Bug 1272768 - Teach `mach resource-usage` to load arbitrary URLs; r=chmanchester

Firefox automation now uploads resource usage JSON files as
job artifacts (see bug 1272202). Now that the build system
writes the same data format and `mach resource-usage` can
read this data format, let's teach `mach resource-usage`
to load arbitrary URLs. This allows people to view system
resource usage for arbitrary jobs in automation.

Currently, you have to look at Treeherder to find the URL to
the build-resources.json artifact. Perhaps in the future
we can make finding the URL easier. Or we could integrate
source resource viewing into Treeherder itself (this is
probably preferred).

This commit continues the tradition of `mach resource-usage`
being a hacked up mess. Instead of loading the URL in
the browser, we download the URL from Python then serve it
from the HTTP server running as part of `mach resource-usage`.
This is somewhat horrible. But it was easiest to implement.
It also conveniently bypasses any cross origin request
restrictions the browser may impose. So it is useful.

MozReview-Commit-ID: IR1Cfs7SrRN

--HG--
extra : rebase_source : 91f5f807c19643ac4d1edb8f6652110813f7e53f

python/mozbuild/mozbuild/html_build_viewer.py

@@ -10,6 +10,8 @@ import BaseHTTPServer
 import json
 import os
 
+import requests
+
 
 class HTTPHandler(BaseHTTPServer.BaseHTTPRequestHandler):
     def do_GET(self):
@@ -36,9 +38,7 @@ class HTTPHandler(BaseHTTPServer.BaseHTTPRequestHandler):
             self.send_header('Content-Type', 'application/json; charset=utf-8')
             self.end_headers()
 
-            with open(s.json_files[key], 'rb') as fh:
-                self.wfile.write(fh.read())
-
+            self.wfile.write(s.json_files[key])
             return
 
         if p == '/':
@@ -105,7 +105,15 @@ class BuildViewerServer(object):
         """Register a resource JSON file with the server.
 
         The file will be made available under the name/key specified."""
-        self.json_files[key] = path
+        with open(path, 'rb') as fh:
+            self.json_files[key] = fh.read()
+
+    def add_resource_json_url(self, key, url):
+        """Register a resource JSON file at a URL."""
+        r = requests.get(url)
+        if r.status_code != 200:
+            raise Exception('Non-200 HTTP response code')
+        self.json_files[key] = r.text
 
     def run(self):
         while not self.do_shutdown:

python/mozbuild/mozbuild/mach_commands.py

@@ -579,19 +579,25 @@ class Build(MachCommandBase):
         help='Port number the HTTP server should listen on.')
     @CommandArgument('--browser', default='firefox',
         help='Web browser to automatically open. See webbrowser Python module.')
-    def resource_usage(self, address=None, port=None, browser=None):
+    @CommandArgument('--url',
+        help='URL of JSON document to display')
+    def resource_usage(self, address=None, port=None, browser=None, url=None):
         import webbrowser
         from mozbuild.html_build_viewer import BuildViewerServer
 
-        last = self._get_state_filename('build_resources.json')
-        if not os.path.exists(last):
-            print('Build resources not available. If you have performed a '
-                'build and receive this message, the psutil Python package '
-                'likely failed to initialize properly.')
-            return 1
-
         server = BuildViewerServer(address, port)
-        server.add_resource_json_file('last', last)
+
+        if url:
+            server.add_resource_json_url('url', url)
+        else:
+            last = self._get_state_filename('build_resources.json')
+            if not os.path.exists(last):
+                print('Build resources not available. If you have performed a '
+                    'build and receive this message, the psutil Python package '
+                    'likely failed to initialize properly.')
+                return 1
+
+            server.add_resource_json_file('last', last)
         try:
             webbrowser.get(browser).open_new_tab(server.url)
         except Exception: