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/*
* Copyright 2022 VMware, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.micrometer.observation.transport;
import io.micrometer.common.lang.Nullable;
/**
* Inspired by OpenZipkin Brave and OpenTelemetry. Most of the documentation is taken
* directly from OpenTelemetry.
*
* 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.
*
* @author OpenZipkin Brave Authors
* @author OpenTelemetry Authors
* @author Marcin Grzejszczak
* @since 1.10.0
*/
public interface Propagator {
/**
* Class that allows to set propagated fields into a carrier.
*
*
* {@code Setter} is stateless and allows to be saved as a constant to avoid runtime
* allocations.
*
* @param carrier of propagation fields, such as an http request
* @since 1.10.0
*/
interface Setter {
/**
* Replaces a propagated field with the given value.
*
*
* For example, a setter for an {@link java.net.HttpURLConnection} would be the
* method reference
* {@link java.net.HttpURLConnection#addRequestProperty(String, String)}
* @param carrier holds propagation fields. For example, an outgoing message or
* http request. To facilitate implementations as java lambdas, this parameter may
* be null.
* @param key the key of the field.
* @param value the value of the field.
*/
void set(@Nullable C carrier, String key, String value);
}
/**
* Interface that allows to read propagated fields from a carrier.
*
*
* {@code Getter} is stateless and allows to be saved as a constant to avoid runtime
* allocations.
*
* @param carrier of propagation fields, such as an http request.
* @since 1.10.0
*/
interface Getter {
/**
* Returns the first value of the given propagation {@code key} or returns
* {@code null}.
* @param carrier carrier of propagation fields, such as an http request.
* @param key the key of the field.
* @return the first value of the given propagation {@code key} or returns
* {@code null}.
*/
@Nullable
String get(C carrier, String key);
}
}