[PATCH iproute2 1/3] utils: add hexstring_alloc and print_hexstring helpers

[Stephen Hemminger <stephen@networkplumber.org>]

hexstring_n2a() writes into a caller-supplied buffer and silently
truncates when it is too small: the loop stops once fewer than three
bytes remain and returns the partial string. Callers using a fixed
SPRINT_BUF therefore drop trailing bytes for keys wider than 31 bytes.

Add hexstring_alloc(), which formats into a buffer sized to the input
so the full value is always emitted, and print_hexstring(), a wrapper
that formats and prints a binary attribute in one call with no local
buffer to size. print_hexstring() covers the common
print_string(..., hexstring_n2a(...)) pattern.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 include/json_print.h |  3 +++
 include/utils.h      |  1 +
 lib/json_print.c     | 12 ++++++++++++
 lib/utils.c          | 21 +++++++++++++++++++++
 4 files changed, 37 insertions(+)

diff --git a/include/json_print.h b/include/json_print.h
index c0d6315f..6a458189 100644
--- a/include/json_print.h
+++ b/include/json_print.h
@@ -84,6 +84,9 @@ _PRINT_FUNC(float, double)
 _PRINT_FUNC(tv, const struct timeval *)
 #undef _PRINT_FUNC
 
+void print_hexstring(const char *key, const char *fmt,
+		     const __u8 *data, unsigned int len);
+
 #define _PRINT_NAME_VALUE_FUNC(type_name, type, format_char)		  \
 	void print_##type_name##_name_value(const char *name, type value) \
 
diff --git a/include/utils.h b/include/utils.h
index f0d45bad..6a8872bf 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -162,6 +162,7 @@ int get_size64(__u64 *size, const char *str);
 
 int hex2mem(const char *buf, uint8_t *mem, int count);
 char *hexstring_n2a(const __u8 *str, int len, char *buf, int blen);
+char *hexstring_alloc(const __u8 *str, unsigned int len);
 __u8 *hexstring_a2n(const char *str, __u8 *buf, int blen, unsigned int *len);
 #define ADDR64_BUF_SIZE sizeof("xxxx:xxxx:xxxx:xxxx")
 int addr64_n2a(__u64 addr, char *buff, size_t len);
diff --git a/lib/json_print.c b/lib/json_print.c
index 810d496e..21589073 100644
--- a/lib/json_print.c
+++ b/lib/json_print.c
@@ -179,6 +179,18 @@ int print_color_string(enum output_type type,
 	return ret;
 }
 
+/* Print binary data as a hex string. The buffer is sized to the input,
+ * so keys of any length are printed in full rather than truncated.
+ */
+void print_hexstring(const char *key, const char *fmt,
+		     const __u8 *data, unsigned int len)
+{
+	char *hex = hexstring_alloc(data, len);
+
+	print_string(PRINT_ANY, key, fmt, hex ? : "");
+	free(hex);
+}
+
 /*
  * value's type is bool. When using this function in FP context you can't pass
  * a value to it, you will need to use "is_json_context()" to have different
diff --git a/lib/utils.c b/lib/utils.c
index 50602e59..7a1d8b48 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -1186,6 +1186,27 @@ char *hexstring_n2a(const __u8 *str, int len, char *buf, int blen)
 	return buf;
 }
 
+/* Format binary as hex into a freshly allocated string; caller frees.
+ * Unlike hexstring_n2a() the result is always sized to hold the full
+ * input, so there is no silent truncation. Returns NULL on allocation
+ * failure.
+ */
+char *hexstring_alloc(const __u8 *str, unsigned int len)
+{
+	char *buf, *ptr;
+	unsigned int i;
+
+	buf = malloc(2 * len + 1);
+	if (!buf)
+		return NULL;
+
+	for (i = 0, ptr = buf; i < len; i++, ptr += 2)
+		sprintf(ptr, "%02x", str[i]);
+	*ptr = '\0';
+
+	return buf;
+}
+
 __u8 *hexstring_a2n(const char *str, __u8 *buf, int blen, unsigned int *len)
 {
 	unsigned int cnt = 0;
-- 
2.53.0