Start to sketch APIs for subsetting

util/hb-subset.cc

diff --git a/util/hb-subset.cc b/util/hb-subset.cc
new file mode 100644
index 0000000..ad7ceb1
--- /dev/null
+++ b/util/hb-subset.cc
@@ -0,0 +1,61 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "hb-private.hh"
+#include "hb-blob.h"
+
+int
+main (int argc, char **argv)
+{
+  int exit_code = 0;
+  int fd = open("/tmp/Lobster-Regular.ttf", O_RDONLY);
+  if (fd == -1) {
+    perror("Unable to open file");
+    exit(1);
+  }
+
+  void *mapped_file = MAP_FAILED;
+  char *raw_font = nullptr;
+
+  struct stat stat;
+  if (fstat(fd, &stat) != -1) {
+    printf("File is %zu bytes\n", stat.st_size);
+
+    void *mapped_file = mmap(NULL, stat.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
+    if (mapped_file != MAP_FAILED) {
+      raw_font = static_cast<char*>(mapped_file);
+    } else {
+      perror("Failed to map file");
+    }
+  } else {
+    perror("Unable to fstat");
+  }
+
+  if (raw_font) {
+      printf("Mapped file\n");      
+      for (int i = 0; i < 4; i++) {
+        printf("%02x", *(raw_font + i));
+      }
+      printf("\n");
+
+      hb_blob_t *font_blob = hb_blob_create(raw_font, stat.st_size, HB_MEMORY_MODE_READONLY, nullptr, nullptr);
+  }
+
+  if (mapped_file != MAP_FAILED) {
+    if (munmap(mapped_file, stat.st_size) == -1) {
+      perror("Unable to unmap file");
+      exit_code = 1;
+    }
+  }
+
+  if (close(fd) == -1) {
+    perror("Unable to close file");
+    exit_code = 1;
+  }
+  return exit_code;
+}