Better error message on socket (#1477)

* checking errno

* improved socket error message

* improved message

* decode error code

* format

* clearer msg

* report write errors, handle SIGPIPE

* retry and cleaned up timeout

* removed read/write in DataSocket

slsSupportLib/src/string_utils.cpp

@@ -66,4 +66,11 @@ std::pair<std::string, uint16_t> ParseHostPort(const std::string &s) {
     return std::make_pair(host, port);
 }
 
+std::string to_lower(const std::string &s) {
+    std::string result = s;
+    std::transform(result.begin(), result.end(), result.begin(),
+                       [](unsigned char c) { return std::tolower(c); });
+    return result;
+}
+
 }; // namespace sls