Reading emails from gmail POP3 account using libCurl

Question

I'm currently working in a C++ project which has to be able to read emails from an gmail POP3 account just like the title says. Also is important to say that I need to download the attachments (is encode base64?) of the mail and its body. The fact is that everyone recommend to use libCurl for this task, but the code sample on their web is not working. I saw this example on Libcurl website:

#include <stdio.h>
#include <curl/curl.h>

int main(void)
{
    CURL *curl;
    CURLcode res;

    curl = curl_easy_init();
    if(curl)
    {
         /* Set username and password */ 
         curl_easy_setopt(curl, CURLOPT_USERPWD, "user:password");

         /* This will only fetch the message with ID "1" of the given mailbox */ 
         curl_easy_setopt(curl, CURLOPT_URL, "pop3s://user@pop.example.com/1");

         /* Perform the request, res will get the return code */ 
         res = curl_easy_perform(curl);

         /* Check for errors */ 
         if(res != CURLE_OK)
         fprintf(stderr, "curl_easy_perform() failed: %s\n",
                curl_easy_strerror(res));

         /* always cleanup */ 
         curl_easy_cleanup(curl);
    }
    return 0;
}

As you see, the code looks pretty easy for fetching email by email inside the inbox, but when i try to perform the operation with CURLcode curl_easy_perform(CURL *) the function doesn't return anything and the process 'dies' so i can't skip this line. My code is the following one:

void MailServer::Open(char *username,char *password)
{
    m_username = username; //username = example@gmail.com
    m_password = password; //password = blabla123

    curl = curl_easy_init();
    curl_easy_setopt(curl,CURLOPT_USERNAME,username);
    curl_easy_setopt(curl,CURLOPT_PASSWORD,password);

    m_popsAccount = "pop3s://" + m_username +"/1";      

    curl_easy_setopt(curl, CURLOPT_URL, m_popsAccount.c_str());
    res = curl_easy_perform(curl); //here does not return anything

}

I tried to find some 'clear' example on the web, but i really couldn't... Someone could give me a hand with it? :)

Answer 1

I made it guys! Here's a good sample about how you can access a gmail acount and see what's inside. I'm currently working on parsing the information inside, because actually it only retrieves the amount of mails on inbox and its size. If you change the url as "pops://pop.gmail.com:995/1" it will return the content of the messege and also including a base64 encoding for the attachments. Thanks Anyway... here is the code! :)

#pragma region Types
struct MemoryStruct {
    char *memory;
    size_t size;
};  
#pragma endregion

void MailServer::Open(char *username,char *password)
{
    m_username = username;
    m_password = password;
    struct MemoryStruct chunk;

    chunk.memory = (char*) malloc(1);  //crecerá según sea necesario con el realloc
    chunk.size = 0;    //no hay datos en este punto

    //inicializacion
    curl_global_init(CURL_GLOBAL_ALL);
    curl = curl_easy_init();


    //login
    curl_easy_setopt(curl,CURLOPT_USERNAME,username);
    curl_easy_setopt(curl,CURLOPT_PASSWORD,password);

    m_popsAccount = "pop3s://pop.gmail.com:995/";       

    curl_easy_setopt(curl, CURLOPT_URL, m_popsAccount.c_str());
    curl_easy_setopt(curl, CURLOPT_USE_SSL, CURLUSESSL_ALL); 
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0); 
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0); 

    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1); 

    curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&chunk);

    //some servers needs this validation
    curl_easy_setopt(curl, CURLOPT_USERAGENT, "libcurl-agent/1.0");

    res = curl_easy_perform(curl); 

    if(res != CURLE_OK)
    {
        fprintf(stderr, "curl_easy_perform() failed: %s\n",
        curl_easy_strerror(res));
    }
    else 
    {
        /*
        here is where you can work with the data inside the chunk...
        */  
        printf("%s\n",chunk.memory); //here is the information
        printf("%lu bytes retrieved\n", (long)chunk.size);  
  }

    //se libera la memoria si hay datos
    if(chunk.memory)
        free(chunk.memory);
    /* always cleanup */ 

    curl_global_cleanup();
}


size_t MailServer::WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
{
    size_t realsize = size * nmemb;
    struct MemoryStruct *mem = (struct MemoryStruct *)userp;

    mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
    if(mem->memory == NULL) {
        /* out of memory! */ 
        printf("not enough memory (realloc returned NULL)\n");
        return 0;
    }

    memcpy(&(mem->memory[mem->size]), contents, realsize);
    mem->size += realsize;
    mem->memory[mem->size] = 0;

    return realsize;
}