utils: add osmo_escape_str()

To report invalid characters in identifiers, it is desirable to escape any
weird characters. Otherwise we might print stray newlines or control characters
in the log output.

ctrl_test.c already uses a print_escaped() function, which will be replaced by
osmo_escape_str() in a subsequent patch.

control_cmd.c will use osmo_escape_str() to log invalid identifiers.

Change-Id: Ic685eb63dead3967d01aaa4f1e9899e5461ca49a

include/osmocom/core/utils.h

@@ -120,4 +120,7 @@ bool osmo_is_hexstr(const char *str, int min_digits, int max_digits,
 bool osmo_identifier_valid(const char *str);
 bool osmo_separated_identifiers_valid(const char *str, const char *sep_chars);
 
+const char *osmo_escape_str(const char *str, int len);
+const char *osmo_escape_str_buf(const char *str, int in_len, char *buf, size_t bufsize);
+
 /*! @} */

src/utils.c

@@ -467,4 +467,91 @@ bool osmo_identifier_valid(const char *str)
 	return osmo_separated_identifiers_valid(str, NULL);
 }
 
+/*! Return the string with all non-printable characters escaped.
+ * \param[in] str  A string that may contain any characters.
+ * \param[in] len  Pass -1 to print until nul char, or >= 0 to force a length.
+ * \param[inout] buf  string buffer to write escaped characters to.
+ * \param[in] bufsize  size of \a buf.
+ * \returns buf containing an escaped representation, possibly truncated, or str itself.
+ */
+const char *osmo_escape_str_buf(const char *str, int in_len, char *buf, size_t bufsize)
+{
+	int in_pos = 0;
+	int next_unprintable = 0;
+	int out_pos = 0;
+	char *out = buf;
+	/* -1 to leave space for a final \0 */
+	int out_len = bufsize-1;
+
+	if (!str)
+		return "(null)";
+
+	if (in_len < 0)
+		in_len = strlen(str);
+
+	while (in_pos < in_len) {
+		for (next_unprintable = in_pos;
+		     next_unprintable < in_len && isprint((int)str[next_unprintable])
+		     && str[next_unprintable] != '"'
+		     && str[next_unprintable] != '\\';
+		     next_unprintable++);
+
+		if (next_unprintable == in_len
+		    && in_pos == 0)
+			return str;
+
+		while (in_pos < next_unprintable && out_pos < out_len)
+			out[out_pos++] = str[in_pos++];
+
+		if (out_pos == out_len || in_pos == in_len)
+			goto done;
+
+		switch (str[next_unprintable]) {
+#define BACKSLASH_CASE(c, repr) \
+		case c: \
+			if (out_pos > out_len-2) \
+				goto done; \
+			out[out_pos++] = '\\'; \
+			out[out_pos++] = repr; \
+			break
+
+		BACKSLASH_CASE('\n', 'n');
+		BACKSLASH_CASE('\r', 'r');
+		BACKSLASH_CASE('\t', 't');
+		BACKSLASH_CASE('\0', '0');
+		BACKSLASH_CASE('\a', 'a');
+		BACKSLASH_CASE('\b', 'b');
+		BACKSLASH_CASE('\v', 'v');
+		BACKSLASH_CASE('\f', 'f');
+		BACKSLASH_CASE('\\', '\\');
+		BACKSLASH_CASE('"', '"');
+#undef BACKSLASH_CASE
+
+		default:
+			out_pos += snprintf(&out[out_pos], out_len - out_pos, "\\%u", (unsigned char)str[in_pos]);
+			if (out_pos > out_len) {
+				out_pos = out_len;
+				goto done;
+			}
+			break;
+		}
+		in_pos ++;
+	}
+
+done:
+	out[out_pos] = '\0';
+	return out;
+}
+
+/*! Return the string with all non-printable characters escaped.
+ * Call osmo_escape_str_buf() with a static buffer.
+ * \param[in] str  A string that may contain any characters.
+ * \param[in] len  Pass -1 to print until nul char, or >= 0 to force a length.
+ * \returns buf containing an escaped representation, possibly truncated, or str itself.
+ */
+const char *osmo_escape_str(const char *str, int in_len)
+{
+	return osmo_escape_str_buf(str, in_len, namebuf, sizeof(namebuf));
+}
+
 /*! @} */

