ser-write

Writer-style serializers and deserializers for convenience designed with embedded (no_std) targets in mind.

• Writer-style serializers use the common writer trait found in this crate.
• Designed for no_std.
• Fully supports std or alloc when enabled for code portability and testablilty.
• For each serializer a deserializer is provided for convenience.
• Embedded projects can implement SerWrite trait for custom containers, frame builders and more.

This crate provides:

• the trait - SerWrite which should be used by serializers to write the serialized output,
• SerError - a convenient error type,
• SliceWriter - a convenient slice writer object implementing SerWrite,
• SerWrite implementations for foreign types.

Depending on the enabled crate features, SerWrite is implemented for:

• SliceWriter - example slice writer implementation,
• arrayvec::ArrayVec<u8,CAP> - arrayvec feature,
• heapless::Vec<u8,CAP> - heapless feature,
• smallvec::SmallVec<[u8; CAP]> - smallvec feature,
• tinyvec::ArrayVec<[u8; CAP]> - tinyvec feature,
• tinyvec::SliceVec<'_, u8> - tinyvec feature,
• tinyvec::TinyVec<[u8; CAP]> - tinyvec with alloc or std feature,
• Vec<u8> - alloc or std feature,
• VecDeque<u8> - alloc or std feature,
• io::Cursor<T: io::Write> - std feature,

smallvec also enables alloc.

Usage

Start by adding a dependency to the serializer:

For example:

[dependencies]
ser-write-json = { version = "0.3", default-features = false }

If you want to also pull implementations of SerWrite for the foreign types add:

ser-write = { version = "0.3", default-features = false, features = ["arrayvec", "heapless"] }

In the above example implementations for: arrayvec::ArrayVec<u8;_> and heapless::Vec<u8> are selected.

Serializers

Currently available serializers and deserializers are:

• JSON (compact) - ser-write-json
• MessagePack - ser-write-msgpack

Example

An example SliceWriter implementation:

use ser_write::{SerWrite, SerResult, SerError};

#[derive(Debug, PartialEq)]
pub struct SliceWriter<'a> {
    pub buf: &'a mut [u8],
    pub len: usize
}

impl SerWrite for SliceWriter<'_> {
    fn write(&mut self, buf: &[u8]) -> SerResult<()> {
        let end = self.len + buf.len();
        match self.buf.get_mut(self.len..end) {
            Some(chunk) => {
                chunk.copy_from_slice(buf);
                self.len = end;
                Ok(())
            }
            None => Err(SerError::BufferFull)
        }
    }
}

Alternatives

For alloc only:

• serde_json

Alternatively there's a Rust Embedded Community crate for serializeing JSONs without std:

• serde-json-core
• serde-json-core-fmt (a writer-style attempt abusing fmt::Display trait)

serde-json-core is a true no_std, no alloc alternative but rather inconvenient. One has to serialize data into intermediate slices instead just pushing data to outgoing buffers or frame builder implementations.

Motivation

• This crate would not be needed once something like io::Write lands in the Rust core.
• Unique features of the deserializers adds some functionality missing in the other crates.

Rust Version Requirements

ser-write requires Rustc version 1.87 or greater.