Add RTCAudioSession proxy class.

webrtc/modules/audio_device/ios/objc/RTCAudioSession.h

Index: webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
diff --git a/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h b/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
new file mode 100644
index 0000000000000000000000000000000000000000..e797a05b4b86410af99585368e0fbafa42e0e06f
--- /dev/null
+++ b/webrtc/modules/audio_device/ios/objc/RTCAudioSession.h
@@ -0,0 +1,153 @@
+/*
+ *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#import <AVFoundation/AVFoundation.h>
+#import <Foundation/Foundation.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+extern NSString * const kRTCAudioSessionErrorDomain;
+extern NSInteger const kRTCAudioSessionErrorLockRequired;
+
+@class RTCAudioSession;
+
+// Surfaces AVAudioSession events. WebRTC will listen directly for notifications
+// from AVAudioSession and handle them before calling these delegate methods,
+// at which point applications can perform additional processing if required.
+@protocol RTCAudioSessionDelegate <NSObject>
+
+/** Called when AVAudioSession starts an interruption event. */
+- (void)audioSessionDidBeginInterruption:(RTCAudioSession *)session;
+
+/** Called when AVAudioSession ends an interruption event. */
+- (void)audioSessionDidEndInterruption:(RTCAudioSession *)session
+                   shouldResumeSession:(BOOL)shouldResumeSession;
+
+/** Called when AVAudioSession changes the route. */
+- (void)audioSessionDidChangeRoute:(RTCAudioSession *)session
+           reason:(AVAudioSessionRouteChangeReason)reason
+    previousRoute:(AVAudioSessionRouteDescription *)previousRoute;
+
+/** Called when AVAudioSession media server terminates. */
+- (void)audioSessionMediaServicesWereLost:(RTCAudioSession *)session;
+
+/** Called when AVAudioSession media server restarts. */
+- (void)audioSessionMediaServicesWereReset:(RTCAudioSession *)session;
+
+// TODO(tkchin): Maybe handle SilenceSecondaryAudioHintNotification.
+
+@end
+
+/** Proxy class for AVAudioSession that adds a locking mechanism similar to
+ *  AVCaptureDevice. This is used to that interleaving configurations between
+ *  WebRTC and the application layer are avoided. Only setter methods are
+ *  currently proxied. Getters can be accessed directly off AVAudioSession.
+ *
+ *  RTCAudioSession also coordinates activation so that the audio session is
+ *  activated only once. See |setActive:error:|.
+ */
+@interface RTCAudioSession : NSObject
+
+/** Convenience property to access the AVAudioSession singleton. Callers should
+ *  not call setters on AVAudioSession directly, but other method invocations
+ *  are fine.
+ */
+@property(nonatomic, readonly) AVAudioSession *session;
+
+/** Our best guess at whether the session is active based on results of calls to
+ *  AVAudioSession.
+ */
+@property(nonatomic, readonly) BOOL isActive;
+/** Whether RTCAudioSession is currently locked for configuration. */
+@property(nonatomic, readonly) BOOL isLocked;
+
+// Proxy properties.
+@property(readonly) NSString *category;
+@property(readonly) AVAudioSessionCategoryOptions categoryOptions;
+@property(readonly) NSString *mode;
+@property(readonly) BOOL secondaryAudioShouldBeSilencedHint;
+@property(readonly) AVAudioSessionRouteDescription *currentRoute;
+@property(readonly) NSInteger maximumInputNumberOfChannels;
+@property(readonly) NSInteger maximumOutputNumberOfChannels;
+@property(readonly) float inputGain;
+@property(readonly) BOOL inputGainSettable;
+@property(readonly) BOOL inputAvailable;
+@property(readonly, nullable)
+    NSArray<AVAudioSessionDataSourceDescription *> * inputDataSources;
+@property(readonly, nullable)
+  AVAudioSessionDataSourceDescription *inputDataSource;
+@property(readonly, nullable)
+    NSArray<AVAudioSessionDataSourceDescription *> * outputDataSources;
+@property(readonly, nullable)
+    AVAudioSessionDataSourceDescription *outputDataSource;
+@property(readonly) double sampleRate;
+@property(readonly) NSInteger inputNumberOfChannels;
+@property(readonly) NSInteger outputNumberOfChannels;
+@property(readonly) float outputVolume;
+@property(readonly) NSTimeInterval inputLatency;
+@property(readonly) NSTimeInterval outputLatency;
+@property(readonly) NSTimeInterval IOBufferDuration;
+
+/** Default constructor. Do not call init. */
++ (instancetype)sharedInstance;
+
+/** Adds a delegate, which is held weakly. Even though it's held weakly, callers
+ *  should still call |removeDelegate| when it's no longer required to ensure
+ *  proper dealloc. This is due to internal use of an NSHashTable.
+ */
+- (void)addDelegate:(id<RTCAudioSessionDelegate>)delegate;
+/** Removes an added delegate. */
+- (void)removeDelegate:(id<RTCAudioSessionDelegate>)delegate;
+
+/** Request exclusive access to the audio session for configuration. This call
+ *  will block if the lock is held by another object.
+ */
+- (void)lockForConfiguration;
+/** Relinquishes exclusive access to the audio session. */
+- (void)unlockForConfiguration;
+
+/** If |active|, activates the audio session if it isn't already active.
+ *  Successful calls must be balanced with a setActive:NO when activation is no
+ *  longer required. If not |active|, deactivates the audio session if one is
+ *  active and this is the last balanced call. When deactivating, the
+ *  AVAudioSessionSetActiveOptionNotifyOthersOnDeactivation option is passed to
+ *  AVAudioSession.
+ */
+- (BOOL)setActive:(BOOL)active
+            error:(NSError **)outError;
+
+// The following methods are proxies for the associated methods on
+// AVAudioSession. |lockForConfiguration| must be called before using them
+// otherwise they will fail with kRTCAudioSessionErrorLockRequired.
+
+- (BOOL)setCategory:(NSString *)category
+        withOptions:(AVAudioSessionCategoryOptions)options
+              error:(NSError **)outError;
+- (BOOL)setMode:(NSString *)mode error:(NSError **)outError;
+- (BOOL)setInputGain:(float)gain error:(NSError **)outError;
+- (BOOL)setPreferredSampleRate:(double)sampleRate error:(NSError **)outError;
+- (BOOL)setPreferredIOBufferDuration:(NSTimeInterval)duration
+                               error:(NSError **)outError;
+- (BOOL)setPreferredInputNumberOfChannels:(NSInteger)count
+                                    error:(NSError **)outError;
+- (BOOL)setPreferredOutputNumberOfChannels:(NSInteger)count
+                                     error:(NSError **)outError;
+- (BOOL)overrideOutputAudioPort:(AVAudioSessionPortOverride)portOverride
+                          error:(NSError **)outError;
+- (BOOL)setPreferredInput:(AVAudioSessionPortDescription *)inPort
+                    error:(NSError **)outError;
+- (BOOL)setInputDataSource:(AVAudioSessionDataSourceDescription *)dataSource
+                     error:(NSError **)outError;
+- (BOOL)setOutputDataSource:(AVAudioSessionDataSourceDescription *)dataSource
+                      error:(NSError **)outError;
+
+@end
+
+NS_ASSUME_NONNULL_END