slipee

Slipee

Slipee is a server, CLI tool and GO package for making static maps from a slippy map type tile server.

Motivation

Slipee fills the need for a server (microservice) to serve static map images to backend services in the EIND tech stack. It provides static map images from a OSM-type tile server. The size, zoom and center lat/long coordinates of the image is adjustable. Images a cached on disk, with no eviction currently implemented.

Request types

Clients requests images on a single endpoint in one of three ways.

NORMAL - HTTP GET - served from cache or queued for next request

If the image exists in cache, it is served with HTTP 200. If not, then the request is queued with an empty HTTP 202 (Accepted) response.

PRONTO - HTTP GET - synchronously/on the fly

If the image is not cache, the server will generate and serve the image on the fly. Pronto is disabled by default.

QUEUE - HTTP POST - queue for later

The image is put on queue and served later on NORMAL requests.

Example usage

Run the server using the command slipee serve. It will listen on port 8090.

Then visit the browser or curl an url like:

http://localhost:7654/?zoom=16&width=500&height=500&lat=59.926181&long=10.775909

Supported query args are:

• zoom
• width
• height
• lat
• long
• pronto

These are the same as the ones mentioned in configuration below.

Installation

Download your binary from the releases page and (otionally) put it in your path.

Linux

wget -c https://github.com/krilor/slipee/releases/download/v0.0.2/slipee_0.0.2_Linux_x86_64.tar.gz -O slipee.tar.gz
tar --exclude='*.md' --exclude=LICENSE -xzf slipee.tar.gz
sudo mv slipee /usr/local/bin/slipee
rm slipee.tar.gz

GO(lang)

go get -u github.com/krilor/slipee

Configuration

You can use command line flags or environment variables.

$ slipee help
USAGE:
  slipee <command> [flags]

COMMANDS:
  help           See this message
  serve          Serve slipee as a server

FLAGS:
  -address string
    the address to listen on
  -cache string
    directory for cached maps (default "./slipee_cache")
  -height int
    width in pixels (default 500)
  -label string
    the label to add to the image (default "Slipee | © OpenStreetMap contributors")
  -lat float
    latitude
  -long float
    longitude
  -port int
    port to listen on (default 7654)
  -pronto
    if clients are allowed to buypass queue and ask for static images promtly
  -queue int
    queue size (default 1000)
  -tileserver string
    the tile server url with ${[xyz]} type variables (default "https://a.tile.openstreetmap.org/${z}/${x}/${y}.png")
  -width int
    width in pixels (default 500)
  -zoom int
    zoom level (default 16)

ENVIRONMENT VARIABLES:
  Flags parameters can also be specified as environment variables.
  Use uppercase flag name and the prefix 'SLIPEE_'.
  Example: tileserver -> SLIPEE_TILESERVER
  Command line flags have precedence over environment variables.

TODOs

The following things needs to be done:

• Docker container
• Handle edge cases (like 0 zoom, where canvas is bigger than 256x256)
• Context
• Add more docs
• Add docs for Varnish cache recommendations

Alternatives

Check out the the list over at Open Street Map wiki. There are some pretty good alternatives.

The name

Slipee is taken from the phonetic respelling of the word slippy, referring to a slippy map map. It's prononced as slip-ee, aka. in IPA, its / ˈslɪp i /

Releasing with goreleaser

1. Check the current version tag using git tag -l
2. Create a new tag using git tag -a v0.0.1 -m "some message"
3. Push the tag using git push origin v0.0.1
4. Run goreleaser goreleaser