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diff --git a/lib/dynstr.h b/lib/dynstr.h
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+/*
+ * dynstr.h - dynamic C string library
+ *
+ * This is a library for managing dynamic C strings of bytes (not
+ * multibyte characters).
+ *
+ * Each dynamic string is immutable: once created, it cannot be modified.
+ * To achieve changes, create new strings. This allows an implementation
+ * of the API to make use of copy-on-write techniques to save memory,
+ * and avoid unnecessary copying.
+ *
+ * Dynamic allocation can fail. By default, the routines in this library
+ * return NULL for failures. The caller may use the 
+ * dynstr_set_malloc_error_handler function to set a function that gets
+ * called before NULL is returned. This function can, for example, abort
+ * the program (see dynstr_malloc_error_abort), or use longjmp to jump
+ * some error handling routine.
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef DYNSTR_H
+#define DYNSTR_H
+
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stddef.h>
+
+
+/* Version number of the shared library. */
+#define DYNSTR_VERSION_MAJOR 0
+#define DYNSTR_VERSION_MINOR 0
+#define DYNSTR_VERSION_PATCH 0
+
+
+/* Magic value returned by functions that search for things within
+ * dynamic strings, to indicate 'not found'. */
+#define DYNSTR_NOT_FOUND (~(size_t)0)
+
+
+/* The abstract type for dynamic strings. The type is opaque: the caller
+ * may only operate on it using the functions declared in this header. */
+typedef struct Dynstr Dynstr;
+
+
+/* Initialize or re-initialize the library. This sets all global variables
+ * used internally to their defaults. This is mainly useful for unit
+ * tests. */
+void dynstr_init(void);
+
+/* Set the memory allocator to use, instead of malloc. This is mainly
+ * useful for unit tests. */
+void dynstr_set_malloc(void *(*allocator)(size_t));
+
+/* Get the memory allocator being used. This is mainly useful for unit 
+ * tests. */
+void *(*dynstr_get_malloc(void))(size_t);
+
+/* Type of callback functions for handling malloc failures. */
+typedef void dynstr_error_handler(int error, size_t size, void *oldptr);
+
+/* Get and set malloc error handler. */
+dynstr_error_handler *dynstr_get_malloc_error_handler(void);
+void dynstr_set_malloc_error_handler(dynstr_error_handler *handler);
+
+/* Malloc error handler that aborts the program (using abort, not exit). */
+void dynstr_malloc_error_abort(int error, size_t size, void *oldptr);
+
+/* Malloc error handler that does nothing. This is the default handler.
+ * It causes NULL to be returned. */
+void dynstr_malloc_error_indicate(int error, size_t size, void *oldptr);
+
+
+/* Create a new, empty string. */
+Dynstr *dynstr_new_empty(void);
+
+/* Create a new string, copy contents from a NUL-terminated C string. */
+Dynstr *dynstr_new_from_cstring(const char *cstring);
+
+/* Create a new string, copy contents from an arbitrary memory area. */
+Dynstr *dynstr_new_from_memory(const void *mem, size_t size);
+
+/* Create a new string, use contents from a constant C string. The caller
+ * MUST make sure the contents of the C string do not change while the
+ * dynamic string exists, since the dynamic string will not copy the
+ * contents, but use it directly. */
+Dynstr *dynstr_new_from_constant_cstring(const char *cstring);
+
+/* Create a new string, use contents from an arbitrary memory area. The caller
+ * MUST make sure the contents of the memory area do not change while the
+ * dynamic string exists, since the dynamic string will not copy the
+ * contents, but use it directly. */
+Dynstr *dynstr_new_from_constant_memory(const void *mem, size_t size);
+
+/* Free a dynamic string. */
+void dynstr_free(Dynstr *dynstr);
+
