curl使用自定义函数追加slist

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

struct string {
    char *ptr;
    size_t len;
};

void init_string(struct string *s) {
    s->len = 0;
    s->ptr = malloc(s->len+1);
    if (s->ptr == NULL) {
        fprintf(stderr, "malloc() failed\n");
        exit(EXIT_FAILURE);
    }
    s->ptr[0] = '\0';
}

size_t writefunc(void *ptr, size_t size, size_t nmemb, struct string *s) {
    size_t new_len = s->len + size*nmemb;
    s->ptr = realloc(s->ptr, new_len+1);
    if (s->ptr == NULL) {
        fprintf(stderr, "realloc() failed\n");
        exit(EXIT_FAILURE);
    }
    memcpy(s->ptr+s->len, ptr, size*nmemb);
    s->ptr[new_len] = '\0';
    s->len = new_len;

    return size*nmemb;
}

int append_header_callback(char *buffer, size_t size, size_t nitems, void *userdata) {
    struct string *slist = (struct string *)userdata;
    init_string(slist);
    slist->ptr = strdup(buffer);
    return (int)(size * nitems);
}

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

    struct string header;
    init_string(&header);

    curl_global_init(CURL_GLOBAL_DEFAULT);

    curl = curl_easy_init();
    if(curl) {
        curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

        // 使用自定义函数追加请求头
        curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, append_header_callback);
        curl_easy_setopt(curl, CURLOPT_HEADERDATA, &header);

        // 追加自定义请求头
        struct curl_slist *headers = NULL;
        headers = curl_slist_append(headers, header.ptr);
        headers = curl_slist_append(headers, "Custom-Header: Value");
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);

        res = curl_easy_perform(curl);
        if(res != CURLE_OK)
            fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));

        curl_easy_cleanup(curl);
        curl_slist_free_all(headers);
    }

    curl_global_cleanup();
    free(header.ptr);

    return 0;
}

gcc -o curl_example curl_example.c -lcurl

./curl_example