feat(metrics): add summary metric type

README.md

@@ -21,6 +21,7 @@ into existing Prometheus/Grafana monitoring infrastructure.
     - [Metric Types](#metric-types)
       - [Counter](#counter)
       - [Gauge](#gauge)
+      - [Summary](#summary)
     - [Registries](#registries)
   - [Planned Features](#planned-features)
   - [Known Issues](#known-issues)
@@ -38,26 +39,25 @@ MicroPython 4.1.0 or better, with an [Adafruit Ethernet FeatherWing](https://www
 This module implements a very rudimentary HTTP server that likely violates some part of the spec. However, it works
 with Chrome, curl, and Prometheus itself.
 
-Call `start_http_server(port)` to bind a socket and begin listening.
-
-Call `await_http_request(server, registry)` to await an incoming HTTP request and respond with the metrics in
-`registry`.
-
 ### Labels
 
 Labels are not yet implemented.
 
 ### Metric Types
 
-Currently, `Counter` and `Gauge` are the only metric types implemented.
+`Counter`, `Gauge`, and `Summary` are implemented. Labels are not (yet).
 
 #### Counter
 
-Both `inc` and `dec` are implemented.
+Incremental values. Implements `inc(value)` and `dec(value)`.
 
 #### Gauge
 
-Extends [counter](#counter) with `set`.
+Absolute values. Extends [counter](#counter) with `set(value)`.
+
+#### Summary
+
+Prints count and total of `observe(value)`.
 
 ### Registries
 

prometheus_express/metric.py

@@ -1,4 +1,19 @@
+def print_help(name, desc, type):
+    return [
+        '# HELP {} {}'.format(name, desc),
+        '# TYPE {} {}'.format(name, type),
+    ]
+
+
+def print_name(namespace, name):
+    if namespace != '':
+        return '{}_{}'.format(namespace, name)
+    else:
+        return name
+
 # base class for metric types
+
+
 class Metric():
     name = ''
     desc = ''
@@ -21,17 +36,7 @@ def labels(self, *labelValues):
         return self
 
     def print(self, namespace):
-        name = self.printName(namespace)
-        return [
-            '# HELP {} {}'.format(name, self.desc),
-            '# TYPE {} {}'.format(name, self.metricType),
-        ]
-
-    def printName(self, namespace):
-        if namespace != '':
-            return '{}_{}'.format(namespace, self.name)
-        else:
-            return self.name
+        return print_help(print_name(namespace, self.name), self.desc, self.metricType)
 
 
 class Counter(Metric):
@@ -46,7 +51,7 @@ def dec(self, value):
 
     def print(self, namespace):
         return super().print(namespace) + [
-            '{} {}'.format(self.printName(namespace), self.value)
+            '{} {}'.format(print_name(namespace, self.name), self.value)
         ]
 
 
@@ -55,3 +60,21 @@ class Gauge(Counter):
 
     def set(self, value):
         self.value = value
+
+
+class Summary(Metric):
+    metricType = 'summary'
+    valueCount = 0
+    valueTotal = 0
+
+    def observe(self, value):
+        self.valueCount += 1
+        self.valueTotal += value
+
+    def print(self, namespace):
+        nn = print_name(namespace, self.name)
+        return print_help(nn + '_count', self.desc, self.metricType) + [
+            '{}_count {}'.format(nn, self.valueCount),
+        ] + print_help(nn + '_total', self.desc, self.metricType) + [
+            '{}_total {}'.format(nn, self.valueTotal),
+        ]