+/* Return length of dynamic string, in bytes. */
+size_t dynstr_len(Dynstr *dynstr);
+
+/* Is the dynamic string empty? In other words, is its length 0? */
+bool dynstr_is_empty(Dynstr *dynstr);
+
+/* Create a new string, copying its contents from an existing one. */
+Dynstr *dynstr_substr(Dynstr *dynstr, size_t offset, size_t size);
+
+/* Create a new string by catenating two existing ones. Return NULL on
+ * failure. */
+Dynstr *dynstr_cat(Dynstr *dynstr1, Dynstr *dynstr2);
+
+/* Create a new string by catenating zero or more existing ones. The
+ * argument list has zero or more pointers to dynamic strings, and
+ * then a NULL pointer. */
+Dynstr *dynstr_cat_many(Dynstr *dynstr, ...);
+
+/* Return value of byte at a given offset. The value is non-negative. If
+ * the offset is past the end of the string, -1 is returned. */
+int dynstr_byte_at(Dynstr *dynstr, size_t offset);
+
+/* Copy contents of a dynamic string into a memory area. If the offset or 
+ * size extends past the end of the string, only as much as actually exists 
+ * in the string is actually copied. The rest of the output memory area will 
+ * be filled with garbage. Return number of bytes actually copied, which may 
+ * be less than requested, and may be zero. */
+size_t dynstr_memcpy(void *mem, Dynstr *dynstr, size_t offset, size_t size);
+
+/* Create a dynamically allocated C string copy of the dynamic string.
+ * This is like strdup. If the dynamic string contains NUL bytes, then
+ * that is the caller's problem. Return pointer to the C string. The
+ * caller is responsible for freeing it. Return NULL on error. */
+char *dynstr_strdup(Dynstr *dynstr);
+
+/* Search for first or last byte with a given value in a string, 
+ * starting at a given offset and until the end of the string. Return offset 
+ * of matching byte, or DYNSTR_NOT_FOUND if not found. Offset is from 
+ * beginning of string. */
+size_t dynstr_first_byte(Dynstr *dynstr, size_t offset, int byte);
+size_t dynstr_last_byte(Dynstr *dynstr, size_t offset, int byte);
+
+/* Search for first or last occurrence of a substring in a string, 
+ * starting at a given offset and until the end of the string. Return 
+ * offset of match, or DYNSTR_NOT_FOUND if not found. Offset is from 
+ * beginning of string. */
+size_t dynstr_first_string(Dynstr *dynstr, size_t offset, Dynstr *pattern);
+size_t dynstr_last_string(Dynstr *dynstr, size_t offset, Dynstr *pattern);
+
+/* Compare two strings, return 0 if they are equal, negative if the
+ * first comes before the second, and positive if second comes first.
+ * Comparisons are done byte-by-byte using unsigned values. */
+int dynstr_cmp(Dynstr *dynstr1, Dynstr *dynstr2);
+
+/* Write a dynamic string into an open file (using stdio). Return value is 
+ * number of bytes written, just like for fwrite(3).
+ * If an error occurs, the size is less than the length of the string,
+ * and errno has been set by fwrite(3). */
+size_t dynstr_fwrite(FILE *file, Dynstr *dynstr);
+
+/* Write a dynamic string into an open Unix file handle. Return value is 
+ * number of bytes written, or -1. */
+ssize_t dynstr_write(int file, Dynstr *dynstr);
+
+/* Read a number of bytes from an open file, either FILE or a Unix file
+ * handle. Return value is the string that was read. The string is empty
+ * to indicate EOF, or NULL for error. */
+Dynstr *dynstr_fread(FILE *file, size_t size);
+Dynstr *dynstr_read(int file, size_t size);
+
+/* Read a line from an open file, either a FILE or a Unix file handle.
+ * The line ends with the first newline byte, or at the end of the file.
+ * If there was an error, NULL is returned, and errno is set, and the
+ * partially read line is discarded. */
+Dynstr *dynstr_freadline(FILE *file);
+Dynstr *dynstr_readline(int file);
+
+#endif