Fonts

Fonts is a package that provides helpers to access font details, easily retrieve font bytes and proxy font requests.

This package has ZERO 3rd-party dependencies.

For now, Google Fonts is supported, but other fonts are planned.

Motivation

When working with images, PDFs or any other format that requires us to embed fonts, we can decide to download the fonts and embed them directly into our application.

However, if our application could use multiple different fonts which are decided at runtime, then there are a couple complications:

1. There is no easy way to know what fonts are available and what variants they have. Google Fonts provides an API, but you can only receive a dump of all FONT details.
2. It becomes tedious to download the font bytes during runtime, and manage caching.

This package helps to simplify this process

Reference

See https://pkg.go.dev/github.com/go-swiss/fonts

How to use

Proxy Google Font Requests

The Proxy() function returns a http.Handler that will proxy all requests to the Google Fonts server.
It takes a path, which is used when generating the urls of the font bytes For example, if you want to proxy requests on example.com/fonts:

http.Handle("/fonts", http.StripPrefix("/fonts", google.Proxy("/fonts")))

Get Font Details

To get the details of a Google Font, use the GetFontDetails function:

package main 

import (
    "fmt"
    "context"

    "github.com/go-swiss/fonts/google"
)

func main() {
    ctx := context.Background()
    details, err := google.GetFontDetails(ctx, "Roboto")
    if err != nil {
        panic(err)
    }

    fmt.Printf("Family: %s\nVariants: %v", details.Family, details.Variants)
}

Family: Roboto
Variants: [100 100italic 300 300italic regular italic 500 500italic 700 700italic 900 900italic]

Get Font Bytes

To get the bytes of a font, use the GetFontBytes method. This will download the font bytes from the appropriate URL.

family := "Open Sans"
variant := "900"

fontBytes, err := google.GetFontBytes(ctx, family, variant, nil)
if errors.Is(err, fonts.ErrMissingVariant) {
    fontBytes, err = google.GetFontBytes(ctx, family, "regular", nil)
}

if err != nil {
    panic(err)
}

font, err := opentype.Parse(fontBytes)
if err != nil {
    panic(err)
}

// Do something with the font

Caching Responses

In our application it is possible that we need to frequetnly get fonts. To reduce duplicate requests, a fonts.Cache implementation can be passed as the 4th parameter to the GetFontBytes function.

Here is an example using https://github.com/ReneKroon/ttlcache

package main 

import (
    "time"

    "github.com/ReneKroon/ttlcache/v2"
)

type cache struct {
	c *ttlcache.Cache
}

func (c cache) Get(key string) ([]byte, bool) {
	fontInterface, err := c.c.Get(key)
	if err != nil {
		return nil, false
	}

	fontBytes, ok := fontInterface.([]byte)
	return fontBytes, ok
}

func (c cache) Set(key string, val []byte) {
	c.c.Set(key, val)
}

func main() {
	c := ttlcache.NewCache()
	c.SetTTL(time.Duration(20 * time.Second))
	c.SetCacheSizeLimit(64)

    fontBytes, err := google.GetFontBytes(config.Context, family, variant, cache{c})
    if err != nil {
        panic(err)
    }

    font, err := opentype.Parse(fontBytes)
    if err != nil {
        panic(err)
    }

    // Do something with the font
}

Contributing

Feature requests and Pull Requests are welcome!

If working locally, the google/all directory can be refreshed by running go generate. See generate/main.go for details.