Add Forge handshake support. Closes #88 (#134)

Adds support for connecting to 1.7.10 modded servers using the FML|HS protocol:
https://wiki.vg/Minecraft_Forge_Handshake

* Handle client-bound plugin message packets

* Parse FML|HS plugin channel messages

* Add ModList serialization using Mod serializable, LenPrefixed<VarInt, Mod>

* Save forge_mods from server ping and send in FML|HS ModList packet

* Show Forge mod count in server ping listing

* Send acknowledgements, completing the handshake

* Add VarShort to custom payload len prefix replaces i16, fixes OOM on large modded servers

* Add custom CoFHLib's SendUUID packet -26

See explanation at https://github.com/SpigotMC/BungeeCord/issues/1437
This packet is defined by CoFHLib in https://github.com/CoFH/CoFHLib/blob/1.7.10/src/main/java/cofh/lib/util/helpers/SecurityHelper.java#L40
Fixes thread '' panicked at 'bad packet id 0xffffffe6 in Clientbound Play' with FTB:IE

protocol/src/protocol/forge.rs

@@ -0,0 +1,180 @@
+
+/// Implements https://wiki.vg/Minecraft_Forge_Handshake
+use std::io;
+use byteorder::WriteBytesExt;
+
+use crate::protocol::{Serializable, Error, LenPrefixed, VarInt};
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Phase {
+    // Client handshake states (written)
+    Start,
+    WaitingServerData,
+    WaitingServerComplete,
+    PendingComplete,
+
+    // Server handshake states (read)
+    WaitingCAck,
+
+    // Both client and server handshake states (different values on the wire)
+    Complete,
+}
+
+impl Serializable for Phase {
+    /// Read server handshake state from server
+    fn read_from<R: io::Read>(buf: &mut R) -> Result<Self, Error> {
+        let phase: i8 = Serializable::read_from(buf)?;
+        Ok(match phase {
+            2 => Phase::WaitingCAck,
+            3 => Phase::Complete,
+            _ => panic!("bad FML|HS server phase: {}", phase),
+        })
+    }
+
+    /// Send client handshake state from client
+    fn write_to<W: io::Write>(&self, buf: &mut W) -> Result<(), Error> {
+        buf.write_u8(match self {
+            Phase::WaitingServerData => 2,
+            Phase::WaitingServerComplete => 3,
+            Phase::PendingComplete => 4,
+            Phase::Complete => 5,
+            _ => panic!("bad FML|HS client phase: {:?}", self),
+        })?;
+        Ok(())
+    }
+}
+
+
+#[derive(Clone, Debug, Default)]
+pub struct ForgeMod {
+    pub modid: String,
+    pub version: String,
+}
+
+impl Serializable for ForgeMod {
+    fn read_from<R: io::Read>(buf: &mut R) -> Result<Self, Error> {
+        Ok(ForgeMod {
+            modid: Serializable::read_from(buf)?,
+            version: Serializable::read_from(buf)?,
+        })
+    }
+
+    fn write_to<W: io::Write>(&self, buf: &mut W) -> Result<(), Error> {
+        self.modid.write_to(buf)?;
+        self.version.write_to(buf)
+    }
+}
+
+#[derive(Debug)]
+pub struct ModIdMapping {
+    pub name: String,
+    pub id: VarInt,
+}
+
+impl Serializable for ModIdMapping {
+    fn read_from<R: io::Read>(buf: &mut R) -> Result<Self, Error> {
+        Ok(ModIdMapping {
+            name: Serializable::read_from(buf)?,
+            id: Serializable::read_from(buf)?,
+        })
+    }
+
