Chrly

Chrly is a lightweight implementation of Minecraft skins system server with ability to proxy requests to Mojang's skins system. It's packaged and distributed as a Docker image and can be downloaded from Dockerhub. App is written in Go, can withstand heavy loads and is production ready.

Installation

You can easily install Chrly using docker-compose. The configuration below (save it as docker-compose.yml) can be used to start a Chrly server. It relies on CHRLY_SECRET and CHRLY_SIGNING_KEY environment variables that you must set before running docker-compose up -d. Other possible variables are described below.

version: '2'
services:
  app:
    image: elyby/chrly
    hostname: chrly0
    restart: always
    links:
      - redis
    volumes:
      - ./data/capes:/data/capes
    ports:
      - "80:80"
    environment:
      CHRLY_SECRET: replace_this_value_in_production
      CHRLY_SIGNING_KEY: base64:LS0tLS1CRUdJTiBSU0EgUFJJVkFURSBLRVktLS0tLQpNSUlCT3dJQkFBSkJBTmJVcFZDWmtNS3BmdllaMDhXM2x1bWRBYVl4TEJubVVEbHpIQlFIM0RwWWVmNVdDTzMyClREVTZmZUlKNThBMGxBeXdndFo0d3dpMmRHSE96LzFoQXZjQ0F3RUFBUUpBSXRheFNIVGU2UEtieUVVLzlweGoKT05kaFlSWXdWTExvNTZnbk1ZaGt5b0VxYWFNc2ZvdjhoaG9lcGtZWkJNdlpGQjJiRE9zUTJTYUorRTJlaUJPNApBUUloQVBzc1MwK0JSOXcwYk9kbWpHcW1kRTlOck41VUpRY09XMTNzMjkrNlF6VUJBaUVBMnZXT2VwQTVBcGl1CnBFQTNwd29HZGtWQ3JOU25uS2pEUXpEWEJucGQzL2NDSUVGTmQ5c1k0cVVHNEZXZFhONlJubVhMN1NqMHVaZkgKRE13enU4ckVNNXNCQWlFQWh2ZG9ETnFMbWJNZHEzYytGc1BTT2VMMWQyMVpwL0pLOGtiUHRGbUhOZjhDSVFEVgo2RlNaRHd2V2Z1eGFNN0JzeWNRT05rakRCVFBOdStscWN0SkJHbkJ2M0E9PQotLS0tLUVORCBSU0EgUFJJVkFURSBLRVktLS0tLQo=

  redis:
    image: redis:4.0-32bit
    restart: always
    volumes:
      - ./data/redis:/data

Tip: to generate a value for the CHRLY_SIGNING_KEY use the command below and then join it with a base64: prefix.

openssl genrsa 4096 | base64 -w0

Chrly uses some volumes to persist storage for capes and Redis database. The configuration above mounts them to the host machine to do not lose data on container recreations.

Config

Application's configuration is based on the environment variables. You can adjust config by modifying environment key inside your docker-compose.yml file. After value will have been changed, container should be stopped and recreated. If environment variables have been changed, Docker will automatically recreate the container, so you only need to up it again:

docker-compose up -d app

Variables to adjust:

ENV	Description	Example
STORAGE_REDIS_HOST	By default, Chrly tries to connect to the redis host (by service name in docker-compose configuration).	localhost
STORAGE_REDIS_PORT	Specifies the Redis connection port.	6379
STORAGE_REDIS_POOL	By default, Chrly creates pool with 10 connection, but you may want to increase it	20
STATSD_ADDR	StatsD can be used to collect metrics	localhost:8125
SENTRY_DSN	Sentry can be used to collect app errors	https://public:private@your.sentry.io/1
QUEUE_STRATEGY	Sets the strategy for the queue in the batch provider of Mojang UUIDs. Allowed values are periodic and full-bus (see #24).	periodic
QUEUE_LOOP_DELAY	Parameter is sets the delay before each iteration of the Mojang's textures queue (Go's duration)	3s200ms
QUEUE_BATCH_SIZE	Sets the count of usernames, which will be sent to the Mojang's API to exchange them to their UUIDs. The current limit is 10, but it may change in the future, so you may want to adjust it.	10
MOJANG_TEXTURES_ENABLED	Allows to completely disable Mojang textures provider for unknown usernames. Enabled by default.	true
MOJANG_TEXTURES_UUIDS_PROVIDER_DRIVER	Specifies the preferred provider of the Mojang's UUIDs. Takes remote value. In any other case, the local queue will be used.	remote
MOJANG_TEXTURES_UUIDS_PROVIDER_URL	When the UUIDs driver set to remote, sets the remote URL. The trailing slash won't cause any problems.	http://remote-provider.com/api/worker/mojang-uuid
MOJANG_API_BASE_URL	Allows you to spoof the Mojang's API server address.	https://api.mojang.com
MOJANG_SESSION_SERVER_BASE_URL	Allows you to spoof the Mojang's Session server address.	https://sessionserver.mojang.com
TEXTURES_EXTRA_PARAM_NAME	Sets the name of the extra property in the signed textures response.	your-name
TEXTURES_EXTRA_PARAM_VALUE	Sets the value of the extra property in the signed textures response.	your awesome joke!

