[CRE-42] Fix partial or truncated writes (#989)

* fix: check size and len(src) match to avoid partial or truncated writes

* fix: return the number of bytes copied

* chore: align test naming

pkg/workflows/wasm/host/module.go

@@ -728,11 +728,13 @@ func write(memory, src []byte, ptr, size int32) int64 {
 		return -1
 	}
 
+	if len(src) != int(size) {
+		return -1
+	}
+
 	if int32(len(memory)) < ptr+size {
 		return -1
 	}
 	buffer := memory[ptr : ptr+size]
-	dataLen := int64(len(src))
-	copy(buffer, src)
-	return dataLen
+	return int64(copy(buffer, src))
 }

pkg/workflows/wasm/host/module_test.go

@@ -565,17 +565,31 @@ func Test_write(t *testing.T) {
 		giveSrc := []byte("hello, world")
 		memory := make([]byte, len(giveSrc)-1)
 		n := write(memory, giveSrc, 0, int32(len(giveSrc)))
-		assert.Equal(t, n, int64(-1))
+		assert.Equal(t, int64(-1), n)
 	})
 
 	t.Run("fails to write to invalid access", func(t *testing.T) {
 		giveSrc := []byte("hello, world")
 		memory := make([]byte, len(giveSrc))
 		n := write(memory, giveSrc, 0, -1)
-		assert.Equal(t, n, int64(-1))
+		assert.Equal(t, int64(-1), n)
 
 		n = write(memory, giveSrc, -1, 1)
-		assert.Equal(t, n, int64(-1))
+		assert.Equal(t, int64(-1), n)
+	})
+
+	t.Run("truncated write due to size being smaller than len", func(t *testing.T) {
+		giveSrc := []byte("hello, world")
+		memory := make([]byte, 12)
+		n := write(memory, giveSrc, 0, int32(len(giveSrc)-2))
+		assert.Equal(t, int64(-1), n)
+	})
+
+	t.Run("unwanted data when size exceeds written data", func(t *testing.T) {
+		giveSrc := []byte("hello, world")
+		memory := make([]byte, 20)
+		n := write(memory, giveSrc, 0, 20)
+		assert.Equal(t, int64(-1), n)
 	})
 }