问C中的工作curl_multi_perform()示例

EN

#ifndef MULTICURL_HEADER_H
#define MULTICURL_HEADER_H

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


// A data structure used to hold the result of the cURL request.
typedef struct{ 
    size_t size;
    char *memory;
} MemType;

// Function Prototypes
void *SetUpCurlHandle(CURLM *, char *, MemType *);
CURLM *SetUpMultiCurlHandle();
void *PerformMultiCurl(CURLM*);

#endif

#include "multicurl.h"

#define MAX_WAIT_MSECS 5*1000 /* Wait max. 5 seconds */

size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata){// cURL callback function [read in datastream to memory]
    // This prototype is provided by cURL, with an argument at the end for our data structure.
    // This function is repeatedly called by cURL until there is no more data in the data stream; *ptr [it is assumed cURL handles memory management for this pointer].
    size_t realsize = size * nmemb;// The number of bytes in the datastream [there is no NULL char]

    MemType *mem = (MemType *)userdata;
    char *tmp = realloc(mem->memory, mem->size + realsize + 1);// We add 1 for the NULL char.

    if (tmp == NULL){
        printf("Not Enough Memory, realloc returned NULL.\n");
        exit(EXIT_FAILURE);
    }

    mem->memory = tmp;
    memcpy(&(mem->memory[mem->size]), ptr, realsize);// Starting at the last element copy in datastream
    mem->size += realsize;// The actual size is realsize + 1, however realsize gives us the location of the last element.
    mem->memory[mem->size] = 0;// The datastream doesn't include a NULL char, so we zeroize the last element.
    // We overwrite the NULL char {the zeroized element} on the next callback iteration, if any.

    return realsize;// cURL crosschecks the datastream with this return value.
}

void *SetUpCurlHandle(CURLM * mh, char *url, MemType *output){// Take in a multi handle pointer, a URL and a struct pointer address, add an easy handle to the multi handle.
    CURL *hnd = NULL;
    output->memory = malloc(1);              // Initialize the memory component of the structure.
    output->size = 0;                        // Initialize the size component of the structure.

    // Initialize the cURL handle.
    hnd = curl_easy_init();

    if(hnd){

        // Setup the cURL options.
        curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
        curl_easy_setopt(hnd, CURLOPT_URL, url);// Set the request URL
        curl_easy_setopt(hnd, CURLOPT_NOPROGRESS, 1L);
        curl_easy_setopt(hnd, CURLOPT_USERAGENT, "curl/7.76.0");
        curl_easy_setopt(hnd, CURLOPT_MAXREDIRS, 50L);
        curl_easy_setopt(hnd, CURLOPT_HTTP_VERSION, (long)CURL_HTTP_VERSION_2TLS);
        curl_easy_setopt(hnd, CURLOPT_FTP_SKIP_PASV_IP, 1L);
        curl_easy_setopt(hnd, CURLOPT_TCP_KEEPALIVE, 1L);
        curl_easy_setopt(hnd, CURLOPT_WRITEFUNCTION, write_callback);// The callback function to write data to.
        curl_easy_setopt(hnd, CURLOPT_WRITEDATA, (void *)output);// Send the address of the data struct to callback func.
        //curl_easy_setopt(hnd, CURLOPT_VERBOSE, 1);

        curl_multi_add_handle(mh, hnd);
    }else{
        output->memory[0] = '\0';
    }    
    return NULL;// The output struct was passed by reference no need to return anything.
}

CURLM *SetUpMultiCurlHandle(){
    curl_global_init(CURL_GLOBAL_ALL);

    CURLM * mh = curl_multi_init();
    return mh;
}

void *PerformMultiCurl(CURLM * mh)
/*Take in a preset multi handle, request data from the remote server asynchronously {it's assumed cURL is using threads transparent to the calling program}.
   Remove the handles from memory.*/
{
    CURLMsg *msg=NULL;
    CURL *hnd = NULL;
    CURLcode return_code = 0;
    int still_running = 0;
    int msgs_left = 0;

    curl_multi_perform(mh, &still_running); // You could potentially place this function call in an infinite loop from a separate thread and keep adding requests, such that they are conducted immediately and asynchronously with other requests.  I haven't researched this though.
    do {
        int numfds=0;
        int res = curl_multi_wait(mh, NULL, 0, MAX_WAIT_MSECS, &numfds);
        if(res != CURLM_OK) {
            fprintf(stderr, "error: curl_multi_wait() returned %d\n", res);
            return NULL;
        }
        curl_multi_perform(mh, &still_running);
        /* Without this loop the program will proceed to the next statement, most likely before the messages are retrieved from the server.
           The easy handle requests are conducted asynchronously, but one multi handle request is obviously conducted sequentially (can use pthreads to make asynchronous multi requests via this function).*/
    } while(still_running);
    
    /* This portion of the code will clean up and remove the handles from memory, you could change this to make them more persistent */
    while ((msg = curl_multi_info_read(mh, &msgs_left))) {
        if (msg->msg == CURLMSG_DONE) {
            hnd = msg->easy_handle;

            return_code = msg->data.result;
            if(return_code!=CURLE_OK) {
                fprintf(stderr, "CURL error code: %d\n", msg->data.result);
                continue;
            }

            curl_multi_remove_handle(mh, hnd);
            curl_easy_cleanup(hnd);
            hnd = NULL;
        }
        else {
            fprintf(stderr, "error: after curl_multi_info_read(), CURLMsg=%d\n", msg->msg);
        }
    }

    curl_multi_cleanup(mh);
    curl_global_cleanup();
    return NULL;
}

//gcc -o multicurl -lcurl multicurlexample.c multicurl.c
#include "multicurl.h"

int main(){
    CURLM *mult_hnd = SetUpMultiCurlHandle();
    /* I didn't incorporate this function because the use is arbitrary in this case (stack then heap memory vs just stack memory), but here for reference: #include <string.h>
    char *MyUrl1 = strdup("https://api.weather.gov/stations/KBOS/observations/latest"); // strdup() A posix function that incorporates malloc with a strcpy for convenience
    char *MyUrl2 = strdup("https://api.weather.gov/stations/KLGA/observations/latest"); 
    */
    
    char* MyUrl1 = "https://api.weather.gov/stations/KBOS/observations/latest"; //Boston Weather
    char* MyUrl2 = "https://api.weather.gov/stations/KLGA/observations/latest"; //NYC Weather
    MemType MyOutputStruct1;
    MemType MyOutputStruct2;
    

    SetUpCurlHandle( mult_hnd, MyUrl1, &MyOutputStruct1 );
    SetUpCurlHandle( mult_hnd, MyUrl2, &MyOutputStruct2 );

    PerformMultiCurl( mult_hnd );

    printf("Output:\n%s\n", MyOutputStruct1.memory);
    printf("Output:\n%s\n", MyOutputStruct2.memory);

    free( MyOutputStruct1.memory );
    free( MyOutputStruct2.memory );
    /*
    free( MyUrl1 ); // If using strdup()
    free( MyUrl2 );    
    */
    return 0;
}