Units with cc-units (#64)

* Add option to normalize units with cc-unit

* Add unit conversion to router

* Add option to change unit prefix in the router

* Add to MetricRouter README

* Add order of operations in router to README

* Use second add_tags/del_tags only if metric gets renamed

internal/metricRouter/README.md

@@ -52,6 +52,11 @@ The CCMetric router sits in between the collectors and the sinks and can be used
     ],
     "rename_metrics" : {
         "metric_12345" : "mymetric"
+    },
+    "normalize_units" : true,
+    "change_unit_prefix" {
+      "mem_used" : "G",
+      "mem_total" : "G"
     }
 }
 ```
@@ -192,6 +197,14 @@ This option takes a list of evaluable conditions and performs them one after the
 ```
 The first line is comparable with the example in `drop_metrics`, it drops all metrics starting with `drop_metric_` and ending with a number. The second line drops all metrics of the first hardware thread (**not** recommended)
 
+# Manipulating the metric units
+
+## The `normalize_units` option
+The cc-metric-collector tries to read the data from the system as it is reported. If available, it tries to read the metric unit from the system as well (e.g. from `/proc/meminfo`). The problem is that, depending on the source, the metric units are named differently. Just think about `byte`, `Byte`, `B`, `bytes`, ...
+The [cc-units](https://github.com/ClusterCockpit/cc-units) package provides us a normalization option to use the same metric unit name for all metrics. It this option is set to true, all `unit` meta tags are normalized.
+
+## The `change_unit_prefix` section
+It is often the case that metrics are reported by the system using a rather outdated unit prefix (like `/proc/meminfo` still uses kByte despite current memory sizes are in the GByte range). If you want to change the prefix of a unit, you can do that with the help of [cc-units](https://github.com/ClusterCockpit/cc-units). The setting works on the metric name and requires the new prefix for the metric. The cc-units package determines the scaling factor.
 
 # Aggregate metric values of the current interval with the `interval_aggregates` option
 
@@ -239,3 +252,22 @@ Use cases for `interval_aggregates`:
     }
   }
 ```
+
+# Order of operations
+
+The router performs the above mentioned options in a specific order. In order to get the logic you want for a specific metric, it is crucial to know the processing order:
+
+- Add the `hostname` tag (c)
+- Manipulate the timestamp to the interval timestamp (c,r)
+- Drop metrics based on `drop_metrics` and `drop_metrics_if` (c,r)
+- Add tags based on `add_tags` (c,r)
+- Delete tags based on `del_tags` (c,r)
+- Rename metric based on `rename_metric` (c,r)
+  - Add tags based on `add_tags` to still work if the configuration uses the new name (c,r) 
+  - Delete tags based on `del_tags` to still work if the configuration uses the new name (c,r)
+- Normalize units when `normalize_units` is set (c,r)
+- Convert unit prefix based on `change_unit_prefix` (c,r)
+
+Legend:
+- 'c' if metric is coming from a collector
+- 'r' if metric is coming from a receiver

internal/metricRouter/metricRouter.go

@@ -12,6 +12,7 @@ import (
 	lp "github.com/ClusterCockpit/cc-metric-collector/internal/ccMetric"
 	agg "github.com/ClusterCockpit/cc-metric-collector/internal/metricAggregator"
 	mct "github.com/ClusterCockpit/cc-metric-collector/internal/multiChanTicker"
+	units "github.com/ClusterCockpit/cc-units"
 )
 
 const ROUTER_MAX_FORWARD = 50
@@ -35,6 +36,8 @@ type metricRouterConfig struct {
 	IntervalStamp     bool                                 `json:"interval_timestamp"`  // Update timestamp periodically by ticker each interval?
 	NumCacheIntervals int                                  `json:"num_cache_intervals"` // Number of intervals of cached metrics for evaluation
 	MaxForward        int                                  `json:"max_forward"`         // Number of maximal forwarded metrics at one select
+	NormalizeUnits    bool                                 `json:"normalize_units"`     // Check unit meta flag and normalize it using cc-units
+	ChangeUnitPrefix  map[string]string                    `json:"change_unit_prefix"`  // Add prefix that should be applied to the metrics
 	dropMetrics       map[string]bool                      // Internal map for O(1) lookup
 }
 
@@ -207,6 +210,38 @@ func (r *metricRouter) dropMetric(point lp.CCMetric) bool {
 	return false
 }
 
+func (r *metricRouter) prepareUnit(point lp.CCMetric) bool {
+	if r.config.NormalizeUnits {
+		if in_unit, ok := point.GetMeta("unit"); ok {
+			u := units.NewUnit(in_unit)
+			if u.Valid() {
+				point.AddMeta("unit", u.Short())
+			}
+		}
+	}
+	if newP, ok := r.config.ChangeUnitPrefix[point.Name()]; ok {
+
+		newPrefix := units.NewPrefix(newP)
+
+		if in_unit, ok := point.GetMeta("unit"); ok && newPrefix != units.InvalidPrefix {
+			u := units.NewUnit(in_unit)
+			if u.Valid() {
+				cclog.ComponentDebug("MetricRouter", "Change prefix to", newP, "for metric", point.Name())
+				conv, out_unit := units.GetUnitPrefixFactor(u, newPrefix)
+				if conv != nil && out_unit.Valid() {
+					if val, ok := point.GetField("value"); ok {
+						point.AddField("value", conv(val))
+						point.AddMeta("unit", out_unit.Short())
+					}
+				}
+			}
+
+		}
+	}
+
+	return true
+}
+
 // Start starts the metric router
 func (r *metricRouter) Start() {
 	// start timer if configured
@@ -232,9 +267,11 @@ func (r *metricRouter) Start() {
 		if new, ok := r.config.RenameMetrics[name]; ok {
 			point.SetName(new)
 			point.AddMeta("oldname", name)
+			r.DoAddTags(point)
+			r.DoDelTags(point)
 		}
-		r.DoAddTags(point)
-		r.DoDelTags(point)
+
+		r.prepareUnit(point)
 
 		for _, o := range r.outputs {
 			o <- point