Bug 995070 - Add preference to send 'Prefer: Safe' header as defined by draft-nottingham-safe-hint-01. r=mcmanus

netwerk/protocol/http/nsHttpAtomList.h

@@ -62,6 +62,7 @@ HTTP_ATOM(Location,                  "Location")
 HTTP_ATOM(Max_Forwards,              "Max-Forwards")
 HTTP_ATOM(Overwrite,                 "Overwrite")
 HTTP_ATOM(Pragma,                    "Pragma")
+HTTP_ATOM(Prefer,                    "Prefer")
 HTTP_ATOM(Proxy_Authenticate,        "Proxy-Authenticate")
 HTTP_ATOM(Proxy_Authorization,       "Proxy-Authorization")
 HTTP_ATOM(Proxy_Connection,          "Proxy-Connection")

netwerk/protocol/http/nsHttpHandler.cpp

@@ -86,6 +86,7 @@ extern PRThread *gSocketThread;
 #define DONOTTRACK_VALUE_UNSET    2
 #define TELEMETRY_ENABLED        "toolkit.telemetry.enabled"
 #define ALLOW_EXPERIMENTS        "network.allow-experiments"
+#define SAFE_HINT_HEADER_VALUE   "safeHint.enabled"
 
 #define UA_PREF(_pref) UA_PREF_PREFIX _pref
 #define HTTP_PREF(_pref) HTTP_PREF_PREFIX _pref
@@ -172,6 +173,7 @@ nsHttpHandler::nsHttpHandler()
     , mEnablePersistentHttpsCaching(false)
     , mDoNotTrackEnabled(false)
     , mDoNotTrackValue(1)
+    , mSafeHintEnabled(false)
     , mTelemetryEnabled(false)
     , mAllowExperiments(true)
     , mHandlerActive(false)
@@ -270,6 +272,7 @@ nsHttpHandler::Init()
         prefBranch->AddObserver(TELEMETRY_ENABLED, this, true);
         prefBranch->AddObserver(HTTP_PREF("tcp_keepalive.short_lived_connections"), this, true);
         prefBranch->AddObserver(HTTP_PREF("tcp_keepalive.long_lived_connections"), this, true);
+        prefBranch->AddObserver(SAFE_HINT_HEADER_VALUE, this, true);
         PrefsChanged(prefBranch, nullptr);
     }
 
@@ -417,6 +420,11 @@ nsHttpHandler::AddStandardRequestHeaders(nsHttpHeaderArray *request)
       if (NS_FAILED(rv)) return rv;
     }
 
+    // add the "Send Hint" header
+    if (mSafeHintEnabled) {
+      rv = request->SetHeader(nsHttp::Prefer, NS_LITERAL_CSTRING("safe"));
+      if (NS_FAILED(rv)) return rv;
+    }
     return NS_OK;
 }
 
@@ -1293,6 +1301,15 @@ nsHttpHandler::PrefsChanged(nsIPrefBranch *prefs, const char *pref)
         }
     }
 
+    // Hint option
+    if (PREF_CHANGED(SAFE_HINT_HEADER_VALUE)) {
+        cVar = false;
+        rv = prefs->GetBoolPref(SAFE_HINT_HEADER_VALUE, &cVar);
+        if (NS_SUCCEEDED(rv)) {
+            mSafeHintEnabled = cVar;
+        }
+    }
+
     // toggle to true anytime a token bucket related pref is changed.. that
     // includes telemetry and allow-experiments because of the abtest profile
     bool requestTokenBucketUpdated = false;

netwerk/protocol/http/nsHttpHandler.h

@@ -434,6 +434,9 @@ private:
     bool           mDoNotTrackEnabled;
     uint8_t        mDoNotTrackValue;
 
+    // for broadcasting safe hint;
+    bool           mSafeHintEnabled;
+
     // Whether telemetry is reported or not
     uint32_t           mTelemetryEnabled : 1;