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Add ability to set custom stylesheets for SVG renderer (#105)

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* Add ability to set custom stylesheets for SVG renderer

This allow to set custom inline CSS and a optional CSP nonce. This
solves the problem mentioned in #103 and is best used with it, as seen
in the added examples. Without this one would have to write a custom
renderer.

* Add note with link to the custom_stylesheets example
This commit is contained in:
Justin Kromlinger 2018-10-12 18:43:30 +02:00 committed by Will Charczuk
parent 96acfc6a9f
commit 3cb33d48d3
5 changed files with 168 additions and 0 deletions
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2
_examples/css_classes/main.go
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@ -7,6 +7,8 @@ import (
"net/http"
)
// Note: Additional examples on how to add Stylesheets are in the custom_stylesheets example
func inlineSVGWithClasses(res http.ResponseWriter, req *http.Request) {
res.Write([]byte(
"<!DOCTYPE html><html><head>" +

21
_examples/custom_stylesheets/inlineOutput.svg Normal file
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@ -0,0 +1,21 @@
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="512" height="512">\n<style type="text/css"><![CDATA[svg .background { fill: white; }svg .canvas { fill: white; }svg path.blue { fill: blue; stroke: lightblue; }svg path.green { fill: green; stroke: lightgreen; }svg path.gray { fill: gray; stroke: lightgray; }svg text.blue { fill: white; }svg text.green { fill: white; }svg text.gray { fill: white; }]]></style><path d="M 0 0
L 512 0
L 512 512
L 0 512
L 0 0" class="background"/><path d="M 5 5
L 507 5
L 507 507
L 5 507
L 5 5" class="canvas"/><path d="M 256 256
L 507 256
A 251 251 128.56 0 1 100 452
L 256 256
Z" class="blue"/><path d="M 256 256
L 100 452
A 251 251 128.56 0 1 201 12
L 256 256
Z" class="green"/><path d="M 256 256
L 201 12
A 251 251 102.85 0 1 506 256
L 256 256
Z" class="gray"/><text x="313" y="413" class="blue">Blue</text><text x="73" y="226" class="green">Green</text><text x="344" y="133" class="gray">Gray</text></svg>
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87
_examples/custom_stylesheets/main.go Normal file
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@ -0,0 +1,87 @@
package main
import (
"fmt"
"github.com/hashworks/go-chart"
"log"
"net/http"
)
const style = "svg .background { fill: white; }" +
"svg .canvas { fill: white; }" +
"svg path.blue { fill: blue; stroke: lightblue; }" +
"svg path.green { fill: green; stroke: lightgreen; }" +
"svg path.gray { fill: gray; stroke: lightgray; }" +
"svg text.blue { fill: white; }" +
"svg text.green { fill: white; }" +
"svg text.gray { fill: white; }"
func svgWithCustomInlineCSS(res http.ResponseWriter, _ *http.Request) {
res.Header().Set("Content-Type", chart.ContentTypeSVG)
// Render the CSS with custom css
err := pieChart().Render(chart.SVGWithCSS(style, ""), res)
if err != nil {
fmt.Printf("Error rendering pie chart: %v\n", err)
}
}
func svgWithCustomInlineCSSNonce(res http.ResponseWriter, _ *http.Request) {
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy/style-src
// This should be randomly generated on every request!
const nonce = "RAND0MBASE64"
res.Header().Set("Content-Security-Policy", fmt.Sprintf("style-src 'nonce-%s'", nonce))
res.Header().Set("Content-Type", chart.ContentTypeSVG)
// Render the CSS with custom css and a nonce.
// Try changing the nonce to a different string - your browser should block the CSS.
err := pieChart().Render(chart.SVGWithCSS(style, nonce), res)
if err != nil {
fmt.Printf("Error rendering pie chart: %v\n", err)
}
}
func svgWithCustomExternalCSS(res http.ResponseWriter, _ *http.Request) {
// Add external CSS
res.Write([]byte(
`<?xml version="1.0" standalone="no"?>`+
`<?xml-stylesheet href="/main.css" type="text/css"?>`+
`<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">`))
res.Header().Set("Content-Type", chart.ContentTypeSVG)
err := pieChart().Render(chart.SVG, res)
if err != nil {
fmt.Printf("Error rendering pie chart: %v\n", err)
}
}
func pieChart() chart.PieChart {
return chart.PieChart{
// Note that setting ClassName will cause all other inline styles to be dropped!
Background: chart.Style{ClassName: "background"},
Canvas: chart.Style{
ClassName: "canvas",
},
Width: 512,
Height: 512,
Values: []chart.Value{
{Value: 5, Label: "Blue", Style: chart.Style{ClassName: "blue"}},
{Value: 5, Label: "Green", Style: chart.Style{ClassName: "green"}},
{Value: 4, Label: "Gray", Style: chart.Style{ClassName: "gray"}},
},
}
}
func css(res http.ResponseWriter, req *http.Request) {
res.Header().Set("Content-Type", "text/css")
res.Write([]byte(style))
}
func main() {
http.HandleFunc("/", svgWithCustomInlineCSS)
http.HandleFunc("/nonce", svgWithCustomInlineCSSNonce)
http.HandleFunc("/external", svgWithCustomExternalCSS)
http.HandleFunc("/main.css", css)
log.Fatal(http.ListenAndServe(":8080", nil))
}

