diff --git a/c/buf.c b/c/buf.c
new file mode 100644
index 0000000..d278db1
--- /dev/null
+++ b/c/buf.c
@@ -0,0 +1,50 @@
+// Copyright 2019 Lassi Kortela
+// SPDX-License-Identifier: BSD-3-Clause
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "buf.h"
+
+struct buf *buf_new(void) { return calloc(1, sizeof(struct buf)); }
+
+char *buf_resb(struct buf *buf, size_t nbyte)
+{
+    char *place;
+
+    while (buf->cap - buf->fill < nbyte) {
+        if (!(buf->cap *= 2)) {
+            buf->cap = 64;
+        }
+    }
+    if (!(buf->bytes = realloc(buf->bytes, buf->cap))) {
+        exit(1);
+    }
+    place = buf->bytes + buf->fill;
+    buf->fill += nbyte;
+    return place;
+}
+
+void buf_putc(struct buf *buf, int c) { buf_resb(buf, 1)[0] = c; }
+
+void buf_putb(struct buf *buf, const void *bytes, size_t nbyte)
+{
+    memcpy(buf_resb(buf, nbyte), bytes, nbyte);
+}
+
+void buf_puts(struct buf *buf, const char *s) { buf_putb(buf, s, strlen(s)); }
+
+void buf_putu(struct buf *buf, uint64_t u)
+{
+    char tmp[24];
+
+    snprintf(tmp, sizeof(tmp), "%llu", u);
+    buf_puts(buf, tmp);
+}
+
+void buf_free(struct buf *buf)
+{
+    free(buf->bytes);
+    free(buf);
+}
diff --git a/c/buf.h b/c/buf.h
new file mode 100644
index 0000000..f870eb6
--- /dev/null
+++ b/c/buf.h
@@ -0,0 +1,16 @@
+// Copyright 2019 Lassi Kortela
+// SPDX-License-Identifier: BSD-3-Clause
+
+struct buf {
+    size_t cap;
+    size_t fill;
+    char *bytes;
+};
+
+struct buf *buf_new(void);
+char *buf_resb(struct buf *buf, size_t nbyte);
+void buf_putc(struct buf *buf, int c);
+void buf_putb(struct buf *buf, const void *bytes, size_t nbyte);
+void buf_puts(struct buf *buf, const char *s);
+void buf_putu(struct buf *buf, uint64_t u);
+void buf_free(struct buf *buf);