Implemented message splitter for ios ble server

Author: nadraliev

ios/BLEServer.swift

@@ -24,6 +24,8 @@ class BLEServer: NSObject, CBPeripheralManagerDelegate {
 
     private var advertiseCompletion: ((Result<Any?, BLEError>) -> Void)?
 
+    private var outboundQueue: [Data] = []
+    
     func isReady() -> Bool {
         return true
     }
@@ -66,8 +68,17 @@ class BLEServer: NSObject, CBPeripheralManagerDelegate {
             return
         }
 
-        // TODO: implement message splitter
-        peripheralManager.updateValue(Data(message.appending("\0").utf8), for: characteristic, onSubscribedCentrals: nil)
+        let chunks = splitMessage(data: Data(message.utf8), maxChunkLength: 180)
+        
+        for i in chunks.indices {
+            let result = peripheralManager.updateValue(chunks[i], for: characteristic, onSubscribedCentrals: nil)
+            if !result {
+                log(tag: tag, message: "Cannot send the update chunk, the internal queue is full, adding to our own queue")
+                outboundQueue.append(contentsOf: chunks.dropFirst(i))
+                break
+            }
+        }
+        
     }
 
     func finish() -> Void {
@@ -128,6 +139,32 @@ class BLEServer: NSObject, CBPeripheralManagerDelegate {
         }
     }
 
+    func peripheralManagerIsReady(toUpdateSubscribers peripheral: CBPeripheralManager) {
+        // peripheral is ready to send updates again, taking from the queue
+        log(tag: tag, message: "Peripheral is ready to send updates again")
+        guard let characteristic = characteristic else {
+            log(tag: tag, message: "Characteristic is nil after sending some updates, this should not happen, something went terribly wrong")
+            return
+        }
+        
+        var updateResult = false
+        
+        repeat {
+            if outboundQueue.isEmpty {
+                break
+            }
+            
+            let nextUpdate = outboundQueue.removeFirst()
+            updateResult = peripheral.updateValue(nextUpdate, for: characteristic, onSubscribedCentrals: nil)
+            
+            if !updateResult {
+                log(tag: tag, message: "Cannot send the update chunk, the internal queue is full, returning to our own queue")
+                outboundQueue.insert(nextUpdate, at: 0)
+            }
+            
+        } while !outboundQueue.isEmpty && updateResult
+    }
+    
     private func handleWriteRequest(request: CBATTRequest) {
         log(tag: tag, message: "Handling write request")
 

ios/Ble.xcodeproj/project.pbxproj

@@ -8,6 +8,7 @@
 
 /* Begin PBXBuildFile section */
 		63048A562934165300EC7BF5 /* BLEServer.swift in Sources */ = {isa = PBXBuildFile; fileRef = 63048A552934165300EC7BF5 /* BLEServer.swift */; };
+		6338BC482934F981003286FE /* MessageSplitter.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6338BC472934F981003286FE /* MessageSplitter.swift */; };
 		6373FBEE290D6E5F00DB22BB /* BLEModule.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6373FBED290D6E5F00DB22BB /* BLEModule.swift */; };
 		6373FBF5290D714400DB22BB /* BLEModuleExport.m in Sources */ = {isa = PBXBuildFile; fileRef = 6373FBF4290D714400DB22BB /* BLEModuleExport.m */; };
 		639275CA290ED3AD00713511 /* BLEEventType.swift in Sources */ = {isa = PBXBuildFile; fileRef = 639275C9290ED3AD00713511 /* BLEEventType.swift */; };
@@ -34,6 +35,7 @@
 /* Begin PBXFileReference section */
 		4523902D931F99DFFA85303A /* Pods-Ble.release.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-Ble.release.xcconfig"; path = "Target Support Files/Pods-Ble/Pods-Ble.release.xcconfig"; sourceTree = "<group>"; };
 		63048A552934165300EC7BF5 /* BLEServer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BLEServer.swift; sourceTree = "<group>"; };
+		6338BC472934F981003286FE /* MessageSplitter.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MessageSplitter.swift; sourceTree = "<group>"; };
 		6373FBED290D6E5F00DB22BB /* BLEModule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = BLEModule.swift; sourceTree = "<group>"; };
 		6373FBF2290D6F0400DB22BB /* Ble-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "Ble-Bridging-Header.h"; sourceTree = "<group>"; };
 		6373FBF4290D714400DB22BB /* BLEModuleExport.m */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.objc; path = BLEModuleExport.m; sourceTree = "<group>"; };
@@ -79,6 +81,7 @@
 		58B511D21A9E6C8500147676 = {
 			isa = PBXGroup;
 			children = (
+				6338BC472934F981003286FE /* MessageSplitter.swift */,
 				63048A552934165300EC7BF5 /* BLEServer.swift */,
 				639275C9290ED3AD00713511 /* BLEEventType.swift */,
 				63A673EB290EA10F00D80A11 /* Peripheral.swift */,
@@ -191,6 +194,7 @@
 				6373FBEE290D6E5F00DB22BB /* BLEModule.swift in Sources */,
 				639275CA290ED3AD00713511 /* BLEEventType.swift in Sources */,
 				6373FBF5290D714400DB22BB /* BLEModuleExport.m in Sources */,
+				6338BC482934F981003286FE /* MessageSplitter.swift in Sources */,
 				63A673E4290E7EDB00D80A11 /* BLEClient.swift in Sources */,
 				63A673E6290E7F0400D80A11 /* Constants.swift in Sources */,
 				63048A562934165300EC7BF5 /* BLEServer.swift in Sources */,

ios/MessageSplitter.swift

@@ -0,0 +1,41 @@
+//
+//  MessageSplitter.swift
+//  Ble
+//
+//  Created by AndrewNadraliev on 28.11.2022.
+//  Copyright © 2022 Facebook. All rights reserved.
+//
+
+import Foundation
+
+func splitMessage(data: Data, maxChunkLength: Int) -> [Data] {
+    if data.isEmpty {
+        return []
+    }
+    
+    var result: [Data] = []
+    
+    var index = 0
+    
+    repeat {
+        let bottomBar = index * maxChunkLength
+        let upperBar = min(data.count, (index + 1) * maxChunkLength)
+        
+        result.append(data.subdata(in: bottomBar..<upperBar))
+        
+        index += 1
+    } while index * maxChunkLength < data.count
+    
+    let lastChunk = result.last
+    
+    if var lastChunk = lastChunk, lastChunk.count < maxChunkLength {
+        // there is enough space for terminal operator
+        lastChunk.append(contentsOf: [0])
+        result[result.count - 1] = lastChunk
+    } else {
+        // not enough space in the last chunk, create a new one
+        result.append(Data(repeating: 0, count: 1))
+    }
+    
+    return result
+}

ios/Utils.swift

@@ -10,7 +10,7 @@ import Foundation
 
 func log(tag: String, message: String, error: Error? = nil) {
     if let error = error {
-        NSLog("%s: %s \n %s", tag, message, error.localizedDescription)
+        NSLog("%@: %@ \n %@", tag, message, error.localizedDescription)
     } else {
         NSLog("%@: %@", tag, message)
     }