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/* =========================================================================================
* Copyright © 2013-2018 the kamon project <http://kamon.io/>
*
* 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
*
* http://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 kamon.context
/**
* Inter-process Context propagation interface. Implementations are responsible from reading and writing a lossless
* representation of a given Context instance to the appropriate mediums. Out of the box, Kamon ships with two
* implementations:
*
* * HttpPropagation: Uses HTTP headers as the medium to transport the Context data.
* * BinaryPropagation: Uses byte streams as the medium to transport the Context data.
*
*/
trait Propagation[ReaderMedium, WriterMedium] {
/**
* Attempts to read a Context from the [[ReaderMedium]].
*
* @param medium An abstraction the reads data from the medium transporting the Context data.
* @return The decoded Context instance or an empty Context if no entries or tags could be read from the medium.
*/
def read(medium: ReaderMedium): Context
/**
* Attempts to write a Context instance to the [[WriterMedium]].
*
* @param context Context instance to be written.
* @param medium An abstraction that writes data into the medium that will transport the Context data.
*/
def write(context: Context, medium: WriterMedium): Unit
}
object Propagation {
/**
* Encapsulates logic required to read a single context entry from a medium. Implementations of this trait
* must be aware of the entry they are able to read.
*/
trait EntryReader[Medium] {
/**
* Tries to read a context entry from the medium. If a context entry is successfully read, implementations
* must return an updated context instance that includes such entry. If no entry could be read simply return the
* context instance that was passed in, unchanged.
*
* @param medium An abstraction the reads data from the medium transporting the Context data.
* @param context Current context.
* @return Either the original context passed in or a modified version of it, including the read entry.
*/
def read(medium: Medium, context: Context): Context
}
/**
* Encapsulates logic required to write a single context entry to the medium. Implementations of this trait
* must be aware of the entry they are able to write.
*/
trait EntryWriter[Medium] {
/**
* Tries to write a context entry into the medium.
*
* @param context The context from which entries should be written.
* @param medium An abstraction that writes data into the medium that will transport the Context data.
*/
def write(context: Context, medium: Medium): Unit
}
}
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