Add support for gzip content-encoding (#776)

* Add support for gzip Content-Encoding

Signed-off-by: ivan-valkov <iv.v.valkov@gmail.com>

* remove the case insensitive check for accept header

Signed-off-by: ivan-valkov <iv.v.valkov@gmail.com>

* Add option to disable compression

Signed-off-by: ivan-valkov <iv.v.valkov@gmail.com>

* sMake disable_compression an argument instead of env var

Signed-off-by: ivan-valkov <iv.v.valkov@gmail.com>

* Update readme

Signed-off-by: ivan-valkov <iv.v.valkov@gmail.com>

* Fix linters

Signed-off-by: ivan-valkov <iv.v.valkov@gmail.com>

README.md

@@ -338,6 +338,14 @@ from prometheus_client import start_wsgi_server
 start_wsgi_server(8000)
 ```
 
+By default, the WSGI application will respect `Accept-Encoding:gzip` headers used by Prometheus
+and compress the response if such a header is present. This behaviour can be disabled by passing
+`disable_compression=True` when creating the app, like this:
+
+```python
+app = make_wsgi_app(disable_compression=True)
+```
+
 #### ASGI
 
 To use Prometheus with [ASGI](http://asgi.readthedocs.org/en/latest/), there is
@@ -351,6 +359,14 @@ app = make_asgi_app()
 Such an application can be useful when integrating Prometheus metrics with ASGI
 apps.
 
+By default, the WSGI application will respect `Accept-Encoding:gzip` headers used by Prometheus
+and compress the response if such a header is present. This behaviour can be disabled by passing 
+`disable_compression=True` when creating the app, like this:
+
+```python
+app = make_asgi_app(disable_compression=True)
+```
+
 #### Flask
 
 To use Prometheus with [Flask](http://flask.pocoo.org/) we need to serve metrics through a Prometheus WSGI application. This can be achieved using [Flask's application dispatching](http://flask.pocoo.org/docs/latest/patterns/appdispatch/). Below is a working example.

prometheus_client/asgi.py

@@ -5,7 +5,7 @@
 from .registry import CollectorRegistry, REGISTRY
 
 
-def make_asgi_app(registry: CollectorRegistry = REGISTRY) -> Callable:
+def make_asgi_app(registry: CollectorRegistry = REGISTRY, disable_compression: bool = False) -> Callable:
     """Create a ASGI app which serves the metrics from a registry."""
 
     async def prometheus_app(scope, receive, send):
@@ -14,20 +14,25 @@ async def prometheus_app(scope, receive, send):
         params = parse_qs(scope.get('query_string', b''))
         accept_header = "Accept: " + ",".join([
             value.decode("utf8") for (name, value) in scope.get('headers')
-            if name.decode("utf8") == 'accept'
+            if name.decode("utf8").lower() == 'accept'
+        ])
+        accept_encoding_header = ",".join([
+            value.decode("utf8") for (name, value) in scope.get('headers')
+            if name.decode("utf8").lower() == 'accept-encoding'
         ])
         # Bake output
-        status, header, output = _bake_output(registry, accept_header, params)
+        status, headers, output = _bake_output(registry, accept_header, accept_encoding_header, params, disable_compression)
+        formatted_headers = []
+        for header in headers:
+            formatted_headers.append(tuple(x.encode('utf8') for x in header))
         # Return output
         payload = await receive()
         if payload.get("type") == "http.request":
             await send(
                 {
                     "type": "http.response.start",
                     "status": int(status.split(' ')[0]),
-                    "headers": [
-                        tuple(x.encode('utf8') for x in header)
-                    ]
+                    "headers": formatted_headers,
                 }
             )
             await send({"type": "http.response.body", "body": output})

prometheus_client/exposition.py

@@ -1,5 +1,6 @@
 import base64
 from contextlib import closing
+import gzip
 from http.server import BaseHTTPRequestHandler
 import os
 import socket
@@ -93,32 +94,39 @@ def redirect_request(self, req, fp, code, msg, headers, newurl):
         return new_request
 
 
-def _bake_output(registry, accept_header, params):
+def _bake_output(registry, accept_header, accept_encoding_header, params, disable_compression):
     """Bake output for metrics output."""
