emergence/go-imap - imap.FetchRFC822: Invalid memory address or nil pointer dereference

php editor Xigua may encounter a common error message when using the emergence/go-imap library: "imap.FetchRFC822: invalid memory address or nil pointer dereference". This error message is usually caused by not properly initializing the imap client or not correctly connecting to the IMAP server. The solution to this problem is simple, just make sure you initialize the imap client correctly and successfully connect to the IMAP server. This article will introduce in detail how to solve this problem and help readers successfully use the emergence/go-imap library to perform imap operations.

Question content

I am trying to get all emails from the server using the following source code (this function is called in the main module):

package internal

import (
    "fmt"
    "io"
    "io/ioutil"
    "log"

    "github.com/emersion/go-imap"
    "github.com/emersion/go-imap/client"
    "github.com/emersion/go-message"
)

func fetchemail(server string, username string, password string) error {
    //connect to server
    log.println("connecting to server...")

    c, err := client.dialtls(server, nil)
    log.println("connected to " + server)
    defer c.logout()

    //check if connection successful
    if err != nil {
        log.println("in connection error")
        return err
    }

    //err = nil

    //login
    log.println("logging in...")
    err = c.login(username, password)
    log.println("logged in as " + username)

    //check if login successful
    if err != nil {
        log.println("in login error")
        return err
    }

    //select inbox
    log.println("selecting inbox...")
    mbox, err := c.select("inbox", false)
    log.println("selected inbox")

    //check if select successful
    if err != nil {
        return err
    }

    //fetch all messages
    log.println("fetching all messages...")
    seqset := new(imap.seqset)
    seqset.addrange(1, mbox.messages)
    items := []imap.fetchitem{imap.fetchrfc822}
    messages := make(chan *imap.message, 10)
    done := make(chan error, 1)
    go func() {
        done <- c.fetch(seqset, items, messages)
    }()

    //check if fetch successful
    if err := <-done; err != nil {
        log.println("in fetch error")
        return err
    }

    log.println("run successful - terminating...")
    return nil
}

This results in the following error:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x5ee505]
goroutine 1 [running]:

I've tried imap.fetchevelope() and it works, but for some reason imap.fetchrfc822 doesn't work.

My main goal is to export all email attachments (.gz, .zip...) from all emails, that's why I need the entire email, not just the envelope.

Solution

I think the problem lies in this line items := []imap.fetchitem{imap.fetchrfc822}.
First, let’s clarify what the fetchitem type is. This represents the different parts of the email that can be obtained (envelope, body, uid, flags, etc.).
Then, let’s talk about the fetch method. It requires passing in a slice of imap.fetchitem. It retrieves all parts specified by this slice from the email.
So the solution to your problem is to replace this line with items := []imap.fetchitem{imap.fetchrfc822, imap.fetchenvelope}.
I fixed and tested your program as you can see from the code snippet below:

package main

import (
    "fmt"
    "log"

    "github.com/emersion/go-imap"
    "github.com/emersion/go-imap/client"
)

func FetchEMail(server string, username string, password string) error {
    // Connect to Server
    log.Println("Connecting to server...")

    c, err := client.Dial(server)
    log.Println("Connected to " + server)
    defer c.Logout()

    // check if connection successful
    if err != nil {
        log.Println("In connection Error")
        return err
    }

    // Login
    log.Println("Logging in...")
    err = c.Login(username, password)
    log.Println("Logged in as " + username)

    // check if login successful
    if err != nil {
        log.Println("In login Error")
        return err
    }

    // Select INBOX
    log.Println("Selecting INBOX...")
    mbox, err := c.Select("INBOX", false)
    log.Println("Selected INBOX")

    // check if select successful
    if err != nil {
        return err
    }

    // Fetch all messages
    log.Println("Fetching all messages...")
    seqset := new(imap.SeqSet)
    seqset.AddRange(1, mbox.Messages)
    items := []imap.FetchItem{imap.FetchRFC822, imap.FetchEnvelope}
    messages := make(chan *imap.Message, 10)
    done := make(chan error, 1)
    go func() {
        done <- c.Fetch(seqset, items, messages)
    }()

    for msg := range messages {
        fmt.Printf("suject: %v\n", msg.Envelope.Subject)
    }

    // check if fetch successful
    if err := <-done; err != nil {
        log.Println("In fetch Error")
        return err
    }

    log.Println("Run Successful - Terminating...")
    return nil
}

func main() {
    err := FetchEMail("xxxxxxx", "xxxxx", "xxxxx")
    if err != nil {
        panic(err)
    }
}

Towards the end, I added for to print the subject of the retrieved email. Here you can replace the code with your own logic. nil pointer dereference The error disappears.
If this solves your problem, please let me know!

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