util.bitops: Library to find appropriate bitwise library (closes #1395)

net/websocket/frames.lua

@@ -9,8 +9,7 @@
 local softreq = require "util.dependencies".softreq;
 local random_bytes = require "util.random".bytes;
 
-local bit = assert(softreq"bit32" or softreq"bit",
-	"No bit module found. See https://prosody.im/doc/depends#bitop");
+local bit = require "util.bitcompat";
 local band = bit.band;
 local bor = bit.bor;
 local bxor = bit.bxor;

util/bit53.lua

@@ -0,0 +1,7 @@
+-- Only the operators needed by net.websocket.frames are provided at this point
+return {
+	band   = function (a, b) return a & b end;
+	bor    = function (a, b) return a | b end;
+	bxor   = function (a, b) return a ~ b end;
+};
+

util/bitcompat.lua

@@ -0,0 +1,32 @@
+-- Compatibility layer for bitwise operations
+
+-- First try the bit32 lib
+-- Lua 5.3 has it with compat enabled
+-- Lua 5.2 has it by default
+if _G.bit32 then
+	return _G.bit32;
+else
+	-- Lua 5.1 may have it as a standalone module that can be installed
+	local ok, bitop = pcall(require, "bit32")
+	if ok then
+		return bitop;
+	end
+end
+
+do
+	-- Lua 5.3 and 5.4 would be able to use native infix operators
+	local ok, bitop = pcall(require, "util.bit53")
+	if ok then
+		return bitop;
+	end
+end
+
+do
+	-- Lastly, try the LuaJIT bitop library
+	local ok, bitop = pcall(require, "bit")
+	if ok then
+		return bitop;
+	end
+end
+
+error "No bit module found. See https://prosody.im/doc/depends#bitop";