Add type annotations to synapse.metrics (#10847)

synapse/metrics/_exposition.py

@@ -25,27 +25,25 @@ import math
 import threading
 from http.server import BaseHTTPRequestHandler, HTTPServer
 from socketserver import ThreadingMixIn
-from typing import Dict, List
+from typing import Any, Dict, List, Type, Union
 from urllib.parse import parse_qs, urlparse
 
-from prometheus_client import REGISTRY
+from prometheus_client import REGISTRY, CollectorRegistry
+from prometheus_client.core import Sample
 
 from twisted.web.resource import Resource
+from twisted.web.server import Request
 
 from synapse.util import caches
 
 CONTENT_TYPE_LATEST = "text/plain; version=0.0.4; charset=utf-8"
 
 
-INF = float("inf")
-MINUS_INF = float("-inf")
-
-
-def floatToGoString(d):
+def floatToGoString(d: Union[int, float]) -> str:
     d = float(d)
-    if d == INF:
+    if d == math.inf:
         return "+Inf"
-    elif d == MINUS_INF:
+    elif d == -math.inf:
         return "-Inf"
     elif math.isnan(d):
         return "NaN"
@@ -60,7 +58,7 @@ def floatToGoString(d):
         return s
 
 
-def sample_line(line, name):
+def sample_line(line: Sample, name: str) -> str:
     if line.labels:
         labelstr = "{{{0}}}".format(
             ",".join(
@@ -82,7 +80,7 @@ def sample_line(line, name):
     return "{}{} {}{}\n".format(name, labelstr, floatToGoString(line.value), timestamp)
 
 
-def generate_latest(registry, emit_help=False):
+def generate_latest(registry: CollectorRegistry, emit_help: bool = False) -> bytes:
 
     # Trigger the cache metrics to be rescraped, which updates the common
     # metrics but do not produce metrics themselves
@@ -187,7 +185,7 @@ class MetricsHandler(BaseHTTPRequestHandler):
 
     registry = REGISTRY
 
-    def do_GET(self):
+    def do_GET(self) -> None:
         registry = self.registry
         params = parse_qs(urlparse(self.path).query)
 
@@ -207,11 +205,11 @@ class MetricsHandler(BaseHTTPRequestHandler):
         self.end_headers()
         self.wfile.write(output)
 
-    def log_message(self, format, *args):
+    def log_message(self, format: str, *args: Any) -> None:
         """Log nothing."""
 
     @classmethod
-    def factory(cls, registry):
+    def factory(cls, registry: CollectorRegistry) -> Type:
         """Returns a dynamic MetricsHandler class tied
         to the passed registry.
         """
@@ -236,7 +234,9 @@ class _ThreadingSimpleServer(ThreadingMixIn, HTTPServer):
     daemon_threads = True
 
 
-def start_http_server(port, addr="", registry=REGISTRY):
+def start_http_server(
+    port: int, addr: str = "", registry: CollectorRegistry = REGISTRY
+) -> None:
     """Starts an HTTP server for prometheus metrics as a daemon thread"""
     CustomMetricsHandler = MetricsHandler.factory(registry)
     httpd = _ThreadingSimpleServer((addr, port), CustomMetricsHandler)
@@ -252,10 +252,10 @@ class MetricsResource(Resource):
 
     isLeaf = True
 
-    def __init__(self, registry=REGISTRY):
+    def __init__(self, registry: CollectorRegistry = REGISTRY):
         self.registry = registry
 
-    def render_GET(self, request):
+    def render_GET(self, request: Request) -> bytes:
         request.setHeader(b"Content-Type", CONTENT_TYPE_LATEST.encode("ascii"))
         response = generate_latest(self.registry)
         request.setHeader(b"Content-Length", str(len(response)))