grab font and use it in one go

foo.c

/* gcc -o foo foo.c -D_GNU_SOURCE -std=c11 -pedantic -Wall $(pkg-config --cflags --libs freetype2 xft x11 libcurl) */

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <curl/curl.h>
#include <X11/Xft/Xft.h>

static void die(const char *msg) {
    fprintf(stderr, "%s", msg);
    exit(1);
}

static void win() {
    Display *dpy;
    int scr;
    Visual *visual;
    Colormap cmap;
    Window win;
    XftFont *font;
    const char *fontname = "Hanalei:size=11:antialias=true";
    XftDraw *draw;
    XftColor color;

    /* Initialization. */
    dpy = XOpenDisplay(NULL);
    if (!dpy) {
        die("cannot open X11 display\n");
    }
    scr = DefaultScreen(dpy);
    visual = DefaultVisual(dpy, scr);
    cmap = DefaultColormap(dpy, scr);

    /* Window. */
    win = XCreateSimpleWindow(dpy, RootWindow(dpy, scr), 100, 100, 200, 100, 1, BlackPixel(dpy, scr), WhitePixel(dpy, scr));
    XSelectInput(dpy, win, ExposureMask | KeyPressMask);
    XMapWindow(dpy, win);

    /* Xft. */
    font = XftFontOpenName(dpy, scr, fontname);
    if (!font) {
        die("cannot load font\n");
    }
    if (!XftColorAllocName(dpy, visual, cmap, "#0000ee", &color)) {
        die("cannot allocate xft color\n");
    }
    draw = XftDrawCreate(dpy, win, visual, cmap);

    while(1) {
        XEvent ev;

        XNextEvent(dpy, &ev);
        if (ev.type == Expose) {
            XftDrawStringUtf8(draw, &color, font, 50, 50, (const FcChar8 *)"Hello Xft!", 10);
        }
        else if (ev.type == KeyPress) {
            break;
        }
    }

    /* Cleanup. Not necessary, only for the sake of completeness. */
    XftColorFree(dpy, visual, cmap, &color);
    XftDrawDestroy(draw);
    XDestroyWindow(dpy, win);
    XCloseDisplay(dpy);
}

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

static void grab(FILE* fontfile) {
    CURL *curl_handle;
    CURLcode res;

    curl_handle = curl_easy_init();
    if (!curl_handle) {
        die("cannot init curl");
    }
    curl_easy_setopt(curl_handle, CURLOPT_URL, "https://r.chipaca.com/hanalei.ttf");
    curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, write_data);
    curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, fontfile);
    /* Perform the request, res will get the return code */ 
    res = curl_easy_perform(curl_handle);
    /* Check for errors */ 
    if(res != CURLE_OK) {
        die(curl_easy_strerror(res));
    }

    /* always cleanup */ 
    curl_easy_cleanup(curl_handle);
    curl_global_cleanup();
}

void ensurefontfile() {
    /*
      This should try, in order, $HOME/.font, and otherwise
      ${XDG_DATA_HOME:-$HOME/.local/share}/fonts/, and if neither
      exist, create the latter.
     */

    /* getting $HOME instead of getent is me being lazy */
    const char *home = getenv("HOME");
    if (!home) {
        die("cannot get $HOME");
    }
    // XXX: check home exists?

    char path[1024]; /* sue me */

    // XXX: check these return values
    stpcpy(stpcpy(path, home), "/.fonts");

    int dfd = open(path, O_RDONLY|O_DIRECTORY);
    if (dfd<0) {
        // TODO: check for ${XDG_DATA_HOME:-$HOME/.local/share/fonts}
        die("can't open ~/.fonts, and can't be arsed to look in XDG data dir");
    }

    int fd = openat(dfd, "hanalei.ttf", O_WRONLY|O_CREAT|O_EXCL, 0664);
    if (fd == -1) {
        if (errno == EEXIST) {
            return;
        }
        die("cannot open font file location for download");
    }
    FILE *f = fdopen(fd, "wb");
    if (!f) {
        die("cannot _really_open font file (what)");
    }
    grab(f);

    fclose(f);
    close(dfd);
}

int main() {
    ensurefontfile();
    win();
    return 0;
}