Add Blob.slice implementation #89

This commit includes Android and IOS implementations.

src/android/src/main/java/com/RNFetchBlob/RNFetchBlob.java

     }
 
     @ReactMethod
-    public void slice(String src, String dest, int start, int end, String encode, Callback callback) {
-        RNFetchBlobFS.slice(src, dest, start, end, encode, callback);
+    public void slice(String src, String dest, int start, int end, Promise promise) {
+        RNFetchBlobFS.slice(src, dest, start, end, "", promise);
     }
 
     @ReactMethod

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java

      * @param encode
      * @param callback
      */
-    public static void slice(String src, String dest, int start, int end, String encode, Callback callback) {
+    public static void slice(String src, String dest, int start, int end, String encode, Promise promise) {
         try {
             long expected = end - start;
             long now = 0;
             byte [] buffer = new byte[10240];
             while(now < expected) {
                 long read = in.read(buffer, 0, 10240);
+                long remain = expected - now;
                 if(read <= 0) {
                     break;
                 }
+                if(remain < 10240) {
+                    out.write(buffer, 0, (int) remain);
+                }
+                else
+                    out.write(buffer, 0, (int) read);
                 now += read;
-                out.write(buffer, 0, (int) read);
+
             }
             in.close();
+            out.flush();
             out.close();
-            callback.invoke(null, dest);
+            promise.resolve(dest);
         } catch (Exception e) {
             e.printStackTrace();
+            promise.reject(e.getLocalizedMessage());
         }
     }
 

src/fs.js

 
 }
 
+function slice(src:string, dest:string, start:number, end:number):Promise {
+  return RNFetchBlob.slice(src, dest, start, end)
+}
+
 function isDir(path:string):Promise<bool, bool> {
 
   return new Promise((resolve, reject) => {
   lstat,
   scanFile,
   dirs,
+  slice,
   asset
 }

src/ios/RNFetchBlob/RNFetchBlob.m

     [RNFetchBlobNetwork enableUploadProgress:taskId];
 })
 
-RCT_EXPORT_METHOD(slice:(NSString *)src dest:(NSString *)dest start:(NSNumber *)start end:(NSNumber *)end resolver:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject
+RCT_EXPORT_METHOD(slice:(NSString *)src dest:(NSString *)dest start:(nonnull NSNumber *)start end:(nonnull NSNumber *)end resolver:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject
 {
-    [RNFetchBlobFS slice:src dest:dest start:start end:end encode:@"" resolver:resolve rejecter:reject];
+     dispatch_sync(dispatch_get_main_queue(),^(void){
+         [RNFetchBlobFS slice:src dest:dest start:start end:end encode:@"" resolver:resolve rejecter:reject];
+     });
 })
 
 #pragma mark RNFetchBlob private methods

src/ios/RNFetchBlobFS.h

 + (void) writeFile:(NSString *)path encoding:(NSString *)encoding data:(NSString *)data append:(BOOL)append resolver:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject;
 + (void) readFile:(NSString *)path encoding:(NSString *)encoding resolver:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject onComplete:(void (^)(NSData * content))onComplete;
 + (void) readAssetFile:(NSData *)assetUrl completionBlock:(void(^)(NSData * content))completionBlock failBlock:(void(^)(NSError * err))failBlock;
-+ (void) slice:(NSString *)path dest:(NSString *)dest start:(NSNumber *)start end:(NSNumber *)end encode:(NSString *)encode resolver:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject;
++ (void)slice:(NSString *)path
+         dest:(NSString *)dest
+        start:(nonnull NSNumber *)start
+          end:(nonnull NSNumber *)end
+        encode:(NSString *)encode
+     resolver:(RCTPromiseResolveBlock)resolve
+     rejecter:(RCTPromiseRejectBlock)reject;
 //+ (void) writeFileFromFile:(NSString *)src toFile:(NSString *)dest append:(BOOL)append;
 
 // constructor

src/ios/RNFetchBlobFS.m

 }
 
 // Slice a file into another file, generally for support Blob implementation.
-- (void)slice:(NSString *)path
++ (void)slice:(NSString *)path
          dest:(NSString *)dest
-        start:(NSNumber *)start
-          end:(NSNumber *)end
-        encod:(NSString *)encode
+        start:(nonnull NSNumber *)start
+          end:(nonnull NSNumber *)end
+        encode:(NSString *)encode
      resolver:(RCTPromiseResolveBlock)resolve
      rejecter:(RCTPromiseRejectBlock)reject
 {
     }
     long size = [fm attributesOfItemAtPath:path error:nil].fileSize;
     // abort for the file size is less than start
-    if(size < start)
+    if(size < [start longValue])
     {
-        reject(@"RNFetchBlob slice failed", @"start is greater than file size", @"");
+        reject(@"RNFetchBlob slice failed", @"start is greater than file size", @"start is greater than file size");
         return;
     }
     if(![fm fileExistsAtPath:dest]) {
         [fm createFileAtPath:dest contents:@"" attributes:nil];
     }
-    [handle seekToFileOffset:start];
+    [handle seekToFileOffset:[start longValue]];
     while(read < expected)
     {
+
         NSData * chunk = [handle readDataOfLength:10240];
+        long remain = expected - read;
+        if(remain < 10240)
+        {
+            [os write:[chunk bytes] maxLength:remain];
+        }
+        else
+        {
+            [os write:[chunk bytes] maxLength:10240];
+        }
         read += [chunk length];
-        [os write:[chunk bytes] maxLength:10240];
     }
     [handle closeFile];
     [os close];

src/polyfill/Blob.js

 const log = new Log('Blob')
 const blobCacheDir = fs.dirs.DocumentDir + '/RNFetchBlob-blobs/'
 
-log.disable()
-// log.level(3)
+// log.disable()
+log.level(3)
 
 /**
  * A RNFetchBlob style Blob polyfill class, this is a Blob which compatible to
     return this
   }
 
+  markAsDerived() {
+    this._isDerived = true
+  }
+
+  get isDerived() {
+    return this._isDerived || false
+  }
+
   /**
    * Get file reference of the Blob object.
    * @nonstandard
    * @param  {string} contentType Optional, content type of new Blob object
    * @return {Blob}
    */
-  slice(start:?number, end:?number, encoding:?string):Blob {
+  slice(start:?number, end:?number, contentType:?string):Blob {
     if(this._closed)
       throw 'Blob has been released.'
-    log.verbose('slice called', start, end, encoding)
-    console.warn('RNFB#Blob.slice() is not implemented yet, to read Blob content, use Blob.readBlob(encoding:string) instead.')
-    // TODO : fs.slice
-    // return fs.slice(this.cacheName, getBlobName(), contentType, start, end)
+    log.verbose('slice called', start, end, contentType)
+    let resPath = blobCacheDir + getBlobName()
+    let pass = false
+    log.debug('fs.slice new blob will at', resPath)
+    fs.slice(this._ref, resPath, start, end).then((dest) => {
+      log.debug('fs.slice done', dest)
+      pass = true
+    })
+    .catch((err) => {
+      pass = true
+    })
+    log.debug('slice returning new Blob')
+    return new Blob(RNFetchBlob.wrap(resPath))
   }
 
   /**