Automatically give JSON response for /machine/<id>/ when using curl.

The view already accepts ?json=1 as a request parameter to force a JSON
response.

This commit extends that behaviour to additionally check the HTML Accept
header, such that text-only requests (curl) give a JSON result
automatically..

Finally, we use the machine __json__ method rather than adding name/id
manually, which gives us the full machine fields in the result.

Change-Id: I0214d23996b68ee1cb23dae55b6929b40f52ea0b

Author: georges-arm

lnt/server/ui/views.py

@@ -66,6 +66,21 @@ def get_redirect_target():
         if is_safe_url(target):
             return target
 
+
+def prefer_json_response(request):
+    # most browsers will accept both html and json (or just */*), but with json
+    # weighted lower.
+    # e.g. firefox: text/html: 1.0, application/json (implicit in */*): 0.8
+    #      chrome: text/html: 1.0, application/json (implicit in */*): 0.8
+    #      lynx: text/html: 1.0, application/json (implicit in */*): 0.01
+    #      curl: */* (both implicitly 1.0)
+    # since we want curl to return json if possible by default, break ties such
+    # that we prefer json
+    json_weight = request.accept_mimetypes['application/json']
+    html_weight = request.accept_mimetypes['text/html']
+    return json_weight >= html_weight or request.args.get('json')
+
+
 ###
 # Root-Only Routes
 
@@ -317,10 +332,8 @@ def v4_machine(id):
     except NoResultFound:
         abort(404, "Invalid machine id {}".format(id))
 
-    if request.args.get('json'):
-        json_obj = dict()
-        json_obj['name'] = machine.name
-        json_obj['id'] = machine.id
+    if prefer_json_response(request):
+        json_obj = machine.__json__()
         json_obj['runs'] = []
         for order in associated_runs:
             rev = order[0].llvm_project_revision