[Bug] fix replace function bug (#6605)

* fix replace function bug

* fix replace docs

be/src/exprs/string_functions.cpp

@@ -972,14 +972,19 @@ StringVal StringFunctions::replace(FunctionContext* context, const StringVal& or
     if (origStr.is_null || oldStr.is_null || newStr.is_null) {
         return StringVal::null();
     }
+    // Empty string is a substring of all strings. 
+    // If old str is an empty string, the std::string.find(oldStr) is always return 0.
+    // With an empty old str, there is no need to do replace. 
+    if (oldStr.len == 0) {
+        return origStr;
+    }
     std::string orig_str = std::string(reinterpret_cast<const char*>(origStr.ptr), origStr.len);
     std::string old_str = std::string(reinterpret_cast<const char*>(oldStr.ptr), oldStr.len);
     std::string new_str = std::string(reinterpret_cast<const char*>(newStr.ptr), newStr.len);
     std::string::size_type pos = 0;
     std::string::size_type oldLen = old_str.size();
     std::string::size_type newLen = new_str.size();
-    while ((pos = orig_str.find(old_str, pos))) {
-        if (pos == std::string::npos) break;
+    while ((pos = orig_str.find(old_str, pos)) != std::string::npos) {
         orig_str.replace(pos, oldLen, new_str);
         pos += newLen;
     }

be/test/exprs/string_functions_test.cpp

@@ -559,6 +559,11 @@ TEST_F(StringFunctionsTest, replace) {
     ASSERT_EQ(StringVal("http://华夏zhongguo:9090"),
               StringFunctions::replace(ctx, StringVal("http://中国hello:9090"),
                                        StringVal("中国hello"), StringVal("华夏zhongguo")));
+
+    //old substring is at the beginning of string
+    ASSERT_EQ(StringVal("ftp://www.baidu.com:9090"),
+              StringFunctions::replace(ctx, StringVal("http://www.baidu.com:9090"),
+                                       StringVal("http"), StringVal("ftp")));
 }
 
 TEST_F(StringFunctionsTest, parse_url) {

docs/.vuepress/sidebar/en.js

@@ -346,6 +346,7 @@ module.exports = [
               "money_format",
               "null_or_empty",
               "repeat",
+              "replace",
               "reverse",
               "right",
               "rpad",

docs/.vuepress/sidebar/zh-CN.js

@@ -350,6 +350,7 @@ module.exports = [
               "money_format",
               "null_or_empty",
               "repeat",
+              "replace",
               "reverse",
               "right",
               "rpad",