protocol/io: (Func)SliceOfLen: Use interface for checking if IO is …

…reader.

Fixes an issue where multiprotocol implementations that return their own `*Reader` would lead to broken slice reading.

minecraft/protocol/io.go

@@ -143,11 +143,9 @@ const maxSliceLength = 1024
 
 // SliceOfLen reads/writes the elements of a slice of type T with length l.
 func SliceOfLen[T any, S ~*[]T, A PtrMarshaler[T]](r IO, l uint32, x S) {
-	rd, reader := r.(*Reader)
-	if reader {
-		if rd.limitsEnabled && l > maxSliceLength {
-			rd.panicf("slice length was too long: length of %v", l)
-		}
+	limit, ok := r.(sliceReader)
+	if ok {
+		limit.SliceLimit(l, maxSliceLength)
 		*x = make([]T, l)
 	}
 
@@ -158,11 +156,9 @@ func SliceOfLen[T any, S ~*[]T, A PtrMarshaler[T]](r IO, l uint32, x S) {
 
 // FuncSliceOfLen reads/writes the elements of a slice of type T with length l using func f.
 func FuncSliceOfLen[T any, S ~*[]T](r IO, l uint32, x S, f func(*T)) {
-	rd, reader := r.(*Reader)
-	if reader {
-		if rd.limitsEnabled && l > maxSliceLength {
-			rd.panicf("slice length was too long: length of %v", l)
-		}
+	limit, ok := r.(sliceReader)
+	if ok {
+		limit.SliceLimit(l, maxSliceLength)
 		*x = make([]T, l)
 	}
 
@@ -171,6 +167,10 @@ func FuncSliceOfLen[T any, S ~*[]T](r IO, l uint32, x S, f func(*T)) {
 	}
 }
 
+type sliceReader interface {
+	SliceLimit(value uint32, max uint32)
+}
+
 // FuncIOSliceOfLen reads/writes the elements of a slice of type T with length l using func f.
 func FuncIOSliceOfLen[T any, S ~*[]T](r IO, l uint32, x S, f func(IO, *T)) {
 	FuncSliceOfLen(r, l, x, func(v *T) {

minecraft/protocol/reader.go

@@ -611,24 +611,11 @@ func (r *Reader) Bitset(x *Bitset, size int) {
 	r.panic(errBitsetOverflow)
 }
 
-// LimitUint32 checks if the value passed is lower than the limit passed. If not, the Reader panics.
-func (r *Reader) LimitUint32(value uint32, max uint32) {
-	if max == math.MaxUint32 {
-		// Account for 0-1 overflowing into max.
-		max = 0
-	}
-	if value > max {
-		r.panicf("uint32 %v exceeds maximum of %v", value, max)
-	}
-}
-
-// LimitInt32 checks if the value passed is lower than the limit passed and higher than the minimum. If not,
-// the Reader panics.
-func (r *Reader) LimitInt32(value int32, min, max int32) {
-	if value < min {
-		r.panicf("int32 %v exceeds minimum of %v", value, min)
-	} else if value > max {
-		r.panicf("int32 %v exceeds maximum of %v", value, max)
+// SliceLimit checks if the value passed is lower than the limit passed. If
+// not, the Reader panics.
+func (r *Reader) SliceLimit(value uint32, max uint32) {
+	if value > max && r.limitsEnabled {
+		r.panicf("slice length was too long: length of %v (max %v)", value, max)
 	}
 }