| 1 | package slides |
| 2 | |
| 3 | import ( |
| 4 | "errors" |
| 5 | "strings" |
| 6 | "testing" |
| 7 | ) |
| 8 | |
| 9 | // TestSvgIsSanitised is the file-level half of the brief's test of the |
| 10 | // same name (the endpoint's half is in internal/slidestest): what |
| 11 | // survives an upload, what is quietly removed from it, and what makes |
| 12 | // the whole document a refusal. |
| 13 | func TestSvgIsSanitised(t *testing.T) { |
| 14 | t.Run("a plain drawing survives, byte for byte where it can", func(t *testing.T) { |
| 15 | in := `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 10 10">` + |
| 16 | `<!-- a comment --><title>A red square</title>` + |
| 17 | `<rect x="1" y="1" width="8" height="8" fill="#c00"/>` + |
| 18 | `<use href="#other"/></svg>` |
| 19 | out, err := sanitiseSVG([]byte(in)) |
| 20 | if err != nil { |
| 21 | t.Fatalf("sanitiseSVG: %v", err) |
| 22 | } |
| 23 | for _, want := range []string{`viewBox="0 0 10 10"`, `<title>A red square</title>`, |
| 24 | `fill="#c00"`, `<use href="#other"/>`, `<!-- a comment -->`} { |
| 25 | if !strings.Contains(string(out), want) { |
| 26 | t.Errorf("the drawing lost %s:\n%s", want, out) |
| 27 | } |
| 28 | } |
| 29 | }) |
| 30 | |
| 31 | t.Run("script, foreign HTML and event handlers are stripped", func(t *testing.T) { |
| 32 | in := `<svg xmlns="http://www.w3.org/2000/svg" onload="steal()">` + |
| 33 | `<script>fetch('/steal')</script>` + |
| 34 | `<foreignObject width="10" height="10"><body xmlns="http://www.w3.org/1999/xhtml">` + |
| 35 | `<script>more()</script>hi</body></foreignObject>` + |
| 36 | `<rect onclick="alert(1)" ONMOUSEOVER="alert(2)" fill="#000"/>` + |
| 37 | `<a href="javascript:alert(3)"><text>go</text></a>` + |
| 38 | `<a href="javascript:alert(4)"><text>sneaky</text></a>` + |
| 39 | `</svg>` |
| 40 | out, err := sanitiseSVG([]byte(in)) |
| 41 | if err != nil { |
| 42 | t.Fatalf("sanitiseSVG: %v", err) |
| 43 | } |
| 44 | s := strings.ToLower(string(out)) |
| 45 | for _, gone := range []string{"script", "foreignobject", "onload", "onclick", |
| 46 | "onmouseover", "javascript", "steal", "alert", "hi"} { |
| 47 | if strings.Contains(s, gone) { |
| 48 | t.Errorf("%q survived:\n%s", gone, out) |
| 49 | } |
| 50 | } |
| 51 | // What was around the removed parts is still a drawing. |
| 52 | if !strings.Contains(string(out), `fill="#000"`) { |
| 53 | t.Errorf("the rect lost its fill:\n%s", out) |
| 54 | } |
| 55 | if !strings.Contains(string(out), "<text>go</text>") { |
| 56 | t.Errorf("the link's text was dropped with its href:\n%s", out) |
| 57 | } |
| 58 | }) |
| 59 | |
| 60 | t.Run("an external reference is refused, not patched", func(t *testing.T) { |
| 61 | for name, in := range map[string]string{ |
| 62 | "an image from another site": `<svg xmlns="http://www.w3.org/2000/svg"><image href="https://example.test/x.png"/></svg>`, |
| 63 | "a protocol-relative use": `<svg xmlns="http://www.w3.org/2000/svg"><use xlink:href="//example.test/s.svg#a"/></svg>`, |
| 64 | "an @import in a style": `<svg xmlns="http://www.w3.org/2000/svg"><style>@import url("https://example.test/x.css");</style></svg>`, |
| 65 | "a url() in a style attr": `<svg xmlns="http://www.w3.org/2000/svg"><rect style="fill:url(https://example.test/x.png)"/></svg>`, |
| 66 | "an external svg stylesheet": `<svg xmlns="http://www.w3.org/2000/svg"><style>rect{fill:url("http://example.test/p.png")}</style></svg>`, |
| 67 | } { |
| 68 | if _, err := sanitiseSVG([]byte(in)); !errors.Is(err, errSVGExternal) { |
| 69 | t.Errorf("%s: want errSVGExternal, got %v", name, err) |
| 70 | } |
| 71 | } |
| 72 | }) |
| 73 | |
| 74 | t.Run("a document that is not a safe SVG at all is refused", func(t *testing.T) { |
| 75 | for name, in := range map[string]string{ |
| 76 | "a doctype": `<!DOCTYPE svg [<!ENTITY x "boom">]><svg xmlns="http://www.w3.org/2000/svg">&x;</svg>`, |
| 77 | "not XML": `<svg><rect fill=red></svg>`, |
| 78 | "another root": `<html><body>hi</body></html>`, |
| 79 | "nothing at all": ``, |
| 80 | "a proc inst": `<?xml-stylesheet href="x.css"?><svg xmlns="http://www.w3.org/2000/svg"/>`, |
| 81 | } { |
| 82 | if _, err := sanitiseSVG([]byte(in)); !errors.Is(err, errNotSVG) { |
| 83 | t.Errorf("%s: want errNotSVG, got %v", name, err) |
| 84 | } |
| 85 | } |
| 86 | }) |
| 87 | |
| 88 | t.Run("an inline raster stays, an inline SVG does not", func(t *testing.T) { |
| 89 | raster := `<svg xmlns="http://www.w3.org/2000/svg"><image href="data:image/png;base64,iVBOR"/></svg>` |
| 90 | out, err := sanitiseSVG([]byte(raster)) |
| 91 | if err != nil { |
| 92 | t.Fatalf("an inline PNG should be kept: %v", err) |
| 93 | } |
| 94 | if !strings.Contains(string(out), "data:image/png") { |
| 95 | t.Errorf("the inline PNG was dropped:\n%s", out) |
| 96 | } |
| 97 | // A nested SVG through a data: URL is a second document with a |
| 98 | // second set of everything this file strips, and there is no |
| 99 | // second pass — so it is refused rather than silently emptied. |
| 100 | nested := `<svg xmlns="http://www.w3.org/2000/svg"><image href="data:image/svg+xml;base64,PHN2Zz4="/></svg>` |
| 101 | if _, err := sanitiseSVG([]byte(nested)); !errors.Is(err, errSVGExternal) { |
| 102 | t.Errorf("a nested SVG: want errSVGExternal, got %v", err) |
| 103 | } |
| 104 | }) |
| 105 | } |
| 106 | |
amadan