libnm: return output buffer from _nm_utils_bin2hexstr_full()

It's just more convenient, as it allows better chaining.

Also, allow passing %NULL as @out buffer. It's clear how
large the output buffer must be, so for convenience let the
function (optionally) allocate a new buffer.

This behavior of whether to
  - take @out, fill it, and return @out
  - take no @out, allocate new buffer, fill and and return it
is slightly error prone. But it was already error prone before, when
it would accept an input buffer without explicit buffer length. I think
this makes it more safe, because in the common case the caller can avoid
pre-allocating a buffer of the right size and the function gets it
right.

libnm-core/nm-core-internal.h

@@ -213,7 +213,7 @@ guint8 *_nm_utils_hwaddr_aton (const char *asc, gpointer buffer, gsize buffer_le
 const char *nm_utils_hwaddr_ntoa_buf (gconstpointer addr, gsize addr_len, gboolean upper_case, char *buf, gsize buf_len);
 
 char *_nm_utils_bin2hexstr (gconstpointer addr, gsize length, gboolean upper_case);
-void _nm_utils_bin2hexstr_full (gconstpointer addr, gsize length, const char delimiter, gboolean upper_case, char *out);
+char *_nm_utils_bin2hexstr_full (gconstpointer addr, gsize length, const char delimiter, gboolean upper_case, char *out);
 
 guint8 *_nm_utils_hexstr2bin_full (const char *asc,
                                    gboolean delimiter_required,

libnm-core/nm-utils.c

@@ -3728,16 +3728,46 @@ nm_utils_hwaddr_aton (const char *asc, gpointer buffer, gsize length)
 	return buffer;
 }
 
-void
-_nm_utils_bin2hexstr_full (gconstpointer addr, gsize length, const char delimiter, gboolean upper_case, char *out)
+/**
+ * _nm_utils_bin2hexstr_full:
+ * @addr: pointer of @length bytes.
+ * @length: number of bytes in @addr
+ * @delimiter: either '\0', otherwise the output string will have the
+ *   given delimiter character between each two hex numbers.
+ * @upper_case: if TRUE, use upper case ASCII characters for hex.
+ * @out: if %NULL, the function will allocate a new buffer of
+ *   either (@length*2+1) or (@length*3) bytes, depending on whether
+ *   a @delimiter is specified. In that case, the allocated buffer will
+ *   be returned and must be freed by the caller.
+ *   If not %NULL, the buffer must already be preallocated and contain
+ *   at least (@length*2+1) or (@length*3) bytes, depending on the delimiter.
+ *
+ * Returns: the binary value converted to a hex string. If @out is given,
+ *   this always returns @out. If @out is %NULL, a newly allocated string
+ *   is returned.
+ */
+char *
+_nm_utils_bin2hexstr_full (gconstpointer addr,
+                           gsize length,
+                           char delimiter,
+                           gboolean upper_case,
+                           char *out)
 {
 	const guint8 *in = addr;
 	const char *LOOKUP = upper_case ? "0123456789ABCDEF" : "0123456789abcdef";
+	char *out0;
 
 	nm_assert (addr);
-	nm_assert (out);
 	nm_assert (length > 0);
 
+	if (out)
+		out0 = out;
+	else {
+		out0 = out = g_new (char, delimiter == '\0'
+		                          ? length * 2 + 1
+		                          : length * 3);
+	}
+
 	/* @out must contain at least @length*3 bytes if @delimiter is set,
 	 * otherwise, @length*2+1. */
 
@@ -3754,6 +3784,7 @@ _nm_utils_bin2hexstr_full (gconstpointer addr, gsize length, const char delimite
 	}
 
 	*out = 0;
+	return out0;
 }
 
 /**
@@ -3779,6 +3810,7 @@ nm_utils_bin2hexstr (gconstpointer src, gsize len, int final_len)
 	g_return_val_if_fail (final_len < 0 || (gsize) final_len < buflen, NULL);
 
 	result = g_malloc (buflen);
+
 	_nm_utils_bin2hexstr_full (src, len, '\0', FALSE, result);
 
 	/* Cut converted key off at the correct length for this cipher type */
@@ -3800,14 +3832,10 @@ nm_utils_bin2hexstr (gconstpointer src, gsize len, int final_len)
 char *
 nm_utils_hwaddr_ntoa (gconstpointer addr, gsize length)
 {
-	char *result;
-
 	g_return_val_if_fail (addr, g_strdup (""));
 	g_return_val_if_fail (length > 0, g_strdup (""));
 
-	result = g_malloc (length * 3);
-	_nm_utils_bin2hexstr_full (addr, length, ':', TRUE, result);
-	return result;
+	return _nm_utils_bin2hexstr_full (addr, length, ':', TRUE, NULL);
 }
 
 const char *
@@ -3819,8 +3847,7 @@ nm_utils_hwaddr_ntoa_buf (gconstpointer addr, gsize addr_len, gboolean upper_cas
 	if (buf_len < addr_len * 3)
 		g_return_val_if_reached (NULL);
 
-	_nm_utils_bin2hexstr_full (addr, addr_len, ':', upper_case, buf);
-	return buf;
+	return _nm_utils_bin2hexstr_full (addr, addr_len, ':', upper_case, buf);
 }
 
 /**
@@ -3836,14 +3863,10 @@ nm_utils_hwaddr_ntoa_buf (gconstpointer addr, gsize addr_len, gboolean upper_cas
 char *
 _nm_utils_bin2hexstr (gconstpointer addr, gsize length, gboolean upper_case)
 {
-	char *result;
-
 	g_return_val_if_fail (addr, g_strdup (""));
 	g_return_val_if_fail (length > 0, g_strdup (""));
 
-	result = g_malloc (length * 3);
-	_nm_utils_bin2hexstr_full (addr, length, ':', upper_case, result);
-	return result;
+	return _nm_utils_bin2hexstr_full (addr, length, ':', upper_case, NULL);
 }
 
 /**