Add RCTDevSupportHttpHeaders singleton (#55586)

Summary:
Pull Request resolved: #55586

Add a thread-safe singleton that holds custom HTTP headers to be applied to all iOS devsupport network requests. This mirrors the Android `DevSupportHttpClient` from D93481539. Uses a GCD concurrent queue with barrier writes for reader-writer synchronization.

Changelog:
[Internal] [Changed] -

Reviewed By: cipolleschi

Differential Revision: D93490954

fbshipit-source-id: addb2f11025a046eedd0e296a7c398eef7211dc4

Author: cortinico

packages/react-native/React/Base/RCTDevSupportHttpHeaders.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <Foundation/Foundation.h>
+
+/**
+ * Thread-safe singleton that holds custom HTTP headers to be applied
+ * to all devsupport network requests (bundle fetches, packager status
+ * checks, inspector and HMR WebSocket connections).
+ */
+@interface RCTDevSupportHttpHeaders : NSObject
+
++ (instancetype)sharedInstance;
+
+- (void)addRequestHeader:(NSString *)name value:(NSString *)value;
+- (void)removeRequestHeader:(NSString *)name;
+- (NSDictionary<NSString *, NSString *> *)allHeaders;
+- (void)applyHeadersToRequest:(NSMutableURLRequest *)request;
+
+@end

packages/react-native/React/Base/RCTDevSupportHttpHeaders.m

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTDevSupportHttpHeaders.h"
+
+@implementation RCTDevSupportHttpHeaders {
+  NSMutableDictionary<NSString *, NSString *> *_headers;
+  dispatch_queue_t _queue;
+}
+
++ (instancetype)sharedInstance
+{
+  static RCTDevSupportHttpHeaders *sharedInstance;
+  static dispatch_once_t onceToken;
+  dispatch_once(&onceToken, ^{
+    sharedInstance = [[RCTDevSupportHttpHeaders alloc] init];
+  });
+  return sharedInstance;
+}
+
+- (instancetype)init
+{
+  if (self = [super init]) {
+    _headers = [NSMutableDictionary new];
+    _queue = dispatch_queue_create("com.facebook.react.RCTDevSupportHttpHeaders", DISPATCH_QUEUE_SERIAL);
+  }
+  return self;
+}
+
+- (void)addRequestHeader:(NSString *)name value:(NSString *)value
+{
+  dispatch_sync(_queue, ^{
+    self->_headers[name] = value;
+  });
+}
+
+- (void)removeRequestHeader:(NSString *)name
+{
+  dispatch_sync(_queue, ^{
+    [self->_headers removeObjectForKey:name];
+  });
+}
+
+- (NSDictionary<NSString *, NSString *> *)allHeaders
+{
+  __block NSDictionary<NSString *, NSString *> *snapshot;
+  dispatch_sync(_queue, ^{
+    snapshot = [self->_headers copy];
+  });
+  return snapshot;
+}
+
+- (void)applyHeadersToRequest:(NSMutableURLRequest *)request
+{
+  NSDictionary<NSString *, NSString *> *headers = [self allHeaders];
+  [headers enumerateKeysAndObjectsUsingBlock:^(NSString *headerName, NSString *headerValue, BOOL *stop) {
+    [request setValue:headerValue forHTTPHeaderField:headerName];
+  }];
+}
+
+@end