[PATCH BlueZ v1 3/8] shared/util: Add str2utf8

[Luiz Augusto von Dentz <luiz.dentz@gmail.com>]

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

There are five near copies of the same "turn a remote name into a UTF-8
string" helper, in monitor/att.c, profiles/audio/mcp.c, profiles/gap/gas.c,
src/eir.c and src/shared/ad.c, and they do not agree with each other.

Most truncate at the first ill-formed sequence, which throws away the
rest of the name, while the monitor replaces every non-ASCII byte with a
space, which mangles perfectly valid UTF-8 names as soon as one bad byte
appears. Most also copy into a fixed size stack buffer first, which is
what made the missing clamp in src/eir.c a buffer overflow.

Add a single helper they can share. It allocates the result, so there is
no truncation to a buffer size, and replaces each ill-formed sequence
with U+FFFD REPLACEMENT CHARACTER rather than dropping the rest of the
string, matching what g_utf8_make_valid() and the WHATWG Encoding
Standard do.

The result has been checked byte for byte against Python's
bytes.decode('utf-8', errors='replace') over all one and two byte
sequences, a sample of the three byte ones and 200000 random inputs.

Assisted-by: Claude:claude-opus-5
---
 src/shared/util.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 src/shared/util.h |  7 +++++++
 2 files changed, 53 insertions(+)

diff --git a/src/shared/util.c b/src/shared/util.c
index e946214edbb9..8ec9b52e6401 100644
--- a/src/shared/util.c
+++ b/src/shared/util.c
@@ -2315,3 +2315,49 @@ char *strtoutf8(char *str, size_t len)
 	memset(str + i, 0, len - i);
 	return str;
 }
+
+char *str2utf8(const uint8_t *str, size_t len)
+{
+	char *utf8, *out, *stripped;
+	size_t i = 0;
+
+	if (!str)
+		return NULL;
+
+	/*
+	 * Invalid bytes are replaced with U+FFFD REPLACEMENT CHARACTER, which
+	 * is 3 bytes long, so that is the worst case size of the result.
+	 */
+	utf8 = malloc(len * 3 + 1);
+	if (!utf8)
+		return NULL;
+
+	out = utf8;
+
+	while (i < len) {
+		size_t sublen;
+		size_t size = utf8_seqlen(str + i, len - i, &sublen);
+
+		if (size) {
+			memcpy(out, str + i, size);
+			out += size;
+			i += size;
+			continue;
+		}
+
+		/* Replace the maximal subpart with U+FFFD */
+		*out++ = 0xef;
+		*out++ = 0xbf;
+		*out++ = 0xbd;
+		i += sublen;
+	}
+
+	*out = '\0';
+
+	/* Remove leading and trailing whitespace characters */
+	stripped = strstrip(utf8);
+	if (stripped != utf8)
+		memmove(utf8, stripped, strlen(stripped) + 1);
+
+	return utf8;
+}
diff --git a/src/shared/util.h b/src/shared/util.h
index 562a5af31751..1984fb75f09e 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -143,6 +143,13 @@ bool strisutf8(const char *str, size_t length);
 bool argsisutf8(int argc, char *argv[]);
 char *strtoutf8(char *str, size_t len);
 
+/*
+ * Return a newly allocated, NUL terminated and whitespace stripped UTF-8
+ * copy of the first len bytes of str, with each ill-formed sequence replaced
+ * by U+FFFD REPLACEMENT CHARACTER. The result must be freed with free().
+ */
+char *str2utf8(const uint8_t *str, size_t len);
+
 void *util_malloc(size_t size);
 void *util_memdup(const void *src, size_t size);
 
-- 
2.54.0