1 files changed, 181 insertions, 0 deletions
diff --git a/src/basic/strbuf.c b/src/basic/strbuf.c
new file mode 100644
index 0000000..0617acc
--- /dev/null
+++ b/src/basic/strbuf.c
@@ -0,0 +1,181 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "alloc-util.h"
+#include "sort-util.h"
+#include "strbuf.h"
+
+/*
+ * Strbuf stores given strings in a single continuous allocated memory
+ * area. Identical strings are de-duplicated and return the same offset
+ * as the first string stored. If the tail of a string already exists
+ * in the buffer, the tail is returned.
+ *
+ * A trie (http://en.wikipedia.org/wiki/Trie) is used to maintain the
+ * information about the stored strings.
+ *
+ * Example of udev rules:
+ *   $ ./udevadm test .
+ *   ...
+ *   read rules file: /usr/lib/udev/rules.d/99-systemd.rules
+ *   rules contain 196608 bytes tokens (16384 * 12 bytes), 39742 bytes strings
+ *   23939 strings (207859 bytes), 20404 de-duplicated (171653 bytes), 3536 trie nodes used
+ *   ...
+ */
+
+struct strbuf* strbuf_new(void) {
+        struct strbuf *str;
+
+        str = new(struct strbuf, 1);
+        if (!str)
+                return NULL;
+        *str = (struct strbuf) {
+                .buf = new0(char, 1),
+                .root = new0(struct strbuf_node, 1),
+                .len = 1,
+                .nodes_count = 1,
+        };
+        if (!str->buf || !str->root) {
+                free(str->buf);
+                free(str->root);
+                return mfree(str);
+        }
+
+        return str;
+}
+
+static struct strbuf_node* strbuf_node_cleanup(struct strbuf_node *node) {
+        size_t i;
+
+        for (i = 0; i < node->children_count; i++)
+                strbuf_node_cleanup(node->children[i].child);
+        free(node->children);
+        return mfree(node);
+}
+
+/* clean up trie data, leave only the string buffer */
+void strbuf_complete(struct strbuf *str) {
+        if (!str)
+                return;
+        if (str->root)
+                str->root = strbuf_node_cleanup(str->root);
+}
+
+/* clean up everything */
+struct strbuf* strbuf_free(struct strbuf *str) {
+        if (!str)
+                return NULL;
+
+        strbuf_complete(str);
+        free(str->buf);
+        return mfree(str);
+}
+
+static int strbuf_children_cmp(const struct strbuf_child_entry *n1,
+                               const struct strbuf_child_entry *n2) {
+        return n1->c - n2->c;
+}
+
+static void bubbleinsert(struct strbuf_node *node,
+                         uint8_t c,
+                         struct strbuf_node *node_child) {
+
+        struct strbuf_child_entry new = {
+                .c = c,
+                .child = node_child,
+        };
+        int left = 0, right = node->children_count;
+
+        while (right > left) {
+                int middle = (right + left) / 2 ;
+                if (strbuf_children_cmp(&node->children[middle], &new) <= 0)
+                        left = middle + 1;
+                else
+                        right = middle;
+        }
+
+        memmove(node->children + left + 1, node->children + left,
+                sizeof(struct strbuf_child_entry) * (node->children_count - left));
+        node->children[left] = new;
+
+        node->children_count++;
+}
+
+/* add string, return the index/offset into the buffer */
+ssize_t strbuf_add_string(struct strbuf *str, const char *s, size_t len) {
+        uint8_t c;
+        char *buf_new;
+        struct strbuf_child_entry *child;
+        struct strbuf_node *node;
+        ssize_t off;
+
+        if (!str->root)
+                return -EINVAL;
+
+        /* search string; start from last character to find possibly matching tails */
+
+        str->in_count++;
+        if (len == 0) {
+                str->dedup_count++;
+                return 0;
+        }
+        str->in_len += len;
+
+        node = str->root;
+        for (size_t depth = 0; depth <= len; depth++) {
+                struct strbuf_child_entry search;
+
+                /* match against current node */
+                off = node->value_off + node->value_len - len;
+                if (depth == len || (node->value_len >= len && memcmp(str->buf + off, s, len) == 0)) {
+                        str->dedup_len += len;
+                        str->dedup_count++;
+                        return off;
+                }
+
+                c = s[len - 1 - depth];
+
+                /* lookup child node */
+                search.c = c;
+                child = typesafe_bsearch(&search, node->children, node->children_count, strbuf_children_cmp);
+                if (!child)
+                        break;
+                node = child->child;
+        }
+
+        /* add new string */
+        buf_new = realloc(str->buf, str->len + len+1);
+        if (!buf_new)
+                return -ENOMEM;
+        str->buf = buf_new;
+        off = str->len;
+        memcpy(str->buf + off, s, len);
+        str->len += len;
+        str->buf[str->len++] = '\0';
+
+        /* new node */
+        _cleanup_free_ struct strbuf_node *node_child = NULL;
+
+        node_child = new(struct strbuf_node, 1);
+        if (!node_child)
+                return -ENOMEM;
+        *node_child = (struct strbuf_node) {
+                .value_off = off,
+                .value_len = len,
+        };
+
+        /* extend array, add new entry, sort for bisection */
+        child = reallocarray(node->children, node->children_count + 1, sizeof(struct strbuf_child_entry));
+        if (!child)
+                return -ENOMEM;
+
+        str->nodes_count++;
+
+        node->children = child;
+        bubbleinsert(node, c, TAKE_PTR(node_child));
+
+        return off;
+}