package xyz.driver.core.reporting
import com.typesafe.scalalogging.Logger
import org.slf4j.helpers.NOPLogger
import xyz.driver.core.reporting.Reporter.CausalRelation
import scala.concurrent.Future
/** Context-aware diagnostic utility for distributed systems, combining logging and tracing.
*
* Diagnostic messages (i.e. logs) are a vital tool for monitoring applications. Tying such messages to an
* execution context, such as a stack trace, simplifies debugging greatly by giving insight to the chains of events
* that led to a particular message. In synchronous systems, execution contexts can easily be determined by an
* external observer, and, as such, do not need to be propagated explicitly to sub-components (e.g. a stack trace on
* the JVM shows all relevant information). In asynchronous systems and especially distributed systems however,
* execution contexts are not easily determined by an external observer and hence need to be explcictly passed across
* service boundaries.
*
* This reporter provides tracing and logging utilities that explicitly require references to execution contexts
* (called [[SpanContext]]s here) intended to be passed across service boundaries. It embraces Scala's
* implicit-parameter-as-a-context paradigm.
*
* Tracing is intended to be compatible with the
* [[https://github.com/opentracing/specification/blob/master/specification.md OpenTrace specification]], and hence its
* guidelines on naming and tagging apply to methods provided by this Reporter as well.
*
* Usage example:
* {{{
* val reporter: Reporter = ???
* object Repo {
* def getUserQuery(userId: String)(implicit ctx: SpanContext) = reporter.trace("query"){ implicit ctx =>
* reporter.debug("Running query")
* // run query
* }
* }
* object Service {
* def getUser(userId: String)(implicit ctx: SpanContext) = reporter.trace("get_user"){ implicit ctx =>
* reporter.debug("Getting user")
* Repo.getUserQuery(userId)
* }
* }
* reporter.traceRoot("static_get", Map("user" -> "john")) { implicit ctx =>
* Service.getUser("john")
* }
* }}}
*
* Note that computing traces may be a more expensive operation than traditional logging frameworks provide (in terms
* of memory and processing). It should be used in interesting and actionable code paths.
*
* @define rootWarning Note: the idea of the reporting framework is to pass along references to traces as
* implicit parameters. This method should only be used for top-level traces when no parent
* traces are available.
*/
trait Reporter {
def traceWithOptionalParent[A](
name: String,
tags: Map[String, String],
parent: Option[(SpanContext, CausalRelation)])(op: SpanContext => A): A
def traceWithOptionalParentAsync[A](
name: String,
tags: Map[String, String],
parent: Option[(SpanContext, CausalRelation)])(op: SpanContext => Future[A]): Future[A]
/** Trace the execution of an operation, if no parent trace is available.
*
* $rootWarning
*/
def traceRoot[A](name: String, tags: Map[String, String])(op: SpanContext => A): A =
traceWithOptionalParent(
name,
tags,
None
)(op)
/** Trace the execution of an asynchronous operation, if no parent trace is available.
*
* $rootWarning
*
* @see traceRoot
*/
def traceRootAsync[A](name: String, tags: Map[String, String])(op: SpanContext => Future[A]): Future[A] =
traceWithOptionalParentAsync(
name,
tags,
None
)(op)
/** Trace the execution of an operation, in relation to a parent context.
*
* @param name The name of the operation. Note that this name should not be too specific. According to the
* OpenTrace RFC: "An operation name, a human-readable string which concisely represents the work done
* by the Span (for example, an RPC method name, a function name, or the name of a subtask or stage
* within a larger computation). The operation name should be the most general string that identifies a
* (statistically) interesting class of Span instances. That is, `"get_user"` is better than
* `"get_user/314159"`".
* @param tags Attributes associated with the traced event. Following the above example, if `"get_user"` is an
* operation name, a good tag would be `("account_id" -> 314159)`.
* @param relation Relation of the operation to its parent context.
* @param op The operation to be traced. The trace will complete once the operation returns.
* @param ctx Context of the parent trace.
* @tparam A Return type of the operation.
* @return The value of the child operation.
*/
def trace[A](name: String, tags: Map[String, String], relation: CausalRelation = CausalRelation.Child)(
op: /* implicit (gotta wait for Scala 3) */ SpanContext => A)(implicit ctx: SpanContext): A =
traceWithOptionalParent(
name,
tags,
Some(ctx -> relation)
)(op)
/** Trace the operation of an asynchronous operation.
*
* Contrary to the synchronous version of this method, a trace is completed once the child operation completes
* (rather than returns).
*
* @see trace
*/
def traceAsync[A](name: String, tags: Map[String, String], relation: CausalRelation = CausalRelation.Child)(
op: /* implicit (gotta wait for Scala 3) */ SpanContext => Future[A])(implicit ctx: SpanContext): Future[A] =
traceWithOptionalParentAsync(
name,
tags,
Some(ctx -> relation)
)(op)
/** Log a debug message. */
def debug(message: String)(implicit ctx: SpanContext): Unit
/** Log an informational message. */
def info(message: String)(implicit ctx: SpanContext): Unit
/** Log a warning message. */
def warn(message: String)(implicit ctx: SpanContext): Unit
/** Log a error message. */
def error(message: String)(implicit ctx: SpanContext): Unit
/** Log a error message with an associated throwable that caused the error condition. */
def error(message: String, reason: Throwable)(implicit ctx: SpanContext): Unit
}
object Reporter {
val NoReporter: Reporter = new NoTraceReporter(Logger.apply(NOPLogger.NOP_LOGGER))
/** A relation in cause.
*
* Corresponds to
* [[https://github.com/opentracing/specification/blob/master/specification.md#references-between-spans OpenTrace references between spans]]
*/
sealed trait CausalRelation
object CausalRelation {
/** One event is the child of another. The parent completes once the child is complete. */
case object Child extends CausalRelation
/** One event follows from another, not necessarily being the parent. */
case object Follows extends CausalRelation
}
}
