light: handle too high errors correctly (backport #6346) (#6351)

light/client.go

@@ -770,7 +770,17 @@ func (c *Client) verifySkipping(
  pivotHeight := verifiedBlock.Height + (blockCache[depth].Height-verifiedBlock.
  Height)*verifySkippingNumerator/verifySkippingDenominator
  interimBlock, providerErr := source.LightBlock(ctx, pivotHeight)
- if providerErr != nil {
+ switch providerErr {
+ case nil:
+ blockCache = append(blockCache, interimBlock)
+
+ // if the error is benign, the client does not need to replace the primary
+ case provider.ErrLightBlockNotFound, provider.ErrNoResponse, provider.ErrHeightTooHigh:
+ return nil, err
+
+ // all other errors such as ErrBadLightBlock or ErrUnreliableProvider are seen as malevolent and the
+ // provider is removed
+ default:
  return nil, ErrVerificationFailed{From: verifiedBlock.Height, To: pivotHeight, Reason: providerErr}
  }
  blockCache = append(blockCache, interimBlock)
@@ -1008,7 +1018,7 @@ func (c *Client) lightBlockFromPrimary(ctx context.Context, height int64) (*type
  // Everything went smoothly. We reset the lightBlockRequests and return the light block
  return l, nil
 
- case provider.ErrNoResponse, provider.ErrLightBlockNotFound:
+ case provider.ErrNoResponse, provider.ErrLightBlockNotFound, provider.ErrHeightTooHigh:
  // we find a new witness to replace the primary
  c.logger.Debug("error from light block request from primary, replacing...",
  "error", err, "height", height, "primary", c.primary)
@@ -1111,7 +1121,7 @@ func (c *Client) findNewPrimary(ctx context.Context, height int64, remove bool)
  return response.lb, nil
 
  // process benign errors by logging them only
- case provider.ErrNoResponse, provider.ErrLightBlockNotFound:
+ case provider.ErrNoResponse, provider.ErrLightBlockNotFound, provider.ErrHeightTooHigh:
  lastError = response.err
  c.logger.Debug("error on light block request from witness",
  "error", response.err, "primary", c.witnesses[response.witnessIndex])