check null pointer before using memcpy()

Author: ygj6

include/msgpack/sbuffer.h

@@ -81,8 +81,10 @@ static inline int msgpack_sbuffer_write(void* data, const char* buf, size_t len)
         sbuf->alloc = nsize;
     }
 
-    memcpy(sbuf->data + sbuf->size, buf, len);
-    sbuf->size += len;
+    if(buf) {
+        memcpy(sbuf->data + sbuf->size, buf, len);
+        sbuf->size += len;
+    }
     return 0;
 }
 

test/msgpack_c.cpp

@@ -872,6 +872,7 @@ TEST(MSGPACKC, simple_buffer_str_fix_l)
     msgpack_packer pk;
     msgpack_packer_init(&pk, &sbuf, msgpack_sbuffer_write);
     msgpack_pack_str(&pk, str_size);
+    assert(str || str_size == 0);
     msgpack_pack_str_body(&pk, str, str_size);
     EXPECT_EQ(sbuf.size, 0x01u);
     EXPECT_EQ(sbuf.data[0], static_cast<char>(0xa0u));