Helper function to get a valid topic name

include/ignition/transport/TopicUtils.hh

@@ -128,6 +128,14 @@ namespace ignition
         std::string &_partition,
         std::string &_namespaceAndTopic);
 
+      /// \brief Convert a topic name to a valid topic. The input topic is
+      /// modified by:
+      /// * turning white space into `_`.
+      /// * removing special characters and combinations.
+      /// \param[in] _topic Input topic, which may be invalid.
+      /// \return A valid topic, or empty string if not possible to convert.
+      public: static std::string AsValidTopic(const std::string &_topic);
+
       /// \brief The kMaxNameLength specifies the maximum number of characters
       /// allowed in a namespace, a partition name, a topic name, and a fully
       /// qualified topic name.

src/TopicUtils.cc

@@ -15,6 +15,7 @@
  *
 */
 
+#include <regex>
 #include <string>
 
 #include "ignition/transport/TopicUtils.hh"
@@ -154,3 +155,25 @@ bool TopicUtils::DecomposeFullyQualifiedTopic(
   _namespaceAndTopic = possibleTopic;
   return true;
 }
+
+//////////////////////////////////////////////////
+std::string TopicUtils::AsValidTopic(const std::string &_topic)
+{
+  std::string validTopic{_topic};
+
+  // Substitute spaces with _
+  validTopic = std::regex_replace(validTopic, std::regex(" "), "_");
+
+  // Remove special characters and combinations
+  validTopic = std::regex_replace(validTopic, std::regex("@"), "");
+  validTopic = std::regex_replace(validTopic, std::regex("~"), "");
+  validTopic = std::regex_replace(validTopic, std::regex("//"), "");
+  validTopic = std::regex_replace(validTopic, std::regex(":="), "");
+
+  if (!IsValidTopic(validTopic))
+  {
+    return std::string();
+  }
+
+  return validTopic;
+}

src/TopicUtils_TEST.cc

@@ -242,6 +242,55 @@ TEST(TopicUtilsTest, testFullyQualifiedName)
       }
 }
 
+//////////////////////////////////////////////////
+TEST(TopicUtilsTest, asValidTopic)
+{
+  for (auto unmodified :
+    {
+      "/abc",
+      "abc/de",
+      "a",
+      "ABC/",
+      "/abc",
+      "/abc/d",
+      "/abc/d/e",
+      "a(bc)d-e_f=h+i.j"
+    })
+  {
+    auto valid = transport::TopicUtils::AsValidTopic(unmodified);
+    EXPECT_EQ(unmodified, valid);
+    EXPECT_TRUE(transport::TopicUtils::IsValidTopic(valid)) << valid;
+  }
+
+  std::vector<std::pair<std::string, std::string>> modifiedStrings =
+    {
+      {"a b  c", "a_b__c"},
+      {"a@b@c", "abc"},
+      {"a:=b:=c", "abc"},
+      {"a//b/c", "ab/c"},
+      {"a~b~c", "abc"}
+    };
+
+  for (auto modified : modifiedStrings)
+  {
+    auto valid = transport::TopicUtils::AsValidTopic(modified.first);
+    EXPECT_EQ(modified.second, valid);
+    EXPECT_TRUE(transport::TopicUtils::IsValidTopic(valid)) << valid;
+  }
+
+  for (auto fail :
+    {
+      "",
+      "@@@",
+      "~@~",
+    })
+  {
+    auto empty = transport::TopicUtils::AsValidTopic(fail);
+    EXPECT_TRUE(empty.empty());
+    EXPECT_FALSE(transport::TopicUtils::IsValidTopic(empty));
+  }
+}
+
 //////////////////////////////////////////////////
 int main(int argc, char **argv)
 {