Feature 19: Notifications - Web Push and Google Chat (#169)

Co-authored-by: orchestrator-agent <20+orchestrator-agent@code.cubecraftcreations.com>

internal/chat/webhook.go

@@ -0,0 +1,115 @@
+package chat
+
+import (
+	"errors"
+	"fmt"
+	"net/url"
+	"regexp"
+	"strings"
+)
+
+const (
+	// webhookPrefix is how every accepted webhook URL starts, compared
+	// exactly: no other scheme, host spelling, port or user info.
+	webhookPrefix = "https://chat.googleapis.com/v1/spaces/"
+	// webhookHost is the only host a webhook URL may name.
+	webhookHost = "chat.googleapis.com"
+	// MaxWebhookURLLength bounds an accepted webhook URL.
+	MaxWebhookURLLength = 2048
+	// MinCredentialLength is the shortest key or token accepted, so the
+	// masked URL's token tail never gives away most of it.
+	MinCredentialLength = 16
+	// maskedTail is how many trailing characters of the token the masked
+	// URL shows.
+	maskedTail = 4
+)
+
+// webhookPath is the path of a space's incoming webhook; the group is the
+// space id.
+var webhookPath = regexp.MustCompile(`^/v1/spaces/([A-Za-z0-9_-]{1,128})/messages$`)
+
+// credentialChars is the alphabet of a decoded key or token: URL-safe
+// ASCII, so its length in bytes is its length in characters.
+var credentialChars = regexp.MustCompile(`^[A-Za-z0-9_.~=-]*$`)
+
+// Webhook is a validated Google Chat incoming webhook URL. Its String is
+// the full URL, a secret: it is only ever sealed for storage or sent to
+// Google Chat, never logged, shown or put in an error.
+type Webhook struct {
+	raw   string
+	space string
+	token string
+}
+
+// ParseWebhook validates raw as
+// https://chat.googleapis.com/v1/spaces/{space}/messages?key=…&token=…,
+// whose raw query is exactly key=…&token=…, in that order, each decoding to
+// at least MinCredentialLength characters of credentialChars. Its error
+// never quotes raw.
+func ParseWebhook(raw string) (Webhook, error) {
+	switch {
+	case raw == "":
+		return Webhook{}, errors.New("is required")
+	case len(raw) > MaxWebhookURLLength:
+		return Webhook{}, fmt.Errorf("must be at most %d characters", MaxWebhookURLLength)
+	case strings.ContainsFunc(raw, func(r rune) bool { return r <= ' ' || r == 0x7f }):
+		return Webhook{}, errors.New("must not contain spaces or control characters")
+	case !strings.HasPrefix(raw, webhookPrefix):
+		return Webhook{}, errors.New("must be a Google Chat incoming webhook URL starting with " + webhookPrefix)
+	case strings.Contains(raw, "#"):
+		return Webhook{}, errors.New("must not have a fragment")
+	}
+	u, err := url.Parse(raw)
+	if err != nil {
+		return Webhook{}, errors.New("is not a valid URL")
+	}
+	if u.Scheme != "https" || u.Host != webhookHost || u.User != nil || u.Opaque != "" || u.RawPath != "" {
+		return Webhook{}, errors.New("must be a Google Chat incoming webhook URL starting with " + webhookPrefix)
+	}
+	m := webhookPath.FindStringSubmatch(u.Path)
+	if m == nil {
+		return Webhook{}, errors.New("path must be /v1/spaces/{space}/messages")
+	}
+	// The raw query is exactly key=…&token=…: no empty segment, no second
+	// "?", no other or repeated parameter.
+	if strings.Contains(u.RawQuery, "?") {
+		return Webhook{}, errors.New("query must not contain ?")
+	}
+	segments := strings.Split(u.RawQuery, "&")
+	if len(segments) != 2 {
+		return Webhook{}, errors.New("query must be exactly key=…&token=…")
+	}
+	creds := make([]string, 2)
+	for i, name := range []string{"key", "token"} {
+		escaped, ok := strings.CutPrefix(segments[i], name+"=")
+		if !ok {
+			return Webhook{}, errors.New("query must be exactly key=…&token=…")
+		}
+		v, err := url.QueryUnescape(escaped)
+		if err != nil {
+			return Webhook{}, errors.New("query is not valid")
+		}
+		if !credentialChars.MatchString(v) {
+			return Webhook{}, fmt.Errorf("%s must be letters, digits, -, _, ., ~ or =", name)
+		}
+		if len(v) < MinCredentialLength {
+			return Webhook{}, fmt.Errorf("%s must be at least %d characters", name, MinCredentialLength)
+		}
+		creds[i] = v
+	}
+	return Webhook{raw: raw, space: m[1], token: creds[1]}, nil
+}
+
+// String returns the full webhook URL, a secret.
+func (w Webhook) String() string {
+	return w.raw
+}
+
+// Masked returns the URL with its key hidden and only the last few
+// characters of its token, such as
+// "https://chat.googleapis.com/v1/spaces/AAQA1234/messages?key=…&token=…x3Dk".
+func (w Webhook) Masked() string {
+	// The token is ASCII of at least MinCredentialLength bytes, so the
+	// tail is maskedTail of its many characters.
+	return webhookPrefix + w.space + "/messages?key=…&token=…" + w.token[len(w.token)-maskedTail:]
+}