30
vector_renderer.go
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@ -28,6 +28,25 @@ func SVG(width, height int) (Renderer, error) {
}, nil
}
// SVGWithCSS returns a new png/raster renderer with attached custom CSS
// The optional nonce argument sets a CSP nonce.
func SVGWithCSS(css string, nonce string) (func(width, height int)(Renderer, error)) {
return func(width, height int) (Renderer, error) {
buffer := bytes.NewBuffer([]byte{})
canvas := newCanvas(buffer)
canvas.css = css
canvas.nonce = nonce
canvas.Start(width, height)
return &vectorRenderer{
b: buffer,
c: canvas,
s: &Style{},
p: []string{},
dpi: DefaultDPI,
}, nil
}
}
// vectorRenderer renders chart commands to a bitmap.
type vectorRenderer struct {
dpi float64
@ -222,12 +241,23 @@ type canvas struct {
textTheta *float64
width int
height int
css string
nonce string
}
func (c *canvas) Start(width, height int) {
c.width = width
c.height = height
c.w.Write([]byte(fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="%d" height="%d">\n`, c.width, c.height)))
if c.css != "" {
c.w.Write([]byte(`<style type="text/css"`))
if c.nonce != "" {
// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy
c.w.Write([]byte(fmt.Sprintf(` nonce="%s"`, c.nonce)))
}
// To avoid compatibility issues between XML and CSS (f.e. with child selectors) we should encapsulate the CSS with CDATA.
c.w.Write([]byte(fmt.Sprintf(`><![CDATA[%s]]></style>`, c.css)))
}
}
func (c *canvas) Path(d string, style Style) {

28
vector_renderer_test.go
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@ -2,6 +2,7 @@ package chart
import (
"bytes"
"fmt"
"strings"
"testing"
@ -89,3 +90,30 @@ func TestCanvasClassSVG(t *testing.T) {
as.Equal("class=\"test-class\"", canvas.styleAsSVG(set))
}
func TestCanvasCustomInlineStylesheet(t *testing.T) {
b := strings.Builder{}
canvas := &canvas{
w: &b,
css: ".background { fill: red }",
}
canvas.Start(200, 200)
assert.New(t).Contains(b.String(), fmt.Sprintf(`<style type="text/css"><![CDATA[%s]]></style>`, canvas.css))
}
func TestCanvasCustomInlineStylesheetWithNonce(t *testing.T) {
b := strings.Builder{}
canvas := &canvas{
w: &b,
css: ".background { fill: red }",
nonce: "RAND0MSTRING",
}
canvas.Start(200, 200)
assert.New(t).Contains(b.String(), fmt.Sprintf(`<style type="text/css" nonce="%s"><![CDATA[%s]]></style>`, canvas.nonce, canvas.css))
}