The built-in URL protocols supported by NSURLConnection can handle the schemes http, https, file, ftp, about, and data. I want to support sftp. I heard that there is a way to achieve this by subclassing NSURLProtocol. But I'm not getting how to do it. I want to download a image from the folder through sftp.
Source: https://www.raywenderlich.com/76735/using-nsurlprotocol-swift
内调用函数$ _SESSION [usr] - ＆gt; logout（）该教程通过子类化说明我们可以支持自定义URL。但是当我运行代码时，连接总是失败。我想当我们尝试连接到 sftp 时， MyURLProtocol.swift 中的委托方法，即 didReceiveAuthenticationChallenge 会被调用，但这不会发生。而是调用委托方法 didFailWithError 。我没理解连接失败的原因。这两种方法都来自 NSURLConnectionDelegate
我有 ViewController.swift
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
let urlString = "sftp://username@192.168.0.1:22/batman"
// Open a connection for the URL.
var url = NSURL(string: urlString)
request = NSURLRequest(URL: url!)
connection = NSURLConnection(request: request, delegate: self, startImmediately: true)//(request: request, delegate: self)
}
在我的 AppDelegate.swift
中func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
// Override point for customization after application launch.
NSURLProtocol.registerClass(MyURLProtocol)
return true
}
我的 MyURLProtocol.swift
import UIKit
import CoreData
var requestCount = 0
class MyURLProtocol: NSURLProtocol, NSURLConnectionDelegate {
var connection: NSURLConnection!
var mutableData: NSMutableData!
var response: NSURLResponse!
override class func canInitWithRequest(request: NSURLRequest) -> Bool {
print("Request #\(requestCount++): URL = \(request.URL!.absoluteString)")
if NSURLProtocol.propertyForKey("MyURLProtocolHandledKey", inRequest: request) != nil {
return false
}
return true
}
override class func canonicalRequestForRequest(request: NSURLRequest) -> NSURLRequest {
return request
}
override class func requestIsCacheEquivalent(aRequest: NSURLRequest,
toRequest bRequest: NSURLRequest) -> Bool {
return super.requestIsCacheEquivalent(aRequest, toRequest:bRequest)
}
override func startLoading() {
// 1
let possibleCachedResponse = self.cachedResponseForCurrentRequest()
if let cachedResponse = possibleCachedResponse {
print("Serving response from cache")
// 2
let data = cachedResponse.valueForKey("data") as! NSData
let mimeType = cachedResponse.valueForKey("mimeType") as! String
let encoding = cachedResponse.valueForKey("encoding") as! String
// 3
let response = NSURLResponse(URL: self.request.URL!, MIMEType: mimeType, expectedContentLength: data.length, textEncodingName: encoding)
// 4
self.client!.URLProtocol(self, didReceiveResponse: response, cacheStoragePolicy: .NotAllowed)
self.client!.URLProtocol(self, didLoadData: data)
self.client!.URLProtocolDidFinishLoading(self)
} else {
// 5
print("Serving response from NSURLConnection")
let newRequest = self.request.mutableCopy() as! NSMutableURLRequest
NSURLProtocol.setProperty(true, forKey: "MyURLProtocolHandledKey", inRequest: newRequest)
self.connection = NSURLConnection(request: newRequest, delegate: self)
}
}
override func stopLoading() {
if self.connection != nil {
self.connection.cancel()
}
self.connection = nil
}
func connection(connection: NSURLConnection!, didReceiveResponse response: NSURLResponse!) {
self.client!.URLProtocol(self, didReceiveResponse: response, cacheStoragePolicy: .NotAllowed)
self.response = response
self.mutableData = NSMutableData()
}
func connection(connection: NSURLConnection!, didReceiveData data: NSData!) {
self.client!.URLProtocol(self, didLoadData: data)
self.mutableData.appendData(data)
}
func connectionDidFinishLoading(connection: NSURLConnection!) {
self.client!.URLProtocolDidFinishLoading(self)
self.saveCachedResponse()
}
func connection(connection: NSURLConnection, didFailWithError error: NSError) {
self.client!.URLProtocol(self, didFailWithError: error)
}
func connection(connection: NSURLConnection, didReceiveAuthenticationChallenge challenge: NSURLAuthenticationChallenge) {
}
func saveCachedResponse () {
print("Saving cached response")
// 1
let delegate = UIApplication.sharedApplication().delegate as! AppDelegate
let context = delegate.managedObjectContext
// 2
let cachedResponse = NSEntityDescription.insertNewObjectForEntityForName("CachedURLResponse", inManagedObjectContext: context) as NSManagedObject
cachedResponse.setValue(self.mutableData, forKey: "data")
cachedResponse.setValue(self.request.URL!.absoluteString, forKey: "url")
cachedResponse.setValue(NSDate(), forKey: "timestamp")
cachedResponse.setValue(self.response.MIMEType, forKey: "mimeType")
cachedResponse.setValue(self.response.textEncodingName, forKey: "encoding")
// 3
do {
try context.save()
} catch let error as NSError {
print(error)
print("Could not cache the response")
}
}
func cachedResponseForCurrentRequest() -> NSManagedObject? {
// 1
let delegate = UIApplication.sharedApplication().delegate as! AppDelegate
let context = delegate.managedObjectContext
// 2
let fetchRequest = NSFetchRequest()
let entity = NSEntityDescription.entityForName("CachedURLResponse", inManagedObjectContext: context)
fetchRequest.entity = entity
// 3
let predicate = NSPredicate(format:"url == %@", self.request.URL!.absoluteString)
fetchRequest.predicate = predicate
// 4
let possibleResult:Array<NSManagedObject>?
do {
possibleResult = try context.executeFetchRequest(fetchRequest) as? Array<NSManagedObject>
if let result = possibleResult {
if !result.isEmpty {
return result[0]
}
}
} catch let error as NSError {
print(error)
}
return nil
}
}
答案 0 :(得分：1)
添加对URL方案本身的支持并不会增加对底层网络协议的支持。 sftp协议与HTTP无关，需要完全不同的网络代码才能建立连接和下载数据。现在，您的自定义协议类基本上只是要求URL加载系统在您的协议获取sftp URL（或任何其他URL）时发出新的sftp请求。这将始终失败，因为URL加载系统不知道如何处理sftp请求。
要添加sftp支持，您需要引入一个实际的sftp库，然后使用它而不是在NSURLConnection方法中创建新的startLoading。您还需要检查canInitWithRequest中的协议，以确保它确实是一个sftp请求，IIRC。否则，您的自定义协议子类将最终处理所有可能的URL方案的所有请求。
话虽如此，除非有使用NSURLConnection或NSURLSession处理sftp的合理理由，否则您最好只使用其中一个sftp库处理sftp直接，而不是试图将它们连接到URL加载系统。
有关sftp库的信息，请参阅此问题：