--- /dev/null
+/*
+ * path-helper.c
+ * Copyright 2018 Peter Jones <pjones@redhat.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of the
+ * License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#include "efivar.h"
+
+static bool
+cinpat(const char c, const char *pat)
+{
+ for (unsigned int i = 0; pat[i]; i++)
+ if (pat[i] == c)
+ return true;
+ return false;
+}
+
+static unsigned int
+strxcspn(const char *s, const char *pattern)
+{
+ unsigned int i;
+ for (i = 0; s[i]; i++) {
+ if (!cinpat(s[i], pattern))
+ break;
+ }
+ return i;
+}
+
+struct span {
+ const char *pos;
+ size_t len;
+};
+
+/*
+ * count how many parts of a path there are, with some caveats:
+ * a leading / is one because it's a directory, but all other slashes are
+ * treated as separators, so i.e.:
+ * 1: /
+ * 2: /foo foo/bar foo/bar/
+ * 3: /foo/bar /foo/bar/ foo/bar/baz
+ *
+ * the usage model here is 1 pass to count, one allocation, one pass to
+ * separate.
+ */
+unsigned int HIDDEN
+count_spans(const char *str, const char *reject, unsigned int *chars)
+{
+ unsigned int s = 0, c = 0, pos = 0;
+
+ if (str[0] == '/') {
+ s += 1;
+ c += 2;
+ pos += 1;
+ }
+
+ while (str[pos]) {
+ unsigned int n;
+
+ n = strcspn(str + pos, reject);
+ if (n) {
+ s += 1;
+ c += n + 1;
+ pos += n;
+ }
+
+ pos += strxcspn(str + pos, reject);
+ }
+
+ if (chars)
+ *chars = c;
+ return s;
+}
+
+void HIDDEN
+fill_spans(const char *str, const char *reject, void *spanbuf)
+{
+ struct span *spans = (struct span *)spanbuf;
+ struct span *span = spans;
+ unsigned int pos = 0;
+
+ if (str[0] == '/') {
+ span->pos = str;
+ span->len = 1;
+ span++;
+ pos += 1;
+ }
+
+ while (str[pos]) {
+ unsigned int n;
+
+ n = strcspn(str + pos, reject);
+ if (n) {
+ span->pos = str + pos;
+ span->len = n;
+ span++;
+ pos += n;
+ }
+
+ pos += strxcspn(str + pos, reject);
+ }
+ span->pos = NULL;
+ span->len = 0;
+}
+
+#define split_spans(str, reject) \
+ ({ \
+ struct span *ret_ = NULL; \
+ unsigned int s_, c_; \
+ \
+ s_ = count_spans(str, "/", &c_); \
+ if (s_) { \
+ ret_ = alloca(sizeof(struct span[s_+1])); \
+ if (ret_) \
+ fill_spans(str, reject, ret_); \
+ } else { \
+ errno = 0; \
+ } \
+ ret_; \
+ })
+
+int HIDDEN
+find_path_segment(const char *path, int segment, const char **pos, size_t *len)
+{
+ struct span *span, *last;
+ int nspans = 0;
+
+ if (!pos || !len) {
+ errno = EINVAL;
+ return -1;
+ }
+
+ span = split_spans(path, "/");
+ if (!span) {
+ if (errno)
+ return -1;
+ *pos = NULL;
+ *len = 0;
+ return 0;
+ }
+
+ for (last = span; last->pos; last++)
+ nspans += 1;
+
+ if (segment < 0)
+ segment = nspans + segment;
+
+ if (nspans < 1 || segment < 0 || segment >= nspans) {
+ errno = ENOENT;
+ return -1;
+ }
+
+ for (int i = 0; i < segment; i++)
+ span++;
+
+ *pos = span->pos;
+ *len = span->len;
+ return 0;
+}
+
+// vim:fenc=utf-8:tw=75:et
--- /dev/null
+/*
+ * path-helper.h
+ * Copyright 2018 Peter Jones <pjones@redhat.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of the
+ * License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see
+ * <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef PATH_HELPER_H_
+#define PATH_HELPER_H_
+
+void HIDDEN fill_spans(const char *str, const char *reject, void *spanbuf);
+unsigned int HIDDEN count_spans(const char *str, const char *reject, unsigned int *chars);
+int HIDDEN find_path_segment(const char *path, int segment, const char **pos, size_t *len);
+
+#define pathseg(path, seg) \
+ ({ \
+ const char *pos_ = NULL; \
+ char *ret_ = NULL; \
+ size_t len_ = 0; \
+ int rc_; \
+ \
+ rc_ = find_path_segment(path, seg, &pos_, &len_); \
+ if (rc_ >= 0) { \
+ ret_ = alloca(len_ + 1); \
+ if (ret_) { \
+ memcpy(ret_, pos_, len_); \
+ ret_[len_] = '\0'; \
+ } \
+ } \
+ ret_; \
+ })
+
+
+
+#endif /* !PATH_HELPER_H_ */
+// vim:fenc=utf-8:tw=75:et
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