1 files changed, 145 insertions, 0 deletions
diff --git a/modules/retry/retry.go b/modules/retry/retry.go
new file mode 100644
index 0000000..9c00275
--- /dev/null
+++ b/modules/retry/retry.go
@@ -0,0 +1,145 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package retry
+
+import (
+	"errors"
+	"io"
+	"net"
+	"net/http"
+	"slices"
+	"strconv"
+	"time"
+
+	"github.com/philippta/flyscrape"
+)
+
+func init() {
+	flyscrape.RegisterModule(Module{})
+}
+
+type Module struct {
+	ticker    *time.Ticker
+	semaphore chan struct{}
+
+	RetryDelays []time.Duration
+}
+
+func (Module) ModuleInfo() flyscrape.ModuleInfo {
+	return flyscrape.ModuleInfo{
+		ID:  "retry",
+		New: func() flyscrape.Module { return new(Module) },
+	}
+}
+
+func (m *Module) Provision(flyscrape.Context) {
+	if m.RetryDelays == nil {
+		m.RetryDelays = defaultRetryDelays
+	}
+}
+
+func (m *Module) AdaptTransport(t http.RoundTripper) http.RoundTripper {
+	return flyscrape.RoundTripFunc(func(r *http.Request) (*http.Response, error) {
+		resp, err := t.RoundTrip(r)
+		if !shouldRetry(resp, err) {
+			return resp, err
+		}
+
+		for _, delay := range m.RetryDelays {
+			drainBody(resp, err)
+
+			time.Sleep(retryAfter(resp, delay))
+
+			resp, err = t.RoundTrip(r)
+			if !shouldRetry(resp, err) {
+				break
+			}
+		}
+
+		return resp, err
+	})
+}
+
+func shouldRetry(resp *http.Response, err error) bool {
+	statusCodes := []int{
+		http.StatusRequestTimeout,
+		http.StatusTooEarly,
+		http.StatusTooManyRequests,
+		http.StatusInternalServerError,
+		http.StatusBadGateway,
+		http.StatusServiceUnavailable,
+		http.StatusGatewayTimeout,
+	}
+
+	if resp != nil {
+		if slices.Contains(statusCodes, resp.StatusCode) {
+			return true
+		}
+	}
+	if err == nil {
+		return false
+	}
+	if _, ok := err.(net.Error); ok {
+		return true
+	}
+	if errors.Is(err, io.ErrUnexpectedEOF) {
+		return true
+	}
+
+	return false
+}
+
+func drainBody(resp *http.Response, err error) {
+	if err == nil && resp != nil && resp.Body != nil {
+		io.Copy(io.Discard, resp.Body)
+		resp.Body.Close()
+	}
+}
+
+func retryAfter(resp *http.Response, fallback time.Duration) time.Duration {
+	if resp == nil {
+		return fallback
+	}
+
+	timeexp := resp.Header.Get("Retry-After")
+	if timeexp == "" {
+		return fallback
+	}
+
+	if seconds, err := strconv.Atoi(timeexp); err == nil {
+		return time.Duration(seconds) * time.Second
+	}
+
+	formats := []string{
+		time.RFC1123, // HTTP Spec
+		time.RFC1123Z,
+		time.ANSIC,
+		time.UnixDate,
+		time.RubyDate,
+		time.RFC822,
+		time.RFC822Z,
+		time.RFC850,
+		time.RFC3339,
+	}
+	for _, format := range formats {
+		if t, err := time.Parse(format, timeexp); err == nil {
+			return t.Sub(time.Now())
+		}
+	}
+
+	return fallback
+}
+
+var defaultRetryDelays = []time.Duration{
+	1 * time.Second,
+	2 * time.Second,
+	5 * time.Second,
+	10 * time.Second,
+}
+
+var (
+	_ flyscrape.TransportAdapter = (*Module)(nil)
+	_ flyscrape.Provisioner      = (*Module)(nil)
+)