add string utility to join strings

utils/errors.h

@@ -73,7 +73,9 @@ typedef enum {
 
 	NSERROR_FRAME_DEPTH,            /**< Exceeded frame depth */
 
-	NSERROR_PERMISSION             /**< Permission error */
+	NSERROR_PERMISSION,             /**< Permission error */
+
+	NSERROR_NOSPACE                 /**< Insufficient space */
 } nserror;
 
 #endif

utils/utils.c

@@ -160,6 +160,85 @@ bool is_dir(const char *path)
 	return S_ISDIR(s.st_mode) ? true : false;
 }
 
+/* exported interface documented in utils/utils.h */
+nserror vsnstrjoin(char **str, size_t *size, char sep, size_t nelm, va_list ap)
+{
+	const char *elm[16];
+	size_t elm_len[16];
+	size_t elm_idx;
+	char *fname;
+	size_t fname_len = 0;
+	char *curp;
+
+	/* check the parameters are all sensible */
+	if ((nelm == 0) || (nelm > 16)) {
+		return NSERROR_BAD_PARAMETER;
+	}
+	if ((*str != NULL) && (size == NULL)) {
+		/* if the caller is providing the buffer they must say
+		 * how much space is available.
+		 */
+		return NSERROR_BAD_PARAMETER;
+	}
+
+	/* calculate how much storage we need for the complete path
+	 * with all the elements.
+	 */
+	for (elm_idx = 0; elm_idx < nelm; elm_idx++) {
+		elm[elm_idx] = va_arg(ap, const char *);
+		elm_len[elm_idx] = strlen(elm[elm_idx]);
+		fname_len += elm_len[elm_idx];
+	}
+	fname_len += nelm; /* allow for separators and terminator */
+
+	/* ensure there is enough space */
+	fname = *str;
+	if (fname != NULL) {
+		if (fname_len > *size) {
+			return NSERROR_NOSPACE;
+		}
+	} else {
+		fname = malloc(fname_len);
+		if (fname == NULL) {
+			return NSERROR_NOMEM;
+		}
+	}
+
+	/* copy the elements in with apropriate separator */
+	curp = fname;
+	for (elm_idx = 0; elm_idx < nelm; elm_idx++) {
+		memmove(curp, elm[elm_idx], elm_len[elm_idx]);
+		curp += elm_len[elm_idx];
+		/* ensure string are separated */
+		if (curp[-1] != sep) {
+			*curp = sep;
+			curp++;
+		}
+	}
+	curp[-1] = 0; /* NULL terminate */
+
+	assert((curp - fname) <= (int)fname_len);
+
+	*str = fname;
+	if (size != NULL) {
+		*size = fname_len;
+	}
+
+	return NSERROR_OK;
+}
+
+/* exported interface documented in utils/utils.h */
+nserror snstrjoin(char **str, size_t *size, char sep, size_t nelm, ...)
+{
+	va_list ap;
+	nserror ret;
+
+	va_start(ap, nelm);
+	ret = vsnstrjoin(str, size, sep, nelm, ap);
+	va_end(ap);
+
+	return ret;
+}
 
 /**
  * Compile a regular expression, handling errors.

utils/utils.h

@@ -28,6 +28,9 @@
 #include <sys/time.h>
 #include <regex.h>
 #include <assert.h>
+#include <stdarg.h>
+
+#include "utils/errors.h"
 
 struct dirent;
 
@@ -145,6 +148,49 @@ char *human_friendly_bytesize(unsigned long bytesize);
 const char *rfc1123_date(time_t t);
 unsigned int wallclock(void);
 
+/**
+ * Generate a string from one or more component elemnts separated with
+ * a single value.
+ *
+ * This is similar in intent to the perl join function creating a
+ * single delimited string from an array of several.
+ *
+ * @note If a string is allocated it must be freed by the caller.
+ *
+ * @param[in,out] str pointer to string pointer if this is NULL enough
+ *                    storage will be allocated for the complete path.
+ * @param[in,out] size The size of the space available if \a str not
+ *                     NULL on input and if not NULL set to the total
+ *                     output length on output.
+ * @param[in] sep The character to separete the elemnts with.
+ * @param[in] nemb The number of elements up to a maximum of 16.
+ * @param[in] ap The elements of the path as string pointers.
+ * @return NSERROR_OK and the complete path is written to str or error
+ *         code on faliure.
+ */
+nserror vsnstrjoin(char **str, size_t *size, char sep, size_t nelm, va_list ap);
+
+/**
+ * Generate a string from one or more component elemnts separated with
+ * a single value.
+ *
+ * This is similar in intent to the perl join function creating a
+ * single delimited string from an array of several.
+ *
+ * @note If a string is allocated it must be freed by the caller.
+ *
+ * @param[in,out] str pointer to string pointer if this is NULL enough
+ *                    storage will be allocated for the complete path.
+ * @param[in,out] size The size of the space available if \a str not
+ *                     NULL on input and if not NULL set to the total
+ *                     output length on output.
+ * @param[in] sep The character to separete the elemnts with.
+ * @param[in] nemb The number of elements up to a maximum of 16.
+ * @param[in] ... The elements of the path as string pointers.
+ * @return NSERROR_OK and the complete path is written to str or error
+ *         code on faliure.
+ */
+nserror snstrjoin(char **str, size_t *size, char sep, size_t nelm, ...);
 
 /**
  * Comparison function for sorting directories.