[PATCH v4 2/3] lib/string_helpers.c: Refactor string_escape_mem

[Rasmus Villemoes]

When printf is given the format specifier %pE, it needs a way of
obtaining the total output size that would be generated if the buffer
was large enough, and string_escape_mem doesn't easily provide
that. This is a refactorization of string_escape_mem in preparation of
changing its external API to provide that information.

The somewhat ugly early returns and subsequent seemingly redundant
conditionals are to make the following patch touch as little as
possible in string_helpers.c while still preserving the current
behaviour of never outputting partial escape sequences. That behaviour
must also change for %pE to work as one expects from every other
printf specifier.

Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
 lib/string_helpers.c | 208 ++++++++++++++++++++++++++-------------------------
 1 file changed, 105 insertions(+), 103 deletions(-)

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 8f8c4417f228..9c48ddad0f0d 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -239,29 +239,21 @@ int string_unescape(char *src, char *dst, size_t size, unsigned int flags)
 }
 EXPORT_SYMBOL(string_unescape);
 
-static int escape_passthrough(unsigned char c, char **dst, size_t *osz)
+static bool escape_passthrough(unsigned char c, char **dst, char *end)
 {
 	char *out = *dst;
 
-	if (*osz < 1)
-		return -ENOMEM;
-
-	*out++ = c;
-
-	*dst = out;
-	*osz -= 1;
-
-	return 1;
+	if (out < end)
+		*out = c;
+	*dst = out + 1;
+	return true;
 }
 
-static int escape_space(unsigned char c, char **dst, size_t *osz)
+static bool escape_space(unsigned char c, char **dst, char *end)
 {
 	char *out = *dst;
 	unsigned char to;
 
-	if (*osz < 2)
-		return -ENOMEM;
-
 	switch (c) {
 	case '\n':
 		to = 'n';
@@ -279,26 +271,30 @@ static int escape_space(unsigned char c, char **dst, size_t *osz)
 		to = 'f';
 		break;
 	default:
-		return 0;
+		return false;
 	}
 
-	*out++ = '\\';
-	*out++ = to;
+	if (out + 2 > end) {
+		*dst = out + 2;
+		return true;
+	}
 
-	*dst = out;
-	*osz -= 2;
+	if (out < end)
+		*out = '\\';
+	++out;
+	if (out < end)
+		*out = to;
+	++out;
 
-	return 1;
+	*dst = out;
+	return true;
 }
 
-static int escape_special(unsigned char c, char **dst, size_t *osz)
+static bool escape_special(unsigned char c, char **dst, char *end)
 {
 	char *out = *dst;
 	unsigned char to;
 
-	if (*osz < 2)
-		return -ENOMEM;
-
 	switch (c) {
 	case '\\':
 		to = '\\';
@@ -310,71 +306,98 @@ static int escape_special(unsigned char c, char **dst, size_t *osz)
 		to = 'e';
 		break;
 	default:
-		return 0;
+		return false;
 	}
 
-	*out++ = '\\';
-	*out++ = to;
+	if (out + 2 > end) {
+		*dst = out + 2;
+		return true;
+	}
 
-	*dst = out;
-	*osz -= 2;
+	if (out < end)
+		*out = '\\';
+	++out;
+	if (out < end)
+		*out = to;
+	++out;
 
-	return 1;
+	*dst = out;
+	return true;
 }
 
-static int escape_null(unsigned char c, char **dst, size_t *osz)
+static bool escape_null(unsigned char c, char **dst, char *end)
 {
 	char *out = *dst;
 
-	if (*osz < 2)
-		return -ENOMEM;
-
 	if (c)
-		return 0;
+		return false;
 
-	*out++ = '\\';
-	*out++ = '0';
+	if (out + 2 > end) {
+		*dst = out + 2;
+		return true;
+	}
 
-	*dst = out;
-	*osz -= 2;
+	if (out < end)
+		*out = '\\';
+	++out;
+	if (out < end)
+		*out = '0';
+	++out;
 
-	return 1;
+	*dst = out;
+	return true;
 }
 
-static int escape_octal(unsigned char c, char **dst, size_t *osz)
+static bool escape_octal(unsigned char c, char **dst, char *end)
 {
 	char *out = *dst;
 
