1 files changed, 106 insertions, 0 deletions
diff --git a/xstring.h b/xstring.h
new file mode 100644
index 00000000..16f9b179
--- /dev/null
+++ b/xstring.h
@@ -0,0 +1,106 @@
+#ifndef STRACE_XSTRING_H
+#define STRACE_XSTRING_H
+
+#include <stdarg.h>
+#include <stdio.h>
+
+#include "error_prints.h"
+#include "gcc_compat.h"
+
+/**
+ * Print to static buffer and die on (really unexpected) errors and overflows.
+ * Shouldn't be used directly; please refer to helper macros xsnprintf and
+ * xsprint instead.
+ *
+ * @param str    String buffer to print into.
+ * @param size   Size of the string buffer in bytes.
+ * @param func   Function name from which this function is called.
+ * @param argstr Stringified arguments (including format argument).
+ * @param format Format string.
+ * @param ...    Format arguments.
+ * @return       Number of characters printed, excluding terminating null byte
+ *               (the same as s(n)printf).
+ */
+static inline int ATTRIBUTE_FORMAT((printf, 5, 6))
+xsnprintf_(char *str, size_t size, const char *func, const char *argstr,
+	   const char *format, ...)
+{
+	int ret;
+	va_list ap;
+
+	va_start(ap, format);
+	ret = vsnprintf(str, size, format, ap);
+	va_end(ap);
+
+	if (ret < 0 || (unsigned int) ret >= size)
+		error_msg_and_die("%s: got unexpected return value %d for "
+				  "snprintf(buf, %zu, %s)",
+				  func, ret, size, argstr);
+
+	return ret;
+}
+
+/**
+ * snprintf that dies on (really unexpected) errors and overflows.
+ *
+ * @param str_  String buffer to print into.
+ * @param size_ Size of the string buffer in bytes.
+ * @param fmt_  Format string.
+ * @param ...   Format arguments.
+ */
+#define xsnprintf(str_, size_, fmt_, ...) \
+	xsnprintf_((str_), (size_), __func__, #fmt_ ", " #__VA_ARGS__, \
+		   (fmt_), __VA_ARGS__)
+
+/**
+ * Print to a character array buffer and die on (really unexpected) errors and
+ * overflows.  Buffer size is obtained with sizeof().
+ *
+ * @param str_  Character array buffer to print into.
+ * @param fmt_  Format string.
+ * @param ...   Format arguments.
+ */
+#define xsprintf(str_, fmt_, ...) \
+	xsnprintf((str_), sizeof(str_) + MUST_BE_ARRAY(str_), (fmt_), \
+		  __VA_ARGS__)
+
+static inline size_t
+get_pos_diff_(char *str, size_t size, char *pos, const char *func,
+	   const char *call)
+{
+	if ((str + size) < str)
+		error_msg_and_die("%s: string size overflow (%p+%zu) in %s",
+				  func, str, size, call);
+
+	if (pos > (str + size))
+		error_msg_and_die("%s: got position (%p) beyond string "
+				  "(%p+%zu) in %s",
+				  func, pos, str, size, call);
+
+	if (pos < str)
+		error_msg_and_die("%s: got position %p before string %p in %s",
+				  func, pos, str, call);
+
+	return pos - str;
+}
+
+/**
+ * Helper function for constructing string in a character array by appending
+ * new formatted parts.  Returns new position.  Fails on error or buffer
+ * overflow, in line with the rest of x* functions.  Obtains buffer size via
+ * sizeof(str_).
+ *
+ * @param str_  Character array buffer to print into.
+ * @param pos_  Current position.
+ * @param fmt_  Format string.
+ * @param ...   Format arguments.
+ * @return      New position.
+ */
+#define xappendstr(str_, pos_, fmt_, ...) \
+	(xsnprintf((pos_), sizeof(str_) + MUST_BE_ARRAY(str_) - \
+		   get_pos_diff_((str_), sizeof(str_), (pos_), __func__, \
+				 "xappendstr(" #str_ ", " #pos_ ", " #fmt_ ", " \
+				 #__VA_ARGS__ ")"), \
+		   (fmt_), ##__VA_ARGS__) + (pos_))
+
+#endif /* !STRACE_XSTRING_H */