Miscellaneous

Of course, there’s a lot more to Cripts than URLs, headers and connections. This chapter in the Cripts documentation covers a variety of topics that don’t fit into the their own chapter.

Errors

Often it’s useful to be able to abort a client transaction prematurely, and return an error to the client. Cripts provides a simple way to do this, using the cripts::Error object.

Note

Explicitly forcing an HTTP error overrides any other response status that may have been set.

Function	Description
`cripts::Error::Status::Set()`	Sets the response to the status code, and force the request to error.
`cripts::Error::Status::Get()`	Get the current response status for the request.
`cripts::Error::Reason::Set()`	Sets an explicit reason message with the status code. TBD

Example:

do_remap()
{
  borrow req  = cripts::Client::Request::Get();

  if (req["X-Header"] == "yes") {
    cripts::Error::Status::Set(403);
  }
  // Do more stuff here

  if (cripts::Error::Status::Get() != 403) {
    // Do even more stuff here if we're not in error state
  }
}

The Status and Reason can optionally be set in one single call to the status setter:

cripts::Error::Status::Set(403, "Go Away");

Transaction

ATS transactions are generally hidden within Cripts, but for power users, the transaction object provides access to the underlying transaction. In this object, the following functions are available:

Function	Description
`DisableCallback()`	Disables a future callback in this Cript, for this transaction.
`Aborted()`	Has the transaction been aborted.
`LookupStatus()`	Returns the cache lookup status for the transaction.

When disabling a callback, use the following names:

Callback	Description
`cripts::Callback::DO_REMAP`	The `do_remap()` hook.
`cripts::Callback::DO_POST_REMAP`	The `do_post_remap()` hook.
`cripts::Callback::DO_SEND_RESPONSE`	The `do_send_response()` hook.
`cripts::Callback::DO_CACHE_LOOKUP`	The `do_cache_lookup()` hook.
`cripts::Callback::DO_SEND_REQUEST`	The `do_send_request()` hook.
`cripts::Callback::DO_READ_RESPONSE`	The `do_read_response()` hook.
`cripts::Callback::DO_TXN_CLOSE`	The `do_txn_close()` hook.

Finally, the transaction object also provides access to these ATS objects, which can be used with the lower level ATS APIs:

Object	Description
`txnp`	The TSHttpTxn pointer.
`ssnp`	TSHttpSsn pointer.

The transaction object is a global available everywhere, just like the instance object. Example usage to turn off a particular hook conditionally:

do_remap()
{
  static borrow req = cripts::Client::Request::Get();

  if (req["X-Header"] == "yes") {
    transaction.DisableCallback(cripts::Callback::DO_READ_RESPONSE);
  }
}

Note

Disabling callbacks like this is an optimization, avoiding for the hook to be called at all. It can be particularly useful when the decision to run the hook is made early in the Cript.

Transaction Data

Cripts provides a per-transaction data storage mechanism through the txn_data array. This allows you to store data that persists across different hooks within the same transaction. The txn_data array has 4 slots (indexed 0-3) and can store different data types.

Data Type	Description
`integer`	64-bit signed integer values.
`double`	Double-precision floating point values.
`boolean`	Boolean true/false values.
`cripts::string`	String values.
`void *`	Generic pointer values (advanced usage).

Example usage:

do_remap()
{
  // Store data in transaction data slots
  txn_data[0] = integer(42);
  txn_data[1] = cripts::string("example");
  txn_data[2] = boolean(true);
}

do_send_response()
{
  // Retrieve data from transaction data slots
  auto count = AsInteger(txn_data[0]);
  auto name  = AsString(txn_data[1]);
  auto flag  = AsBoolean(txn_data[2]);

  CDebug("Retrieved: count={}, name={}, flag={}", count, name, flag);
}

Note

Transaction data is automatically cleaned up when the transaction ends. Use the appropriate As*() functions to safely extract typed values.

Time

Cripts has encapsulated some common time-related functions in the core. At the moment only the localtime is available, via the cripts::Time::Local object and its Now() method. The Now() method returns the current time as an object with the following functions:

Function	Description
`Epoch()`	Returns the number of seconds since the Unix epoch (00:00:00 UTC, January 1, 1970).
`Year()`	Returns the year.
`Month()`	Returns the month (1-12).
`Day()`	Returns the day of the month (1-31).
`Hour()`	Returns the hour (0-23).
`Minute()`	Returns the minute (0-59).
`Second()`	Returns the second (0-59).
`WeekDay()`	Returns the day of the week (0-6, Sunday is 0).
`YearDay()`	Returns the day of the year (0-365).

The time as returned by Now() can also be used directly in comparisons with previous or future times, and can be cast to an integer to get the epoch time.

Example usage:

do_remap()
{
  auto now = cripts::Time::Local::Now();

  CDebug("Current time: year={}, month={}, day={}",
         now.Year(), now.Month(), now.Day());
  CDebug("Epoch time: {}", now.Epoch());

  // Can also be used directly as integer
  integer epoch_time = now;
}

Plugins

While Cripts provides a lot of functionality out of the box, there are times when you want to continue using existing remap plugins conditionally. Cripts allows you to load and run existing remap plugins from within your Cripts. This opens up new possibilities for your existing plugins, as you gain the full power of Cript to decide when to run such plugins.

