在我的应用程序中，一个 tcp 客户端正在处理来自远程 tcp 服务器的数据流。当接收到的字符是 1 字节字符时，一切正常。当 tcp 服务器发送特殊字符如“ü”(十六进制“c3b5”-> 2 字节字符)时，我开始遇到问题。
这是 Swift 3 代码行，只要接收到的数据包含一些超过 1 个字节的 UTF8 字符，就会得到一个 nil 字符串:
let convertedString = String(bytes: data, encoding: String.Encoding.utf8)
知道如何解决这个问题吗？基本上，传入流可能包含编码为 UTF8 的 1 字节或 2 字节字符，我需要将数据流毫无问题地转换为字符串。
这是我遇到问题的全部代码:
func startRead(for task: URLSessionStreamTask) {
task.readData(ofMinLength: 1, maxLength: 65535, timeout: 300) { (data, eof, error) in
if let data = data {
NSLog("stream task read %@", data as NSData)
let convertedString1 = String(data: data, encoding: String.Encoding(rawValue: String.Encoding.utf8.rawValue))
if let convertedString = String(bytes: data, encoding: String.Encoding.utf8) {
self.partialMessage = self.partialMessage + convertedString
NSLog(convertedString)
// Assign lengths (delimiter, MD5 digest, minimum expected length, message length)
let delimiterLength = Constants.END_OF_MESSAGE_DELIMITER.lengthOfBytes(using: String.Encoding.utf8)
let MD5Length = 32 // 32 characters -> hex representation of 16 bytes
// 3 = CR+LF+1 char at least
let minimumExpectedMessageLength = MD5Length + delimiterLength + 3
let messageLength = self.partialMessage.lengthOfBytes(using: String.Encoding.utf8)
// Check for delimiter and minimum expected message length (2 char msg + MD5 digest + delimiter)
if (self.partialMessage.contains(Constants.END_OF_MESSAGE_DELIMITER)) &&
(messageLength >= minimumExpectedMessageLength) {
var message = self.partialMessage
// Get rid of optional CR+LF
var lowBound = message.index(message.endIndex, offsetBy: -1)
var hiBound = message.index(message.endIndex, offsetBy: 0)
var midRange = lowBound ..< hiBound
let optionalCRLF = message.substring(with: midRange)
if (optionalCRLF == "\r\n") || (optionalCRLF == "\0") { // Remove CR+LF if present
lowBound = message.index(message.endIndex, offsetBy: -1)
hiBound = message.index(message.endIndex, offsetBy: 0)
midRange = lowBound ..< hiBound
message.removeSubrange(midRange)
}
// Check for delimiter proper position (has to be at the end)
lowBound = message.index(message.endIndex, offsetBy: -delimiterLength)
hiBound = message.index(message.endIndex, offsetBy: 0)
midRange = lowBound ..< hiBound
let delimiter = message.substring(with: midRange)
if (delimiter == Constants.END_OF_MESSAGE_DELIMITER) // Delimiter in proper position?
{
// Acquire the MD digest
lowBound = message.index(message.endIndex, offsetBy: -(MD5Length+delimiterLength))
hiBound = message.index(message.endIndex, offsetBy: -(delimiterLength))
midRange = lowBound ..< hiBound
let receivedMD5 = message.substring(with: midRange)
// Acquire the deframed message (normalized message)
lowBound = message.index(message.startIndex, offsetBy: 0)
hiBound = message.index(message.endIndex, offsetBy: -(MD5Length+delimiterLength))
midRange = lowBound ..< hiBound
let normalizedMessage = message.substring(with: midRange)
// Calculate the MD5 digest on the normalized message
let calculatedMD5Digest = normalizedMessage.md5()
// Debug
print(delimiter)
print(normalizedMessage)
print(receivedMD5)
print(calculatedMD5Digest!)