-    encoder, content_type = choose_encoder(accept_header)
+    # Choose the correct plain text format of the output.
+    formatter, content_type = choose_formatter(accept_header)
     if 'name[]' in params:
         registry = registry.restricted_registry(params['name[]'])
-    output = encoder(registry)
-    return '200 OK', ('Content-Type', content_type), output
+    output = formatter(registry)
+    headers = [('Content-Type', content_type)]
+    # If gzip encoding required, gzip the output.
+    if not disable_compression and gzip_accepted(accept_encoding_header):
+        output = gzip.compress(output)
+        headers.append(('Content-Encoding', 'gzip'))
+    return '200 OK', headers, output
 
 
-def make_wsgi_app(registry: CollectorRegistry = REGISTRY) -> Callable:
+def make_wsgi_app(registry: CollectorRegistry = REGISTRY, disable_compression: bool = False) -> Callable:
     """Create a WSGI app which serves the metrics from a registry."""
 
     def prometheus_app(environ, start_response):
         # Prepare parameters
         accept_header = environ.get('HTTP_ACCEPT')
+        accept_encoding_header = environ.get('HTTP_ACCEPT_ENCODING')
         params = parse_qs(environ.get('QUERY_STRING', ''))
         if environ['PATH_INFO'] == '/favicon.ico':
             # Serve empty response for browsers
             status = '200 OK'
-            header = ('', '')
+            headers = [('', '')]
             output = b''
         else:
             # Bake output
-            status, header, output = _bake_output(registry, accept_header, params)
+            status, headers, output = _bake_output(registry, accept_header, accept_encoding_header, params, disable_compression)
         # Return output
-        start_response(status, [header])
+        start_response(status, headers)
         return [output]
 
     return prometheus_app
@@ -152,8 +160,10 @@ def _get_best_family(address, port):
 
 def start_wsgi_server(port: int, addr: str = '0.0.0.0', registry: CollectorRegistry = REGISTRY) -> None:
     """Starts a WSGI server for prometheus metrics as a daemon thread."""
+
     class TmpServer(ThreadingWSGIServer):
         """Copy of ThreadingWSGIServer to update address_family locally"""
+
     TmpServer.address_family, addr = _get_best_family(addr, port)
     app = make_wsgi_app(registry)
     httpd = make_server(addr, port, app, TmpServer, handler_class=_SilentHandler)
@@ -227,7 +237,7 @@ def sample_line(line):
     return ''.join(output).encode('utf-8')
 
 
-def choose_encoder(accept_header: str) -> Tuple[Callable[[CollectorRegistry], bytes], str]:
+def choose_formatter(accept_header: str) -> Tuple[Callable[[CollectorRegistry], bytes], str]:
     accept_header = accept_header or ''
     for accepted in accept_header.split(','):
         if accepted.split(';')[0].strip() == 'application/openmetrics-text':
@@ -236,6 +246,14 @@ def choose_encoder(accept_header: str) -> Tuple[Callable[[CollectorRegistry], by
     return generate_latest, CONTENT_TYPE_LATEST
 
 
+def gzip_accepted(accept_encoding_header: str) -> bool:
+    accept_encoding_header = accept_encoding_header or ''
+    for accepted in accept_encoding_header.split(','):
+        if accepted.split(';')[0].strip().lower() == 'gzip':
+            return True
+    return False
+
+
 class MetricsHandler(BaseHTTPRequestHandler):
     """HTTP handler that gives metrics from ``REGISTRY``."""
     registry: CollectorRegistry = REGISTRY
@@ -244,12 +262,14 @@ def do_GET(self) -> None:
         # Prepare parameters
         registry = self.registry
         accept_header = self.headers.get('Accept')
+        accept_encoding_header = self.headers.get('Accept-Encoding')
         params = parse_qs(urlparse(self.path).query)
         # Bake output
-        status, header, output = _bake_output(registry, accept_header, params)
+        status, headers, output = _bake_output(registry, accept_header, accept_encoding_header, params, False)
         # Return output
         self.send_response(int(status.split(' ')[0]))
-        self.send_header(*header)
+        for header in headers:
+            self.send_header(*header)
         self.end_headers()
         self.wfile.write(output)
 
