feat(solana): Add SolanaTransaction.insertTransferInstruction()

[satoshiotomakan]

This pull request introduces support for sponsored transfers in Solana transactions, allowing an additional transfer to a fee payer to be included in various transaction types. It also adds a utility for programmatically inserting transfer instructions at arbitrary positions in a transaction, improves account permission validation logic, and updates the FFI interface to expose the new functionality.

Sponsored transfer support and builder enhancements:

• Added the transfer_to_fee_payer field to transaction inputs, and implemented the transfer_to_fee_payer method in MessageBuilder to conditionally create and append a sponsored transfer instruction when requested. The InstructionBuilder now includes a new maybe_add_instruction method to facilitate optional instruction addition. [1] [2]
• Updated all transaction builder flows in MessageBuilder (e.g., token transfer, deposit, withdraw, deactivate, etc.) to call maybe_add_instruction(self.transfer_to_fee_payer()?), ensuring the sponsored transfer is included when present. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

Transaction utility and FFI interface:

• Added insert_transfer_instruction to SolanaTransaction, enabling insertion of a transfer instruction at a specified index in an encoded transaction. This is also exposed via FFI as tw_solana_transaction_insert_transfer_instruction. [1] [2]
• Updated dependencies and imports to support new functionality, including tw_number for U256 parsing and SystemInstructionBuilder for transfer construction. [1] [2]

Account permission validation improvements:

• Refactored logic in InsertInstruction to use pattern matching for signer/writable permission checks, and clarified error handling and comments for cases where stronger permissions would require account reordering (with a TODO for future implementation). [1] [2]

Testing:

• Added a new test for sponsored token transfers (test_solana_sign_sponsored_transfer), verifying correct encoding and behavior.
• Updated FFI transaction tests to cover the new sponsored transfer and instruction insertion functionality. [1] [2]

These changes collectively enable more flexible transaction construction in Solana, especially for scenarios involving external fee payers or custom transaction flows.

[Copilot]

Pull Request Overview

This PR introduces sponsored transfer support for Solana transactions, allowing SOL transfers to fee payers to be included in various transaction types. The implementation adds a new transfer_to_fee_payer field to signing inputs and provides programmatic insertion of transfer instructions at arbitrary positions.

Key changes include:

• Added transfer_to_fee_payer field to SigningInput proto for optional SOL transfers to fee payers
• Implemented insert_transfer_instruction method in SolanaTransaction for programmatically inserting transfer instructions
• Enhanced all transaction builder flows to conditionally include sponsored transfers when specified

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/proto/Solana.proto	Added transfer_to_fee_payer field to SigningInput message
rust/wallet_core_rs/src/ffi/solana/transaction.rs	Added FFI function tw_solana_transaction_insert_transfer_instruction
rust/tw_tests/tests/chains/solana/solana_transaction_ffi.rs	Added test for new transfer instruction insertion functionality
rust/tw_tests/tests/chains/solana/solana_sign.rs	Added test for sponsored transfer transaction signing
rust/chains/tw_solana/src/modules/utils.rs	Implemented insert_transfer_instruction method with address parsing and instruction insertion
rust/chains/tw_solana/src/modules/message_builder.rs	Added transfer_to_fee_payer method and integrated sponsored transfers into all transaction builders
rust/chains/tw_solana/src/modules/instruction_builder/mod.rs	Added maybe_add_instruction method for conditional instruction addition
rust/chains/tw_solana/src/modules/insert_instruction.rs	Refactored account permission validation using pattern matching
rust/chains/tw_solana/Cargo.toml	Added tw_number dependency for U256 parsing

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[satoshiotomakan]

Hi @10gic, thank you so much for the SolanaTransaction.insertInstruction() FFI, it's very useful!
I made a minor change, please take a look when you have time

[github-actions]

Binary size comparison

➡️ aarch64-apple-ios:

- 14.15 MB
+ 14.16 MB 	 +10 KB

➡️ aarch64-apple-ios-sim:

- 14.16 MB
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➡️ aarch64-linux-android:

- 18.64 MB
+ 18.65 MB 	 +14 KB

➡️ armv7-linux-androideabi:

- 15.59 MB
+ 15.60 MB 	 +9 KB

➡️ wasm32-unknown-emscripten:

- 13.29 MB
+ 13.30 MB 	 +12 KB

[gupnik]

@satoshiotomakan Added a comment about compute limit/price instructions. Could you please take a look?