If something goes wrong, you can always access logs by executing docker-compose logs -f app.

Endpoints

Each endpoint that accepts username as a part of an url takes it case-insensitive. The .png postfix can be omitted.

GET /skins/{username}.png

This endpoint responds to requested username with a skin texture. If user's skin was set as texture's link, then it'll respond with the 301 redirect to that url. If the skin entry isn't found, it'll request textures information from Mojang's API and if it has a skin, than it'll return a 301 redirect to it.

GET /cloaks/{username}.png

It responds to requested username with a cape texture. If the cape entry isn't found, it'll request textures information from Mojang's API and if it has a cape, than it'll return a 301 redirect to it.

GET /textures/{username}

This endpoint forms response payloads as if it was the textures' property, but without base64 encoding. For example:

{
    "SKIN": {
        "url": "http://example.com/skin.png",
        "metadata": {
            "model": "slim"
        }
    },
    "CAPE": {
        "url": "http://example.com/cape.png"
    }
}

If both the skin and the cape entries aren't found, it'll request textures information from Mojang's API and if it has a textures property, than it'll return decoded contents.

That request is handy in case when your server implements authentication for a game server (e.g. join/hasJoined operation) and you have to respond with hasJoined request with an actual user textures. You have to simply send request to the Chrly server and put the result in your hasJoined response.

GET /profile/{username}

This endpoint behaves exactly like the Mojang's UUID -> Profile + Skin/Cape endpoint, but using a username instead of the UUID. Just like in the Mojang's API, you can append ?unsigned=false part to URL to sign the textures property. If the textures for the requested username aren't found, it'll request them through the Mojang's API, but the Mojang's signature will be discarded and the textures will be re-signed using the signature key for your Chrly instance.

Response example:

{
    "id": "0f657aa8bfbe415db7005750090d3af3",
    "name": "username",
    "properties": [
        {
            "name": "textures",
            "signature": "signature value",
            "value": "base64 encoded value"
        },
        {
            "name": "chrly",
            "value": "how do you tame a horse in Minecraft?"
        }
    ]
}

The base64 value string for the textures property decoded:

{
    "timestamp": 1614387238630,
    "profileId": "0f657aa8bfbe415db7005750090d3af3",
    "profileName": "username",
    "textures": {
        "SKIN": {
            "url": "http://example.com/skin.png"
        },
        "CAPE": {
            "url": "http://example.com/cape.png"
        }
    }
}

If username can't be found locally and can't be obtained from the Mojang's API, empty response with 204 status code will be sent.

Note that this endpoint will try to use the UUID for the stored profile in the database. This is an edge case, related to the situation where the user is available in the database but has no textures, which caused them to be retrieved from the Mojang's API.

GET /signature-verification-key.der

This endpoint returns a public key that can be used to verify textures signatures. The key is provided in DER format, so it can be used directly in the Authlib, without modifying the signature checking algorithm.

GET /signature-verification-key.pem

The same endpoint as the previous one, except that it returns the key in PEM format.

GET /textures/signed/{username}

Actually, this is the Ely.by's feature called Server Skins System, but if you have your own source of Mojang's signatures, then you can pass it with textures and it'll be displayed in response of this endpoint. Received response should be directly sent to the client without any modification via game server API.

Response example:

{
    "id": "0f657aa8bfbe415db7005750090d3af3",
    "name": "username",
    "properties": [
        {
            "name": "textures",
            "signature": "signature value",
            "value": "base64 encoded value"
        },
        {
            "name": "chrly",
            "value": "how do you tame a horse in Minecraft?"
        }
    ]
}

If there is no requested username or mojangSignature field isn't set, 204 status code will be sent.