tests/utils/utils_test.c

@@ -323,6 +323,53 @@ static void bcd_test(void)
 	}
 }
 
+static void str_escape_test(void)
+{
+	int i;
+	int j;
+	uint8_t in_buf[32];
+	char out_buf[11];
+	const char *printable = "printable";
+	const char *res;
+
+	printf("\nTesting string escaping\n");
+	printf("- all chars from 0 to 255 in batches of 16:\n");
+	for (j = 0; j < 16; j++) {
+		for (i = 0; i < 16; i++)
+			in_buf[i] = (j << 4) | i;
+		printf("\"%s\"\n", osmo_escape_str((const char*)in_buf, 16));
+	}
+
+	printf("- nul terminated:\n");
+	printf("\"%s\"\n", osmo_escape_str("termi\nated", -1));
+
+	printf("- passthru:\n");
+	res = osmo_escape_str(printable, -1);
+	if (res != printable)
+		printf("NOT passed through! \"%s\"\n", res);
+	else
+		printf("passed through unchanged \"%s\"\n", res);
+
+	printf("- zero length:\n");
+	printf("\"%s\"\n", osmo_escape_str("omitted", 0));
+
+	printf("- truncation when too long:\n");
+	memset(in_buf, 'x', sizeof(in_buf));
+	in_buf[0] = '\a';
+	in_buf[7] = 'E';
+	memset(out_buf, 0x7f, sizeof(out_buf));
+	printf("\"%s\"\n", osmo_escape_str_buf((const char *)in_buf, sizeof(in_buf), out_buf, 10));
+	OSMO_ASSERT(out_buf[10] == 0x7f);
+
+	printf("- passthrough without truncation when no escaping needed:\n");
+	memset(in_buf, 'x', sizeof(in_buf));
+	in_buf[19] = 'E';
+	in_buf[20] = '\0';
+	memset(out_buf, 0x7f, sizeof(out_buf));
+	printf("\"%s\"\n", osmo_escape_str_buf((const char *)in_buf, -1, out_buf, 10));
+	OSMO_ASSERT(out_buf[0] == 0x7f);
+}
+
 int main(int argc, char **argv)
 {
 	static const struct log_info log_info = {};
@@ -333,5 +380,6 @@ int main(int argc, char **argv)
 	test_idtag_parsing();
 	test_is_hexstr();
 	bcd_test();
+	str_escape_test();
 	return 0;
 }

tests/utils/utils_test.ok

@@ -75,3 +75,32 @@ Testing BCD conversion
 	val=0xd, expected=D, found=D
 	val=0xe, expected=E, found=E
 	val=0xf, expected=F, found=F
+
+Testing string escaping
+- all chars from 0 to 255 in batches of 16:
+"\0\1\2\3\4\5\6\a\b\t\n\v\f\r\14\15"
+"\16\17\18\19\20\21\22\23\24\25\26\27\28\29\30\31"
+" !\"#$%&'()*+,-./"
+"0123456789:;<=>?"
+"@ABCDEFGHIJKLMNO"
+"PQRSTUVWXYZ[\\]^_"
+"`abcdefghijklmno"
+"pqrstuvwxyz{|}~\127"
+"\128\129\130\131\132\133\134\135\136\137\138\139\140\141\142\143"
+"\144\145\146\147\148\149\150\151\152\153\154\155\156\157\158\159"
+"\160\161\162\163\164\165\166\167\168\169\170\171\172\173\174\175"
+"\176\177\178\179\180\181\182\183\184\185\186\187\188\189\190\191"
+"\192\193\194\195\196\197\198\199\200\201\202\203\204\205\206\207"
+"\208\209\210\211\212\213\214\215\216\217\218\219\220\221\222\223"
+"\224\225\226\227\228\229\230\231\232\233\234\235\236\237\238\239"
+"\240\241\242\243\244\245\246\247\248\249\250\251\252\253\254\255"
+- nul terminated:
+"termi\nated"
+- passthru:
+passed through unchanged "printable"
+- zero length:
+""
+- truncation when too long:
+"\axxxxxxE"
+- passthrough without truncation when no escaping needed:
+"xxxxxxxxxxxxxxxxxxxE"