Allow 256MiB payloads

Author: snichme

spec/io_spec.cr

@@ -304,20 +304,18 @@ describe MQTT::Protocol::IO do
     end
   end
 
-  it "can checks max_packet_size on remainin length" do
+  it "checks max_packet_size on remaining length" do
     mio = IO::Memory.new
     mio.write Bytes[0xFFu8, 0xFFu8, 0xFFu8, 0x7Fu8]
 
     mio.rewind
 
     io = MQTT::Protocol::IO.new(mio)
 
+    io = MQTT::Protocol::IO.new(mio, max_packet_size: 268435454u32)
     expect_raises(MQTT::Protocol::Error::PacketTooLarge) do
       io.read_remaining_length
     end
-    mio.rewind
-    io = MQTT::Protocol::IO.new(mio, max_packet_size: 268435455u32)
-    io.read_remaining_length
   end
 
   it "checks read_string for max_packet_size" do

src/mqtt/protocol/io.cr

@@ -1,15 +1,16 @@
 require "./packets"
 
 module MQTT
-  MAX_REMAINING_LENGTH = (128 * 128 * 128).to_u32
+  MAX_PAYLOAD_SIZE = 268_435_455u32 # 256MiB
+  MAX_MULTIPLIER   = (128 * 128 * 128).to_u32
 
   module Protocol
     struct IO
       getter io
 
       def self.new(io : ::IO, max_packet_size : UInt32? = nil,
                    byte_format = ::IO::ByteFormat::NetworkEndian)
-        new(io, max_packet_size || MAX_REMAINING_LENGTH, byte_format)
+        new(io, max_packet_size || MAX_PAYLOAD_SIZE, byte_format)
       end
 
       protected def initialize(@io : ::IO, @max_packet_size : UInt32,
@@ -56,7 +57,7 @@ module MQTT
           value += (b.to_u32 & 127u32) * multiplier
           break if b & 128 == 0
           multiplier *= 128
-          raise Error::PacketDecode.new "invalid remaining length" if multiplier > MAX_REMAINING_LENGTH
+          raise Error::PacketDecode.new "invalid remaining length" if multiplier > MAX_MULTIPLIER
         end
         raise Error::PacketTooLarge.new(@max_packet_size, value) if value > @max_packet_size
         value