Proxy has been introduced as a design pattern to separate data and code in an application to two different types of smart contracts, namely proxy and logic contracts, respectively. Data is stored in the proxy contracts, while the code to be executed is fetched from the logic contracts. Proxy patterns facilitate the flexibility of smart contract development by enabling upgradeability, extensibility, code reuse, etc. Despite its popularity and importance, there is currently no systematic study to understand the prevalence, use scenarios, and development pitfalls of proxies. In this work, we conduct the first comprehensive study on Ethereum proxies. To collect a comprehensive dataset of proxies, we propose ProxyEx, the first framework designed to detect proxy directly from bytecode. Our evaluation shows that ProxyEx achieves over 99% accuracy.

With ProxyEx, we collect a large-scale dataset of 2,031,422 proxies from all contracts in Ethereum and conduct the first systematic empirical study. We first measure the total number of proxies and their transaction traffic, to obtain an overall understanding of the status quo of proxies on Ethereum. Then, we categorize the design pattern and use scenarios of proxies into four types: upgradeability, extensibility, code-sharing, and code-hiding. We further identify three types of common pitfalls in proxies: proxy-logic storage collision, logic-logic storage collision, and uninitialized contracts. We also design three checkers for these common pitfalls in proxies by replaying historical transactions. Our study leads to many interesting findings. For instance, we find that upgradeability is not the only reason that developers adopt the proxy pattern in developing Decentralized Applications (DApps). We also find that many proxies suffer from bugs such as storage collision and uninitialized contracts. Our study sheds light on the proxies landscape, and provides valuable insights to future smart contract research on the development, usage, quality assurance, and bug detection of proxies.