[Qt first entered the rivers and lakes] Detailed description of the underlying architecture and principles of Qt IMAP

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Qt provides a class called QImap that can be used to implement an IMAP client. The QImap class provides a set of convenient functions to send IMAP commands and process data returned by the IMAP server.

The following is the basic implementation architecture diagram of QImap:

+-------------------+
|        QImap      |
+-------------------+
| - imapCommand     |
| - imapReply       |
| - currentDevice   |
| - currentState   |
| - currentId       |
| - pendingCommands |
+-------------------+
          /_\
           |
           | 继承
           |
+-------------------+
|      QObject      |
+-------------------+

It can be seen that QImap inherits from the QObject class, and it realizes the function of the IMAP client through the underlying socket. The imapCommand member variable in the QImap class represents the currently executed IMAP command, the imapReply member variable represents the response message returned by the IMAP server, the currentDevice member variable represents the currently transmitted file name, the currentState member variable represents the current IMAP state, and the currentId member variable represents the current IMAP session ID, the pendingCommands member variable indicates the queue of IMAP commands waiting to be executed.

The functions in the QImap class are mainly divided into two categories: IMAP command functions and response processing functions. The IMAP command function is used to send the IMAP command and process the returned response, and the response processing function is used to parse and process the response message returned by the IMAP server.

IMAP command functions include:

• connectToHost(): connect to the IMAP server.
• login(): Log in to the IMAP server.
• select(): Select a mailbox on the IMAP server.
• search(): Search for eligible emails.
• fetch(): Download the mail on the IMAP server.
• store(): Modify the mail on the IMAP server.
• logout(): Disconnect the IMAP connection.

Response handlers include:

• imapCommandStarted(): The IMAP command starts to execute.
• imapCommandFinished(): IMAP command execution is complete.
• readyRead(): The IMAP server returns data.
• error(): An error occurred in the IMAP operation.
• stateChanged(): The IMAP state has changed.

The underlying architecture of Qt IMAP consists of the following parts:

1. QSslSocket

QSslSocket is a class used in Qt to implement SSL/TLS encrypted communication. It can be used to connect to an IMAP server and send IMAP commands. In Qt IMAP, we can use QSslSocket to establish a connection with the IMAP server.

1. QImapClient

QImapClient is the client class of Qt IMAP, which is responsible for implementing the logic of the IMAP client. QImapClient includes various commands in the IMAP protocol, such as LOGIN, SELECT, FETCH, STORE, etc., as well as methods and signals for processing IMAP responses.

1. QImapMessage

QImapMessage is a class used to represent mail in Qt IMAP, which contains various properties of mail, such as sender, recipient, subject, body, etc. In Qt IMAP, we can use QImapMessage to receive mail and parse it.

The following is the underlying architecture diagram of Qt IMAP:

In Qt IMAP, we can use the following methods to achieve mail receiving and management:

1. connectToHostEncrypted()

The connectToHostEncrypted() method is used to connect to the IMAP server. It accepts a parameter of string type, indicating the host name or IP address of the IMAP server, and a parameter of integer type, indicating the port number of the IMAP server. For example:

QImapClient imap;
imap.connectToHostEncrypted("imap.example.com", 993);

1. login()

The login() method is used to log in to the IMAP server, and it accepts two parameters of string type, representing the user name and password of the IMAP server respectively. For example:

QImapClient imap;
imap.connectToHostEncrypted("imap.example.com", 993);
imap.login("username", "password");

1. select()

The select() method is used to select a mailbox, which accepts a parameter of type string, indicating the name of the mailbox to be selected. For example:

QImapClient imap;
imap.connectToHostEncrypted("imap.example.com", 993);
imap.login("username", "password");
imap.select("INBOX");

1. fetch()

The fetch() method is used to receive emails with a specified UID. It accepts two parameters, an integer type parameter indicating the UID of the email to be received, and a string type parameter indicating the attributes of the email to be received. The fetch() method will return a QByteArray type of mail content, and we can use the QImapMessage::fromData() method to parse the mail content into a QImapMessage object. For example:

QImapClient imap;
imap.connectToHostEncrypted("imap.example.com", 993);
imap.login("username", "password");
imap.select("INBOX");

QByteArray data = imap.fetch(1, "RFC822");
QImapMessage message = QImapMessage::fromData(data);
qDebug() << "Message UID:" << message.uid();
qDebug() << "Message from:" << message.from();
qDebug() << "Message to:" << message.to();
qDebug() << "Message subject:" << message.subject();
qDebug() << "Message body:" << message.body();

1. store()

The store() method is used to modify the attributes of the email with the specified UID. It accepts three parameters, an integer type parameter indicating the UID of the email to be modified, a string type parameter indicating the attribute of the email to be modified, and A parameter of type string representing the value of the property to be modified. For example:

QImapClient imap;
imap.connectToHostEncrypted("imap.example.com", 993);
imap.login("username", "password");
imap.select("INBOX");

imap.store(1, "+FLAGS", "\\Seen");

1. logout()

The logout() method is used to close the connection with the IMAP server, it does not accept any parameters. For example:

QImapClient imap;
imap.connectToHostEncrypted("imap.example.com", 993);
imap.login("username", "password");
imap.select("INBOX");

imap.logout();

The above is the basic usage and function introduction of Qt IMAP. Among them, the connectToHostEncrypted(), login(), select() and logout() methods are used to connect to the IMAP server, log in to the server, select a mailbox and close the connection, and the fetch() and store() methods are used to receive and modify emails.

Here is a simple Qt IMAP sample code:

#include <QCoreApplication>
#include <QDebug>
#include <QImapClient>
#include <QImapMessage>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QImapClient imap;
    imap.connectToHostEncrypted("imap.example.com", 993);
    imap.login("username", "password");
    imap.select("INBOX");

    QByteArray data = imap.fetch(1, "RFC822");
    QImapMessage message = QImapMessage::fromData(data);
    qDebug() << "Message UID:" << message.uid();
    qDebug() << "Message from:" << message.from();
    qDebug() << "Message to:" << message.to();
    qDebug() << "Message subject:" << message.subject();
    qDebug() << "Message body:" << message.body();

    imap.store(1, "+FLAGS", "\\Seen");

    imap.logout();

    return a.exec();
}

In this sample code, we first create a QImapClient object and use the connectToHostEncrypted() method to connect to the IMAP server. Then, we log in to the server using the login() method and select the INBOX mailbox using the select() method. Next, we use the fetch() method to receive the mail with UID 1, and use the QImapMessage::fromData() method to parse the mail content into a QImapMessage object.

Finally, we mark the message with UID 1 as read using the store() method and close the connection to the IMAP server using the logout() method.