impressionist

A flexible image server written in go, using chained image filters.

Two backend are available : a pure Go backend, and a ImageMagick/GraphicsMagick backend.

Status: alpha

Building the server (pure Go):

go build -o impressionist server/pure/server.go

Building the server (ImageMagick):

go build -o impressionist server/magick/server.go

On ubuntu, you will need to install libmagickcore-dev and libgif-dev

Building the server (GraphicsMagick):

go build -tags gm -o impressionist server/magick/server.go

Running the server :

impressionist -cfg impressionist.json [-debug]

Configuration

Example configuration file :

{
	"http": {
		"port": 80,
		"root": "/impressionist",
		"timeout": "30s",
		"workers": 10
	},
	"filters": [
		{
			"name": "small",
			"definition": "s,100x0"
		}
	],
	"image": {
		"quality": 90
	},
	"storages": [
		{
			"name": "local",
			"type": "local",
			"path": "/tmp"
		}
	],
	"caches": {
		"source": 100
	}
}

Storage

One type of storage is currently supported : local.

URL structure

/impressionist/:filter/:format/:storage/:path

• :filter is a comma separated list of filters, as explained below,
• :format see below,
• :storage is the name of the storage, as defined in the configuration,
• :path is the path of the image, relative to the storage root.

Filters

• crop : c,[x]x[y]-[w]x[h]
• resize : s,[w]x[h][+|-]
• flip : f,[h|v] h = horizontal, v = vertical
• rotate: r,[90|180|270]
• grayscale: gs
• blur: b,s s = float (e.g: 1.0)

Note on resize :

• s,500x100 resizes exactly to 500x100
• s,500x0 and s,0x100 resize to a width of 500px (height of 100px), keeping the ratio
• s,500x100+ resizes to the maximum size within the specified dimensions, keeping the ratio
• s,500x100- resizes to the minimum dimension above the specified dimensions, keeping the ratio, and crops to 500x100

Predefined filters can be configured.

With the following configuration :

{
	"filters": [
		{
			"name": "small",
			"definition": "s,100x0"
		}
	]
}

/impressionist/small/:format/:storage/:path is translated to /impressionist/s,100x0/:format/:storage/:path.

Filters supported by each backend :

filter	pure Go	magick
crop	yes	yes
resize	yes	yes
flip	yes	yes
rotate	yes	no
grayscale	yes	yes
blur	yes	no

Formats

• PNG: png,
• JPEG: jpeg[,quality] - if not specified, quality is set to the default value (image.quality config variable, or 75 if not configured).

Caching

A in-memory cache is available. It stores source files to avoid accessing filesystem for each access.

By default, it caches 100 entries, and cache size can be changed by setting caches.source. A -1 value disables the cache.

Workers

Image manipulation is delegated to a pool of workers. If a request is not finished within the configured timeout (http.timeout, by default, 30s), the request returns a 503 error.

TODO

This is a first draft, everything is still pretty rough

• Tests, tests & tests
• Clean stuff
• Tuning
• Add more storage types (eg: AWS, http)
• Support environment variables for configuration tokens
• Add more filters
• Cache resized images
• Secure URL using hashes
• Token support
• Optimize images using pngcrush/JPEGOptim/...
• Format negociation & webp
• Graceful restart & configuration reloading
• Metrics

LICENSE

MIT, see LICENSE