Implement generator and type for packet IDs

data/gen_packetIDs.go

@@ -0,0 +1,196 @@
+// gen_packetIDs.go generates the enumeration of packet IDs used on the wire.
+
+//+build ignore
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"os"
+	"strings"
+
+	"github.com/iancoleman/strcase"
+)
+
+const (
+	protocolURL = "https://raw.githubusercontent.com/PrismarineJS/minecraft-data/master/data/pc/1.16.2/protocol.json"
+)
+
+// unnest is a utility function to unpack a value from a nested map, given
+// an arbitrary set of keys to reach through.
+func unnest(input map[string]interface{}, keys ...string) (map[string]interface{}, error) {
+	for _, k := range keys {
+		sub, ok := input[k]
+		if !ok {
+			return nil, fmt.Errorf("key %q not found", k)
+		}
+		next, ok := sub.(map[string]interface{})
+		if !ok {
+			return nil, fmt.Errorf("key %q was %T, expected a string map", k, sub)
+		}
+		input = next
+	}
+	return input, nil
+}
+
+type duplexMappings struct {
+	Clientbound map[string]string
+	Serverbound map[string]string
+}
+
+func (m *duplexMappings) EnsureUniqueNames() {
+	// Assemble a slice of keys to check across both maps, because we cannot
+	// mutate a map while iterating it.
+	clientKeys := make([]string, 0, len(m.Clientbound))
+	for k, _ := range m.Clientbound {
+		clientKeys = append(clientKeys, k)
+	}
+
+	for _, k := range clientKeys {
+		if _, alsoServerKey := m.Serverbound[k]; alsoServerKey {
+			cVal, sVal := m.Clientbound[k], m.Serverbound[k]
+			delete(m.Clientbound, k)
+			delete(m.Serverbound, k)
+			m.Clientbound[k+"Clientbound"] = cVal
+			m.Serverbound[k+"Serverbound"] = sVal
+		}
+	}
+}
+
+// unpackMapping returns the set of packet IDs and their names for a given
+// game state.
+func unpackMapping(data map[string]interface{}, gameState string) (duplexMappings, error) {
+	out := duplexMappings{
+		Clientbound: make(map[string]string),
+		Serverbound: make(map[string]string),
+	}
+
+	info, err := unnest(data, gameState, "toClient", "types")
+	if err != nil {
+		return duplexMappings{}, err
+	}
+	pType := info["packet"].([]interface{})[1].([]interface{})[0].(map[string]interface{})["type"]
+	mappings := pType.([]interface{})[1].(map[string]interface{})["mappings"].(map[string]interface{})
+	for k, v := range mappings {
+		out.Clientbound[strcase.ToCamel(v.(string))] = k
+	}
+	info, err = unnest(data, gameState, "toServer", "types")
+	if err != nil {
+		return duplexMappings{}, err
+	}
+	pType = info["packet"].([]interface{})[1].([]interface{})[0].(map[string]interface{})["type"]
+	mappings = pType.([]interface{})[1].(map[string]interface{})["mappings"].(map[string]interface{})
+	for k, v := range mappings {
+		out.Serverbound[strcase.ToCamel(v.(string))] = k
+	}
+
+	return out, nil
+}
+
+type protocolIDs struct {
+	Login  duplexMappings
+	Play   duplexMappings
+	Status duplexMappings
+	// Handshake state has no packets
+}
+
+func (p protocolIDs) MaxLen() int {
+	var max int
+	for _, m := range []duplexMappings{p.Login, p.Play, p.Status} {
+		for k, _ := range m.Clientbound {
+			if len(k) > max {
+				max = len(k)
+			}
+		}
+		for k, _ := range m.Serverbound {
+			if len(k) > max {
+				max = len(k)
+			}
+		}
+	}
+	return max
+}
+
+func downloadInfo() (*protocolIDs, error) {
+	resp, err := http.Get(protocolURL)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	var data map[string]interface{}
+	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
+		return nil, err
+	}
+
+	var out protocolIDs
+	if out.Login, err = unpackMapping(data, "login"); err != nil {
+		return nil, fmt.Errorf("login: %v", err)
+	}
+	out.Login.EnsureUniqueNames()
+	if out.Play, err = unpackMapping(data, "play"); err != nil {
+		return nil, fmt.Errorf("play: %v", err)
+	}
+	out.Play.EnsureUniqueNames()
+	if out.Status, err = unpackMapping(data, "status"); err != nil {
+		return nil, fmt.Errorf("play: %v", err)
+	}
+	out.Status.EnsureUniqueNames()
+
+	return &out, nil
+}
+
+func main() {
+	pIDs, err := downloadInfo()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
+	}
+
+	maxLen := pIDs.MaxLen()
+
+	fmt.Println("package data")
+	fmt.Println()
+	fmt.Println("//go:generate bash -c \"go run gen_packetIDs.go > packetIDs.go\"")
+	fmt.Println()
+	fmt.Println("// This file is automatically generated by gen_packetIDs.go. DO NOT EDIT.")
+	fmt.Println()
+	fmt.Println("// PktID represents a packet ID used in the minecraft protocol.")
+	fmt.Println("type PktID int32")
+	fmt.Println()
+	fmt.Println("// Valid PktID values.")
+	fmt.Println("const (")
+
+	fmt.Println("  // Clientbound packets for connections in the login state.")
+	for k, v := range pIDs.Login.Clientbound {
+		fmt.Printf("  %s%s PktID = %s\n", k, strings.Repeat(" ", maxLen-len(k)), v)
+	}
+	fmt.Println("  // Serverbound packets for connections in the login state.")
+	for k, v := range pIDs.Login.Serverbound {
+		fmt.Printf("  %s%s PktID = %s\n", k, strings.Repeat(" ", maxLen-len(k)), v)
+	}
+	fmt.Println()
+
+	fmt.Println("  // Clientbound packets for connections in the play state.")
+	for k, v := range pIDs.Play.Clientbound {
+		fmt.Printf("  %s%s PktID = %s\n", k, strings.Repeat(" ", maxLen-len(k)), v)
+	}
+	fmt.Println("  // Serverbound packets for connections in the play state.")
+	for k, v := range pIDs.Play.Serverbound {
+		fmt.Printf("  %s%s PktID = %s\n", k, strings.Repeat(" ", maxLen-len(k)), v)
+	}
+	fmt.Println()
+
+	fmt.Println("  // Clientbound packets used to respond to ping/status requests.")
+	for k, v := range pIDs.Status.Clientbound {
+		fmt.Printf("  %s%s PktID = %s\n", k, strings.Repeat(" ", maxLen-len(k)), v)
+	}
+	fmt.Println("  // Serverbound packets used to ping or read server status.")
+	for k, v := range pIDs.Status.Serverbound {
+		fmt.Printf("  %s%s PktID = %s\n", k, strings.Repeat(" ", maxLen-len(k)), v)
+	}
+	fmt.Println()
+
+	fmt.Println(")")
+}