This commit adds metrics support to the http client (clojure and java, sync
and async). A metric registry can optionally be passed into the client as a
client option on creation. If a metric registry is present, timers will be
added to time each request.
By default, a timer is added for the URL (stripped of username, password,
query string, and path fragments) and the URL plus the method used for the
request. In addition, a request can include a `metric-id` option, which takes
a tuple of metric ids. If this request option is specified, a timer will be
created for each element of the metric id tuple - thus if the tuple is [:foo
:bar :baz] there will be a foo timer, a foo.bar timer, and a foo.bar.baz
timer.
In addition, each timer has a "MetricType" - currently there is only one
metric type, bytes-read, which is stopped when the full response has been
read. In the future, we may add "response-init" timers that get stopped when
the first byte of the response has been read.
This commit also adds a `get-client-metrics`/`.getClientMetrics` function that
takes a client instance and returns the http client-specific metrics from the
metric registry and a `get-client-metrics-data`/`.getClientMetricsData`
function for clojure and java sync and async clients to get out metrics data
from the client. This function takes a client instance and returns a map of
metric name to a map of metric data (for clojure) or a ClientMetricData object
(for java), both of which include the mean, count, and aggregate for the timer
These `get-client-metrics*`/`.getClientMetrics*` functions also have versions
that take a url, url and method, or metric id to allow for filtering of the
timers/metrics data returned by these functions.
The clojure versions of these functions take a metric filter map. There are
also metric filter builder functions to build up the type of metric filter
desired from a url, a url and method, or a metric id. These will prevent users
from having to know the specifics of how to build a metric themselves; instead
they can use a convenience function.
An empty metric id can be passed in to the filter to return all metric-id
timers.
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