random: add getrandom fallback for android

Signed-off-by: William Casarin <[email protected]>

src/random.h

@@ -42,6 +42,26 @@ static int fill_random(unsigned char* data, size_t size) {
     } else {
         return 1;
     }
+#elif defined(__ANDROID__)
+    int fd = open("/dev/urandom", O_RDONLY);
+    if (fd < 0) {
+        return 0; // Failed to open /dev/urandom
+    }
+    ssize_t read_bytes = 0;
+    while (size > 0) {
+        read_bytes = read(fd, data, size);
+        if (read_bytes <= 0) {
+            if (errno == EINTR) {
+                continue; // If interrupted by signal, try again
+            }
+            close(fd);
+            return 0; // Failed to read
+        }
+        data += read_bytes;
+        size -= read_bytes;
+    }
+    close(fd);
+    return 1;
 #elif defined(__linux__) || defined(__FreeBSD__)
     /* If `getrandom(2)` is not available you should fallback to /dev/urandom */
     ssize_t res = getrandom(data, size, 0);