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Contract Size Optimization

Soroban enforces a 100 KB WASM size limit. The CI gate in .github/workflows/contract-size.yml blocks merges that exceed this limit and warns at 80%.

Checking size locally

bash scripts/check_contract_size.sh

Outputs the size, % of limit used, trend vs previous build, and a markdown report at deployment-records/size_report.md.

Compiler profile (biggest wins first)

Add to contracts/stellar-save/Cargo.toml:

[profile.release]
opt-level = "z"      # optimize for size (not speed)
lto = true           # link-time optimization removes dead code across crates
codegen-units = 1    # single codegen unit enables better LTO
strip = true         # strip debug symbols from WASM

Expected combined saving: 20–40%.

Post-build optimization with wasm-opt

wasm-opt (from the binaryen toolchain) can shrink the output further:

wasm-opt -Oz \
  target/wasm32-unknown-unknown/release/stellar_save.wasm \
  -o target/wasm32-unknown-unknown/release/stellar_save.wasm

Expected saving: 10–20% on top of compiler flags.

Code-level techniques

Technique Why it helps
Use Symbol instead of String for fixed identifiers String pulls in allocator + UTF-8 machinery
Use i128/u128 instead of BigInt wrappers Avoids extra abstraction layers
Avoid Vec<T> in storage keys — use fixed-size types Reduces monomorphization
Remove unused soroban-sdk features Each feature adds WASM sections
Keep functions small and avoid generics where possible Reduces monomorphization bloat
Use #[contracttype] only for types that cross the contract boundary Internal types don't need XDR encoding

Thresholds

Level Threshold Action
OK < 80 KB ✅ Pass
Warning 80–100 KB ⚠️ Pass with suggestions
Fail > 100 KB 🚨 CI blocks merge

Thresholds are configurable via env vars:

WASM_SIZE_LIMIT_KB=100 WARN_THRESHOLD_PCT=80 bash scripts/check_contract_size.sh

Trend tracking

Every CI run appends to deployment-records/size_history.json (kept as a GitHub Actions artifact, last 50 entries). The PR comment shows a trend table of the last 5 builds so regressions are visible immediately.