windowed-infinity

This crate provides the WindowedInfinity struct and implementations of various traits to write to it.

Its primary purpose is to wrap a small buffer such that writes to it advance a cursor over a larger imaginary buffer, only persisting writes to the small buffer. After the buffer has been processed, a new WindowedInfinity can be set up and the writing process repeated. This is wasteful when the writes are computationally expensive, but convenient when operations only rarely exceed the buffer.

A typical practical example of a WindowedInfinity application is the implementation of CoAP block-wise transfer according to RFC7959; a simpler example is available in the demo.rs example.

Features

The set of traits implemented by WindowedInfinity depends on the configured cargo features:

• With the std feature, it implements std::io::Write
• With the with_serde_cbor feature, it uses serde_cbor’s trait unsealing feature to implement its Write trait.
• Likewise, there are features for ciborium and minicbor. The minicbor version is a bit special in that there is both a with_minicbor / with_minicbor_0_19 feature.
• Starting at with_minicbor_0_19, features carry a version. This allows users of different minicbor versions to coexist in the same crate, and moreover ensures that the dependencies expressed in the Cargo.toml files to describe the requirements precisely.
• With the with_embedded_io_0_4, _0_6 and _async_0_6 features, the Write trait of embedded-io / -async is implemented.

Crate size

Compared to the original plan of “doing one thing, and doing that right”, this crate has grown a bit, in that it contains trait implementations for several serializers, and extra mechanism for combining the own writer with others (from cryptographic digests or CRCs). Both these are temporary – once there is a 1.0 version of embedded-io, the Tee will be split out into a dedicated crate (with only compatibility re-exports and constructors / destructors remaining), and once serializers start using the stable embedded-io, no more writer implementations will need to be added.