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Add Getter's Keys operation. #825

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Aug 25, 2020
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Add Getter's Keys operation. #825

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Add of Getter's Keys operation.
carlosalberto Aug 18, 2020
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carlosalberto Aug 19, 2020
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Update specification/context/api-propagators.md
carlosalberto Aug 21, 2020
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Merge branch 'master' into getter_keys
carlosalberto Aug 21, 2020
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Merge branch 'master' into getter_keys
SergeyKanzhelev Aug 21, 2020
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Remove extra trailing space.
carlosalberto Aug 22, 2020
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Merge branch 'master' into getter_keys
carlosalberto Aug 24, 2020
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Merge branch 'master' into getter_keys
carlosalberto Aug 25, 2020
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Merge branch 'master' into getter_keys
SergeyKanzhelev Aug 25, 2020
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25 changes: 23 additions & 2 deletions specification/context/api-propagators.md
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ Table of Contents
- [Set](#set)
- [Extract](#extract-1)
- [Getter argument](#getter-argument)
- [Keys](#keys)
- [Get](#get)
- [Composite Propagator](#composite-propagator)
- [Global Propagators](#global-propagators)
Expand Down Expand Up @@ -116,7 +117,7 @@ avoid runtime allocations.

### Fields

The propagation fields defined. If your carrier is reused, you should delete the fields here
The predefined propagation fields. If your carrier is reused, you should delete the fields here
before calling [inject](#inject).

Fields are defined as string keys identifying format-specific components in a carrier.
Expand All @@ -132,6 +133,10 @@ The use cases of this are:

Returns list of fields that will be used by the `TextMapPropagator`.

Observe that some `Propagator`s may define, besides the returned values, additional fields with
variable names. To get a full list of fields for a specific carrier object, use the
[Keys](#keys) operation.

### Inject

Injects the value into a carrier. The required arguments are the same as defined by
Expand Down Expand Up @@ -180,7 +185,23 @@ Getter is an argument in `Extract` that get value from given field

`Getter` allows a `TextMapPropagator` to read propagated fields from a carrier.

One of the ways to implement it is `Getter` class with `Get` method as described below.
One of the ways to implement it is `Getter` class with `Get` and `Keys` methods
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as described below. Languages may decide on alternative implementations and
expose corresponding methods as delegates or other ways.

##### Keys

The `Keys` function MUST return the list of all the keys in the carrier.

Required arguments:

- The carrier of the propagation fields, such as an HTTP request.

The `Keys` function can be called by `Propagator`s which are using variable key names in order to
iterate over all the keys in the specified carrier.

For example, it can be used to detect all keys following the `uberctx-{user-defined-key}` pattern, as defined by the
[Jaeger Propagation Format](https://www.jaegertracing.io/docs/1.18/client-libraries/#baggage).

##### Get

Expand Down