@@ -289,14 +309,13 @@ def write_to_textfile(path: str, registry: CollectorRegistry) -> None:
 
 
 def _make_handler(
-    url: str,
-    method: str,
-    timeout: Optional[float],
-    headers: Sequence[Tuple[str, str]],
-    data: bytes,
-    base_handler: type,
+        url: str,
+        method: str,
+        timeout: Optional[float],
+        headers: Sequence[Tuple[str, str]],
+        data: bytes,
+        base_handler: type,
 ) -> Callable[[], None]:
-
     def handle() -> None:
         request = Request(url, data=data)
         request.get_method = lambda: method  # type: ignore
@@ -310,11 +329,11 @@ def handle() -> None:
 
 
 def default_handler(
-    url: str,
-    method: str,
-    timeout: Optional[float],
-    headers: List[Tuple[str, str]],
-    data: bytes,
+        url: str,
+        method: str,
+        timeout: Optional[float],
+        headers: List[Tuple[str, str]],
+        data: bytes,
 ) -> Callable[[], None]:
     """Default handler that implements HTTP/HTTPS connections.
 
@@ -324,11 +343,11 @@ def default_handler(
 
 
 def passthrough_redirect_handler(
-    url: str,
-    method: str,
-    timeout: Optional[float],
-    headers: List[Tuple[str, str]],
-    data: bytes,
+        url: str,
+        method: str,
+        timeout: Optional[float],
+        headers: List[Tuple[str, str]],
+        data: bytes,
 ) -> Callable[[], None]:
     """
     Handler that automatically trusts redirect responses for all HTTP methods.
@@ -344,13 +363,13 @@ def passthrough_redirect_handler(
 
 
 def basic_auth_handler(
-    url: str,
-    method: str,
-    timeout: Optional[float],
-    headers: List[Tuple[str, str]],
-    data: bytes,
-    username: str = None,
-    password: str = None,
+        url: str,
+        method: str,
+        timeout: Optional[float],
+        headers: List[Tuple[str, str]],
+        data: bytes,
+        username: str = None,
+        password: str = None,
 ) -> Callable[[], None]:
     """Handler that implements HTTP/HTTPS connections with Basic Auth.
 
@@ -371,12 +390,12 @@ def handle():
 
 
 def push_to_gateway(
-    gateway: str,
-    job: str,
-    registry: CollectorRegistry,
-    grouping_key: Optional[Dict[str, Any]] = None,
-    timeout: Optional[float] = 30,
-    handler: Callable = default_handler,
+        gateway: str,
+        job: str,
+        registry: CollectorRegistry,
+        grouping_key: Optional[Dict[str, Any]] = None,
+        timeout: Optional[float] = 30,
+        handler: Callable = default_handler,
 ) -> None:
     """Push metrics to the given pushgateway.
 
@@ -420,12 +439,12 @@ def push_to_gateway(
 
 
 def pushadd_to_gateway(
-    gateway: str,
-    job: str,
-    registry: Optional[CollectorRegistry],
-    grouping_key: Optional[Dict[str, Any]] = None,
-    timeout: Optional[float] = 30,
-    handler: Callable = default_handler,
+        gateway: str,
+        job: str,
+        registry: Optional[CollectorRegistry],
+        grouping_key: Optional[Dict[str, Any]] = None,
+        timeout: Optional[float] = 30,
+        handler: Callable = default_handler,
 ) -> None:
     """PushAdd metrics to the given pushgateway.
 
@@ -451,11 +470,11 @@ def pushadd_to_gateway(
 
 
 def delete_from_gateway(
-    gateway: str,
-    job: str,
-    grouping_key: Optional[Dict[str, Any]] = None,
-    timeout: Optional[float] = 30,
-    handler: Callable = default_handler,
+        gateway: str,
+        job: str,
+        grouping_key: Optional[Dict[str, Any]] = None,
+        timeout: Optional[float] = 30,
+        handler: Callable = default_handler,
 ) -> None:
     """Delete metrics from the given pushgateway.
 
@@ -480,13 +499,13 @@ def delete_from_gateway(
 
 
 def _use_gateway(
-    method: str,
-    gateway: str,
-    job: str,
-    registry: Optional[CollectorRegistry],
-    grouping_key: Optional[Dict[str, Any]],
-    timeout: Optional[float],
-    handler: Callable,
+        method: str,
+        gateway: str,
+        job: str,
+        registry: Optional[CollectorRegistry],
+        grouping_key: Optional[Dict[str, Any]],
+        timeout: Optional[float],
+        handler: Callable,
 ) -> None:
     gateway_url = urlparse(gateway)
     # See https://bugs.python.org/issue27657 for details on urlparse in py>=3.7.6.