From 0d25e68c50ad533c5a8ce0521496e7ce2fa22f4b Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Wed, 18 Sep 2019 10:53:51 -0700
Subject: [PATCH] ircd::m: Support query for non-membership with empty string
 to interface.

---
 include/ircd/m/membership.h | 11 +++++++----
 ircd/m.cc                   | 26 +++++++++++++++++++-------
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/include/ircd/m/membership.h b/include/ircd/m/membership.h
index 01bbcbdfa..d5da58f83 100644
--- a/include/ircd/m/membership.h
+++ b/include/ircd/m/membership.h
@@ -20,13 +20,16 @@ namespace ircd::m
 	// is not checked here, only content.membership is sought.
 	string_view membership(const mutable_buffer &out, const event::idx &);
 
-	// Query and compare membership string to argument string. Returns
-	// true on equal; false on not equal; false on not found.
-	bool membership(const event::idx &, const string_view &);
-
 	// Query and copy membership string to buffer; queries room state. (also room.h)
 	string_view membership(const mutable_buffer &out, const room &, const id::user &);
 
+	// Query and compare membership string to argument string. Returns true on
+	// equal; false on not equal; false on not found. Note in addition to this
+	// we allow the user to pass an empty membership string which will test for
+	// non-membership as well and return true.
+	bool membership(const event::idx &, const string_view &);
+
 	// Query and compare membership string; queries room state. (also room.h)
+	// also see overload notes.
 	bool membership(const room &, const id::user &, const string_view &);
 }
diff --git a/ircd/m.cc b/ircd/m.cc
index b97c92dba..b51581c2f 100644
--- a/ircd/m.cc
+++ b/ircd/m.cc
@@ -2363,16 +2363,28 @@ bool
 ircd::m::membership(const event::idx &event_idx,
                     const string_view &membership)
 {
-	return m::query(std::nothrow, event_idx, "content", [&membership]
-	(const json::object &content)
+	bool ret; // not initialized unless fetched=true below
+	const auto closure
 	{
-		const json::string &content_membership
+		[&membership, &ret](const json::object &content)
 		{
-			content["membership"]
-		};
+			const json::string &content_membership
+			{
+				content["membership"]
+			};
 
-		return content_membership == membership;
-	});
+			ret = membership && content_membership == membership;
+		}
+	};
+
+	const bool fetched
+	{
+		m::get(std::nothrow, event_idx, "content", closure)
+	};
+
+	// In addition to the intuitive behavior of this function, we allow the
+	// user to pass an empty membership string to test non-membership as well.
+	return (fetched && ret) || (!fetched && !membership);
 }
 
 ircd::string_view