Table of Contents
Propagators API consists of two main formats:
BinaryFormatis used to serialize and deserialize a value into a binary representation.HTTPTextFormatis used to inject and extract a value as text into carriers that travel in-band across process boundaries.
Deserializing must set IsRemote to true on the returned SpanContext.
BinaryFormat is a formatter to serialize and deserialize a value into a binary format.
BinaryFormat MUST expose the APIs that serializes values into bytes,
and deserializes values from bytes.
Serializes the given value into the on-the-wire representation.
Required arguments:
- the value to serialize, can be
SpanContextorDistributedContext.
Returns the on-the-wire byte representation of the value.
Creates a value from the given on-the-wire encoded representation.
If the value could not be parsed, the underlying implementation SHOULD decide to return ether an empty value, an invalid value, or a valid value.
Required arguments:
- on-the-wire byte representation of the value.
Returns a value deserialized from bytes.
HTTPTextFormat is a formatter that injects and extracts a value as text into carriers that
travel in-band across process boundaries.
Encoding is expected to conform to the HTTP Header Field semantics. Values are often encoded as RPC/HTTP request headers.
The carrier of propagated data on both the client (injector) and server (extractor) side is usually an http request. Propagation is usually implemented via library-specific request interceptors, where the client-side injects values and the server-side extracts them.
HTTPTextFormat MUST expose the APIs that injects values into carriers,
and extracts values from carriers.
The propagation fields defined. If your carrier is reused, you should delete the fields here before calling inject.
For example, if the carrier is a single-use or immutable request object, you don't need to clear fields as they couldn't have been set before. If it is a mutable, retryable object, successive calls should clear these fields first.
The use cases of this are:
- allow pre-allocation of fields, especially in systems like gRPC Metadata
- allow a single-pass over an iterator
Returns list of fields that will be used by this formatter.
Injects the value downstream. For example, as http headers.
Required arguments:
- the value to be injected, can be
SpanContextorDistributedContext. - the carrier that holds propagation fields. For example, an outgoing message or http request.
- the setter invoked for each propagation key to add or remove.
Setter allows a HTTPTextFormat to set propagated fields into a carrier.
Setter MUST be stateless and allowed to be saved as a constant to avoid runtime allocations.
Replaces a propagated field with the given value.
Required arguments:
- the carrier holds propagation fields. For example, an outgoing message or http request.
- the key of the field.
- the value of the field.
Extracts the value from upstream. For example, as http headers.
If the value could not be parsed, the underlying implementation will decide to return an object representing either an empty value, an invalid value, or a valid value. Implementations MUST not return null.
Required arguments:
- the carrier holds propagation fields. For example, an outgoing message or http request.
- the getter invoked for each propagation key to get.
Returns the non-null extracted value.
Getter allows a HttpTextFormat to read propagated fields from a carrier.
Getter MUST be stateless and allowed to be saved as a constant to avoid runtime allocations.
Returns the first value of the given propagation key or returns null if the key doesn't exist.
Required arguments:
- the carrier of propagation fields, such as an http request.
- the key of the field.
Returns the first value of the given propagation key or returns null if the key doesn't exist.