feat(oo): kontoblatt bulk tools, oo dav, update, retry (#22)

retry.go

@@ -0,0 +1,60 @@
+package onlyoffice
+
+import (
+	"context"
+	"regexp"
+	"time"
+)
+
+// RetryPolicy controls deterministic retries against OnlyOffice: fixed linear
+// backoff without jitter, so repeated runs wait exactly the same schedule.
+// OnlyOffice throttles bulk reads/writes with 429 (and occasional 502/503/504
+// from openresty), so every bulk tool routes API calls through DoRetry.
+type RetryPolicy struct {
+	Attempts int           // total attempts, including the first try
+	Base     time.Duration // wait before retry N is N*Base
+	Max      time.Duration // per-wait cap
+}
+
+// DefaultRetryPolicy retries up to 5 times with 1s, 2s, 3s, 4s waits.
+func DefaultRetryPolicy() RetryPolicy {
+	return RetryPolicy{Attempts: 5, Base: time.Second, Max: 30 * time.Second}
+}
+
+var transientRe = regexp.MustCompile(`:\s*(429|502|503|504)\b`)
+
+// Transient reports whether err looks like a transient OnlyOffice answer
+// (an HTTP 429/502/503/504 surfaced as "...: <code> ...").
+func Transient(err error) bool {
+	if err == nil {
+		return false
+	}
+	return transientRe.MatchString(err.Error())
+}
+
+// DoRetry runs fn until it succeeds, fails non-transiently, or attempts run
+// out. Waits are deterministic: N*Base capped at Max, no jitter.
+func DoRetry(ctx context.Context, p RetryPolicy, fn func() error) error {
+	if p.Attempts < 1 {
+		p.Attempts = 1
+	}
+	var err error
+	for attempt := 1; attempt <= p.Attempts; attempt++ {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+		if err = fn(); err == nil || !Transient(err) || attempt == p.Attempts {
+			return err
+		}
+		wait := time.Duration(attempt) * p.Base
+		if wait > p.Max {
+			wait = p.Max
+		}
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-time.After(wait):
+		}
+	}
+	return err
+}