91 lines
3.9 KiB
Markdown
91 lines
3.9 KiB
Markdown
# Solana ABI management process
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This document proposes the Solana ABI management process. The ABI management
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process is an engineering practice and a supporting technical framework to avoid
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introducing unintended incompatible ABI changes.
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# Problem
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The Solana ABI (binary interface to the cluster) is currently only defined
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implicitly by the implementation and requires a very careful eye to notice
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breaking changes. This makes it extremely difficult to upgrade the software
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on an existing cluster without rebooting the ledger.
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# Requirements and objectives
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- Unintended ABI changes can be detected as CI failures mechanically.
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- Newer implementation must be able to process the oldest data (since genesis)
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once we go mainnet.
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- The objective of this proposal is to protect the ABI while sustaining rather
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rapid development by opting for a mechanical process rather than a very long
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human-driven auditing process.
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- Once signed cryptographically, data blob must be identical, so no
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in-place data format update is possible regardless of inbound and outbound of
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the online system. Also, considering the sheer volume of transactions we're
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aiming to handle, retrospective in-place update is undesirable at best.
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# Solution
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Instead of natural human's eye due-diligence, which should be assumed to fail
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regularly, we need a systematic assurance of not breaking the cluster when
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changing the source code.
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For that purpose, we introduce a mechanism of marking every ABI-related things
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in source code (`struct`s, `enum`s) with the new `#[frozen_abi]` attribute. This
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takes hard-coded digest value derived from types of its fields via
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`ser::Serialize`. And the attribute automatically generates a unit test to try
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to detect any unsanctioned changes to the marked ABI-related things.
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However, the detection cannot be complete; no matter how hard we statically
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analyze the source code, it's still possible to break ABI. For example, this
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includes not-`derive`d hand-written `ser::Serialize`, underlying library's
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implementation changes (for example `bincode`), CPU architecture differences.
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The detection of these possible ABI incompatibilities is out-of-scope for this
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ABI management.
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# Definitions
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ABI item/type: various types to be used for serialization, which collectively
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comprises the whole ABI for any system components. For example, those types
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include `struct`s and `enum`s.
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ABI item digest: Some fixed hash derived from type information of ABI item's
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fields.
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# Example
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```patch
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+#[frozen_abi(digest="1c6a53e9")]
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#[derive(Serialize, Default, Deserialize, Debug, PartialEq, Eq, Clone)]
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pub struct Vote {
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/// A stack of votes starting with the oldest vote
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pub slots: Vec<Slot>,
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/// signature of the bank's state at the last slot
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pub hash: Hash,
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}
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```
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# Developer's workflow
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To know the digest for new ABI items, developers can add `frozen_abi` with a
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random digest value and run the unit tests and replace it with the correct
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digest from the assertion test error message.
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In general, once we add `frozen_abi` and its change is published in the stable
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release channel, its digest should never change. If such a change is needed, we
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should opt for defining a new struct like `FooV1`. And special release flow like
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hard forks should be approached.
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# Implementation remarks
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We use some degree of macro machinery to automatically generate unit tests
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and calculate a digest from ABI items. This is doable by clever use of
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`serde::Serialize` ([1]) and `any::typename` ([2]). For a precedent for similar
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implementation, `ink` from the Parity Technologies [3] could be informational.
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# References
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1. [(De)Serialization with type info · Issue #1095 · serde-rs/serde](https://github.com/serde-rs/serde/issues/1095#issuecomment-345483479)
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2. [`std::any::type_name` - Rust](https://doc.rust-lang.org/std/any/fn.type_name.html)
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3. [Parity's ink to write smart contracts](https://github.com/paritytech/ink)
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