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Configuration

Retry Strategy

Overview

The SDK ships with a built-in retry strategy (BoxRetryStrategy) that implements the RetryStrategy interface. The BoxNetworkClient, which serves as the default network client, uses this strategy to automatically retry failed API requests with exponential backoff.

The retry strategy exposes two methods:

  • shouldRetry — Determines whether a failed request should be retried based on the HTTP status code, response headers, attempt count, and authentication state.
  • retryAfter — Computes the delay (in seconds) before the next retry attempt, using either the server-provided Retry-After header or an exponential backoff formula.

Default Configuration

Parameter Default Description
maxAttempts 5 Maximum number of retry attempts for HTTP error responses (status 4xx/5xx).
retryBaseInterval 1 (second) Base interval used in the exponential backoff calculation.
retryRandomizationFactor 0.5 Jitter factor applied to the backoff delay. The actual delay is multiplied by a random value between 1 - factor and 1 + factor.
maxRetriesOnException 2 Maximum number of retries for network-level exceptions (connection failures, timeouts). These are tracked by a separate counter from HTTP error retries.

Retry Decision Flow

The following diagram shows how BoxRetryStrategy.shouldRetry decides whether to retry a request:

                    shouldRetry(fetchOptions, fetchResponse, attemptNumber)
                                        |
                                        v
                             +-----------------------+
                             | status == 0           |     Yes
                             | (network exception)?  |----------> attemptNumber <= maxRetriesOnException?
                             +-----------------------+               |            |
                                        | No                        Yes          No
                                        v                            |            |
                             +-----------------------+           [RETRY]      [NO RETRY]
                             | attemptNumber >=      |
                             | maxAttempts?          |
                             +-----------------------+
                                  |            |
                                 Yes          No
                                  |            |
                             [NO RETRY]        v
                             +-----------------------+
                             | status == 202 AND     |     Yes
                             | Retry-After header?   |----------> [RETRY]
                             +-----------------------+
                                        | No
                                        v
                             +-----------------------+
                             | status >= 500         |     Yes
                             | (server error)?       |----------> [RETRY]
                             +-----------------------+
                                        | No
                                        v
                             +-----------------------+
                             | status == 429         |     Yes
                             | (rate limited)?       |----------> [RETRY]
                             +-----------------------+
                                        | No
                                        v
                             +-----------------------+
                             | status == 401 AND     |     Yes
                             | auth available?       |----------> Refresh token, then [RETRY]
                             +-----------------------+
                                        | No
                                        v
                                   [NO RETRY]

Exponential Backoff Algorithm

When the response does not include a Retry-After header, the retry delay is computed using exponential backoff with randomized jitter:

delay = 2^attemptNumber * retryBaseInterval * random(1 - factor, 1 + factor)

Where:

  • attemptNumber is the current attempt (1-based)
  • retryBaseInterval defaults to 1 second
  • factor is retryRandomizationFactor (default 0.5)
  • random(min, max) returns a uniformly distributed value in [min, max]

Example Delays (with default settings)

Attempt Base Delay Min Delay (factor=0.5) Max Delay (factor=0.5)
1 2s 1.0s 3.0s
2 4s 2.0s 6.0s
3 8s 4.0s 12.0s
4 16s 8.0s 24.0s

Retry-After Header

When the server includes a Retry-After header in the response, the SDK uses the header value directly as the delay in seconds instead of computing an exponential backoff delay. This applies to any retryable response that includes the header, including:

  • 202 Accepted with Retry-After (long-running operations)
  • 429 Too Many Requests with Retry-After
  • 5xx server errors with Retry-After

The header value is parsed as a floating-point number representing seconds.

Network Exception Handling

Network-level failures (connection refused, DNS resolution errors, timeouts, TLS errors) are represented internally as responses with status 0. These exceptions are tracked by a separate counter (maxRetriesOnException, default 2) from the regular HTTP error retry counter (maxAttempts).

This means:

  • Network exception retries are tracked independently from HTTP error retries, each with their own counter and backoff progression.
  • A request can fail up to maxRetriesOnException times due to network exceptions, but each exception retry also increments the overall attempt counter, so the total number of retries across both exception and HTTP error types is bounded by maxAttempts.

Customizing Retry Parameters

You can customize all retry parameters by initializing BoxRetryStrategy with the desired values and passing it to NetworkSession:

const auth = new BoxDeveloperTokenAuth({ token: 'DEVELOPER_TOKEN_GOES_HERE' });
const networkSession = new NetworkSession({
  retryStrategy: new BoxRetryStrategy({
    maxAttempts: 3,
    retryBaseInterval: 2,
    retryRandomizationFactor: 0.3,
    maxRetriesOnException: 1,
  }),
});
const client = new BoxClient({ auth, networkSession });

Custom Retry Strategy

You can implement your own retry strategy by implementing the RetryStrategy interface and overriding the shouldRetry and retryAfter methods:

class CustomRetryStrategy implements RetryStrategy {
  async shouldRetry(
    fetchOptions: FetchOptions,
    fetchResponse: FetchResponse,
    attemptNumber: number,
  ): Promise<boolean> {
    return fetchResponse.status >= 500 && attemptNumber < 3;
  }

  retryAfter(
    fetchOptions: FetchOptions,
    fetchResponse: FetchResponse,
    attemptNumber: number,
  ): number {
    return 1.0;
  }
}

const auth = new BoxDeveloperTokenAuth({ token: 'DEVELOPER_TOKEN_GOES_HERE' });
const networkSession = new NetworkSession({
  retryStrategy: new CustomRetryStrategy(),
});
const client = new BoxClient({ auth, networkSession });

Timeouts

You can configure request timeout using timeoutConfig on NetworkSession. timeoutMs is in milliseconds and applies to each HTTP request attempt.

const auth = new BoxDeveloperTokenAuth({ token: 'DEVELOPER_TOKEN_GOES_HERE' });
const networkSession = new NetworkSession({
  timeoutConfig: { timeoutMs: 30000 },
});
const client = new BoxClient({ auth, networkSession });

How timeout handling works:

  • The SDK does not apply any timeout by default. Without explicit configuration, requests will wait indefinitely for a response.
  • The SDK applies timeout only when timeoutMs is provided and greater than 0.
  • To disable SDK timeout handling, set timeoutMs to 0 (or a negative value), or omit timeoutMs.
  • On timeout, the request is aborted and treated as a network error (Connection timeout after <timeoutMs>ms); if retries are exhausted, the SDK throws BoxSdkError.
  • Timeout failures are handled as request exceptions, then retry behavior is controlled by the configured retry strategy.
  • Timeout applies to a single HTTP request attempt to the Box API (not the total time across all retries).