Add connection webhook notifications (#392)

Also 

* Added decode of LoginStart message
* Add metrics backend constants
* Updated usage section
* Documented MaxFrameLength

mcproto/read_test.go

@@ -1,8 +1,15 @@
 package mcproto
 
 import (
+	"bufio"
 	"bytes"
+	"encoding/hex"
+	"fmt"
+	"github.com/google/uuid"
+	"os"
+	"strings"
 	"testing"
+	"unicode"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -35,3 +42,69 @@ func TestReadVarInt(t *testing.T) {
 		})
 	}
 }
+
+func TestHandshakeThenStatus(t *testing.T) {
+	content, err := ReadHexDumpFile("handshake-status.hex")
+	require.NoError(t, err)
+
+	reader := bufio.NewReader(bytes.NewReader(content))
+
+	handshakePacket, err := ReadPacket(reader, nil, StateHandshaking)
+	require.NoError(t, err)
+
+	handshake, err := DecodeHandshake(handshakePacket.Data)
+	require.NoError(t, err)
+
+	assert.Equal(t, "localhost", handshake.ServerAddress)
+	assert.Equal(t, uint16(25565), handshake.ServerPort)
+	assert.Equal(t, 770 /*for 1.21.5*/, handshake.ProtocolVersion)
+	assert.Equal(t, StateStatus, handshake.NextState)
+}
+
+func TestHandshakeThenLoginStart(t *testing.T) {
+	content, err := ReadHexDumpFile("handshake-login-start.hex")
+	require.NoError(t, err)
+
+	reader := bufio.NewReader(bytes.NewReader(content))
+
+	handshakePacket, err := ReadPacket(reader, nil, StateHandshaking)
+	require.NoError(t, err)
+
+	handshake, err := DecodeHandshake(handshakePacket.Data)
+	require.NoError(t, err)
+
+	assert.Equal(t, "localhost", handshake.ServerAddress)
+	assert.Equal(t, uint16(25565), handshake.ServerPort)
+	assert.Equal(t, 770 /*for 1.21.5*/, handshake.ProtocolVersion)
+	assert.Equal(t, StateLogin, handshake.NextState)
+
+	loginStartPacket, err := ReadPacket(reader, nil, StateLogin)
+	require.NoError(t, err)
+
+	loginStart, err := DecodeLoginStart(loginStartPacket.Data)
+	require.NoError(t, err)
+
+	assert.Equal(t, "itzg", loginStart.Name)
+	assert.Equal(t, uuid.MustParse("5cddfd26-fc86-4981-b52e-c42bb10bfdef"), loginStart.PlayerUuid)
+}
+
+func ReadHexDumpFile(filename string) ([]byte, error) {
+	// Read the file content
+	content, err := os.ReadFile(filename)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read file: %w", err)
+	}
+
+	// Convert content to string and clean it up
+	hexString := string(content)
+
+	// Remove whitespace and newlines
+	hexString = strings.Map(func(r rune) rune {
+		if unicode.IsSpace(r) {
+			return -1 // Remove spaces, tabs, newlines
+		}
+		return r
+	}, hexString)
+
+	return hex.DecodeString(hexString)
+}