[Patch v8 06/18] util/hex-escape: add a function to check strings unchanged by hex encoding.

[david@tethera.net]

From: David Bremner <bremner@debian.org>

Initial use case is to recognize input tokens for batch tagging that
need quoting.
---
 util/hex-escape.c |    7 +++++++
 util/hex-escape.h |    8 ++++++++
 2 files changed, 15 insertions(+)

diff --git a/util/hex-escape.c b/util/hex-escape.c
index b7e2e07..b601a33 100644
--- a/util/hex-escape.c
+++ b/util/hex-escape.c
@@ -24,6 +24,7 @@
 #include <ctype.h>
 #include "error_util.h"
 #include "hex-escape.h"
+#include "string-util.h"
 
 static const size_t default_buf_size = 1024;
 
@@ -38,6 +39,12 @@ is_output (char c)
     return (strchr (output_charset, c) != NULL);
 }
 
+size_t
+hex_invariant (const char *str, size_t len)
+{
+    return strnspn (str, len, output_charset);
+}
+
 static int
 maybe_realloc (void *ctx, size_t needed, char **out, size_t *out_size)
 {
diff --git a/util/hex-escape.h b/util/hex-escape.h
index 5182042..e7d0b31 100644
--- a/util/hex-escape.h
+++ b/util/hex-escape.h
@@ -38,4 +38,12 @@ hex_decode (void *talloc_ctx, const char *in, char **out,
  */
 hex_status_t
 hex_decode_inplace (char *s);
+
+/*
+ * Calculate the length of the initial segment of str that would not
+ * be changed by hex encoding. Consider at most `len' characters
+ * (bytes) before stopping.
+ */
+size_t
+hex_invariant (const char *str, size_t len);
 #endif
-- 
1.7.10.4