fix(ethclient): impose upper limit for retry delays on HTTP Ethereum API

Author: renatomaia

pkg/ethutil/client.go

@@ -8,7 +8,9 @@ import (
 	"fmt"
 	"log/slog"
 	"math"
+	"net/http"
 	"net/url"
+	"strconv"
 	"strings"
 	"time"
 
@@ -17,6 +19,34 @@ import (
 	"github.com/hashicorp/go-retryablehttp"
 )
 
+// parseRetryAfterHeader parses the Retry-After header and returns the
+// delay duration according to the spec: https://httpwg.org/specs/rfc7231.html#header.retry-after
+// The bool returned will be true if the header was successfully parsed.
+// Otherwise, the header was either not present, or was not parseable according to the spec.
+func parseRetryAfterHeader(headers []string) (time.Duration, bool) {
+	if len(headers) == 0 || headers[0] == "" {
+		return 0, false
+	}
+	header := headers[0]
+	// 'Retry-After' is provided in seconds.
+	if sleep, err := strconv.ParseInt(header, 10, 64); err == nil {
+		if sleep < 0 { // a negative sleep doesn't make sense
+			return 0, false
+		}
+		return time.Second * time.Duration(sleep), true
+	}
+
+	// 'Retry-After' is provided as a date.
+	retryTime, err := time.Parse(time.RFC1123, header)
+	if err != nil {
+		return 0, false
+	}
+	if duration := retryTime.Sub(time.Now()); duration > 0 {
+		return duration, true
+	}
+	return 0, true  // past date
+}
+
 // RetryConfig holds configuration for the retryable HTTP client.
 type RetryConfig struct {
 	MaxRetries   uint64
@@ -39,6 +69,25 @@ func NewEthClient(
 	rclient.RetryMax = int(min(retryConfig.MaxRetries, uint64(math.MaxInt)))
 	rclient.RetryWaitMin = retryConfig.RetryMinWait
 	rclient.RetryWaitMax = retryConfig.RetryMaxWait
+	// Supply a custom Backoff that takes 'min(serverRetryAfter, RetryMaxWait)'.
+	// The provider keeps its ability to ask for politeness; it loses the ability
+	// to dictate the node's clock.
+	rclient.Backoff = func(minDuration, maxDuration time.Duration, attemptNum int, resp *http.Response) time.Duration {
+		if resp != nil {
+			if resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode == http.StatusServiceUnavailable {
+				if sleep, ok := parseRetryAfterHeader(resp.Header["Retry-After"]); ok {
+					return min(maxDuration, max(sleep, 0))
+				}
+			}
+		}
+
+		mult := math.Pow(2, float64(attemptNum)) * float64(minDuration)
+		sleep := time.Duration(mult)
+		if float64(sleep) != mult || sleep > maxDuration {
+			sleep = maxDuration
+		}
+		return sleep
+	}
 
 	opts := []rpc.ClientOption{
 		rpc.WithHTTPClient(rclient.StandardClient()),