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(pronounced “svæ-lin”)

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Svalinn has an endpoint that receives events as WRP Messages. The service parses these events and inserts them into the database. It also optionally registers to an endpoint to receive events. For more information on how Svalinn fits into codex, check out the codex README.

For registering to an endpoint, Svalinn is capable of registering to Caduceus, a part of XMiDT.

Table of Contents

Code of Conduct

This project and everyone participating in it are governed by the XMiDT Code Of Conduct. By participating, you agree to this Code.


Svalinn has two main functions: registering for events and inserting events into the database. It also has a health endpoint that reports as unhealthy when it can't connect to or ping the database.

MsgPack is used multiple time in Svalinn, specifically ugorji's implementation.

Svalinn utilizes the bascule and wrp-listener packages for webhook registration and request authentication.

Registering for events

Whether or not Svalinn registers to a webhook for events is determined by the configurable webhook registration interval. So long as the interval is greater than 0, the registerer will register at the interval given.

When the registerer contacts the webhook, it includes the following information:

  • URL: where to send the events
  • Content type: what to set as the message's content type and how to send events to Svalinn. Svalinn by default requests for a wrp, which will come as a MsgPack.
  • Secret: the secret the webhook should use when sending events to Svalinn. Svalinn uses it to validate the message. If this is an empty string, Svalinn doesn't authenticate the messages it receives against a hash of the message.
  • Retries: the number of times to retry if sending an event fails.
  • Alternative URLs: other URLs to try if sending an event fails.
  • Device IDs: list of regular expressions to match device id type against. Currently, this defaults to [".*"].
  • Events: list of regular expressions for the webhook to use to determine which events to send to Svalinn.

The registerer sends an authorization header with its request, and determines what that should be based on configuration values. It's possible to not send any authorization header.

Registering is done using the wrp-listener package.

Inserting events into the database

When an event is sent to Svalinn's endpoint, it is initially validated, parsed into a record to be stored in the database, then inserted as part of a batch insert into the database.


In order to ensure that the event was sent from a trusted source, Svalinn gets a SHA1 hash from a request header (the header name is configurable) then creates its own hash using the secret that it sends when registering and the body of the request. If the two hashes match, the event is considered valid.
This validation is done using bascule middleware, and is bypassed if the configurable header and secret are empty strings.

If the request passes through the middleware successfully, the body is decoded from MsgPack into the wrp.Message struct: our event!

Now that the event has been verified and decoded, Svalinn attempts to add it to the parsing queue. If the queue is full, Svalinn returns the Too Many Requests (429) status code, drops the message, and records it as dropped in metrics.
Otherwise, Svalinn adds the event to the queue and returns the Accepted (202) status code.

Parsing (and Encryption)

A goroutine watches the parsing queue and spawns other goroutines to parse the events it finds on the queue into the records we will store in the database.
There is a configurable maximum number of workers to parse the incoming events.

A worker parsing a request runs the following steps:

  1. Checks to see if there are any rules relating to this event's Destination. If a rule's regular expression matches, the rule provides guidance on what the event type of the event's record should be, the TTL for the record, and whether or not to store the payload of the event. Rules are declared in Svalinn's configuration.
  2. Parses the event's Destination to determine the device id, which is added to the record we are going to store.
  3. Determines if the record is in the blacklist.
  4. Checks that the Type is what we expect.
  5. Gets a timestamp from the Payload for the record's birth date. If a timestamp isn't found, Svalinn creates a new one from the current time. The worker also takes the time and adds the TTL for the record in order to find the death date, which is when the record has expired and should be deleted. If a TTL isn't decided by a rule, the (configurable) default TTL is used. Both the birth date and death date are added to the record.
  6. Determines if the event's Payload and Metadata should be stored. The Payload is not stored by default unless it is part of a rule enabling the storage of the Payload. However, if its size is bigger than the configured max size allowed, it isn't stored. The Metadata is stored by default unless it is larger than the configured max size allowed. If the Payload or Metadata shouldn't be stored, they are stripped from the event.
  7. The event (possibly without Metadata and Payload) is encoded into a MsgPack.
  8. If an encryption has been set up, we encrypt the encoded event and add it to the record we plan to insert into the database. If there is no encryption, the encoded event is added to the record.

If any of these steps fail, the worker drops the message, records the drop and the reason in metrics, and then finishes.

At this point, if the worker succeeded, the record has the following information:

  • Type
  • DeviceID
  • BirthDate
  • DeathDate
  • Data (the encoded/encrypted event)
  • Nonce (for the encryption)
  • Alg (for the encryption)
  • KID (for the encryption)

The worker adds the record to the inserting queue, blocking until it succeeds. Once it succeeds, it finishes so a new goroutine can parse a new event.

Batch Insertion

A goroutine watches the inserting queue. When it finds a record, a timer starts while the goroutine waits for more records. If it reaches the configurable maximum batch size, it spawns a worker to batch insert that group of records. The timer that started was the maximum time the goroutine will wait until spawning a goroutine to batch insert the records it has gathered. When the timer goes off, the goroutine spawns a worker to batch insert its records, even though it didn't hit the max batch size yet. The number of maximum inserting workers at a time is a configurable value. If there are no workers available, the goroutine will block until it is able to spawn a new worker to batch insert the records it has.

The spawned worker will attempt to insert the records. Depending on the configuration, it may retry a set number of times. If it ultimately fails, it will count the number of records in the batch and record that number of dropped events in metrics. When the worker is done, it finishes so a new goroutine can do a new insertion.



In order to build from the source, you need a working Go environment with version 1.11 or greater. Find more information on the Go website.

You can directly use go get to put the Svalinn binary into your GOPATH:

GO111MODULE=on go get

You can also clone the repository yourself and build using make:

mkdir -p $GOPATH/src/
cd $GOPATH/src/
git clone
cd svalinn
make build


The Makefile has the following options you may find helpful:

  • make build: builds the Svalinn binary
  • make docker: builds a docker image for Svalinn, making sure to get all dependencies
  • make local-docker: builds a docker image for Svalinn with the assumption that the dependencies can be found already
  • make it: runs make docker, then deploys Svalinn and a cockroachdb database into docker.
  • make test: runs unit tests with coverage for Svalinn
  • make clean: deletes previously-built binaries and object files


First have a local clone of the source and go into the root directory of the repository. Then use rpkg to build the rpm:

rpkg srpm --spec <repo location>/<spec file location in repo>
rpkg -C <repo location>/.config/rpkg.conf sources --outdir <repo location>'


The docker image can be built either with the Makefile or by running a docker command. Either option requires first getting the source code.

See Makefile on specifics of how to build the image that way.

For running a command, either you can run docker build after getting all dependencies, or make the command fetch the dependencies. If you don't want to get the dependencies, run the following command:

docker build -t svalinn:local -f deploy/Dockerfile .

If you want to get the dependencies then build, run the following commands:

GO111MODULE=on go mod vendor
docker build -t svalinn:local -f deploy/Dockerfile.local .

For either command, if you want the tag to be a version instead of local, then replace local in the docker build command.


WIP. TODO: add info


For deploying on Docker or in Kubernetes, refer to the deploy README.

For running locally, ensure you have the binary built. If it's in your GOPATH, run:


If the binary is in your current folder, run:



Refer to