[key] = value
 }
 
-func (s *EphemeralStorage) Get(key string) string {
+// Get returns the previously stored value, or an error if the key is 0-length
+// or unknown.
+func (s *EphemeralStorage) Get(key string) (string, error) {
 	if len(key) == 0 {
-		return ""
+		return "", ErrZeroKey
 	}
-	//fmt.Printf("storage: get %v\n", key)
-	if v, exist := s.data[key]; exist {
-		return v
+	if v, ok := s.data[key]; ok {
+		return v, nil
 	}
-	return ""
+	return "", ErrNotFound
+}
+
+// Del removes a key-value pair. If the key doesn't exist, the method is a noop.
+func (s *EphemeralStorage) Del(key string) {
+	delete(s.data, key)
 }
 
 func NewEphemeralStorage() Storage {
@@ -61,6 +82,7 @@ func NewEphemeralStorage() Storage {
 type NoStorage struct{}
 
 func (s *NoStorage) Put(key, value string) {}
-func (s *NoStorage) Get(key string) string {
-	return ""
+func (s *NoStorage) Del(key string)        {}
+func (s *NoStorage) Get(key string) (string, error) {
+	return "", errors.New("I forgot")
 }