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diff --git a/pam-util/vector.h b/pam-util/vector.h
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+/*
+ * Prototypes for vector handling.
+ *
+ * A vector is a list of strings, with dynamic resizing of the list as new
+ * strings are added and support for various operations on strings (such as
+ * splitting them on delimiters).
+ *
+ * Vectors require list of strings, not arbitrary binary data, and cannot
+ * handle data elements containing nul characters.
+ *
+ * This is based on the util/vector.c library, but that library uses xmalloc
+ * routines to exit the program if memory allocation fails.  This is a
+ * modified version of the vector library that instead returns false on
+ * failure to allocate memory, allowing the caller to do appropriate recovery.
+ *
+ * Only the portions of the vector library used by PAM modules are
+ * implemented.
+ *
+ * The canonical version of this file is maintained in the rra-c-util package,
+ * which can be found at <https://www.eyrie.org/~eagle/software/rra-c-util/>.
+ *
+ * Written by Russ Allbery <eagle@eyrie.org>
+ * Copyright 2010-2011, 2014
+ *     The Board of Trustees of the Leland Stanford Junior University
+ *
+ * Copying and distribution of this file, with or without modification, are
+ * permitted in any medium without royalty provided the copyright notice and
+ * this notice are preserved.  This file is offered as-is, without any
+ * warranty.
+ *
+ * SPDX-License-Identifier: FSFAP
+ */
+
+#ifndef PAM_UTIL_VECTOR_H
+#define PAM_UTIL_VECTOR_H 1
+
+#include <config.h>
+#include <portable/macros.h>
+#include <portable/stdbool.h>
+
+#include <stddef.h>
+
+struct vector {
+    size_t count;
+    size_t allocated;
+    char **strings;
+};
+
+BEGIN_DECLS
+
+/* Default to a hidden visibility for all util functions. */
+#pragma GCC visibility push(hidden)
+
+/* Create a new, empty vector.  Returns NULL on memory allocation failure. */
+struct vector *vector_new(void) __attribute__((__malloc__));
+
+/*
+ * Create a new vector that's a copy of an existing vector.  Returns NULL on
+ * memory allocation failure.
+ */
+struct vector *vector_copy(const struct vector *)
+    __attribute__((__malloc__, __nonnull__));
+
+/*
+ * Add a string to a vector.  Resizes the vector if necessary.  Returns false
+ * on failure to allocate memory.
+ */
+bool vector_add(struct vector *, const char *string)
+    __attribute__((__nonnull__));
+
+/*
+ * Resize the array of strings to hold size entries.  Saves reallocation work
+ * in vector_add if it's known in advance how many entries there will be.
+ * Returns false on failure to allocate memory.
+ */
+bool vector_resize(struct vector *, size_t size) __attribute__((__nonnull__));
+
+/*
+ * Reset the number of elements to zero, freeing all of the strings for a
+ * regular vector, but not freeing the strings array (to cut down on memory
+ * allocations if the vector will be reused).
+ */
+void vector_clear(struct vector *) __attribute__((__nonnull__));
+
+/* Free the vector and all resources allocated for it. */
+void vector_free(struct vector *);
+
+/*
+ * Split functions build a vector from a string.  vector_split_multi splits on
+ * a set of characters.  If the vector argument is NULL, a new vector is
+ * allocated; otherwise, the provided one is reused.  Returns NULL on memory
+ * allocation failure, after which the provided vector may have been modified
+ * to only have partial results.
+ *
+ * Empty strings will yield zero-length vectors.  Adjacent delimiters are
+ * treated as a single delimiter by vector_split_multi.  Any leading or
+ * trailing delimiters are ignored, so this function will never create
+ * zero-length strings (similar to the behavior of strtok).
+ */
+struct vector *vector_split_multi(const char *string, const char *seps,
+                                  struct vector *)
+    __attribute__((__nonnull__(1, 2)));
+
+/*
+ * Exec the given program with the vector as its arguments.  Return behavior
+ * is the same as execv.  Note the argument order is different than the other
+ * vector functions (but the same as execv).  The vector_exec_env variant
+ * calls execve and passes in the environment for the program.
+ */
+int vector_exec(const char *path, struct vector *)
+    __attribute__((__nonnull__));
+int vector_exec_env(const char *path, struct vector *, const char *const env[])
+    __attribute__((__nonnull__));
+
+/* Undo default visibility change. */
+#pragma GCC visibility pop
+
+END_DECLS
+
+#endif /* UTIL_VECTOR_H */