util.dbuffer: Fix bugs, remove multi-char support (more complex than first thought)

Character sequences could be split across chunk boundaries. Would require a bunch
of code to make that work reliably.

Only apply front_consumed on first chunk, and adjust buffer_pos accordingly.

spec/util_dbuffer_spec.lua

@@ -57,27 +57,6 @@ describe("util.dbuffer", function ()
 			assert.equal(nil, b:read_until("\n"));
 			assert.equal("and more", b:read_chunk());
 		end);
-
-		it("works with multi-character sequences", function ()
-			local b = dbuffer.new();
-			b:write("hello\r\n");
-			b:write("world");
-			b:write("\r\n");
-			b:write("\r\n\r\n");
-			b:write("stuff");
-			b:write("more\r\nand more");
-
-			assert.equal(nil, b:read_until("."));
-			assert.equal(nil, b:read_until("%"));
-			assert.equal("hello\r\n", b:read_until("\r\n"));
-			assert.equal("world\r\n", b:read_until("\r\n"));
-			assert.equal("\r\n", b:read_until("\r\n"));
-			assert.equal("\r\n", b:read_until("\r\n"));
-			assert.equal("stu", b:read(3));
-			assert.equal("ffmore\r\n", b:read_until("\r\n"));
-			assert.equal(nil, b:read_until("\r\n"));
-			assert.equal("and more", b:read_chunk());
-		end);
 	end);
 
 	describe(":discard", function ()

util/dbuffer.lua

@@ -80,12 +80,12 @@ end
 function dbuffer_methods:read_until(char)
 	local buffer_pos = 0;
 	for i, chunk in self.items:items() do
-		local start = 1 + self.front_consumed;
+		local start = 1 + ((i == 1) and self.front_consumed or 0);
 		local char_pos = chunk:find(char, start, true);
 		if char_pos then
-			return self:read(buffer_pos + (char_pos - start) + #char);
+			return self:read(1 + buffer_pos + char_pos - start);
 		end
-		buffer_pos = buffer_pos + #chunk;
+		buffer_pos = buffer_pos + #chunk - (start - 1);
 	end
 	return nil;
 end