From c6e685964f0a0d643b50f7b9297d893bd890603c Mon Sep 17 00:00:00 2001
From: Lukas Herman <lherman.cs@gmail.com>
Date: Fri, 15 May 2020 00:35:57 -0400
Subject: [PATCH] Fix wrong required size

---
 pkg/io/io.go      |  2 +-
 pkg/io/io_test.go | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 pkg/io/io_test.go

diff --git a/pkg/io/io.go b/pkg/io/io.go
index d235335..26f3216 100644
--- a/pkg/io/io.go
+++ b/pkg/io/io.go
@@ -4,7 +4,7 @@ package io
 // InsufficientBufferError.
 func Copy(dst, src []byte) (n int, err error) {
 	if len(dst) < len(src) {
-		return 0, &InsufficientBufferError{len(dst)}
+		return 0, &InsufficientBufferError{len(src)}
 	}
 
 	return copy(dst, src), nil
diff --git a/pkg/io/io_test.go b/pkg/io/io_test.go
new file mode 100644
index 0000000..047e3a1
--- /dev/null
+++ b/pkg/io/io_test.go
@@ -0,0 +1,45 @@
+package io
+
+import (
+	"log"
+	"testing"
+)
+
+func TestCopy(t *testing.T) {
+	var dst []byte
+	src := make([]byte, 4)
+
+	n, err := Copy(dst, src)
+	if err == nil {
+		t.Fatal("expected err to be non-nill")
+	}
+
+	if n != 0 {
+		t.Fatalf("expected n to be 0, but got %d", n)
+	}
+
+	e, ok := err.(*InsufficientBufferError)
+	if !ok {
+		t.Fatalf("expected error to be InsufficientBufferError")
+	}
+
+	if e.RequiredSize != len(src) {
+		t.Fatalf("expected required size to be %d, but got %d", len(src), e.RequiredSize)
+	}
+
+	dst = make([]byte, 2*e.RequiredSize)
+	n, err = Copy(dst, src)
+	if err != nil {
+		t.Fatalf("expected to not get an error after expanding the buffer")
+	}
+
+	if n != len(src) {
+		t.Fatalf("expected n to be %d, but got %d", len(src), n)
+	}
+
+	for i := 0; i < len(src); i++ {
+		if src[i] != dst[i] {
+			log.Fatalf("expected value at %d to be %d, but got %d", i, src[i], dst[i])
+		}
+	}
+}