[C++] Fix dangling reference bug in getRandomName (#8596)

* The current getRandomName function contains a simple dangling reference bug: when it attempts to return a "const char*" string value from the temporary string returned by the stringstream "str" function.  This sometimes "works" anyway in release mode, but in debug mode on all the versions of GCC and CLANG I've tried it segfaults.  This makes debugging the c++ client very annoying.

I also found the method for generating random strings rather obscure. So I both fixed the bug and simplified the code, making use of boost::random to provide a much more straightforward implementation.

* Switched to std::random from boost::random, applied clang-format to the changed file.

pulsar-client-cpp/.gitignore

@@ -55,6 +55,9 @@ lib*.so*
 .pydevproject
 .idea/
 *.cbp
+*.ninja*
+.clangd/
+compile_commands.json
 
 # doxygen files
 apidocs/

pulsar-client-cpp/lib/ClientImpl.cc

@@ -29,11 +29,11 @@
 #include "SimpleLoggerImpl.h"
 #include <boost/algorithm/string/predicate.hpp>
 #include <sstream>
-#include <openssl/sha.h>
 #include <lib/HTTPLookupService.h>
 #include <lib/TopicName.h>
 #include <algorithm>
 #include <regex>
+#include <random>
 #include <mutex>
 #ifdef USE_LOG4CXX
 #include "Log4CxxLogger.h"
@@ -45,24 +45,20 @@ namespace pulsar {
 
 static const char hexDigits[] = {'0', '1', '2', '3', '4', '5', '6', '7',
                                  '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
+static std::uniform_int_distribution<> hexDigitsDist(0, sizeof(hexDigits));
+static std::mt19937 randomEngine =
+    std::mt19937(std::chrono::high_resolution_clock::now().time_since_epoch().count());
 
-const std::string generateRandomName() {
-    unsigned char hash[SHA_DIGEST_LENGTH];  // == 20;
-    boost::posix_time::ptime t(boost::posix_time::microsec_clock::universal_time());
-    long nanoSeconds = t.time_of_day().total_nanoseconds();
-    std::stringstream ss;
-    ss << nanoSeconds;
-    SHA1(reinterpret_cast<const unsigned char*>(ss.str().c_str()), ss.str().length(), hash);
-
-    const int nameLength = 10;
-    std::stringstream hexHash;
-    for (int i = 0; i < nameLength / 2; i++) {
-        hexHash << hexDigits[(hash[i] & 0xF0) >> 4];
-        hexHash << hexDigits[hash[i] & 0x0F];
-    }
+std::string generateRandomName() {
+    const int randomNameLength = 10;
 
-    return hexHash.str();
+    std::string randomName;
+    for (int i = 0; i < randomNameLength; ++i) {
+        randomName += hexDigits[hexDigitsDist(randomEngine)];
+    }
+    return randomName;
 }
+
 typedef std::unique_lock<std::mutex> Lock;
 
 typedef std::vector<std::string> StringList;

pulsar-client-cpp/lib/ClientImpl.h

@@ -42,7 +42,7 @@ class ReaderImpl;
 typedef std::shared_ptr<ReaderImpl> ReaderImplPtr;
 typedef std::weak_ptr<ReaderImpl> ReaderImplWeakPtr;
 
-const std::string generateRandomName();
+std::string generateRandomName();
 
 class ClientImpl : public std::enable_shared_from_this<ClientImpl> {
    public: