[PATCH v3 05/15] lib/string_helpers: Introduce ESCAPE_NAP to escape non-ASCII and non-printable

Andy Shevchenko
2021-05-04T18:08:33Z

Some users may want to have an ASCII based filter for printable only characters,
provided by conjunction of isascii() and isprint() functions.

Here is the addition of a such.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
include/linux/string_helpers.h | 1 +
lib/string_helpers.c | 20 ++++++++++++++++----
2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
index d6cf6fe10f74..811c6a627620 100644
--- a/include/linux/string_helpers.h
+++ b/include/linux/string_helpers.h
@@ -53,6 +53,7 @@ static inline int string_unescape_any_inplace(char *buf)
#define ESCAPE_ANY_NP (ESCAPE_ANY | ESCAPE_NP)
#define ESCAPE_HEX BIT(5)
#define ESCAPE_NA BIT(6)
+#define ESCAPE_NAP BIT(7)

int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
unsigned int flags, const char *only);
diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index a963404b8c16..ceca5fbbd92c 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -454,9 +454,11 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
*
* 1. The character is not matched to the one from @only string and thus
* must go as-is to the output.
- * 2. The character is matched to the printable or ASCII class, if asked,
+ * 2. The character is matched to the printable and ASCII classes, if asked,
* and in case of match it passes through to the output.
- * 3. The character is checked if it falls into the class given by @flags.
+ * 3. The character is matched to the printable or ASCII class, if asked,
+ * and in case of match it passes through to the output.
+ * 4. The character is checked if it falls into the class given by @flags.
* %ESCAPE_OCTAL and %ESCAPE_HEX are going last since they cover any
* character. Note that they actually can't go together, otherwise
* %ESCAPE_HEX will be ignored.
@@ -489,11 +491,15 @@ static bool escape_hex(unsigned char c, char **dst, char *end)
* '\xHH' - byte with hexadecimal value HH (2 digits)
* %ESCAPE_NA:
* escape only non-ascii characters, checked by isascii()
+ * %ESCAPE_NAP:
+ * escape only non-printable or non-ascii characters
*
- * One notable caveat, the %ESCAPE_NP and %ESCAPE_NA have higher priority
- * than the rest of the flags (%ESCAPE_NP is higher than %ESCAPE_NA).
+ * One notable caveat, the %ESCAPE_NAP, %ESCAPE_NP and %ESCAPE_NA have the
+ * higher priority than the rest of the flags (%ESCAPE_NAP is the highest).
* It doesn't make much sense to use either of them without %ESCAPE_OCTAL
* or %ESCAPE_HEX, because they cover most of the other character classes.
+ * %ESCAPE_NAP can utilize %ESCAPE_SPACE or %ESCAPE_SPECIAL in addition to
+ * the above.
*
* Return:
* The total size of the escaped output that would be generated for
@@ -515,6 +521,8 @@ int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
* Apply rules in the following sequence:
* - the @only string is supplied and does not contain a
* character under question
+ * - the character is printable and ASCII, when @flags has
+ * %ESCAPE_NAP bit set
* - the character is printable, when @flags has
* %ESCAPE_NP bit set
* - the character is ASCII, when @flags has
@@ -528,6 +536,10 @@ int string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
escape_passthrough(c, &p, end))
continue;

+ if (isascii(c) && isprint(c) &&
+ flags & ESCAPE_NAP && escape_passthrough(c, &p, end))
+ continue;
+
if (isprint(c) &&
flags & ESCAPE_NP && escape_passthrough(c, &p, end))
continue;
--
2.30.2