MM-11175 Add logic to server to understand markdown images with dimensions (#9159)

4 files changed, 314 insertions, 8 deletions

diff --git a/utils/markdown/inlines.go b/utils/markdown/inlines.go
index e6943a57d..453f4bbe5 100644
--- a/utils/markdown/inlines.go
+++ b/utils/markdown/inlines.go
@@ -254,7 +254,7 @@ func (p *inlineParser) parseLinkOrImageDelimiter() {
 	}
 }
 
-func (p *inlineParser) peekAtInlineLinkDestinationAndTitle(position int) (destination, title Range, end int, ok bool) {
+func (p *inlineParser) peekAtInlineLinkDestinationAndTitle(position int, isImage bool) (destination, title Range, end int, ok bool) {
 	if position >= len(p.raw) || p.raw[position] != '(' {
 		return
 	}
@@ -273,6 +273,23 @@ func (p *inlineParser) peekAtInlineLinkDestinationAndTitle(position int) (destin
 	}
 	position = end
 
+	if isImage && position < len(p.raw) && isWhitespaceByte(p.raw[position]) {
+		dimensionsStart := nextNonWhitespace(p.raw, position)
+		if dimensionsStart >= len(p.raw) {
+			return
+		}
+
+		if p.raw[dimensionsStart] == '=' {
+			// Read optional image dimensions even if we don't use them
+			_, end, ok = parseImageDimensions(p.raw, dimensionsStart)
+			if !ok {
+				return
+			}
+
+			position = end
+		}
+	}
+
 	if position < len(p.raw) && isWhitespaceByte(p.raw[position]) {
 		titleStart := nextNonWhitespace(p.raw, position)
 		if titleStart >= len(p.raw) {
@@ -281,11 +298,13 @@ func (p *inlineParser) peekAtInlineLinkDestinationAndTitle(position int) (destin
 			return destination, Range{titleStart, titleStart}, titleStart + 1, true
 		}
 
-		title, end, ok = parseLinkTitle(p.raw, titleStart)
-		if !ok {
-			return
+		if p.raw[titleStart] == '"' || p.raw[titleStart] == '\'' || p.raw[titleStart] == '(' {
+			title, end, ok = parseLinkTitle(p.raw, titleStart)
+			if !ok {
+				return
+			}
+			position = end
 		}
-		position = end
 	}
 
 	closingPosition := nextNonWhitespace(p.raw, position)
@@ -317,9 +336,11 @@ func (p *inlineParser) lookForLinkOrImage() {
 			break
 		}
 
+		isImage := d.Type == imageOpeningDelimiter
+
 		var inline Inline
 
-		if destination, title, next, ok := p.peekAtInlineLinkDestinationAndTitle(p.position + 1); ok {
+		if destination, title, next, ok := p.peekAtInlineLinkDestinationAndTitle(p.position+1, isImage); ok {
 			destinationMarkdownPosition := relativeToAbsolutePosition(p.ranges, destination.Position)
 			linkOrImage := InlineLinkOrImage{
 				Children:       append([]Inline(nil), p.inlines[d.TextNode+1:]...),
diff --git a/utils/markdown/links.go b/utils/markdown/links.go
index 419797cb9..9f3128c4f 100644
--- a/utils/markdown/links.go
+++ b/utils/markdown/links.go
@@ -128,3 +128,57 @@ func parseLinkLabel(markdown string, position int) (raw Range, next int, ok bool
 
