Merge pull request #83 from flogy/read-file-chunks

feat: allow reading chunks from files

Author: alpha0010

README.md

@@ -164,6 +164,11 @@ type ManagedFetchResult = {
 - Read the content of a file.
   - Default encoding of returned string is utf8.
 
+`FileSystem.readFileChunk(path: string, offset: number, length: number, encoding?: 'utf8' | 'base64'): Promise<string>`
+
+- Read a chunk of the content of a file, starting from byte at `offset`, reading for `length` bytes.
+  - Default encoding of returned string is utf8.
+
 ```
 FileSystem.stat(path: string): Promise<FileStat>
 

android/src/main/java/com/alpha0010/fs/FileAccessModule.kt

@@ -400,6 +400,30 @@ class FileAccessModule internal constructor(context: ReactApplicationContext) :
     }
   }
 
+  @ReactMethod
+  override fun readFileChunk(path: String, offset: Double, length: Double, encoding: String, promise: Promise) {
+    ioScope.launch {
+      try {
+        val data = openForReading(path).use { inputStream ->
+          inputStream.skip(offset.toLong())
+          val data = ByteArray(length.toInt())
+          inputStream.read(data)
+          data
+        }
+
+        val result = if (encoding == "base64") {
+          Base64.encodeToString(data, Base64.NO_WRAP)
+        } else {
+          data.decodeToString()
+        }
+
+        promise.resolve(result)
+      } catch (e: Throwable) {
+        promise.reject(e)
+      }
+    }
+  }
+
   @ReactMethod
   override fun stat(path: String, promise: Promise) {
     ioScope.launch {

android/src/oldarch/FileAccessSpec.kt

@@ -30,6 +30,7 @@ abstract class FileAccessSpec internal constructor(context: ReactApplicationCont
   abstract fun mkdir(path: String, promise: Promise)
   abstract fun mv(source: String, target: String, promise: Promise)
   abstract fun readFile(path: String, encoding: String, promise: Promise)
+  abstract fun readFileChunk(path: String, offset: Double, length: Double, encoding: String, promise: Promise)
   abstract fun stat(path: String, promise: Promise)
   abstract fun statDir(path: String, promise: Promise)
   abstract fun unlink(path: String, promise: Promise)

ios/FileAccess.mm

@@ -22,6 +22,7 @@ - (void)ls:(NSString * _Nonnull)path withResolver:(RCTPromiseResolveBlock _Nonnu
 - (void)mkdir:(NSString * _Nonnull)path withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
 - (void)mv:(NSString * _Nonnull)source withTarget:(NSString * _Nonnull)target withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
 - (void)readFile:(NSString * _Nonnull)path withEncoding:(NSString * _Nonnull)encoding withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
+- (void)readFileChunk:(NSString * _Nonnull)path withOffset:(NSNumber * _Nonnull)offset withLength:(NSNumber * _Nonnull)length withEncoding:(NSString * _Nonnull)encoding withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
 - (void)stat:(NSString * _Nonnull)path withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
 - (void)statDir:(NSString * _Nonnull)path withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
 - (void)unlink:(NSString * _Nonnull)path withResolver:(RCTPromiseResolveBlock _Nonnull)resolve withRejecter:(RCTPromiseRejectBlock _Nonnull)reject;
@@ -170,6 +171,19 @@ - (instancetype)init
     [impl readFile:path withEncoding:encoding withResolver:resolve withRejecter:reject];
 }
 
+RCT_EXPORT_METHOD(readFileChunk:(NSString *)path
+                  offset:(double)offset
+                  length:(double)length
+                  encoding:(NSString *)encoding
+                  resolve:(RCTPromiseResolveBlock)resolve
+                  reject:(RCTPromiseRejectBlock)reject)
+{
+    NSNumber *offsetNumber = @(offset);
+    NSNumber *lengthNumber = @(length);
+    [impl readFileChunk:path withOffset:offsetNumber withLength:lengthNumber withEncoding:encoding withResolver:resolve withRejecter:reject];
+}
+
+
 RCT_EXPORT_METHOD(stat:(NSString *)path
                   resolve:(RCTPromiseResolveBlock)resolve
                   reject:(RCTPromiseRejectBlock)reject)

ios/FileAccess.swift

@@ -272,6 +272,33 @@ public class FileAccess : NSObject {
         }
     }
 
+    @objc(readFileChunk:withOffset:withLength:withEncoding:withResolver:withRejecter:)
+    public func readFileChunk(path: String, offset: NSNumber, length: NSNumber, encoding: String, resolve: @escaping RCTPromiseResolveBlock, reject: @escaping RCTPromiseRejectBlock) -> Void {
+        DispatchQueue.global().async {
+            do {
+                let fileHandle = try FileHandle(forReadingFrom: URL(fileURLWithPath: path.path()))
+                defer {
+                    fileHandle.closeFile()
+                }
+                
+                fileHandle.seek(toFileOffset: UInt64(truncating: offset))
+                let binaryData = fileHandle.readData(ofLength: Int(truncating: length))
+                
+                if encoding == "base64" {
+                    resolve(binaryData.base64EncodedString())
+                } else {
+                    if let content = String(data: binaryData, encoding: .utf8) {
+                        resolve(content)
+                    } else {
+                        reject("ERR", "Failed to decode content from file '\(path)' with specified encoding.", nil)
+                    }
+                }
+            } catch {
+                reject("ERR", "Failed to read '\(path)'. \(error.localizedDescription)", error)
+            }
+        }
+    }
+
     @objc(stat:withResolver:withRejecter:)
     public func stat(path: String, resolve: @escaping RCTPromiseResolveBlock, reject: @escaping RCTPromiseRejectBlock) -> Void {
         DispatchQueue.global().async {

src/NativeFileAccess.ts

@@ -71,6 +71,12 @@ export interface Spec extends TurboModule {
   mkdir(path: string): Promise<string>;
   mv(source: string, target: string): Promise<void>;
   readFile(path: string, encoding: string): Promise<string>;
+  readFileChunk(
+    path: string,
+    offset: number,
+    length: number,
+    encoding: string
+  ): Promise<string>;
   stat(path: string): Promise<FileStat>;
   statDir(path: string): Promise<FileStat[]>;
   unlink(path: string): Promise<void>;

src/index.ts

@@ -275,6 +275,18 @@ export const FileSystem = {
     return FileAccessNative.readFile(path, encoding);
   },
 
+  /**
+   * Read a chunk of the content of a file.
+   */
+  readFileChunk(
+    path: string,
+    offset: number,
+    length: number,
+    encoding: Encoding = 'utf8'
+  ) {
+    return FileAccessNative.readFileChunk(path, offset, length, encoding);
+  },
+
   /**
    * Read file metadata.
    */