util.dbuffer: Fix traceback when :collapse() is called on empty buffer

2 files changed, 13 insertions, 1 deletions

diff --git a/spec/util_dbuffer_spec.lua b/spec/util_dbuffer_spec.lua
index c4fa22b2..b7f80dc9 100644
--- a/spec/util_dbuffer_spec.lua
+++ b/spec/util_dbuffer_spec.lua
@@ -46,6 +46,13 @@ describe("util.dbuffer", function ()
 		end);
 	end);
 
+	describe(":collapse()", function ()
+		it("works on an empty buffer", function ()
+			local b = dbuffer.new();
+			b:collapse();
+		end);
+	end);
+
 	describe(":sub", function ()
 		-- Helper function to compare buffer:sub() with string:sub()
 		local s = "hello world";
@@ -106,5 +113,10 @@ describe("util.dbuffer", function ()
 			local r = { b:byte(1, 2) };
 			assert.same({ 0, 140 }, r);
 		end);
+
+		it("works on an empty buffer", function ()
+			local b = dbuffer.new();
+			assert.equal("", b:sub(1,1));
+		end);
 	end);
 end);
diff --git a/util/dbuffer.lua b/util/dbuffer.lua
index 63dca750..9ec40eb9 100644
--- a/util/dbuffer.lua
+++ b/util/dbuffer.lua
@@ -142,7 +142,7 @@ function dbuffer_methods:collapse(bytes)
 
 	local front_chunk = self.items:peek();
 
-	if #front_chunk - self.front_consumed >= bytes then
+	if not front_chunk or #front_chunk - self.front_consumed >= bytes then
 		return;
 	end