Setting Time Limits on cURL Requests to Avoid Endless Waiting

Setting Time Limits on cURL Requests to Avoid Endless Waiting

As the saying goes, "Time is money." When making web requests using the cURL command-line tool, you don't want to be stuck waiting indefinitely for a response. Luckily, cURL provides options to set time limits on requests to avoid this frustrating situation.

In this article, we will explore the best practices for setting timeouts on your cURL requests. Whether you are fetching data from an API or downloading a file, putting a cap on request times ensures efficient script execution.

Why Timeouts Matter When Using cURL

cURL is used pervasively for transferring data over web protocols like HTTP, FTP, and more. It is common to execute cURL commands in scripts and cron jobs to automate web interactions.

In these automated contexts, having cURL hang indefinitely on a stalled request can lead to pile-ups and failures down the line. Your scripts may end up blocked, unable to move on to subsequent tasks.

Setting reasonable timeouts allows you to fail fast instead of waiting around hoping for the best. This way, you can handle exceptions and keep your web automation running smoothly.

Setting a Maximum Time for the Whole Request with --max-time

The simplest way to limit a cURL request's total execution time is by using the --max-time option.

This sets the maximum time in seconds that can elapse from the moment you initiate the request to when cURL finishes transferring data or exhausts its retries.

Here is the basic syntax:

curl --max-time <seconds> <url>

For example, to restrict the total time to 30 seconds:

curl --max-time 30

After 30 seconds pass, cURL will abort the request and exit with a 28 error code indicating it timed out.

You can specify times with sub-second precision if desired—for instance, --max-time 0.75 would set a 750 millisecond timeout.

Setting Connection Timeouts with --connect-timeout

The --max-time limit encapsulates the entire process of making the transfer. This includes initial connection time, any data transfers, following redirects, and so on.

To set a narrower timeout applied specifically to the connection phase, you can use --connect-timeout instead.

This allows for restricting the time spent:

  • Resolving the hostname via DNS

  • Opening the initial TCP socket

  • Completing TLS handshakes or other communication setup steps

The syntax mirrors --max-time:

curl --connect-timeout <seconds> <url>

For example, to allow a maximum of 10 seconds to connect:

curl --connect-timeout 10

If cURL cannot fully establish the connection within the allotted window, it will fail with a 28 timeout error.

Tuning Timeouts for Responsiveness vs. Reliability

Choosing appropriate timeout durations requires balancing speed and resilience.

Very short timeouts like 1-2 seconds provide great responsiveness. But they sacrifice stability on flaky networks where brief lags are common.

Conversely, a 60+ second timeout gives plenty of leeway for connections to recover from transient issues. However, your scripts will become sluggish if they encounter genuinely unresponsive endpoints.

As a rule of thumb for APIs and web downloads, good results come from timeout values between 15-45 seconds. This handles typical hiccups without excessive waits.

Of course, your ideal timeout depends on your specific environment and tolerance for failure.

Luckily, the ability to fine-tune these settings per request with cURL empowers you to dictate timeout policies.

Handling Timeouts Gracefully in Scripts

When a request hits your preset timeout, cURL will exit with a 28 error code.

In scripts, you can check for this to avoid outright failures:

curl --max-time 30 || { 
  echo "Request timed out" >&2
  # Take alternate action

This attempts the download with a 30 second timeout, then prints an error message andtakes alternate action if it fails due to timing out.

For retries, an exponential backoff loop also helps by progressively lengthening the timeout:

while retry_count < 3; do
  curl --max-time "$timeout" && break
  timeout=$((timeout * 2)) 
  retry_count=$((retry_count + 1))

This example retries up to 3 times, doubling the timeout period with each iteration.

Avoid Waiting Indefinitely with cURL Timeouts

Whether invoking one-off cURL requests or running automation scripts, timeouts enable you to avoid frustrating waits. cURL's --max-time and --connect-timeout options put sane limits around your transfers over HTTP, FTP, and other protocols.

Set 15-45 seconds as a starting point for responsive yet resilient requests. For scripts, use error handling logic and backoff/retry loops to mitigate transient timeout issues.

By being judicious with timeouts, you can take back control and tame cURL into a well-behaved transfer tool that fails fast rather fails indefinitely.

Now that you know how to constrain cURL request times, go forth and transfer data with confidence! No more twiddling thumbs hoping for the best. And for further cURL tips, check out our guide to using this versatile command-line tool.