imageproxy is a caching image proxy server written in golang. It supports dynamic image resizing and URL whitelisting.
This project was inspired by, and is designed to be an alternative to, WordPress's photon service. Photon is a great free service, but is limited to sites hosted on WordPress.com, or that use the Jetpack plugin. If you don't want to use Jetpack, then you're asked to use a different service. If you're looking for an alternative hosted service, I'd recommend resize.ly, embed.ly, or cloudinary. I decided to try building my own for fun.
imageproxy URLs are of the form http://localhost/{options}/{remote_url}.
Options are specified as a comma delimited list of parameters, which can be supplied in any order. Duplicate parameters overwrite previous values.
The format is a superset of resize.ly's options.
The size option takes the general form {width}x{height}, where width and
height are numbers. Integer values greater than 1 are interpreted as exact
pixel values. Floats between 0 and 1 are interpreted as percentages of the
original image size. If either value is omitted or set to 0, it will be
automatically set to preserve the aspect ratio based on the other dimension.
If a single number is provided (with no "x" separator), it will be used for
both height and width.
Depending on the options specified, an image may be cropped to fit the requested size. In all cases, the original aspect ratio of the image will be preserved; imageproxy will never stretch the original image.
When no explicit crop mode is specified, the following rules are followed:
-
If both width and height values are specified, the image will be scaled to fill the space, cropping if necessary to fit the exact dimension.
-
If only one of the width or height values is specified, the image will be resized to fit the specified dimension, scaling the other dimension as needed to maintain the aspect ratio.
If the fit option is specified together with a width and height value, the
image will be resized to fit within a containing box of the specified size. As
always, the original aspect ratio will be preserved. Specifying the fit
option with only one of either width or height does the same thing as if fit
had not been specified.
The r{degrees} option will rotate the image the specified number of degrees,
counter-clockwise. Valid degrees values are 90, 180, and 270. Images
are rotated after being resized.
The fv option will flip the image vertically. The fh option will flip the
image horizontally. Images are flipped after being resized and rotated.
The URL of the original image to load is specified as the remainder of the
path, without any encoding. For example,
http://localhost/200/https://willnorris.com/logo.jpg.
In order to optimize caching, it is recommended that URLs not contain query strings.
The following live examples demonstrate setting different options on this source image, which measures 1024 by 678 pixels.
| Options | Meaning | Image |
|---|---|---|
| 200x | 200px wide, proportional height |  |
| 0.15x | 15% original width, proportional height |  |
| x100 | 100px tall, proportional width |  |
| 100x150 | 100 by 150 pixels, cropping as needed |  |
| 100 | 100px square, cropping as needed |  |
| 150,fit | scale to fit 150px square, no cropping |  |
| 100,r90 | 100px square, rotated 90 degrees |  |
| 100,fv,fh | 100px square, flipped horizontal and vertical |  |
Install the package using:
go get willnorris.com/go/imageproxy
Once installed, change directories to $GOPATH/willnorris.com/go/imageproxy and run the proxy using:
go run cmd/imageproxy/main.go
This will start the proxy on port 8080, without any caching and with no host whitelist (meaning any remote URL can be proxied). Test this by navigating to http://localhost:8080/500/https://octodex.github.com/images/codercat.jpg and you should see a 500px square coder octocat.
By default, the imageproxy command uses an in-memory cache that will grow
unbounded. To cache images on disk instead, include the cacheDir flag:
go run cmd/imageproxy/main.go -cacheDir /tmp/imageproxy
Reload the codercat URL,
and then inspect the contents of /tmp/imageproxy. There should be two files
there, one for the original full-size codercat image, and one for the resized
500px version.
You can limit the remote hosts that the proxy will fetch images from using the
whitelist flag. This is useful, for example, for locking the proxy down to
your own hosts to prevent others from abusing it. Of course if you want to
support fetching from any host, leave off the whitelist flag. Try it out by
running:
go run cmd/imageproxy/main.go -whitelist example.com
Reload the codercat URL,
and you should now get an error message. You can specify multiple hosts as a
comma separated list, or prefix a host value with *. to allow all sub-domains
as well.
Run go run cmd/imageproxy/main.go -help for a complete list of flags the
command accepts. If you want to use a different caching implementation, it's
probably easiest to just make a copy of cmd/imageproxy/main.go and customize
it to fit your needs... it's a very simple command.
You can build and deploy imageproxy using any standard go toolchain, but here's how I do it.
I use goxc to build and deploy to an Ubuntu
server. I have a $GOPATH/willnorris.com/go/imageproxy/.goxc.local.json file
which limits builds to 64-bit linux:
{
"ConfigVersion": "0.9",
"BuildConstraints": "linux,amd64"
}I then run goxc which compiles the static binary and creates a deb package at
build/0.2.1/imageproxy_0.2.1_amd64.deb (or whatever the current version is).
I copy this file to my server and install it using sudo dpkg -i imageproxy_0.2.1_amd64.deb, which is installed to /usr/bin/imageproxy.
Ubuntu uses upstart to manage services, so I copy
etc/imageproxy.conf to /etc/init/imageproxy.conf on
my server and start it using sudo service imageproxy start. You will
certainly want to modify that upstart script to suit your desired
configuration.
This application is distributed under the Apache 2.0 license found in the LICENSE file.