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FTP-NNN: Your Boring Title

(optional) Your Witty Title

Field Value
Status Draft
Authors your emails
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Reviewed leave blank until reviewed


A one paragraph description of the rest of the proposal.


What problem does this proposal solve?


This is the technically detailed version of your proposal.

One important high-level bit of your proposal is what part of FIDL your proposal modifies. This includes at least:

  • The FIDL source language
  • The FIDL wire format
  • The first-class language bindings (C, C++, Dart, Go, Rust)
  • The FIDL style guide and API rubric
  • The FIDL tuning process

Your proposal should talk about all the relevant areas. For instance, if your proposal adds a new type to the FIDL language, it also needs to discuss the style guide for that feature, and how to implement it in the bindings.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Implementation Strategy

How will you go about making this change? Some FTPs will not involve breaking changes, and might happen as a single CL. Others might be sweeping changes. Either way, think about how you would break down the implementation into tasks.

For more complex implementations that are likely to change, we recommend writing an Intent-to-Implement ("I2I") doc and linking to it in this section. The I2I can then serve as a living, separate design doc that may be updated independently, so that this document isn't constantly re-edited as details change. This also enables your FTP to focus on the high-level important concepts, rather than implementation and execution.


Does your change make FIDL easier to use, and simpler to understand? Does it make the bindings easier to use? If it doesn't, what's the justification for the complexity?

Focus on both the end-user API and the cognitive effort required to understand the concept.

Documentation and Examples

There are potentially several kinds of documentation to address.

How would you write or change a tutorial for this feature, in the style of [the various FIDL tutorials][fidl-tutotials]? Imagine explaining your feature to someone new to Fuchsia.

How would you write reference documentation? For example, suppose your proposal extends the FIDL wire format. How would you update the documentation of the wire format? Imagine explaining your feature to someone in sufficient detail that they could implement it.

What are important examples or use cases of your proposed feature?

Backwards Compatibility

Backwards compatibility comes in two flavors: FIDL file source compatibility, and ABI or wire format compatibility. This section should speak to both. Over time, the ability to make backwards-incompatible changes will get harder.

If you are introducing a new data type or language feature, consider what changes you would expect users to make to FIDL definitions without breaking users of the generated code. If your feature places any new [source compatibility][] restrictions on the generated language bindings, list those here.


What impact will this proposal have on IPC performance? On build performance?


How will your feature impact security? Will your feature be easy to use safely in non-memory-safe languages? Does your feature make it easy to accidentally leak details of a process's address space?


How will your feature be tested? For instance, do you need to write new tests for fidlc, or for the C++ bindings?

If your change affects encoding or decoding, plan to update the conformance test suite.

If your change affects source compatibility, plan to update the [source compatibility test suite][source-compatibility-suite.

How will uses of your new feature be tested? If you add a language feature, how will you test it in each language's bindings?

Drawbacks, Alternatives, and Unknowns

What are the costs of implementing this proposal?

What other strategies might solve the same problem?

What questions still need to be resolved, or details iterated upon, to accept this proposal? Your answer to this is likely to evolve as the proposal evolves.

Prior Art and References

Is there any background material that might be helpful when reading this proposal? For instance, do other serialization or IPC systems address the same problem this proposal addresses?