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lyc233333

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📂 HarmonyOS Practical Practice: Secrets of "Seamless Transmission" for Cross-device File Transfer Systems

As a developer who once passed 1GB of demonstration videos in the conference room and crashed, today I want to share the actual combat of HarmonyOS distributed file transfer!When I used the breakpoint continuous transmission function to save me, I almost got killed. Now I have made all these life-saving techniques public.

1. "Crash moment" and requirements of file transfer

When I demonstrated the plan to customers last week, the videos passed on to three devices almost failed:

  • Retransmission from the Internet: WiFi in the conference room suddenly got stuck, and half of the videos were sent back
  • Multiple device sharing: Mobile phones, tablets, and computers must synchronize the latest version of PPT
  • Permission Control: You have to restrict editing permissions if you are afraid that customers will delete source files by mistake

HarmonyOS's distributed service is simply a savior. It is like installing a "portal" for files, and it can be transmitted after being disconnected from the Internet~

2. System architecture: divide file transfer into "pipeline"

1. The four major modules have clear division of labor

Modules Responsibilities Life Analogy
File discovery Find equipment, like shouting "Who has the file" in the conference room Ask colleagues "PPT to send me"
Transfer module Transfer files, send them in blocks, like disassembly express delivery and boxes Split large files into small portions and deliver them in batches
Relay the breakpoint Record the progress, start from the place where you stopped last time after the internet is cut off Read the book and start from the fold next time
Permission control Key management, who can see who can change it Conference room door card, permission to enter

2. Only when the transmission plan is selected correctly will it be faster

  • Multicast transmission: Like broadcast notifications, transmit the same file block to 3 devices at the same time
  • Block transfer: Split the large file into 1MB small pieces, and only a small piece is lost when the network is cut off

3. Core function implementation: from discovery to continuation

1. Equipment discovery: shout "Report" for the file 

import { mdns } from '@kit.NetworkKit';

// Create a device scanner, like a conference room to call
let fileScanner = mdns.createDiscoveryService(this.context, '_file_share._tcp');

// Write it down when you find the device
fileScanner.on('serviceFound', (device) => {
console.log(`File device found: ${device.serviceName}, IP: ${device.hostName}`);
// Save to the device list to facilitate selection of transmission targets
});

// Start scanning
fileScanner.startSearchingMDNS();
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2. Multicast transmission: File block "batch airdrop" 

import { socket } from '@kit.NetworkKit';

// Create a multicast channel, like creating a file transfer group
let multiSocket = socket.constructMulticastSocketInstance();
let multicast address = { address: '239.255.0.1', port: 8888, family: 1 };

// Join the teleportation group
multiSocket.addMembership(multicast address).then(() => {
console.log('Successfully joined to the file transfer group');

// Disassemble the file into 1MB chunks
let file block = tear file ('Demo video.mp4', 1024*1024);
File block.forEach((block, number) => {
// Send block, with number to facilitate continuous transmission
        multiSocket.send({ 
data: { number, data: block },
address: multicast address
        });
    });
});
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3. Breakpoint Continuation: Record "Transfer Progress Notes" 

// Remember the progress of each file block, like which page to do the homework
let Transfer progress = new Map();

function pass file blocks (file ID, block number, total number of blocks, block data) {
if (block number < total number of blocks) {
// Check if there has been any transmission
if (!Transfer Progress.get(`${File ID}-${Block Number}`)) {
Send block (file ID, block number, block data).then(() => {
// Write it down if the transmission is successful
Transfer progress.set(`${file ID}-${block number}`, true);
Pass file blocks (file ID, block number +1, total number of blocks, block data);
            }).catch(() => {
console.log(`block ${block number} is lost, and it will be retransmitted on the Internet!"
// Write it down if it is not passed, avoid repeated transmission
Transfer progress.set(`${file ID}-${block number}`, false);
            });
        } else {
// The passed block is skipped
Pass file blocks (file ID, block number +1, total number of blocks, block data);
        }
    }
}
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4. Industrial-grade optimization: pass on files without plague

  • Multi-threaded acceleration: When transmitting 4K videos, 4 threads are opened and transmitted simultaneously, and the speed is increased by 3 times.
  • Dynamic block size: WiFi is transmitted by 2MB large pieces, and it will automatically cut 512KB small pieces when it is stuck
  • Encrypted transmission: Important files are encrypted with AES, such as using password locks to express delivery boxes

5. The last thought

Now that you use this system to pass files, you will no longer be afraid of the conference room being disconnected!Last time I passed 3GB of materials to the customer, and the WiFi flashed twice in the middle, and they were automatically uploaded~ But I remember that during the first debugging, the block number was reversed, and the file was spelled out and it was laughed at by my colleagues for a week 😂

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