Add HELP output for auto-created metrics (#470)

Signed-off-by: David Lukac <1215290+davidlukac@users.noreply.github.com>

prometheus_client/exposition.py

@@ -122,6 +122,8 @@ def sample_line(line):
             raise
 
         for suffix, lines in sorted(om_samples.items()):
+            output.append('# HELP {0}{1} {2}\n'.format(metric.name, suffix, 
+                                                       metric.documentation.replace('\\', r'\\').replace('\n', r'\n')))
             output.append('# TYPE {0}{1} gauge\n'.format(metric.name, suffix))
             output.extend(lines)
     return ''.join(output).encode('utf-8')

tests/test_exposition.py

@@ -56,6 +56,7 @@ def test_counter(self):
         self.assertEqual(b"""# HELP cc_total A counter
 # TYPE cc_total counter
 cc_total 1.0
+# HELP cc_created A counter
 # TYPE cc_created gauge
 cc_created 123.456
 """, generate_latest(self.registry))
@@ -66,6 +67,7 @@ def test_counter_total(self):
         self.assertEqual(b"""# HELP cc_total A counter
 # TYPE cc_total counter
 cc_total 1.0
+# HELP cc_created A counter
 # TYPE cc_created gauge
 cc_created 123.456
 """, generate_latest(self.registry))
@@ -82,6 +84,7 @@ def test_summary(self):
 # TYPE ss summary
 ss_count{a="c",b="d"} 1.0
 ss_sum{a="c",b="d"} 17.0
+# HELP ss_created A summary
 # TYPE ss_created gauge
 ss_created{a="c",b="d"} 123.456
 """, generate_latest(self.registry))
@@ -109,6 +112,7 @@ def test_histogram(self):
 hh_bucket{le="+Inf"} 1.0
 hh_count 1.0
 hh_sum 0.05
+# HELP hh_created A histogram
 # TYPE hh_created gauge
 hh_created 123.456
 """, generate_latest(self.registry))
@@ -119,8 +123,10 @@ def test_gaugehistogram(self):
 # TYPE gh histogram
 gh_bucket{le="1.0"} 4.0
 gh_bucket{le="+Inf"} 5.0
+# HELP gh_gcount help
 # TYPE gh_gcount gauge
 gh_gcount 5.0
+# HELP gh_gsum help
 # TYPE gh_gsum gauge
 gh_gsum 7.0
 """, generate_latest(self.registry))