From d17ac6a8bb2b600d7aa050027665dea0953553df Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sat, 30 Mar 2019 16:35:05 -0700
Subject: [PATCH] ircd::m::id: Add id part-swapping interface.

---
 include/ircd/m/id.h |  6 ++++++
 ircd/m_id.cc        | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/ircd/m/id.h b/include/ircd/m/id.h
index e91c72374..5e6ade1da 100644
--- a/include/ircd/m/id.h
+++ b/include/ircd/m/id.h
@@ -74,6 +74,12 @@ struct ircd::m::id
 	uint16_t port() const;            // Just the port number or 0 if none
 	bool literal() const;             // Whether the hostname() is IP literal
 
+	// Rewrites the ID so the local and host parts are swapped; for indexing.
+	// e.g. `$foo:bar.com` becomes `bar.com$foo`; unswap() reverses to normal.
+	static id unswap(const string_view &, const mutable_buffer &);
+	static string_view swap(const id &, const mutable_buffer &);
+	string_view swap(const mutable_buffer &) const;
+
 	IRCD_USING_OVERLOAD(generate, m::generate);
 
 	id(const enum sigil &, const mutable_buffer &, const generate_t &, const string_view &host);
diff --git a/ircd/m_id.cc b/ircd/m_id.cc
index d4b0f54e7..2e43afb2b 100644
--- a/ircd/m_id.cc
+++ b/ircd/m_id.cc
@@ -456,6 +456,48 @@ ircd::m::id::id(const enum sigil &sigil,
 {
 }
 
+ircd::string_view
+ircd::m::id::swap(const mutable_buffer &buf)
+const
+{
+	return swap(*this, buf);
+}
+
+ircd::string_view
+ircd::m::id::swap(const id &id,
+                  const mutable_buffer &buf_)
+{
+	using buffer::consume;
+	using buffer::copy;
+	using buffer::data;
+
+	mutable_buffer buf(buf_);
+	consume(buf, copy(buf, id.host()));
+	consume(buf, copy(buf, id.local()));
+	return { data(buf_), data(buf) };
+}
+
+ircd::m::id
+ircd::m::id::unswap(const string_view &str,
+                    const mutable_buffer &buf)
+{
+	size_t i(0);
+	for(; i < str.size(); ++i)
+		if(is_sigil(str[i]))
+			break;
+
+	if(unlikely(!i || i >= str.size()))
+		throw m::INVALID_MXID
+		{
+			"Failed to reconstruct any MXID out of '%s'", str
+		};
+
+	return id
+	{
+		sigil(str[i]), buf, str.substr(i), str.substr(0, i)
+	};
+}
+
 bool
 ircd::m::id::literal()
 const