Refactor RCTBundleURLProvider

Summary:
- Avoid using `+initialize`, use dispatch_once instead; it should be equivalent but more performant.
- Don't even let the `isPackagerRunning:` and `guessPackagerHost` methods exist unless `RCT_DEV` is on; they didn't do anything interesting when it is off.

Reviewed By: javache

Differential Revision: D3556645

fbshipit-source-id: 7dcdb4ae27f6625010e15846d757269f6f04155c

React/Base/RCTBundleURLProvider.m

@@ -19,19 +19,9 @@ static NSString *const kRCTEnableDevKey = @"RCT_enableDev";
 static NSString *const kRCTEnableMinificationKey = @"RCT_enableMinification";
 
 static NSString *const kDefaultPort = @"8081";
-static NSString *ipGuess;
 
 @implementation RCTBundleURLProvider
 
-#if RCT_DEV
-+ (void)initialize
-{
-  NSString *ipPath = [[NSBundle mainBundle] pathForResource:@"ip" ofType:@"txt"];
-  NSString *ip = [NSString stringWithContentsOfFile:ipPath encoding:NSUTF8StringEncoding error:nil];
-  ipGuess = [ip stringByTrimmingCharactersInSet:[NSCharacterSet newlineCharacterSet]];
-}
-#endif
-
 - (instancetype)init
 {
   self = [super init];
@@ -69,46 +59,53 @@ static NSString *ipGuess;
   [self settingsUpdated];
 }
 
-- (BOOL)isPackagerRunning:(NSString *)host
-{
-  if (RCT_DEV) {
-    NSURL *url = [[NSURL URLWithString:serverRootWithHost(host)] URLByAppendingPathComponent:@"status"];
-    NSURLRequest *request = [NSURLRequest requestWithURL:url];
-    NSURLResponse *response;
-    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL];
-    NSString *status = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
-    return [status isEqualToString:@"packager-status:running"];
-  }
-  return NO;
-}
-
 static NSString *serverRootWithHost(NSString *host)
 {
   return [NSString stringWithFormat:@"http://%@:%@/", host, kDefaultPort];
 }
 
+#if RCT_DEV
+- (BOOL)isPackagerRunning:(NSString *)host
+{
+  NSURL *url = [[NSURL URLWithString:serverRootWithHost(host)] URLByAppendingPathComponent:@"status"];
+  NSURLRequest *request = [NSURLRequest requestWithURL:url];
+  NSURLResponse *response;
+  NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:NULL];
+  NSString *status = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
+  return [status isEqualToString:@"packager-status:running"];
+}
+
 - (NSString *)guessPackagerHost
 {
+  static NSString *ipGuess;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    NSString *ipPath = [[NSBundle mainBundle] pathForResource:@"ip" ofType:@"txt"];
+    ipGuess = [[NSString stringWithContentsOfFile:ipPath encoding:NSUTF8StringEncoding error:nil]
+               stringByTrimmingCharactersInSet:[NSCharacterSet newlineCharacterSet]];
+  });
+
   NSString *host = ipGuess ?: @"localhost";
   if ([self isPackagerRunning:host]) {
     return host;
   }
   return nil;
 }
+#endif
 
 - (NSString *)packagerServerRoot
 {
   NSString *location = [self jsLocation];
   if (location != nil) {
     return serverRootWithHost(location);
-  } else {
-    NSString *host = [self guessPackagerHost];
-    if (!host) {
-      return nil;
-    } else {
-      return serverRootWithHost(host);
-    }
   }
+#if RCT_DEV
+  NSString *host = [self guessPackagerHost];
+  if (host) {
+    return serverRootWithHost(host);
+  }
+#endif
+  return nil;
 }
 
 - (NSURL *)packagerServerURL
@@ -190,4 +187,5 @@ static NSString *serverRootWithHost(NSString *host)
   });
   return sharedInstance;
 }
+
 @end