imageproxy

imageproxy is a caching image proxy server written in go. It features:

• basic image adjustments like resizing, cropping, and rotation
• access control using allowed hosts list or request signing (HMAC-SHA256)
• support for jpeg, png, webp (decode only), tiff, and gif image formats (including animated gifs)
• caching in-memory, on disk, or with Amazon S3, Google Cloud Storage, Azure Storage, or Redis
• easy deployment, since it's pure go

Personally, I use it primarily to dynamically resize images hosted on my own site (read more in this post). But you can also enable request signing and use it as an SSL proxy for remote images, similar to atmos/camo but with additional image adjustment options.

I aim to keep imageproxy compatible with the two most recent major go releases. I also keep track of the minimum go version that still works (currently go1.18), but that might change at any time. You can see the go versions that are tested against in .github/workflows/tests.yml.

URL Structure

imageproxy URLs are of the form http://localhost/{options}/{remote_url}.

Options

Options are available for cropping, resizing, rotation, flipping, and digital signatures among a few others. Options for are specified as a comma delimited list of parameters, which can be supplied in any order. Duplicate parameters overwrite previous values.

See the full list of available options at https://pkg.go.dev/willnorris.com/go/imageproxy#ParseOptions.

Remote URL

The URL of the original image to load is specified as the remainder of the path. It may be included in plain text without any encoding, percent-encoded (aka URL encoded), or base64 encoded (URL safe, no padding).

When no encoding is used, any URL query string is treated as part of the remote URL. For example, given the proxy URL of http://localhost/x/http://example.com/?id=1, the remote URL is http://example.com/?id=1.

When percent-encoding is used, the full URL must be encoded. Any query string on the proxy URL is NOT included as part of the remote URL. Percent-encoded URLs must be absolute URLs; they cannot be relative URLs used with a default base URL. For example, http://localhost/x/http%3A%2F%2Fexample.com%2F%3Fid%3D1.

When base64 encoding is used, the full URL must be encoded. Any query string on the proxy URL is NOT included as part of the remote URL. Base64 encoded URLs may be relative URLs used with a default base URL. For example, http://localhost/x/aHR0cDovL2V4YW1wbGUuY29tLz9pZD0x.

Examples

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 | <a href="https://willnorris.com/api/imageproxy/200x/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/200x/https://willnorris.com/images/imageproxy/small-things.jpg" alt="200x"></a> | | x0.15 | 15% original height, proportional width | <a href="https://willnorris.com/api/imageproxy/x0.15/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/x0.15/https://willnorris.com/images/imageproxy/small-things.jpg" alt="x0.15"></a> | | 100x150 | 100 by 150 pixels, cropping as needed | <a href="https://willnorris.com/api/imageproxy/100x150/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/100x150/https://willnorris.com/images/imageproxy/small-things.jpg" alt="100x150"></a> | | 100 | 100px square, cropping as needed | <a href="https://willnorris.com/api/imageproxy/100/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/100/https://willnorris.com/images/imageproxy/small-things.jpg" alt="100"></a> | | 150,fit | scale to fit 150px square, no cropping | <a href="https://willnorris.com/api/imageproxy/150,fit/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/150,fit/https://willnorris.com/images/imageproxy/small-things.jpg" alt="150,fit"></a> | | 100,r90 | 100px square, rotated 90 degrees | <a href="https://willnorris.com/api/imageproxy/100,r90/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/100,r90/https://willnorris.com/images/imageproxy/small-things.jpg" alt="100,r90"></a> | | 100,fv,fh | 100px square, flipped horizontal and vertical | <a href="https://willnorris.com/api/imageproxy/100,fv,fh/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/100,fv,fh/https://willnorris.com/images/imageproxy/small-things.jpg" alt="100,fv,fh"></a> | | 200x,q60 | 200px wide, proportional height, 60% quality | <a href="https://willnorris.com/api/imageproxy/200x,q60/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/200x,q60/https://willnorris.com/images/imageproxy/small-things.jpg" alt="200x,q60"></a> | | 200x,png | 200px wide, converted to PNG format | <a href="https://willnorris.com/api/imageproxy/200x,png/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/200x,png/https://willnorris.com/images/imageproxy/small-things.jpg" alt="200x,png"></a> | | cx175,cw400,ch300,100x | crop to 400x300px starting at (175,0), scale to 100px wide | <a href="https://willnorris.com/api/imageproxy/cx175,cw400,ch300,100x/https://willnorris.com/images/imageproxy/small-things.jpg"><img src="https://willnorris.com/api/imageproxy/cx175,cw400,ch300,100x/https://willnorris.com/images/imageproxy/small-things.jpg" alt="cx175,cw400,ch300,100x"></a> |

The smart crop feature can best be seen by comparing crops of this source image, with and without smart crop enabled.

| Options | Meaning | Image | | ---------- | ------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | 150x300 | 150x300px, standard crop | <a href="https://willnorris.com/api/imageproxy/150x300/https://judahnorris.com/images/judah-sheets.jpg"><img src="https://willnorris.com/api/imageproxy/150x300/https://judahnorris.com/images/judah-sheets.jpg" alt="200x400,sc"></a> | | 150x300,sc | 150x300px, smart crop | <a href="https://willnorris.com/api/imageproxy/150x300,sc/https://judahnorris.com/images/judah-sheets.jpg"><img src="https://willnorris.com/api/imageproxy/150x300,sc/https://judahnorris.com/images/judah-sheets.jpg" alt="200x400"></a> |

Transformation also works on animated gifs. Here is this source image resized to 200px square and rotated 270 degrees:

<a href="https://willnorris.com/api/imageproxy/200,r270/https://willnorris.com/images/imageproxy/material-animations.gif"><img src="https://willnorris.com/api/imageproxy/200,r270/https