env: Add support for callbacks to environment vars

Add support for per-variable callbacks to the "hashtable" functions.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>

!!!fix comment in callback

common/env_attr.c

@@ -0,0 +1,222 @@
+/*
+ * (C) Copyright 2012
+ * Joe Hershberger, National Instruments, joe.hershberger@ni.com
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * 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 2 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+#include <common.h>
+#include <env_attr.h>
+#include <errno.h>
+#include <linux/string.h>
+#include <malloc.h>
+
+/*
+ * Iterate through the whole list calling the callback for each found element.
+ * "attr_list" takes the form:
+ *	attributes = [^,:\s]*
+ *	entry = name[:attributes]
+ *	list = entry[,list]
+ */
+int env_attr_walk(const char *attr_list,
+	int (*callback)(const char *name, const char *attributes))
+{
+	const char *entry, *entry_end;
+	char *name, *attributes;
+
+	if (!attr_list)
+		/* list not found */
+		return 1;
+
+	entry = attr_list;
+	do {
+		char *entry_cpy = NULL;
+
+		entry_end = strchr(entry, ENV_ATTR_LIST_DELIM);
+		/* check if this is the last entry in the list */
+		if (entry_end == NULL) {
+			int entry_len = strlen(entry);
+
+			if (entry_len) {
+				/*
+				 * allocate memory to copy the entry into since
+				 * we will need to inject '\0' chars and squash
+				 * white-space before calling the callback
+				 */
+				entry_cpy = malloc(entry_len + 1);
+				if (entry_cpy)
+					/* copy the rest of the list */
+					strcpy(entry_cpy, entry);
+				else
+					return -ENOMEM;
+			}
+		} else {
+			int entry_len = entry_end - entry;
+
+			if (entry_len) {
+				/*
+				 * allocate memory to copy the entry into since
+				 * we will need to inject '\0' chars and squash
+				 * white-space before calling the callback
+				 */
+				entry_cpy = malloc(entry_len + 1);
+				if (entry_cpy) {
+					/* copy just this entry and null term */
+					strncpy(entry_cpy, entry, entry_len);
+					entry_cpy[entry_len] = '\0';
+				} else
+					return -ENOMEM;
+			}
+		}
+
+		/* check if there is anything to process (e.g. not ",,,") */
+		if (entry_cpy != NULL) {
+			attributes = strchr(entry_cpy, ENV_ATTR_SEP);
+			/* check if there is a ':' */
+			if (attributes != NULL) {
+				/* replace the ':' with '\0' to term name */
+				*attributes++ = '\0';
+				/* remove white-space from attributes */
+				attributes = strim(attributes);
+			}
+			/* remove white-space from name */
+			name = strim(entry_cpy);
+
+			/* only call the callback if there is a name */
+			if (strlen(name) != 0) {
+				int retval = 0;
+
+				retval = callback(name, attributes);
+				if (retval) {
+					free(entry_cpy);
+					return retval;
+				}
+			}
+		}
+
+		free(entry_cpy);
+		entry = entry_end + 1;
+	} while (entry_end != NULL);
+
+	return 0;
+}
+
+/*
+ * Search for the last matching string in another string with the option to
+ * start looking at a certain point (i.e. ignore anything beyond that point).
+ */
+static char *reverse_strstr(const char *searched, const char *search_for,
+	const char *searched_start)
+{
+	char *result = NULL;
+
+	if (*search_for == '\0')
+		return (char *)searched;
+
+	for (;;) {
+		char *match = strstr(searched, search_for);
+
+		/*
+		 * Stop looking if no new match is found or looking past the
+		 * searched_start pointer
+		 */
+		if (match == NULL || (searched_start != NULL &&
+		    match + strlen(search_for) > searched_start))
+			break;
+
+		result = match;
+		searched = match + 1;
+	}
+
+	return result;
+}
+
+/*
+ * Retrieve the attributes string associated with a single name in the list
+ * There is no protection on attributes being too small for the value
+ */
+int env_attr_lookup(const char *attr_list, const char *name, char *attributes)
+{
+	const char *entry = NULL;
+
+	if (!attributes)
+		/* bad parameter */
+		return -1;
+	if (!attr_list)
+		/* list not found */
+		return 1;
+
+	entry = reverse_strstr(attr_list, name, NULL);
+	while (entry != NULL) {
+		const char *prevch = entry - 1;
+		const char *nextch = entry + strlen(name);
+
+		/* Skip spaces */
+		while (*prevch == ' ')
+			prevch--;
+		while (*nextch == ' ')
+			nextch++;
+
+		/* check for an exact match */
+		if ((entry == attr_list ||
+		     *prevch == ENV_ATTR_LIST_DELIM) &&
+		    (*nextch == ENV_ATTR_SEP ||
+		     *nextch == ENV_ATTR_LIST_DELIM ||
+		     *nextch == '\0'))
+			break;
+
+		entry = reverse_strstr(attr_list, name, entry);
+	}
+	if (entry != NULL) {
+		int len;
+
+		/* skip the name */
+		entry += strlen(name);
+		/* skip spaces */
+		while (*entry == ' ')
+			entry++;
+		if (*entry != ENV_ATTR_SEP)
+			len = 0;
+		else {
+			const char *delim;
+			static const char delims[] = {
+				ENV_ATTR_LIST_DELIM, ' ', '\0'};
+
+			/* skip the attr sep */
+			entry += 1;
+			/* skip spaces */
+			while (*entry == ' ')
+				entry++;
+
+			delim = strpbrk(entry, delims);
+			if (delim == NULL)
+				len = strlen(entry);
+			else
+				len = delim - entry;
+			memcpy(attributes, entry, len);
+		}
+		attributes[len] = '\0';
+
+		/* success */
+		return 0;
+	}
+
+	/* not found in list */
+	return 2;
+}