Add buffer size option to read stream

src/index.js

 // const emitter = (Platform.OS === 'android' ? DeviceEventEmitter : NativeAppEventEmitter)
 const emitter = DeviceEventEmitter
 const RNFetchBlob:RNFetchBlobNative = NativeModules.RNFetchBlob
+const pathPrefix = Platform.OS === 'android' ? 'file://' : ''
 
 emitter.addListener("RNFetchBlobMessage", (e) => {
 
 
 }
 
-function openReadStream(path:string, encoding:'utf8' | 'ascii' | 'base64'):RNFetchBlobStream {
+function openReadStream(
+  path:string,
+  encoding:'utf8' | 'ascii' | 'base64',
+  bufferSize?:?number
+):RNFetchBlobStream {
 
   if(!path)
     throw Error('RNFetchBlob could not open file stream with empty `path`')
 
   // register for file stream event
   let subscription = emitter.addListener(`RNFetchBlobStream+${path}`, (e) => {
+
     let {event, detail} = e
     if(stream._onData && event === 'data')
       stream._onData(detail)
 
   })
 
-  RNFetchBlob.readStream(path, encoding)
-
+  RNFetchBlob.readStream(path, encoding, (bufferSize || "0").toString())
   return stream
 
 }

src/ios/RNFetchBlob/RNFetchBlob.h

     RCTBridge * bridge;
     Boolean isOpen;
     NSString * encoding;
+    int bufferSize;
     NSString * taskId;
     NSString * path;
 }
 @property (nonatomic) NSString * encoding;
 @property (nonatomic) NSString * taskId;
 @property (nonatomic) NSString * path;
+@property (nonatomic) int bufferSize;
 
 + (NSString *) getTempPath;
 - (id) init;

src/ios/RNFetchBlob/RNFetchBlob.m

 @synthesize callback;
 @synthesize taskId;
 @synthesize path;
+@synthesize bufferSize;
 
 
 
     }
 }
 
-- (void)readWithPath:(NSString *)path useEncoding:(NSString *)encoding {
+- (void)readWithPath:(NSString *)path useEncoding:(NSString *)encoding bufferSize:(int) bufferSize{
     
     self.inStream = [[NSInputStream alloc] initWithFileAtPath:path];
     self.inStream.delegate = self;
     self.encoding = encoding;
     self.path = path;
+    self.bufferSize = bufferSize;
     
     // NSStream needs a runloop so let's create a run loop for it
     dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
         case NSStreamEventHasBytesAvailable:
         {
             NSMutableData * chunkData = [[NSMutableData data] init];
-            uint8_t buf[1024];
+            NSInteger chunkSize = 1024;
+            if([[self.encoding lowercaseString] isEqualToString:@"base64"])
+                chunkSize = 1026;
+            if(self.bufferSize > 0)
+                chunkSize = self.bufferSize;
+            uint8_t buf[chunkSize];
             unsigned int len = 0;
-            len = [(NSInputStream *)stream read:buf maxLength:1024];
+
+            len = [(NSInputStream *)stream read:buf maxLength:chunkSize];
             // still have data in stream
             if(len) {
                 [chunkData appendBytes:(const void *)buf length:len];
     });
 }
 
-RCT_EXPORT_METHOD(readStream:(NSString *)path withEncoding:(NSString *)encoding) {
+RCT_EXPORT_METHOD(readStream:(NSString *)path withEncoding:(NSString *)encoding bufferSize:(int)bufferSize) {
     FetchBlobFS *fileStream = [[FetchBlobFS alloc] initWithBridgeRef:self.bridge];
-    [fileStream readWithPath:path useEncoding:encoding];
+    [fileStream readWithPath:path useEncoding:encoding bufferSize:bufferSize];
 }
 
 RCT_EXPORT_METHOD(flush:(NSString *)path) {