 	return
 }
+
+// As a non-standard feature, we allow image links to specify dimensions of the image by adding "=WIDTHxHEIGHT"
+// after the image destination but before the image title like ![alt](http://example.com/image.png =100x200 "title").
+// Both width and height are optional, but at least one of them must be specified.
+func parseImageDimensions(markdown string, position int) (raw Range, next int, ok bool) {
+	if position >= len(markdown) {
+		return
+	}
+
+	originalPosition := position
+
+	// Read =
+	position += 1
+	if position >= len(markdown) {
+		return
+	}
+
+	// Read width
+	hasWidth := false
+	for isNumericByte(markdown[position]) {
+		hasWidth = true
+		position += 1
+	}
+
+	// Look for early end of dimensions
+	if isWhitespaceByte(markdown[position]) || markdown[position] == ')' {
+		return Range{originalPosition, position - 1}, position, true
+	}
+
+	// Read the x
+	if markdown[position] != 'x' && markdown[position] != 'X' {
+		return
+	}
+	position += 1
+
+	// Read height
+	hasHeight := false
+	for isNumericByte(markdown[position]) {
+		hasHeight = true
+		position += 1
+	}
+
+	// Make sure the there's no trailing characters
+	if !isWhitespaceByte(markdown[position]) && markdown[position] != ')' {
+		return
+	}
+
+	if !hasWidth && !hasHeight {
+		// At least one of width or height is required
+		return
+	}
+
+	return Range{originalPosition, position - 1}, position, true
+}
diff --git a/utils/markdown/links_test.go b/utils/markdown/links_test.go
new file mode 100644
index 000000000..15012e26b
--- /dev/null
+++ b/utils/markdown/links_test.go
@@ -0,0 +1,223 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package markdown
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseImageDimensions(t *testing.T) {
+	for name, tc := range map[string]struct {
+		Input         string
+		Position      int
+		ExpectedRange Range
+		ExpectedNext  int
+		ExpectedOk    bool
+	}{
+		"no dimensions, no title": {
+			Input:         `![alt](https://example.com)`,
+			Position:      26,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"no dimensions, title": {
+			Input:         `![alt](https://example.com "title")`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"only width, no title": {
+			Input:         `![alt](https://example.com =100)`,
+			Position:      27,
+			ExpectedRange: Range{27, 30},
+			ExpectedNext:  31,
+			ExpectedOk:    true,
+		},
+		"only width, title": {
+			Input:         `![alt](https://example.com =100 "title")`,
+			Position:      27,
+			ExpectedRange: Range{27, 30},
+			ExpectedNext:  31,
+			ExpectedOk:    true,
+		},
+		"only height, no title": {
+			Input:         `![alt](https://example.com =x100)`,
+			Position:      27,
+			ExpectedRange: Range{27, 31},
+			ExpectedNext:  32,
+			ExpectedOk:    true,
+		},
+		"only height, title": {
+			Input:         `![alt](https://example.com =x100 "title")`,
+			Position:      27,
+			ExpectedRange: Range{27, 31},
+			ExpectedNext:  32,
+			ExpectedOk:    true,
+		},
+		"dimensions, no title": {
+			Input:         `![alt](https://example.com =100x200)`,
+			Position:      27,
+			ExpectedRange: Range{27, 34},
+			ExpectedNext:  35,
+			ExpectedOk:    true,
+		},
+		"dimensions, title": {
+			Input:         `![alt](https://example.com =100x200 "title")`,
+			Position:      27,
+			ExpectedRange: Range{27, 34},
+			ExpectedNext:  35,
+			ExpectedOk:    true,
+		},
+		"no dimensions, no title, trailing whitespace": {
+			Input:         `![alt](https://example.com )`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"only width, no title, trailing whitespace": {
+			Input:         `![alt](https://example.com  =100  )`,
+			Position:      28,
+			ExpectedRange: Range{28, 31},
+			ExpectedNext:  32,
+			ExpectedOk:    true,
+		},
+		"only height, no title, trailing whitespace": {
+			Input:         `![alt](https://example.com   =x100   )`,
+			Position:      29,
+			ExpectedRange: Range{29, 33},
+			ExpectedNext:  34,
+			ExpectedOk:    true,
+		},
+		"dimensions, no title, trailing whitespace": {
+			Input:         `![alt](https://example.com    =100x200   )`,
+			Position:      30,
+			ExpectedRange: Range{30, 37},
+			ExpectedNext:  38,
+			ExpectedOk:    true,
+		},
+		"no width or height": {
+			Input:         `![alt](https://example.com =x)`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"garbage 1": {
