| 1 | package main |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "context" |
| 6 | "errors" |
| 7 | "net/http" |
| 8 | "sort" |
| 9 | "strings" |
| 10 | "sync" |
| 11 | "time" |
| 12 | "unicode/utf8" |
| 13 | |
| 14 | "github.com/fogleman/gg" |
| 15 | "golang.org/x/image/font" |
| 16 | "golang.org/x/image/font/opentype" |
| 17 | ) |
| 18 | |
| 19 | // errRenderBusy signals that the render semaphore was saturated and the request |
| 20 | // gave up rather than piling on. Mapped to HTTP 503 by the OG handler. |
| 21 | var errRenderBusy = errors.New("render busy") |
| 22 | |
| 23 | const ( |
| 24 | ogWidth = 1200 |
| 25 | ogHeight = 630 |
| 26 | ogMargin = 80.0 |
| 27 | ) |
| 28 | |
| 29 | var ( |
| 30 | fontOnce sync.Once |
| 31 | fontRegular, fontBold *opentype.Font |
| 32 | fontErr error |
| 33 | ) |
| 34 | |
| 35 | // loadFonts parses the embedded CommitMono OTFs once. They use CFF outlines, |
| 36 | // which the freetype loader gg ships with can't read, so we parse them with |
| 37 | // x/image/font/opentype (sfnt) instead. |
| 38 | func loadFonts() { |
| 39 | fontOnce.Do(func() { |
| 40 | rb, err := appFS.ReadFile("static/fonts/CommitMono-400-Regular.otf") |
| 41 | if err != nil { |
| 42 | fontErr = err |
| 43 | return |
| 44 | } |
| 45 | bb, err := appFS.ReadFile("static/fonts/CommitMono-700-Regular.otf") |
| 46 | if err != nil { |
| 47 | fontErr = err |
| 48 | return |
| 49 | } |
| 50 | if fontRegular, err = opentype.Parse(rb); err != nil { |
| 51 | fontErr = err |
| 52 | return |
| 53 | } |
| 54 | if fontBold, err = opentype.Parse(bb); err != nil { |
| 55 | fontErr = err |
| 56 | return |
| 57 | } |
| 58 | }) |
| 59 | } |
| 60 | |
| 61 | // newFace builds a font.Face at the given size. Faces are created per call |
| 62 | // because opentype faces are not safe for concurrent use. |
| 63 | func newFace(bold bool, size float64) (font.Face, error) { |
| 64 | loadFonts() |
| 65 | if fontErr != nil { |
| 66 | return nil, fontErr |
| 67 | } |
| 68 | src := fontRegular |
| 69 | if bold { |
| 70 | src = fontBold |
| 71 | } |
| 72 | return opentype.NewFace(src, &opentype.FaceOptions{Size: size, DPI: 72, Hinting: font.HintingFull}) |
| 73 | } |
| 74 | |
| 75 | func (a *App) ogImageHandler(w http.ResponseWriter, r *http.Request) { |
| 76 | urls := feedURLsFromRequest(r) |
| 77 | key := ogCacheKey(urls) |
| 78 | |
| 79 | ctx, cancel := context.WithTimeout(r.Context(), 8*time.Second) |
| 80 | defer cancel() |
| 81 | |
| 82 | // getOrRender serves a cached PNG or, on a miss, runs the render once even |
| 83 | // under concurrent requests for the same key. |
| 84 | png, err := a.Images.getOrRender(key, func() ([]byte, error) { |
| 85 | title, desc := "Feeds", "Experience RSS feeds" |
| 86 | if len(urls) > 0 { |
| 87 | items, titles := previewURLs(ctx, urls, 0, a.Cache, a.Log) |
| 88 | title, desc = feedMeta(urls, titles, len(items)) |
| 89 | } |
| 90 | |
| 91 | // Bound concurrent renders to cap CPU and peak memory (each render |
| 92 | // allocates a ~3MB bitmap). Overloaded requests bail rather than pile up. |
| 93 | select { |
| 94 | case a.renderSem <- struct{}{}: |
| 95 | defer func() { <-a.renderSem }() |
| 96 | case <-ctx.Done(): |
| 97 | return nil, errRenderBusy |
| 98 | } |
| 99 | return renderOGImage(title, desc) |
| 100 | }) |
| 101 | switch { |
| 102 | case err == errRenderBusy: |
| 103 | http.Error(w, "render busy", http.StatusServiceUnavailable) |
| 104 | return |
| 105 | case err != nil: |
| 106 | a.Log.Error("og render failed", "err", err) |
| 107 | http.Error(w, "og render error", http.StatusInternalServerError) |
| 108 | return |
| 109 | } |
| 110 | writePNG(w, png) |
| 111 | } |
| 112 | |
| 113 | // ogCacheKey normalizes a URL set into a stable cache key (order-independent). |
| 114 | func ogCacheKey(urls []string) string { |
| 115 | sorted := append([]string(nil), urls...) |
| 116 | sort.Strings(sorted) |
| 117 | return strings.Join(sorted, "\n") |
| 118 | } |
| 119 | |
| 120 | func writePNG(w http.ResponseWriter, png []byte) { |
| 121 | w.Header().Set("Content-Type", "image/png") |
| 122 | w.Header().Set("Cache-Control", "public, max-age=300") |
| 123 | _, _ = w.Write(png) |
| 124 | } |
| 125 | |
| 126 | // renderOGImage draws a 1200x630 social card with the feed title and a subtitle. |
| 127 | func renderOGImage(title, desc string) ([]byte, error) { |
| 128 | dc := gg.NewContext(ogWidth, ogHeight) |
| 129 | dc.SetHexColor("#ffffff") |
| 130 | dc.Clear() |
| 131 | |
| 132 | // "FEEDS" wordmark. |
| 133 | wordmark, err := newFace(true, 34) |
| 134 | if err != nil { |
| 135 | return nil, err |
| 136 | } |
| 137 | dc.SetFontFace(wordmark) |
| 138 | dc.SetHexColor("#1a1a1a") |
| 139 | dc.DrawString("FEEDS", ogMargin, 120) |
| 140 | |
| 141 | // Title, wrapped, truncated so it can't run into the subtitle. |
| 142 | titleFace, err := newFace(true, 68) |
| 143 | if err != nil { |
| 144 | return nil, err |
| 145 | } |
| 146 | dc.SetFontFace(titleFace) |
| 147 | dc.SetHexColor("#1a1a1a") |
| 148 | dc.DrawStringWrapped(truncate(title, 90), ogMargin, 200, 0, 0, ogWidth-2*ogMargin, 1.35, gg.AlignLeft) |
| 149 | |
| 150 | // Subtitle pinned near the bottom. |
| 151 | subFace, err := newFace(false, 34) |
| 152 | if err != nil { |
| 153 | return nil, err |
| 154 | } |
| 155 | dc.SetFontFace(subFace) |
| 156 | dc.SetHexColor("#6b6b6b") |
| 157 | dc.DrawString(desc, ogMargin, ogHeight-ogMargin) |
| 158 | |
| 159 | var buf bytes.Buffer |
| 160 | if err := dc.EncodePNG(&buf); err != nil { |
| 161 | return nil, err |
| 162 | } |
| 163 | return buf.Bytes(), nil |
| 164 | } |
| 165 | |
| 166 | func truncate(s string, maxRunes int) string { |
| 167 | if utf8.RuneCountInString(s) <= maxRunes { |
| 168 | return s |
| 169 | } |
| 170 | runes := []rune(s) |
| 171 | return string(runes[:maxRunes]) + "…" |
| 172 | } |