Use libcurl from C to download and install the latest build of Chromium.

uchrome.c

/*
 * uchrome.c

 * Copyright (c) 2013, Jeremiah LaRocco [email protected]

 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.

 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

 */

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <stdbool.h>

#include <curl/curl.h>

struct download {
    size_t size;
    void *data;
};

int progress_function(void *clientp, double dltotal, double dlnow, double ultotal, double ulnow) {
    int num = 50 * (dlnow/dltotal);
    char buffer[51] = {0};
    for (int i=0;i<50; ++i) {
        buffer[i] = (i<num)?'#':' ';
    }
    printf("|%50s| %d of %d\r", buffer, (int)dlnow, (int)dltotal);
    /* printf("dltotal = %f, dlnow = %f, ultotal = %f, ulnow = %f\r", dltotal, dlnow, ultotal, ulnow); */
    return 0;
}

// Called when libcurl receives more data
size_t grab_data(void *buffer, size_t size, size_t nmemb, void *userp) {

    // userp is a pointer to a download structure
    struct download *d = userp;

    // The size of the new data
    size_t thisSize = size * nmemb;

    // If there's nothing, just return.  Should never happen, but check anyway
    if (thisSize == 0) return 0;

    // Allocate new space
    size_t newSize = d->size + thisSize;
    void *nm = realloc(d->data, newSize+1);
    if (NULL == nm) {
        printf("Realloc failed!");
        return 0;
    }

    // Copy everything over
    memcpy(nm + d->size, buffer, thisSize);
    ((char*)nm)[newSize] = '\0';

    // Overwrite the old values with the new
    d->data = nm;
    d->size = newSize;

    // returning anything but (nmemb*size) signals an error to libcurl
    return thisSize;
}

// Download the given url into d
// This seems a bit excessive to download a 6 or 7 character build number
// But can also be used to download a lot more
bool download_to_memory(CURL *curl, char *url, struct download *d) {
    CURLcode res;

    if (curl == NULL) return false;
    // Set the URL
    curl_easy_setopt(curl, CURLOPT_URL, url);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);
    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_function);
    // Set the userp parameter used for grab_data
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, d);

    // Tell libcurl to call grab_data when it has new data
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, grab_data);

    // Do the download
    res = curl_easy_perform(curl);
    if (res != 0) {
        printf("An error occured while downloading \"%s\"!\nres = %d\n", url, res);
        // Hard to say whether this should be freed here or not...
        free(d->data);
        d->data = NULL;
        return false;
    }
    return true;
}

size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
    size_t written = fwrite(ptr, size, nmemb, stream);
    return written;
}

bool download_to_file(CURL *curl, char *url, char *fname) {
    CURLcode res;

    if (curl == NULL) return false;
    // Set the URL
    curl_easy_setopt(curl, CURLOPT_URL, url);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);
    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_function);

    FILE *outf = fopen(fname, "wb");
    // Set the userp parameter used for grab_data
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, outf);

    // Tell libcurl to call write_data when it has new data
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);

    // Do the download
    res = curl_easy_perform(curl);
    if (res != 0) {
        printf("An error occured while downloading \"%s\"!\nres = %d\n", url, res);
        return false;
    }
    fclose(outf);
    return true;
}

void initializeLibs(CURL **curl) {
    // Initialize cUrl
    curl_global_init(CURL_GLOBAL_DEFAULT);
    *curl = curl_easy_init();
}

void cleanupLibs(CURL *curl) {
    curl_easy_cleanup(curl);
    curl_global_cleanup();
}

int main(int argc, char *argv[]) {

    CURL *curl = NULL;
    initializeLibs(&curl);
    
    struct download version = {0};

    printf("Fetching latest Chromium build ID.\n");
    if (!download_to_memory(curl, "http://commondatastorage.googleapis.com/chromium-browser-continuous/Win/LAST_CHANGE", &version)) {
        printf("Could not fetch latest version number!\nAborting\n");
        cleanupLibs(curl);
        exit(1);
    }
    printf("\nDownloading Chromium build: %s\n", version.data);

    char urlBuff[512];
    snprintf(urlBuff, sizeof(urlBuff), "http://commondatastorage.googleapis.com/chromium-browser-continuous/Win/%s/mini_installer.exe", version.data);

    char installerFile[512];
    snprintf(installerFile, sizeof(installerFile), "%s/mini_installer.exe", getenv("TEMP"));

    if (!download_to_file(curl, urlBuff, installerFile)) {
        printf("\nCould not download version %s of Chromium.\n", version.data);
        cleanupLibs(curl);
        exit(1);
    }

    printf("\nInstalling Chromium build %s...\n", version.data);
    system(installerFile);

    printf("Done.\n");

    free(version.data);
    cleanupLibs(curl);
    return 0;
}