swaitsandClaude Opus 4.6
3102fc747a
Implement full SSD1306 OLED display support: - Splash screen on boot (1.5s) with project name, version, board - Dashboard showing radio state, config, counters, RSSI/SNR - RSSI history sparkline (64-sample ring buffer, 2px-wide bars) - DisplayOn/DisplayOff host commands routed via dedicated channel - Pure render functions against generic DrawTarget (no hardware coupling) - Display on/off control bypasses radio task entirely Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
70 lines
2.7 KiB
Markdown
70 lines
2.7 KiB
Markdown
# ssmarshal
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[](https://crates.io/crates/ssmarshal)
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[Documentation](https://docs.rs/ssmarshal)
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ssmarshal ("stupid simple marshaling") is a serde-based de/serialization
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library. It is somewhat like [bincode](https://github.com/TyOverby/bincode),
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but doesn't support String/Vec - this library is entirely zero-allocation, for
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use in extremely limited `no_std` contexts. The key invariant is that the
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encoding space for any value of a type is `<= size_of::<T>()`. This allows
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easy reasoning about limited buffer sizes, and how much is always enough.
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## Limitations
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These sorts of types are not supported:
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- Any non-core type (eg, `Vec`, `HashMap`)
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- Slices
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- Strings
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- Types containing references or pointers
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- Enums with more than 256 variants
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All enums MUST be `#[repr(C)]` in order for the size invariant to be upheld.
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Note that this excludes using `Option`, especially with `NonZero` types!
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You can use this crate with non-`#[repr(C)]` enums, but you should thoroughly
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test (I recommend quickcheck, see [the tests](https://gitlab.com/robigalia/ssmarshal/blob/master/tests/roundtrip.rs)
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for an example) de/serializing values of that type to be assured the size
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invariant holds for the type.
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## Details of the format
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The format is not incredibly compact, but doesn't add extra fluff, and is
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quick to en/decode.
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- `bool` is serialized as a byte, 1 if true, 0 is false.
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- the integer types are encoded in their little-endian form.
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- f32 is bitcast to a u32 then encoded as a u32. likewise, f64 and u64.
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- inhabited enums are serialized as 1 byte for the discriminant, and then the fields.
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- structs are serialized as just their fields.
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- the unit type and uninhabited enums are not serialized at all.
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- tuples are serialized as the fields, in order.
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There is no padding.
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As you might see, this format is not self-describing. To successfully
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deserialize a value, the exact layout must be known ahead-of-time.
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## Alternatives
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This is designed for doing IPC in a microkernel, with a stable ABI, not saving
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to disk or transferring over the network. It may be useful for those cases,
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although you'll likely want a format which can handle data evolution, like
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Cap'n Proto.
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If you care about truly minimizing encoding space, you might look into ASN.1
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PER.
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If you need more features (for example, slices or references), but still don't
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care about data evolution, I recommend using bincode.
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## Testing
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The `roundtrip` test suite exercises almost all of the functionality of
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ssmarshal, with coverage over 95% (missing mostly some of the error cases for
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invalid/unsupported types).
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This library is extensively fuzz tested with `cargo-fuzz` (libFuzzer) before
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every release. See the `fuzz` directory for the scripts used.
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