+    fn write_to<W: io::Write>(&self, buf: &mut W) -> Result<(), Error> {
+        self.name.write_to(buf)?;
+        self.id.write_to(buf)
+    }
+}
+
+#[derive(Debug)]
+pub enum FmlHs {
+    ServerHello {
+        fml_protocol_version: i8,
+        override_dimension: Option<i32>,
+    },
+    ClientHello {
+        fml_protocol_version: i8,
+    },
+    ModList {
+        mods: LenPrefixed<VarInt, ForgeMod>,
+    },
+    /* TODO: 1.8+ https://wiki.vg/Minecraft_Forge_Handshake#Differences_from_Forge_1.7.10
+    RegistryData {
+        has_more: bool,
+        name: String,
+        ids: LenPrefixed<VarInt, ModIdMapping>,
+        substitutions: LenPrefixed<VarInt, String>,
+        dummies: LenPrefixed<VarInt, String>,
+    },
+    */
+    ModIdData {
+        mappings: LenPrefixed<VarInt, ModIdMapping>,
+        block_substitutions: LenPrefixed<VarInt, String>,
+        item_substitutions: LenPrefixed<VarInt, String>,
+    },
+    HandshakeAck {
+        phase: Phase,
+    },
+    HandshakeReset,
+}
+
+impl Serializable for FmlHs {
+    fn read_from<R: io::Read>(buf: &mut R) -> Result<Self, Error> {
+        let discriminator: u8 = Serializable::read_from(buf)?;
+
+        match discriminator {
+            0 => {
+                let fml_protocol_version: i8 = Serializable::read_from(buf)?;
+                let override_dimension = if fml_protocol_version > 1 {
+                    let dimension: i32 = Serializable::read_from(buf)?;
+                    Some(dimension)
+                } else {
+                    None
+                };
+
+                println!("FML|HS ServerHello: fml_protocol_version={}, override_dimension={:?}", fml_protocol_version, override_dimension);
+
+                Ok(FmlHs::ServerHello {
+                    fml_protocol_version,
+                    override_dimension,
+                })
+            },
+            1 => panic!("Received unexpected FML|HS ClientHello from server"),
+            2 => {
+                Ok(FmlHs::ModList {
+                    mods: Serializable::read_from(buf)?,
+                })
+            },
+            3 => {
+                Ok(FmlHs::ModIdData {
+                    mappings: Serializable::read_from(buf)?,
+                    block_substitutions: Serializable::read_from(buf)?,
+                    item_substitutions: Serializable::read_from(buf)?, 
+                })
+            },
+            255 => {
+                Ok(FmlHs::HandshakeAck {
+                    phase: Serializable::read_from(buf)?,
+                })
+            },
+            _ => panic!("Unhandled FML|HS packet: discriminator={}", discriminator),
+        }
+    }
+
+    fn write_to<W: io::Write>(&self, buf: &mut W) -> Result<(), Error> {
+        match self {
+            FmlHs::ClientHello { fml_protocol_version } => {
+                buf.write_u8(1)?;
+                fml_protocol_version.write_to(buf)
+            },
+            FmlHs::ModList { mods } => {
+                buf.write_u8(2)?;
+                mods.write_to(buf)
+            },
+            FmlHs::HandshakeAck { phase } => {
+                buf.write_u8(255)?;
+                phase.write_to(buf)
+            },
+            _ => unimplemented!()
+        }
+    }
+}

