下载接口 POST

/* 接口: download
 * 依赖: libcurl + OpenSSL
 * 编译: gcc gn_demo.c -o gn_demo -lcurl -lcrypto
 * 签名: ksort 字典序, 排除 s/sign/safe_code/_ 前缀与空值, MD5(拼接+密钥) 大写
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <curl/curl.h>
#include <openssl/md5.h>

typedef struct { const char *k; const char *v; } kv_t;

static int kv_cmp(const void *a, const void *b) {
    return strcmp(((const kv_t *)a)->k, ((const kv_t *)b)->k);
}

static int should_skip_sign_key(const char *k) {
    if (!k) return 1;
    if (strcmp(k, "s") == 0 || strcmp(k, "sign") == 0 || strcmp(k, "safe_code") == 0) return 1;
    if (k[0] == '_') return 1;
    return 0;
}

static void md5_upper_hex(const char *src, char out[33]) {
    unsigned char dig[MD5_DIGEST_LENGTH];
    MD5((const unsigned char *)src, strlen(src), dig);
    for (int i = 0; i < MD5_DIGEST_LENGTH; i++) sprintf(out + i * 2, "%02X", dig[i]);
    out[32] = '\0';
}

struct mem_buf { char *data; size_t len; };
static size_t write_cb(char *ptr, size_t size, size_t nmemb, void *userdata) {
    size_t n = size * nmemb;
    struct mem_buf *m = (struct mem_buf *)userdata;
    char *p = (char *)realloc(m->data, m->len + n + 1);
    if (!p) return 0;
    m->data = p;
    memcpy(m->data + m->len, ptr, n);
    m->len += n;
    m->data[m->len] = '\0';
    return n;
}

int main(void) {
    const char *api_url  = "https://gnyanzheng.cn/api/download/YOUR_FILE_ID";
    const char *sign_key = "YOUR_SIGN_KEY";
    char tbuf[32];
    snprintf(tbuf, sizeof(tbuf), "%ld", (long)time(NULL));

    kv_t items[] = {
    {"app", "YOUR_APP_ID"},
    {"t", tbuf},
    };
    size_t n = sizeof(items) / sizeof(items[0]);
    qsort(items, n, sizeof(kv_t), kv_cmp);

    /* 拼签名串 */
    char sign_src[4096];
    sign_src[0] = '\0';
    for (size_t i = 0; i < n; i++) {
        if (should_skip_sign_key(items[i].k)) continue;
        if (!items[i].v || items[i].v[0] == '\0') continue;
        if (sign_src[0]) strncat(sign_src, "&", sizeof(sign_src) - strlen(sign_src) - 1);
        strncat(sign_src, items[i].k, sizeof(sign_src) - strlen(sign_src) - 1);
        strncat(sign_src, "=", sizeof(sign_src) - strlen(sign_src) - 1);
        strncat(sign_src, items[i].v, sizeof(sign_src) - strlen(sign_src) - 1);
    }
    strncat(sign_src, sign_key, sizeof(sign_src) - strlen(sign_src) - 1);
    char sign_hex[33];
    md5_upper_hex(sign_src, sign_hex);

    /* 组 form body */
    char body[8192];
    body[0] = '\0';
    CURL *curl = curl_easy_init();
    if (!curl) return 1;
    for (size_t i = 0; i < n; i++) {
        char *ek = curl_easy_escape(curl, items[i].k, 0);
        char *ev = curl_easy_escape(curl, items[i].v ? items[i].v : "", 0);
        if (body[0]) strncat(body, "&", sizeof(body) - strlen(body) - 1);
        strncat(body, ek, sizeof(body) - strlen(body) - 1);
        strncat(body, "=", sizeof(body) - strlen(body) - 1);
        strncat(body, ev, sizeof(body) - strlen(body) - 1);
        curl_free(ek); curl_free(ev);
    }
    {
        char *ek = curl_easy_escape(curl, "s", 0);
        char *ev = curl_easy_escape(curl, sign_hex, 0);
        strncat(body, "&", sizeof(body) - strlen(body) - 1);
        strncat(body, ek, sizeof(body) - strlen(body) - 1);
        strncat(body, "=", sizeof(body) - strlen(body) - 1);
        strncat(body, ev, sizeof(body) - strlen(body) - 1);
        curl_free(ek); curl_free(ev);
    }

    struct mem_buf resp = {0};
    curl_easy_setopt(curl, CURLOPT_URL, api_url);
    curl_easy_setopt(curl, CURLOPT_POST, 1L);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, body);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_cb);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &resp);
    curl_easy_setopt(curl, CURLOPT_TIMEOUT, 30L);
    CURLcode rc = curl_easy_perform(curl);
    if (rc != CURLE_OK) {
        fprintf(stderr, "curl error: %s\n", curl_easy_strerror(rc));
    } else {
        printf("%s\n", resp.data ? resp.data : "");
    }
    free(resp.data);
    curl_easy_cleanup(curl);
    return 0;
}