Add code

diff --git a/README.md b/README.md
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+# Dragonport
+
+Dragonport is a small C library to provide portable implementations of some GNU or Linux only methods that [dragonblocks_alpha](https://github.com/dragonblocks/dragonblocks_alpha) depends on.
+It also includes methods that are technically in the POSIX standard, but are not implemented on some target platforms (or the target platforms only conform with an older standard, like Plan 9 APE).
+Where possible, dragonblocks will use an already existing library, this library is just a collection of code that is part of a bigger project that dragonblocks should not depend on or that is not compatible with dragonblocks without modifications.
+This library is only capable of what dragonblocks needs, and it does not intend to be general purpose.
+
+## Implementations
+* `asprintf.c`: Taken from [libressl-portable](https://github.com/libressl-portable/portable/blob/master/crypto/compat/bsd-asprintf.c).

diff --git a/asprintf.c b/asprintf.c
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+++ b/asprintf.c
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+/*
+ * Copyright (c) 2021 Elias Fleckenstein <eliasfleckenstein@web.de>
+ *
+ * Based on libressl-portable:
+ * Copyright (c) 2004 Darren Tucker.
+ *
+ * Based originally on asprintf.c from OpenBSD:
+ * Copyright (c) 1997 Todd C. Miller <Todd.Miller@courtesan.com>
+ *
+ * Permission to use, copy, modify, and 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 <errno.h>
+#include <limits.h> /* for INT_MAX */
+#include <stdarg.h>
+#include <stdio.h> /* for vsnprintf */
+#include <stdlib.h>
+
+#define INIT_SZ        128
+
+int
+vasprintf(char **str, const char *fmt, va_list ap)
+{
+       int ret;
+       va_list ap2;
+       char *string, *newstr;
+       size_t len;
+
+       if ((string = malloc(INIT_SZ)) == NULL)
+               goto fail;
+
+       va_copy(ap2, ap);
+       ret = vsnprintf(string, INIT_SZ, fmt, ap2);
+       va_end(ap2);
+       if (ret >= 0 && ret < INIT_SZ) { /* succeeded with initial alloc */
+               *str = string;
+       } else if (ret == INT_MAX || ret < 0) { /* Bad length */
+               free(string);
+               goto fail;
+       } else {        /* bigger than initial, realloc allowing for nul */
+               len = (size_t)ret + 1;
+               if ((newstr = realloc(string, len)) == NULL) {
+                       free(string);
+                       goto fail;
+               }
+               va_copy(ap2, ap);
+               ret = vsnprintf(newstr, len, fmt, ap2);
+               va_end(ap2);
+               if (ret < 0 || (size_t)ret >= len) { /* failed with realloc'ed string */
+                       free(newstr);
+                       goto fail;
+               }
+               *str = newstr;
+       }
+       return (ret);
+
+fail:
+       *str = NULL;
+       errno = ENOMEM;
+       return (-1);
+}
+
+int asprintf(char **str, const char *fmt, ...)
+{
+       va_list ap;
+       int ret;
+
+       *str = NULL;
+       va_start(ap, fmt);
+       ret = vasprintf(str, fmt, ap);
+       va_end(ap);
+
+       return ret;
+}

diff --git a/asprintf.h b/asprintf.h
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+++ b/asprintf.h
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+#ifndef _DRAGONPORT_ASPINTF_H_
+#define _DRAGONPORT_ASPINTF_H_
+
+#include <stdarg.h>
+
+int vasprintf(char **str, const char *fmt, va_list ap);
+int asprintf(char **str, const char *fmt, ...);
+
+#endif _DRAGONPORT_ASPINTF_H_