add package "http/transport"

Author: demurky

http/transport/retrier.go

@@ -0,0 +1,78 @@
+package transport
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/http"
+	"time"
+)
+
+// TODO: On the first request attempt of the retrier,
+// read and save the main request's body at the same time
+// as it's sending it to upstream.
+// On subsequent attempts, use the saved body.
+
+// TODO: Use the bufpool package to store the body once it's ready.
+
+type Retrier struct {
+	MaxTries   int
+	RetryDelay time.Duration
+	Transport  http.RoundTripper // The upstream transport to send the requests to.
+}
+
+func (r Retrier) RoundTrip(req *http.Request) (*http.Response, error) {
+
+	if r.Transport == nil {
+		r.Transport = http.DefaultTransport
+	}
+
+	var bodyReader *bytes.Reader
+
+	if req.Body != nil && req.Body != http.NoBody {
+		b, err := io.ReadAll(req.Body)
+		if err != nil {
+			return nil, fmt.Errorf("could not read request body: %w", err)
+		}
+		bodyReader = bytes.NewReader(b)
+	}
+
+	var lastErr error
+
+	i := r.MaxTries
+	if i == 0 {
+		i = -1
+	}
+
+	for {
+		if i == 0 {
+			break
+		}
+		if i > 0 {
+			i--
+		}
+
+		// Clone the request
+		newReq := req.Clone(req.Context())
+
+		// Renew the request body
+		if bodyReader != nil {
+			bodyReader.Seek(0, io.SeekStart)
+			newReq.Body = io.NopCloser(bodyReader)
+		}
+
+		// Make the request and get a response
+		resp, err := r.Transport.RoundTrip(newReq)
+		if err == nil {
+			return resp, nil
+		}
+
+		lastErr = err
+		time.Sleep(r.RetryDelay)
+	}
+
+	return nil, fmt.Errorf(
+		"failed to make the request after %d tries: %w",
+		r.MaxTries, lastErr,
+	)
+}