+			Input:         `![alt](https://example.com =aaa)`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"garbage 2": {
+			Input:         `![alt](https://example.com ====)`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"garbage 3": {
+			Input:         `![alt](https://example.com =100xx200)`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+		"garbage 4": {
+			Input:         `![alt](https://example.com =100x200x300x400)`,
+			Position:      27,
+			ExpectedRange: Range{0, 0},
+			ExpectedNext:  0,
+			ExpectedOk:    false,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			raw, next, ok := parseImageDimensions(tc.Input, tc.Position)
+			assert.Equal(t, tc.ExpectedOk, ok)
+			assert.Equal(t, tc.ExpectedNext, next)
+			assert.Equal(t, tc.ExpectedRange, raw)
+		})
+	}
+}
+
+func TestImageLinksWithDimensions(t *testing.T) {
+	for name, tc := range map[string]struct {
+		Markdown     string
+		ExpectedHTML string
+	}{
+		"regular link": {
+			Markdown:     `[link](https://example.com)`,
+			ExpectedHTML: `<p><a href="https://example.com">link</a></p>`,
+		},
+		"image link": {
+			Markdown:     `![image](https://example.com/image.png)`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" /></p>`,
+		},
+		"image link with title": {
+			Markdown:     `![image](https://example.com/image.png "title")`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with bracketed title": {
+			Markdown:     `![image](https://example.com/image.png (title))`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with width": {
+			Markdown:     `![image](https://example.com/image.png =500)`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" /></p>`,
+		},
+		"image link with width and title": {
+			Markdown:     `![image](https://example.com/image.png =500 "title")`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with width and bracketed title": {
+			Markdown:     `![image](https://example.com/image.png =500 (title))`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with height": {
+			Markdown:     `![image](https://example.com/image.png =x500)`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" /></p>`,
+		},
+		"image link with height and title": {
+			Markdown:     `![image](https://example.com/image.png =x500 "title")`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with height and bracketed title": {
+			Markdown:     `![image](https://example.com/image.png =x500 (title))`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with dimensions": {
+			Markdown:     `![image](https://example.com/image.png =500x400)`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" /></p>`,
+		},
+		"image link with dimensions and title": {
+			Markdown:     `![image](https://example.com/image.png =500x400 "title")`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"image link with dimensions and bracketed title": {
+			Markdown:     `![image](https://example.com/image.png =500x400 (title))`,
+			ExpectedHTML: `<p><img src="https://example.com/image.png" alt="image" title="title" /></p>`,
+		},
+		"no image link 1": {
+			Markdown:     `![image]()`,
+			ExpectedHTML: `<p><img src="" alt="image" /></p>`,
+		},
+		"no image link 2": {
+			Markdown:     `![image]( )`,
+			ExpectedHTML: `<p><img src="" alt="image" /></p>`,
+		},
+		"no image link with dimensions": {
+			Markdown:     `![image]( =500x400)`,
+			ExpectedHTML: `<p><img src="=500x400" alt="image" /></p>`,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			assert.Equal(t, tc.ExpectedHTML, RenderHTML(tc.Markdown))
+		})
+	}
+}
diff --git a/utils/markdown/markdown.go b/utils/markdown/markdown.go
index e0788d906..57b10f3fb 100644
--- a/utils/markdown/markdown.go
+++ b/utils/markdown/markdown.go
@@ -32,8 +32,16 @@ func isWhitespaceByte(c byte) bool {
 	return isWhitespace(rune(c))
 }
 
+func isNumeric(c rune) bool {
+	return c >= '0' && c <= '9'
+}
+
+func isNumericByte(c byte) bool {
+	return isNumeric(rune(c))
+}
+
 func isHex(c rune) bool {
-	return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')
+	return isNumeric(c) || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')
 }
 
 func isHexByte(c byte) bool {
@@ -41,7 +49,7 @@ func isHexByte(c byte) bool {
 }
 
 func isAlphanumeric(c rune) bool {
-	return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+	return isNumeric(c) || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
 }
 
 func isAlphanumericByte(c byte) bool {