| 1 | package home |
| 2 | |
| 3 | import ( |
| 4 | "crypto/sha256" |
| 5 | "encoding/hex" |
| 6 | "net/http" |
| 7 | "regexp" |
| 8 | "strings" |
| 9 | "sync" |
| 10 | ) |
| 11 | |
| 12 | // Asset versioning. Home's stylesheets and pictures are served at stable |
| 13 | // paths (a closed list, mountBrand and friends), and every page links |
| 14 | // them as path?v=<content version>. serveAsset caches a request carrying |
| 15 | // the current version for a year, immutably, and revalidates anything |
| 16 | // else, so a returning visitor fetches only the page, and a deploy still |
| 17 | // takes effect at once: new bytes, new version, new URL. |
| 18 | // |
| 19 | // Scripts are linked the same way where a template can (busy.js); the |
| 20 | // passkey and handoff scripts keep bare paths their own modules import, |
| 21 | // revalidated by ETag. noscript_test.go's closed list names them all. |
| 22 | |
| 23 | // contentVersion is the first 16 hex digits of the body's SHA-256. |
| 24 | func contentVersion(body []byte) string { |
| 25 | sum := sha256.Sum256(body) |
| 26 | return hex.EncodeToString(sum[:8]) |
| 27 | } |
| 28 | |
| 29 | var ( |
| 30 | assetVersionsMu sync.RWMutex |
| 31 | assetVersions = map[string]string{} |
| 32 | ) |
| 33 | |
| 34 | // versionAsset records path's current version. Called where each asset is |
| 35 | // mounted; every router mounts the same bytes, so the value never changes. |
| 36 | func versionAsset(path string, body []byte) { |
| 37 | assetVersionsMu.Lock() |
| 38 | assetVersions[path] = contentVersion(body) |
| 39 | assetVersionsMu.Unlock() |
| 40 | } |
| 41 | |
| 42 | // versioned is path with its version, or path unchanged if it is not a |
| 43 | // versioned asset (a script, an estilo URL already versioned in its path). |
| 44 | func versioned(path string) string { |
| 45 | assetVersionsMu.RLock() |
| 46 | v, ok := assetVersions[path] |
| 47 | assetVersionsMu.RUnlock() |
| 48 | if !ok { |
| 49 | return path |
| 50 | } |
| 51 | return path + "?v=" + v |
| 52 | } |
| 53 | |
| 54 | var staticRef = regexp.MustCompile(`((?:href|src)=")(/static/[^"?#]+)"`) |
| 55 | |
| 56 | // versionStaticRefs rewrites every href/src naming a versioned asset in a |
| 57 | // static page (the front page, which is bytes, not a template). |
| 58 | func versionStaticRefs(page []byte) []byte { |
| 59 | return staticRef.ReplaceAllFunc(page, func(m []byte) []byte { |
| 60 | parts := staticRef.FindSubmatch(m) |
| 61 | return []byte(string(parts[1]) + versioned(string(parts[2])) + `"`) |
| 62 | }) |
| 63 | } |
| 64 | |
| 65 | // etagMatches is If-None-Match's weak comparison (RFC 9110 §13.1.2): |
| 66 | // any listed tag, W/ or not, naming the same opaque value matches, and so |
| 67 | // does "*". Weak matters here: whatever gzips oficina.works on the way out |
| 68 | // turns this binary's strong tag into W/"...", and an exact compare would |
| 69 | // then never answer 304. |
| 70 | func etagMatches(header, etag string) bool { |
| 71 | want := strings.TrimPrefix(etag, "W/") |
| 72 | for _, tag := range strings.Split(header, ",") { |
| 73 | tag = strings.TrimSpace(tag) |
| 74 | if tag == "*" || strings.TrimPrefix(tag, "W/") == want { |
| 75 | return true |
| 76 | } |
| 77 | } |
| 78 | return false |
| 79 | } |
| 80 | |
| 81 | // mountCSS mounts a versioned stylesheet. |
| 82 | func mountCSS(r interface { |
| 83 | Get(string, http.HandlerFunc) |
| 84 | }, path string, body []byte) { |
| 85 | versionAsset(path, body) |
| 86 | r.Get(path, serveAsset(body, "text/css; charset=utf-8")) |
| 87 | } |
| 88 | |
amadan