output/snapcast/Client: work around clang 14 std::span cast bug

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1538

src/output/plugins/snapcast/Client.cxx

@@ -25,6 +25,7 @@
 #include "event/Loop.hxx"
 #include "net/SocketError.hxx"
 #include "net/UniqueSocketDescriptor.hxx"
+#include "util/SpanCast.hxx"
 #include "Log.hxx"
 
 #include <cassert>
@@ -126,7 +127,7 @@ SendT(SocketDescriptor s, const T &buffer) noexcept
 static bool
 Send(SocketDescriptor s, std::string_view buffer) noexcept
 {
-	return Send(s, std::as_bytes(std::span{buffer}));
+	return Send(s, AsBytes(buffer));
 }
 
 static bool

src/util/SpanCast.hxx

@@ -31,6 +31,7 @@
 
 #include <cstddef>
 #include <span>
+#include <string_view>
 
 /**
  * Cast a std::span<std::byte> to a std::span<T>, rounding down to the
@@ -47,3 +48,21 @@ FromBytesFloor(std::span<std::byte> other) noexcept
 		other.size() / sizeof(T),
 	};
 }
+
+constexpr std::span<const char>
+ToSpan(std::string_view sv) noexcept
+{
+#if defined(__clang__) && __clang_major__ < 15
+	/* workaround for old clang/libc++ versions which can't cast
+	   std::string_view to std::span */
+	return {sv.data(), sv.size()};
+#else
+	return std::span{sv};
+#endif
+}
+
+inline std::span<const std::byte>
+AsBytes(std::string_view sv) noexcept
+{
+	return std::as_bytes(ToSpan(sv));
+}