// Check for the integrity of the data
if (receivedMD5.lowercased() == calculatedMD5Digest?.lowercased()) || self.noMD5Check // TEMPORARY
{
if (normalizedMessage == "Unauthorized Access")
{
// Update the authorization status
self.authorized = false
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("Unauthorized Access", comment: "Unauthorized Access Title"), message: NSLocalizedString("Please login with the proper Username and Password before to send any command!", comment: "Unauthorized Access Message"))
}
else if (normalizedMessage == "System Busy")
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("System Busy", comment: "System Busy Title"), message: NSLocalizedString("The system is busy at the moment. Only one connection at a time is allowed!", comment: "System Busy Message"))
}
else if (normalizedMessage == "Error")
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("Error", comment: "Error Title"), message: NSLocalizedString("An error occurred during the execution of the command!", comment: "Command Error Message"))
}
else if (normalizedMessage == "ErrorMachineRunning")
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("Error", comment: "Error Title"), message: NSLocalizedString("The command cannot be executed while the machine is running", comment: "Machine Running Message 1")+"!\r\n\n "+NSLocalizedString("Trying to execute any command in this state could be dangerous for both people and machinery", comment: "Machine Running Message 2")+".\r\n\n "+NSLocalizedString("Please stop the machine and leave the automatic or semi-automatic modes before to provide any command", comment: "Machine Running Message 3")+".")
}
else if (normalizedMessage == "Command Not Recognized")
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("Error", comment: "Error Title"), message: NSLocalizedString("Command not recognized!", comment: "Command Unrecognized Message"))
}
else
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
//let testMessage = "test\r\nf3ea0b9bff4a2c79e60acf6873f4a1ce</EOM>\r\n"
//normalizedMessage = testMessage
// Process the received csv file
self.processCsvData(file: normalizedMessage)
}
}
else
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("Data Error", comment: "Data Error Title"), message: NSLocalizedString("The received data cannot be read since it's corrupted or incomplete!", comment: "Data Error Message"))
}
}
else
{
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Stop the stream
NSLog("stream task stop")
self.stop(task: task)
// Shows an alert
self.showAlert(title: NSLocalizedString("Data Error", comment: "Data Error Title"), message: NSLocalizedString("The received data cannot be read since it's corrupted or incomplete!", comment: "Data Error Message"))
}
}
}
}
if eof {
// Stop the refresh control
if let refreshControl = self.refreshControl {
if refreshControl.isRefreshing {
refreshControl.endRefreshing()
}
}
// Refresh the tableview content
self.tableView.reloadData()
// Stop the stream
NSLog("stream task end")
self.stop(task: task)
} else if error == nil {
self.startRead(for: task)
} else {
// We ignore the error because we'll see it again in `didCompleteWithError`.
NSLog("stream task read error")
}
}
}
最佳答案
重要的是 data 代表整个字符串的数据，而不仅仅是一个子字符串。如果您尝试从整个字符串的部分数据转换子字符串，在许多情况下会失败。
它适用于 1 字节字符，因为无论您在何处截取数据流，部分数据仍然代表有效字符串。但是一旦开始处理多字节字符，部分数据流很容易导致数据的第一个或最后一个字节只是多字节字符的一部分。这会阻止数据被正确解释。
因此，在尝试将数据转换为字符串之前，您必须确保使用给定字符串的所有字节构建一个data 对象。
通常您应该以字节计数开始数据。假设前 4 个字节代表一些商定的“字节序”中的 32 位整数。您读取这 4 个字节以获得长度。然后你读取数据，直到你得到更多的字节。然后您就知道您已到达消息的末尾。
尝试在数据末尾使用“消息结束”标记的问题在于，“消息结束”标记可能会被拆分为多个读取。无论哪种方式，您都需要重构代码以在数据级别进行处理，并且在读取所有字符串数据之前不要尝试将数据转换为字符串。
关于ios - Swift 3 : how to convert a UTF8 data stream (1, 每个字符 2,3 或 4 个字节)到字符串？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41175050/