protocol/src/protocol/mod.rs

@@ -23,6 +23,7 @@ use serde_json;
 use reqwest;
 
 pub mod mojang;
+pub mod forge;
 
 use crate::nbt;
 use crate::format;
@@ -660,6 +661,65 @@ impl fmt::Debug for VarInt {
     }
 }
 
+/// `VarShort` have a variable size (2 or 3 bytes) and are backwards-compatible
+/// with vanilla shorts, used for Forge custom payloads
+#[derive(Clone, Copy)]
+pub struct VarShort(pub i32);
+
+impl Lengthable for VarShort {
+    fn into(self) -> usize {
+        self.0 as usize
+    }
+
+    fn from(u: usize) -> VarShort {
+        VarShort(u as i32)
+    }
+}
+
+impl Serializable for VarShort {
+    fn read_from<R: io::Read>(buf: &mut R) -> Result<VarShort, Error> {
+        let low = buf.read_u16::<BigEndian>()? as u32;
+        let val = if (low & 0x8000) != 0 {
+            let high = buf.read_u8()? as u32;
+
+            (high << 15) | (low & 0x7fff)
+        } else {
+            low
+        };
+
+        Result::Ok(VarShort(val as i32))
+    }
+
+    fn write_to<W: io::Write>(&self, buf: &mut W) -> Result<(), Error> {
+        assert!(self.0 >= 0 && self.0 <= 0x7fffff, "VarShort invalid value: {}", self.0);
+        let mut low = self.0 & 0x7fff;
+        let high = (self.0 & 0x7f8000) >> 15;
+        if high != 0 {
+            low |= 0x8000;
+        }
+
+        buf.write_u16::<BigEndian>(low as u16)?;
+
+        if high != 0 {
+            buf.write_u8(high as u8)?;
+        }
+
+        Ok(())
+    }
+}
+
+impl default::Default for VarShort {
+    fn default() -> VarShort {
+        VarShort(0)
+    }
+}
+
+impl fmt::Debug for VarShort {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
 /// `VarLong` have a variable size (between 1 and 10 bytes) when encoded based
 /// on the size of the number
 #[derive(Clone, Copy)]
@@ -1005,6 +1065,29 @@ impl Conn {
         let version = val.get("version").ok_or(invalid_status())?;
         let players = val.get("players").ok_or(invalid_status())?;
 
+        // For modded servers, get the list of Forge mods installed
+        let mut forge_mods: std::vec::Vec<crate::protocol::forge::ForgeMod> = vec![];
+        if let Some(modinfo) = val.get("modinfo") {
+            if let Some(modinfo_type) = modinfo.get("type") {
+                if modinfo_type == "FML" {
+                    if let Some(modlist) = modinfo.get("modList") {
+                        if let Value::Array(items) = modlist {
+                            for item in items {
+                                if let Value::Object(obj) = item {
+                                    let modid = obj.get("modid").unwrap().as_str().unwrap().to_string();
+                                    let version = obj.get("version").unwrap().as_str().unwrap().to_string();
+
+                                    forge_mods.push(crate::protocol::forge::ForgeMod { modid, version });
+                                }
+                            }
+                        }
+                    }
+                } else {
+                    panic!("Unrecognized modinfo type in server ping response: {} in {}", modinfo_type, modinfo);
+                }
+            }
+        }
+
         Ok((Status {
             version: StatusVersion {
                 name: version.get("name").and_then(Value::as_str).ok_or(invalid_status())?
@@ -1025,6 +1108,7 @@ impl Conn {
             description: format::Component::from_value(val.get("description")
                                                                .ok_or(invalid_status())?),
             favicon: val.get("favicon").and_then(Value::as_str).map(|v| v.to_owned()),
+            forge_mods,
         },
             ping))
     }
@@ -1036,6 +1120,7 @@ pub struct Status {
     pub players: StatusPlayers,
     pub description: format::Component,
     pub favicon: Option<String>,
+    pub forge_mods: Vec<crate::protocol::forge::ForgeMod>,
 }
 
 #[derive(Debug)]

protocol/src/protocol/packet.rs

@@ -161,7 +161,7 @@ state_packets!(
             }
             packet PluginMessageServerbound_i16 {
                 field channel: String =,
-                field data: LenPrefixedBytes<i16> =,
+                field data: LenPrefixedBytes<VarShort> =,
             }
             packet EditBook {
                 field new_book: Option<item::Stack> =,
@@ -875,7 +875,7 @@ state_packets!(
             }
             packet PluginMessageClientbound_i16 {
                 field channel: String =,
-                field data: LenPrefixedBytes<i16> =,
+                field data: LenPrefixedBytes<VarShort> =,
             }
             /// Plays a sound by name on the client
             packet NamedSoundEffect {
@@ -1747,6 +1747,9 @@ state_packets!(
                 field id: VarInt =,
                 field trades: LenPrefixed<u8, packet::Trade> =,
             }
+            packet CoFHLib_SendUUID {
+                field player_uuid: UUID =,
+            }
        }
     }
     login Login {

protocol/src/protocol/versions/v1_7_10.rs

@@ -99,6 +99,7 @@ protocol_packet_ids!(
             0x3e => Teams_NoVisColor
             0x3f => PluginMessageClientbound_i16
             0x40 => Disconnect
+            -0x1a => CoFHLib_SendUUID
         }
     }
     login Login {