refactor webhook *NewPost (#20729)

* refactor webhook *NewPost

* remove empty values

* always show errs.Message

* remove utils.IsValidSlackChannel

* move IsValidSlackChannel to services/webhook package

* binding: handle empty Message case

* make IsValidSlackChannel more strict

services/webhook/slack_test.go

@@ -170,3 +170,22 @@ func TestSlackJSONPayload(t *testing.T) {
 	require.NoError(t, err)
 	assert.NotEmpty(t, json)
 }
+
+func TestIsValidSlackChannel(t *testing.T) {
+	tt := []struct {
+		channelName string
+		expected    bool
+	}{
+		{"gitea", true},
+		{"#gitea", true},
+		{"  ", false},
+		{"#", false},
+		{" #", false},
+		{"gitea   ", false},
+		{"  gitea", false},
+	}
+
+	for _, v := range tt {
+		assert.Equal(t, v.expected, IsValidSlackChannel(v.channelName))
+	}
+}