[ios, macos] Expose the url session configuration object. (#13886)

The `MGLNetworkConfiguration` class was make public, and added `sessionConfiguration` property to let developers customize the `NSURLSessionConfiguration` object that is used to make HTTP requests in the SDK.

4 files changed, 69 insertions, 23 deletions

diff --git a/platform/darwin/filesource-files.json b/platform/darwin/filesource-files.json
index f435c43877..3ee96f9b95 100644
--- a/platform/darwin/filesource-files.json
+++ b/platform/darwin/filesource-files.json
@@ -2,6 +2,7 @@
     "//": "This file can be edited manually and is the canonical source.",
     "sources": [
         "platform/darwin/src/MGLLoggingConfiguration.m",
+        "platform/darwin/src/MGLNetworkConfiguration.m",
         "platform/darwin/src/http_file_source.mm",
         "platform/default/src/mbgl/storage/sqlite3.cpp"
     ],
diff --git a/platform/darwin/src/MGLNetworkConfiguration.h b/platform/darwin/src/MGLNetworkConfiguration.h
index aaac5a330c..6c56050aae 100644
--- a/platform/darwin/src/MGLNetworkConfiguration.h
+++ b/platform/darwin/src/MGLNetworkConfiguration.h
@@ -1,18 +1,37 @@
 #import <Foundation/Foundation.h>
 
+#import "MGLFoundation.h"
+
 NS_ASSUME_NONNULL_BEGIN
 
 /**
- The MGLNetworkConfiguration object provides a global way to set a base API URL for
- retrieval of map data, styles, and other resources.
-
- Currently, MGLNetworkConfiguration is a private API.
+ The `MGLNetworkConfiguration` object provides a global way to set a base
+ `NSURLSessionConfiguration`, and other resources.
  */
+MGL_EXPORT
 @interface MGLNetworkConfiguration : NSObject
 
-/// Returns the shared instance of the `MGLNetworkConfiguration` class.
+/**
+ Returns the shared instance of the `MGLNetworkConfiguration` class.
+ */
 @property (class, nonatomic, readonly) MGLNetworkConfiguration *sharedManager;
 
+/**
+ The session configuration object that is used by the `NSURLSession` objects
+ in this SDK.
+ 
+ If this property is set to nil or if no session configuration is provided this property
+ is set to the default session configuration.
+ 
+ Assign this object before instantiating any `MGLMapView` object.
+ 
+ @note: `NSURLSession` objects store a copy of this configuration. Any further changes
+ to mutable properties on this configuration object passed to a session’s initializer
+ will not affect the behavior of that session.
+ 
+ */
+@property (atomic, strong, null_resettable) NSURLSessionConfiguration *sessionConfiguration;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/platform/darwin/src/MGLNetworkConfiguration.m b/platform/darwin/src/MGLNetworkConfiguration.m
index 61422f7caa..8262e7eea1 100644
--- a/platform/darwin/src/MGLNetworkConfiguration.m
+++ b/platform/darwin/src/MGLNetworkConfiguration.m
@@ -1,23 +1,51 @@
 #import "MGLNetworkConfiguration.h"
 
+@interface MGLNetworkConfiguration ()
+
+@property (strong) NSURLSessionConfiguration *sessionConfig;
+
+@end
+
 @implementation MGLNetworkConfiguration
 
 + (instancetype)sharedManager {
     static dispatch_once_t onceToken;
     static MGLNetworkConfiguration *_sharedManager;
-    void (^setupBlock)(void) = ^{
-        dispatch_once(&onceToken, ^{
-            _sharedManager = [[self alloc] init];
-        });
-    };
-    if (![[NSThread currentThread] isMainThread]) {
-        dispatch_sync(dispatch_get_main_queue(), ^{
-            setupBlock();
-        });
-    } else {
-        setupBlock();
-    }
+    dispatch_once(&onceToken, ^{
+        _sharedManager = [[self alloc] init];
+        _sharedManager.sessionConfiguration = nil;
+    });
+
     return _sharedManager;
 }
 
+- (void)setSessionConfiguration:(NSURLSessionConfiguration *)sessionConfiguration {
+    @synchronized (self) {
+        if (sessionConfiguration == nil) {
+            _sessionConfig = [self defaultSessionConfiguration];
+        } else {
+            _sessionConfig = sessionConfiguration;
+        }
+    }
+}
+
+- (NSURLSessionConfiguration *)sessionConfiguration {
+    NSURLSessionConfiguration *sessionConfig = nil;
+    @synchronized (self) {
+        sessionConfig = _sessionConfig;
+    }
+    return sessionConfig;
+}
+
+- (NSURLSessionConfiguration *)defaultSessionConfiguration {
+    NSURLSessionConfiguration* sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
+    
+    sessionConfiguration.timeoutIntervalForResource = 30;
+    sessionConfiguration.HTTPMaximumConnectionsPerHost = 8;
+    sessionConfiguration.requestCachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
+    sessionConfiguration.URLCache = nil;
+    
+    return sessionConfiguration;
+}
+
 @end
diff --git a/platform/darwin/src/http_file_source.mm b/platform/darwin/src/http_file_source.mm
index f11d44ea54..c3918ad62b 100644
--- a/platform/darwin/src/http_file_source.mm
+++ b/platform/darwin/src/http_file_source.mm
@@ -8,6 +8,7 @@
 
 #import <Foundation/Foundation.h>
 #import "MGLLoggingConfiguration_Private.h"
+#import "MGLNetworkConfiguration.h"
 
 #include <mutex>
 #include <chrono>
@@ -82,13 +83,10 @@ class HTTPFileSource::Impl {
 public:
     Impl() {
         @autoreleasepool {
-            NSURLSessionConfiguration* sessionConfig =
-                [NSURLSessionConfiguration defaultSessionConfiguration];
-            sessionConfig.timeoutIntervalForResource = 30;
-            sessionConfig.HTTPMaximumConnectionsPerHost = 8;
-            sessionConfig.requestCachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
-            sessionConfig.URLCache = nil;
 
+            NSURLSessionConfiguration *sessionConfig =
+            [MGLNetworkConfiguration sharedManager].sessionConfiguration;
+            
             session = [NSURLSession sessionWithConfiguration:sessionConfig];
 
             userAgent = getUserAgent();