EQ2 Packet Parser

A dead-simple way to turn EverQuest 2's binary packet data into Go structs. Just add some tags to your struct fields and let reflection do the heavy lifting.

How it works

// Your packet structure
type LoginPacket struct {
    UserID   uint32             `eq2:"int32"`
    Username common.EQ2String16 `eq2:"string16"`
    Level    uint8              `eq2:"int8"`
}

// Parse some bytes
data := []byte{...} // whatever bytes you got
parser := parser.NewParser(data)

var packet LoginPacket
err := parser.ParseStruct(&packet)
// boom, packet is now filled with data

Tag Syntax

Just slap eq2:"type,options" on your fields and you're good to go.

The usual suspects

PlayerID    uint32  `eq2:"int32"`     // 32-bit integer
Health      uint16  `eq2:"int16"`     // 16-bit integer  
Alive       uint8   `eq2:"int8"`      // 8-bit integer
Damage      float32 `eq2:"float"`     // 32-bit float
Name        common.EQ2String16 `eq2:"string16"` // EQ2's weird string format
Color       common.EQ2Color    `eq2:"color"`    // RGB color

Arrays (because everything's an array in EQ2)

// Fixed size - always 5 items
Stats []uint16 `eq2:"int16,len=5"`

// Dynamic size - read ItemCount first, then that many items
ItemCount uint8  `eq2:"int8"`
Items     []Item `eq2:"array,arraysize=ItemCount"`

Conditionals (the fun stuff)

// Only parse this if Channel equals 1
MessageType uint8 `eq2:"int8,if=Channel==1"`

// Only parse if HasRewards is truthy
HasRewards  uint8       `eq2:"int8"`
RewardData  *RewardInfo `eq2:"substruct,ifvariableset=HasRewards"`

// Only parse if we set the "has_equipment" flag
Equipment []Equipment `eq2:"equipment,ifflag=has_equipment"`

Type switching (when EQ2 reuses the same bytes for different things)

// Normally parse as int32, but if StatType != 6, parse as float instead
StatType  uint8 `eq2:"int8"`
StatValue any   `eq2:"int32,type2=float,type2criteria=StatType!=6"`

Size limits (because EQ2 packets can get weird)

// If the data is bigger than 1000 bytes, just truncate it
DataSize uint16 `eq2:"int16"`
Data     []byte `eq2:"char,len=DataSize,maxsize=1000,skipoversized"`

Multiple client versions

EQ2 has like 50 different client versions, each with slightly different packet layouts. Handle it like this:

registry := parser.NewVersionRegistry()
registry.RegisterStruct("LoginReply", "1.0", reflect.TypeOf(LoginReplyV1{}))
registry.RegisterStruct("LoginReply", "2.0", reflect.TypeOf(LoginReplyV2{}))

// Parser picks the right version (or falls back to closest match)
result, err := parser.ParseWithVersion(registry, "LoginReply", clientVersion)

Real example

type CharacterData struct {
    // Basic stuff
    CharID   uint32             `eq2:"int32"`
    Name     common.EQ2String16 `eq2:"string16"`
    Level    uint8              `eq2:"int8"`
    
    // Guild info (only if they're in a guild)
    HasGuild uint8              `eq2:"int8"`
    GuildID  uint32             `eq2:"int32,ifvariableset=HasGuild"`
    
    // Variable number of items
    ItemCount uint16            `eq2:"int16"`
    Items     []InventoryItem   `eq2:"array,arraysize=ItemCount"`
    
    // Nested stuff
    Stats     PlayerStats       `eq2:"substruct"`
}

type InventoryItem struct {
    ItemID   uint32            `eq2:"int32"`
    Quantity uint16            `eq2:"int16"`
    Color    common.EQ2Color   `eq2:"color"`
}

type PlayerStats struct {
    Health  uint32 `eq2:"int32"`
    Mana    uint32 `eq2:"int32"`
    Stamina uint32 `eq2:"int32"`
}

Converting from XML

If you've got EQ2's XML packet definitions, the conversion is pretty straightforward:

XML	Go Tag
`Type="int32"`	`eq2:"int32"`
`ArraySizeVariable="count"`	`arraysize=Count`
`IfVariableSet="flag"`	`ifvariableset=Flag`
`Size="5"`	`len=5`

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