#write #coap #transfer #writable #io-write #traits #cursor

no-std windowed-infinity

A data structure representing an infinite sequentially writable u8 vector of which a small view has writes to it preserved. This is primarily useful when implementing CoAP block-wise transfers, and also convenient for logging on constrained devices.

5 releases

0.1.4 Feb 1, 2023
0.1.3 Jan 25, 2023
0.1.2 Jan 3, 2023
0.1.1 Oct 22, 2020
0.1.0 Jan 22, 2019

#6 in #writable

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Used in 6 crates (via coap-handler-implementati…)


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

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


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 feature, the Write trait of embedded-io 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.


~17K SLoC