util: add a strreplace function

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

src/util-strings.c

@@ -24,6 +24,8 @@
 
 #include "config.h"
 
+#include <string.h>
+
 #include "util-strings.h"
 
 /**
@@ -156,6 +158,71 @@ strv_join(char **strv, const char *joiner)
 	return str;
 }
 
+char *
+strreplace(const char *string, const char *separator, const char *replacement)
+{
+	assert(string != NULL);
+	assert(string[0] != '\0');
+
+	/* Enough to replace every character in the string with the
+	 * replacement. This will blow up on extremely long strings with long
+	 * replacements, but meh. It saves us having to write resizing code.
+	 */
+	size_t slen = strlen(string);
+	size_t splen = strlen(separator);
+
+	const char *current = string;
+	const char *next;
+
+	next = strstr(current, separator);
+	if (!next) /* No separator found */
+		return xstrdup(string);
+
+	size_t rlen = strlen(replacement);
+	size_t max = slen * max(rlen, 1);
+	char *r = calloc(max + 1, 1); /* the result, one extra for terminating \0 */
+	char *destptr = r;
+
+/* our strncpy calls truncate the second argument, we know... */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wstringop-truncation"
+	while (next) {
+		size_t len = next - current;
+		/* silently truncate because we really don't care about this
+		 * case */
+		if (destptr + len > r + max)
+			break;
+
+		/* Copy the source string over, then append the separator */
+		strncpy(destptr, current, len);
+		destptr += len;
+		if (destptr + rlen > r + max)
+			break;
+		strncpy(destptr, replacement, rlen);
+		destptr += rlen;
+
+		current = next + splen;
+		if (current > string + max)
+			break;
+		next = strstr(current, separator);
+
+	}
+
+	size_t len = strlen(current);
+	/* silently truncate because we really don't care about this
+	 * case */
+	if (destptr + len <= r + max) {
+		strncpy(destptr, current, len);
+		destptr += len;
+	}
+#pragma GCC diagnostic pop
+
+	void *tmp = realloc(r, (destptr - r) + 1);
+	assert(tmp);
+	return tmp;
+}
+
+
 #if _enable_tests_
 #include "util-munit.h"
 
@@ -377,4 +444,30 @@ MUNIT_TEST(test_strendswith)
 
 	return MUNIT_OK;
 }
+
+MUNIT_TEST(test_strreplace)
+{
+	struct strtest {
+		const char *string;
+		const char *separator;
+		const char *replacement;
+		const char *expected;
+	} tests[] = {
+		{ "teststring", "-", ".", "teststring" },
+		{ "test-string", "-", ".", "test.string" },
+		{ "test.string.", ".", "xyz", "testxyzstringxyz" },
+		{ "ftestfstringf", "f", "", "teststring" },
+		{ "xxx", "x", "y", "yyy" },
+		{ "xyz", "x", "y", "yyz" },
+		{ "xyz", "xy", "y", "yz" },
+		{ .string = NULL },
+	};
+
+	for (struct strtest *t = tests; t->string; t++) {
+		_cleanup_free_ char *s = strreplace(t->string, t->separator, t->replacement);
+		munit_assert_string_equal(t->expected, s);
+	}
+
+	return MUNIT_OK;
+}
 #endif

src/util-strings.h

@@ -257,6 +257,8 @@ strv_free(char **strv) {
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(char **, strv_free);
 
+char * strreplace(const char *string, const char *separator, const char *replacement);
+
 struct key_value_str{
 	char *key;
 	char *value;