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diff --git a/src/include/k5-buf.h b/src/include/k5-buf.h
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+/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
+/* include/k5-buf.h - k5buf interface declarations */
+/*
+ * Copyright 2008 Massachusetts Institute of Technology.
+ * All Rights Reserved.
+ *
+ * Export of this software from the United States of America may
+ *   require a specific license from the United States Government.
+ *   It is the responsibility of any person or organization contemplating
+ *   export to obtain such a license before exporting.
+ *
+ * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
+ * distribute this software and its documentation for any purpose and
+ * without fee is hereby granted, provided that the above copyright
+ * notice appear in all copies and that both that copyright notice and
+ * this permission notice appear in supporting documentation, and that
+ * the name of M.I.T. not be used in advertising or publicity pertaining
+ * to distribution of the software without specific, written prior
+ * permission.  Furthermore if you modify this software you must label
+ * your software as modified software and not distribute it in such a
+ * fashion that it might be confused with the original M.I.T. software.
+ * M.I.T. makes no representations about the suitability of
+ * this software for any purpose.  It is provided "as is" without express
+ * or implied warranty.
+ */
+
+#ifndef K5_BUF_H
+#define K5_BUF_H
+
+#include <stdarg.h>
+#include <string.h>
+
+/*
+ * The k5buf module is intended to allow multi-step string construction in a
+ * fixed or dynamic buffer without the need to check for a failure at each step
+ * (and without aborting on malloc failure).  If an allocation failure occurs
+ * or the fixed buffer runs out of room, the buffer will be set to an error
+ * state which can be detected with k5_buf_status.  Data in a buffer is
+ * terminated with a zero byte so that it can be used as a C string.
+ *
+ * k5buf structures are usually stack-allocated.  Do not put k5buf structure
+ * pointers into public APIs.  It is okay to reference the data and len fields
+ * of a buffer (they will be NULL/0 if the buffer is in an error state), but do
+ * not change them.
+ */
+
+/* Buffer type values */
+enum k5buftype { K5BUF_ERROR, K5BUF_FIXED, K5BUF_DYNAMIC };
+
+struct k5buf {
+    enum k5buftype buftype;
+    void *data;
+    size_t space;
+    size_t len;
+};
+
+#define EMPTY_K5BUF { K5BUF_ERROR }
+
+/* Initialize a k5buf using a fixed-sized, existing buffer.  SPACE must be
+ * more than zero, or an assertion failure will result. */
+void k5_buf_init_fixed(struct k5buf *buf, char *data, size_t space);
+
+/* Initialize a k5buf using an internally allocated dynamic buffer. */
+void k5_buf_init_dynamic(struct k5buf *buf);
+
+/* Add a C string to BUF. */
+void k5_buf_add(struct k5buf *buf, const char *data);
+
+/* Add a counted series of bytes to BUF. */
+void k5_buf_add_len(struct k5buf *buf, const void *data, size_t len);
+
+/* Add sprintf-style formatted data to BUF. */
+void k5_buf_add_fmt(struct k5buf *buf, const char *fmt, ...)
+#if !defined(__cplusplus) && (__GNUC__ > 2)
+    __attribute__((__format__(__printf__, 2, 3)))
+#endif
+    ;
+
+/* Extend the length of buf by len and return a pointer to the reserved space,
+ * to be filled in by the caller.  Return NULL on error. */
+void *k5_buf_get_space(struct k5buf *buf, size_t len);
+
+/* Truncate BUF.  LEN must be between 0 and the existing buffer
+ * length, or an assertion failure will result. */
+void k5_buf_truncate(struct k5buf *buf, size_t len);
+
+/* Return ENOMEM if buf is in an error state, 0 otherwise. */
+int k5_buf_status(struct k5buf *buf);
+
+/*
+ * Free the storage used in the dynamic buffer BUF.  The caller may choose to
+ * take responsibility for freeing the data pointer instead of using this
+ * function.  If BUF is a fixed buffer, an assertion failure will result.
+ * Freeing a buffer in the error state, a buffer initialized with EMPTY_K5BUF,
+ * or a zeroed k5buf structure is a no-op.
+ */
+void k5_buf_free(struct k5buf *buf);
+
+#endif /* K5_BUF_H */