-	if (*osz < 4)
-		return -ENOMEM;
+	if (out + 4 > end) {
+		*dst = out + 4;
+		return true;
+	}
 
-	*out++ = '\\';
-	*out++ = ((c >> 6) & 0x07) + '0';
-	*out++ = ((c >> 3) & 0x07) + '0';
-	*out++ = ((c >> 0) & 0x07) + '0';
+	if (out < end)
+		*out = '\\';
+	++out;
+	if (out < end)
+		*out = ((c >> 6) & 0x07) + '0';
+	++out;
+	if (out < end)
+		*out = ((c >> 3) & 0x07) + '0';
+	++out;
+	if (out < end)
+		*out = ((c >> 0) & 0x07) + '0';
+	++out;
 
 	*dst = out;
-	*osz -= 4;
-
-	return 1;
+	return true;
 }
 
-static int escape_hex(unsigned char c, char **dst, size_t *osz)
+static bool escape_hex(unsigned char c, char **dst, char *end)
 {
 	char *out = *dst;
 
-	if (*osz < 4)
-		return -ENOMEM;
+	if (out + 4 > end) {
+		*dst = out + 4;
+		return true;
+	}
 
-	*out++ = '\\';
-	*out++ = 'x';
-	*out++ = hex_asc_hi(c);
-	*out++ = hex_asc_lo(c);
+	if (out < end)
+		*out = '\\';
+	++out;
+	if (out < end)
+		*out = 'x';
+	++out;
+	if (out < end)
+		*out = hex_asc_hi(c);
+	++out;
+	if (out < end)
+		*out = hex_asc_lo(c);
+	++out;
 
 	*dst = out;
-	*osz -= 4;
-
-	return 1;
+	return true;
 }
 
 /**
@@ -436,9 +459,10 @@ static int escape_hex(unsigned char c, char **dst, size_t *osz)
 int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
 		      unsigned int flags, const char *esc)
 {
-	char *out = *dst, *p = out;
+	char *p = *dst;
+	char *end = p + osz;
 	bool is_dict = esc && *esc;
-	int ret = 0;
+	int ret;
 
 	while (isz--) {
 		unsigned char c = *src++;
@@ -458,55 +482,33 @@ int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
 		    (is_dict && !strchr(esc, c))) {
 			/* do nothing */
 		} else {
-			if (flags & ESCAPE_SPACE) {
-				ret = escape_space(c, &p, &osz);
-				if (ret < 0)
-					break;
-				if (ret > 0)
-					continue;
-			}
-
-			if (flags & ESCAPE_SPECIAL) {
-				ret = escape_special(c, &p, &osz);
-				if (ret < 0)
-					break;
-				if (ret > 0)
-					continue;
-			}
-
-			if (flags & ESCAPE_NULL) {
-				ret = escape_null(c, &p, &osz);
-				if (ret < 0)
-					break;
-				if (ret > 0)
-					continue;
-			}
+			if (flags & ESCAPE_SPACE && escape_space(c, &p, end))
+				continue;
+
+			if (flags & ESCAPE_SPECIAL && escape_special(c, &p, end))
+				continue;
+
+			if (flags & ESCAPE_NULL && escape_null(c, &p, end))
+				continue;
 
 			/* ESCAPE_OCTAL and ESCAPE_HEX always go last */
-			if (flags & ESCAPE_OCTAL) {
-				ret = escape_octal(c, &p, &osz);
-				if (ret < 0)
-					break;
+			if (flags & ESCAPE_OCTAL && escape_octal(c, &p, end))
 				continue;
-			}
-			if (flags & ESCAPE_HEX) {
-				ret = escape_hex(c, &p, &osz);
-				if (ret < 0)
-					break;
+
+			if (flags & ESCAPE_HEX && escape_hex(c, &p, end))
 				continue;
-			}
 		}
 
-		ret = escape_passthrough(c, &p, &osz);
-		if (ret < 0)
-			break;
+		escape_passthrough(c, &p, end);
 	}
 
-	*dst = p;
-
-	if (ret < 0)
-		return ret;
+	if (p > end) {
+		*dst = end;
+		return -ENOMEM;
+	}
 
-	return p - out;
+	ret = p - *dst;
+	*dst = p;
+	return ret;
 }
 EXPORT_SYMBOL(string_escape_mem);
-- 
2.1.3

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