features: add local_feature_negotiated / global_feature_negotiated helpers.

We currently generally assume the features we offer are fixed; this
makes the code clearer and handles where we offer features iff
EXPERIMENTAL_FEATURES=1

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/features.c

@@ -133,3 +133,18 @@ bool features_supported(const u8 *globalfeatures, const u8 *localfeatures)
 					  ARRAY_SIZE(our_localfeatures));
 }
 
+bool local_feature_negotiated(const u8 *lfeatures, size_t f)
+{
+	if (!feature_offered(lfeatures, f))
+		return false;
+	return feature_supported(f, our_localfeatures,
+				 ARRAY_SIZE(our_localfeatures));
+}
+
+bool global_feature_negotiated(const u8 *gfeatures, size_t f)
+{
+	if (!feature_offered(gfeatures, f))
+		return false;
+	return feature_supported(f, our_globalfeatures,
+				 ARRAY_SIZE(our_globalfeatures));
+}

common/features.h

@@ -14,6 +14,10 @@ u8 *get_offered_localfeatures(const tal_t *ctx);
 /* Is this feature bit requested? (Either compulsory or optional) */
 bool feature_offered(const u8 *features, size_t f);
 
+/* Was this feature bit offered by them and us? */
+bool local_feature_negotiated(const u8 *lfeatures, size_t f);
+bool global_feature_negotiated(const u8 *gfeatures, size_t f);
+
 #define COMPULSORY_FEATURE(x)	(x)
 #define OPTIONAL_FEATURE(x)	((x)+1)