feat(logic): add bounded buffer utility

x/logic/util/buffer.go

@@ -0,0 +1,75 @@
+package util
+
+import (
+	"fmt"
+	"io"
+)
+
+var (
+	_ = io.Writer(&BoundedBuffer{})
+)
+
+var (
+	ErrInvalidSize = func(size int) error {
+		return fmt.Errorf("invalid buffer size %d", size)
+	}
+)
+
+// BoundedBuffer is a fixed size buffer that overwrites older data when the buffer is full.
+type BoundedBuffer struct {
+	buf       []byte
+	offset    int
+	size      int
+	overflown bool
+}
+
+// NewBoundedBuffer creates a new BoundedBuffer with the given fixed size.
+// If size is 0, the buffer will be disabled.
+func NewBoundedBuffer(size int) (*BoundedBuffer, error) {
+	if size < 0 {
+		return nil, ErrInvalidSize(size)
+	}
+
+	return &BoundedBuffer{
+		buf:  make([]byte, size),
+		size: size,
+	}, nil
+}
+
+// NewBoundedBufferMust is like NewBoundedBuffer but panics if an error occurs.
+func NewBoundedBufferMust(size int) *BoundedBuffer {
+	b, err := NewBoundedBuffer(size)
+	if err != nil {
+		panic(err)
+	}
+
+	return b
+}
+
+// Write implements io.Writer.
+func (b *BoundedBuffer) Write(p []byte) (n int, err error) {
+	size := len(p)
+
+	if b.size == 0 {
+		return size, nil
+	}
+
+	for i := 0; i < size; i++ {
+		b.buf[b.offset] = p[i]
+		b.offset = (b.offset + 1) % b.size
+		b.overflown = b.overflown || b.offset == 0
+	}
+
+	return size, nil
+}
+
+// String returns the contents of the buffer as a string.
+func (b *BoundedBuffer) String() string {
+	if b.overflown {
+		r := string(b.buf[b.offset:]) + string(b.buf[:b.offset])
+
+		return r
+	}
+
+	return string(b.buf[:b.offset])
+}