feat: add upgrade api

example: curl -X POST -H "Authorization: Bearer 123456" http://ip:port/upgrade

hub/updater/limitedreader.go

@@ -0,0 +1,67 @@
+package updater
+
+import (
+	"fmt"
+	"io"
+
+	"golang.org/x/exp/constraints"
+)
+
+// LimitReachedError records the limit and the operation that caused it.
+type LimitReachedError struct {
+	Limit int64
+}
+
+// Error implements the [error] interface for *LimitReachedError.
+//
+// TODO(a.garipov): Think about error string format.
+func (lre *LimitReachedError) Error() string {
+	return fmt.Sprintf("attempted to read more than %d bytes", lre.Limit)
+}
+
+// limitedReader is a wrapper for [io.Reader] limiting the input and dealing
+// with errors package.
+type limitedReader struct {
+	r     io.Reader
+	limit int64
+	n     int64
+}
+
+// Read implements the [io.Reader] interface.
+func (lr *limitedReader) Read(p []byte) (n int, err error) {
+	if lr.n == 0 {
+		return 0, &LimitReachedError{
+			Limit: lr.limit,
+		}
+	}
+
+	p = p[:Min(lr.n, int64(len(p)))]
+
+	n, err = lr.r.Read(p)
+	lr.n -= int64(n)
+
+	return n, err
+}
+
+// LimitReader wraps Reader to make it's Reader stop with ErrLimitReached after
+// n bytes read.
+func LimitReader(r io.Reader, n int64) (limited io.Reader, err error) {
+	if n < 0 {
+		return nil, &updateError{Message: "limit must be non-negative"}
+	}
+
+	return &limitedReader{
+		r:     r,
+		limit: n,
+		n:     n,
+	}, nil
+}
+
+// Min returns the smaller of x or y.
+func Min[T constraints.Integer | ~string](x, y T) (res T) {
+	if x < y {
+		return x
+	}
+
+	return y
+}