Setting up existing remap plugins must be done in the do_create_instance() hook. The instantiated remap plugins must be added to the instance object for the Cript, using the AddPlugin() method. Here’s an example to run the rate limiting plugin based on the client request headers:

do_create_instance()
{
  instance.AddPlugin("my_ratelimit", "rate_limit.so", {"--limit=300", "--error=429"});
}

do_remap()
{
  static borrow plugin = instance.plugins["my_ratelimit"];
  borrow        req    = cripts::Client::Request::Get();

  if (req["X-Header"] == "yes") {
    plugin.RunRemap();
  }
}

Note

The name of the plugin instance, as specified to AddPlugin(), must be unique across all Cripts.

Files

In some cases, albeit not likely, you may need to read lines of text from a file. Cripts of course allows this to be done with C or C++ standard file APIs, but we also provide a few convenience functions to make this easier.

The cripts::File object encapsulates the common C++ files operations. For convenience, and being such a common use case, reading a single line from a file is provided by the cripts::File::Line::Reader object.

Function	Description
`cripts::File::Status()`	Returns file status information.
`cripts::File::Path`	Represents a file system path.
`cripts::File::Type`	File type enumeration (regular, directory, etc.).
`cripts::File::Line::Reader`	Line-by-line file reader.

Example usage:

do_remap()
{
  static const cripts::File::Path p1("/tmp/foo");
  static const cripts::File::Path p2("/tmp/secret.txt");
  borrow req = cripts::Client::Request::Get();

  if (cripts::File::Status(p1).type() == cripts::File::Type::regular) {
    req["X-Foo-Exists"] = "yes";
  } else {
    req["X-Foo-Exists"] = "no";
  }

  cripts::string secret = cripts::File::Line::Reader(p2);
  CDebug("Read secret = {}", secret);
}

UUID

Cripts supports generating a few different UUID (Universally Unique Identifier), for different purposes. The UUID class provides the following objects:

Object	Description
`cripts::UUID::Process`	Returns a UUID for the running process (changes on ATS startup).
`cripts::UUID::Unique`	Returns a completely unique UUID for the server and transaction.
`cripts::UUID::Request`	Returns a unique id for this request.

Using the UUID object is simple, via the Get() method. Here’s an example:

do_remap()
{
  borrow req = cripts::Client::Request::Get();

  req["X-Process-UUID"] = cripts::UUID::Process::Get();
  req["X-Unique-UUID"] = cripts::UUID::Unique::Get();
  req["X-Request-UUID"] = cripts::UUID::Request::Get();
}

Metrics

Cripts metrics are built directly on top of the atomic core ATS metrics. As such, they not only work the same as the core metrics, but they are also as efficient. There are two types of metrics:

Metric	Description
`cripts::Metrics::Counter`	A simple counter, which can only be incremented.
`cripts::Metrics::Gauge`	A gauge, which can be incremented and decremented, and set to a value.

Both metric types support the following operations:

Method	Description
`Increment()`	Increment the metric by 1.
`Increment(value)`	Increment the metric by the specified value.
`Decrement()`	Decrement the metric by 1 (Gauge only).
`Decrement(value)`	Decrement the metric by the specified value (Gauge only).
`Name()`	Get the metric name.
`Id()`	Get the internal metric ID.

Example:

do_create_instance()
{
  instance.metrics[0] = cripts::Metrics::Counter::Create("cript.example1.instance_calls");
  instance.metrics[1] = cripts::Metrics::Gauge::Create("cript.example1.active_requests");
}

do_remap()
{
  static auto plugin_metric = cripts::Metrics::Counter::Create("cript.example1.plugin_calls");

  plugin_metric->Increment();
  instance.metrics[0]->Increment();
  instance.metrics[1]->Increment();
}

do_txn_close()
{
  instance.metrics[1]->Decrement();
}

A cripts::Metrics::Gauge can also be set to a specific value using the assignment operator:

instance.metrics[1] = 42; // Set gauge to specific value

Debugging and Development

Cripts provides several debugging and development aids to help with plugin development:

Function	Description
`CDebug(format, ...)`	Debug logging with format string support.
`CDebugOn()`	Check if debug logging is enabled for this instance.

Debug logging uses the same format string syntax as fmt::format() in libfmt:

do_remap()
{
  if (CDebugOn()) {
    borrow url = cripts::Client::URL::Get();
    CDebug("Processing request for: {}", url.path);
    CDebug("Query parameters: {}", url.query.String());
  }
}

Note

Debug output is controlled by the ATS debug tags system. Use appropriate debug tags in your ATS configuration to enable debug output for your Cripts. The default debug tag for Cripts is the name of the Cript itself, either the Cript source file, or the compiled plugin name.