You can adjust URL to /textures/signed/{username}?proxy=true to obtain textures information for provided username from Mojang's API. The textures will contain unmodified json with addition property with name "chrly" as shown in the example above.

GET /skins?name={username}

Equivalent of the GET /skins/{username}.png, but constructed especially for old Minecraft versions, where username placeholder wasn't used.

GET /cloaks?name={username}

Equivalent of the GET /cloaks/{username}.png, but constructed especially for old Minecraft versions, where username placeholder wasn't used.

Records manipulating API

Each request to the internal API should be performed with the Bearer authorization header. Example curl request:

curl -X POST -i http://chrly.domain.com/api/skins \
  -H "Authorization: Bearer Ym9zY236Ym9zY28="

You can obtain token by executing docker-compose run --rm app token.

POST /api/skins

Endpoint allows you to create or update skin record for a username.

The request body must be encoded as application/x-www-form-urlencoded.

Request params:

Field	Type	Description
identityId	int	Unique record identifier.
username	string	Username. Case insensitive.
uuid	uuid	UUID of the user.
skinId	int	Skin identifier.
is1_8	bool	Does the skin have the new format (64x64).
isSlim	bool	Does skin have slim arms (Alex model).
mojangTextures	string	Mojang textures field. It must be a base64 encoded json string. Not required.
mojangSignature	string	Signature for Mojang textures, which is required when mojangTextures passed.
url	string	Actual url of the skin.

Important: all parameters are always read at least as their default values. So, if you only want to update the username and not pass the skin data it will reset all skin information. If you want to keep the data, you should always pass the full set of parameters.

If successful you'll receive 201 status code. In the case of failure there will be 400 status code and errors list as json:

{
    "errors": {
        "identityId": [
            "The identityId field must be numeric"
        ]
    }
}

DELETE /api/skins/id:{identityId}

Performs record removal by identity id. Request body is not required. On success you will receive 204 status code. On failure it'll be 404 with the json body:

{
    "error": "Cannot find record for requested user id"
}

DELETE /api/skins/{username}

Same endpoint as above but it removes record by identity's username. Have the same behavior, but in case of failure response will be:

{
    "error": "Cannot find record for requested username"
}

Worker mode

The worker mode can be used in cooperation with the remote server mode to exchange Mojang usernames to UUIDs. This mode by itself doesn't solve the problem of extremely strict limits on the number of requests to the Mojang's API. But with a proxying load balancer (e.g. HAProxy, Nginx, etc.) it's easy to build a cluster of workers, which will multiply the bandwidth of the exchanging usernames to its UUIDs.

The instructions for setting up a proxy load balancer are outside the context of this documentation, but you get the idea ;)

GET /api/worker/mojang-uuid/{username}

Performs batch usernames exchange to UUIDs and returns the result in the same format as it returns from the Mojang's API:

{
    "id": "3e3ee6c35afa48abb61e8cd8c42fc0d9",
    "name": "ErickSkrauch"
}

Note: the results aren't cached.

Health check

GET /healthcheck

This endpoint can be used to programmatically check the status of the server. If all internal checks are successful, the server will return 200 status code with the following body:

{
    "status": "OK"
}

If any of the checks fails, the server will return 503 status code with the following body:

{
    "status": "Service Unavailable",
    "errors": {
        "mojang-batch-uuids-provider-queue-length": "the maximum number of tasks in the queue has been exceeded"
    }
}

Development

First of all you should install the latest stable version of Go and set GOPATH environment variable.

Then you must fork this repository. Now follow these steps:

# Get the source code
git clone https://github.com/elyby/chrly.git
# Switch to the project folder
cd chrly
# Install dependencies
go mod download
# Add your fork link as a remote
git remote add fork git@github.com:your-username/chrly.git
# Create a new branch for your task
git checkout -b iss-123

You only need to execute go run main.go to run the project, but without Redis database and a secret key it won't work for very long. You have to export CHRLY_SECRET environment variable globally or pass it via env:

env CHRLY_SECRET=some_local_secret go run main.go serve

Redis can be installed manually, but if you have Docker installed, you can run predefined docker-compose service. Simply execute the next commands:

cp docker-compose.dev.yml docker-compose.yml
docker-compose up -d

If your Redis instance isn't located at the localhost, you can change host by editing environment variable STORAGE_REDIS_HOST.

After all of that go run main.go serve should successfully start the application. To run tests execute go test ./....