Allow pcn_log to be split in multiple lines

This commit fixes a "bug" in the pcn_log function that did not allow
to split the pcn_log body into multiple lines, for example by putting
the text and the parameters in different lines.
It uses an improved regex function to check the end of the
pcn_log function and replace it with the correct version so that
compilation errors can be avoided.

Fixes: #1 (pcn_log cannot be split in multiple lines)
Signed-off-by: Sebastiano Miano <mianosebastiano@gmail.com>

Documentation/developers.rst

@@ -155,7 +155,6 @@ Two special format specifiers are available:
 Please note the the custom specifiers spec the data to be in network byte order while standard specifiers expects it to be in host by order.
 
 Current limitations:
- - The whole call to `pcn_log` should be on the same line
  - Cannot be used inside a macro
  - Maximum 4 arguments are allowed
 

src/polycubed/src/datapath_log.cpp

@@ -199,20 +199,47 @@ void DatapathLog::stop() {
   }
 }
 
+std::string DatapathLog::replace_string(std::string& subject, const std::string& search, const std::string& replace) {
+    size_t start_pos = 0;
+    while((start_pos = subject.find(search, start_pos)) != std::string::npos) {
+        subject.replace(start_pos, search.length(), replace);
+        start_pos += replace.length(); // Handles case where 'to' is a substring of 'from'
+    }
+    return subject;
+}
+
 // matches all C++ comments
 // https://stackoverflow.com/questions/36454069/how-to-remove-c-style-comments-from-code
 static std::regex regComments(R"***((?:\/\/(?:\\\n|[^\n])*)|(?:\/\*[\s\S]*?\*\/)|((?:R"([^(\\\s]{0,16})\([^)]*\)\2")|(?:@"[^"]*?")|(?:"(?:\?\?'|\\\\|\\"|\\\n|[^"])*?")|(?:'(?:\\\\|\\'|\\\n|[^'])*?')))***");
 
 // matches all calls to pcn_log(ctx, ...)
-static std::regex regN(R"***(pcn_log\(([\s\S]+?)\)\s*;)***");
+static std::regex regN(R"***(pcn_log\s*\(([\s\S]+?)\)\s*;)***");
+static std::regex regNewLine(R"***(/(\r\n)+|\r+|\n+|\t+/i)***");
+static std::regex regAddSpaces(R"***( +)***");
+
+static std::regex regNPkt(R"***(pcn_pkt_log\s*\(([\s\S]+?)\)\s*;)***");
+
+std::string DatapathLog::dp_callback(const std::smatch& m) {
+    std::string match = std::regex_replace(m.str(1), regNewLine, "");
+    match = std::regex_replace(match, regAddSpaces, " ");
+    std::string new_string = std::string(REPLACE_BASE);
+    new_string = DatapathLog::replace_string(new_string, "$1", match);
+    return new_string;
+}
 
-static std::regex regNPkt(R"***(pcn_pkt_log\(([\s\S]+?)\)\s*;)***");
+std::string DatapathLog::dp_callback_pkt(const std::smatch& m) {
+    std::string match = std::regex_replace(m.str(1), regNewLine, "");
+    match = std::regex_replace(match, regAddSpaces, " ");
+    std::string new_string = std::string(REPLACE_BASE_PKT);
+    new_string = DatapathLog::replace_string(new_string, "$1", match);
+    return new_string;
+}
 
 std::string DatapathLog::parse_log(const std::string &code) {
   // remove all comments from the code before going on
-  auto code1 = regex_replace(code, regComments, "$1");
-  auto code2 = std::regex_replace(code1, regN, REPLACE_BASE);
-  auto code3 = std::regex_replace(code2, regNPkt, REPLACE_BASE_PKT);
+  auto code1 = std::regex_replace(code, regComments, "$1");
+  auto code2 = std::regex_replace_cb(code1, regN, DatapathLog::dp_callback);
+  auto code3 = std::regex_replace_cb(code2, regNPkt, DatapathLog::dp_callback_pkt);
   return BASE_CODE + code3;
 }
 

src/polycubed/src/datapath_log.h

@@ -19,6 +19,11 @@
 #include <functional>
 #include <thread>
 #include <vector>
+#include <algorithm>
+#include <cstdlib>
+#include <iostream>
+#include <string>
+#include <regex>
 
 #include <api/BPF.h>
 #include <spdlog/spdlog.h>
@@ -42,6 +47,9 @@ class DatapathLog {
   void stop();
 
   static void call_back_proxy(void *cb_cookie, void *data, int data_size);
+  static std::string replace_string(std::string& subject, const std::string& search, const std::string& replace);
+  static std::string dp_callback(const std::smatch& m);
+  static std::string dp_callback_pkt(const std::smatch& m);
 
   // replaces all the log calls to the code that does it
   std::string parse_log(const std::string &code);
@@ -60,3 +68,53 @@ class DatapathLog {
 
 }  // namespace polycubed
 }  // namespace polycube
+
+// Based on solution proposed in: https://stackoverflow.com/questions/22617209/regex-replace-with-callback-in-c11
+namespace std
+{
+
+template<class BidirIt, class Traits, class CharT, class UnaryFunction>
+std::basic_string<CharT> regex_replace_cb(BidirIt first, BidirIt last,
+    const std::basic_regex<CharT,Traits>& re, UnaryFunction f)
+{
+    std::basic_string<CharT> s;
+
+    typename std::match_results<BidirIt>::difference_type
+        positionOfLastMatch = 0;
+    auto endOfLastMatch = first;
+
+    auto callback = [&](const std::match_results<BidirIt>& match)
+    {
+        auto positionOfThisMatch = match.position(0);
+        auto diff = positionOfThisMatch - positionOfLastMatch;
+
+        auto startOfThisMatch = endOfLastMatch;
+        std::advance(startOfThisMatch, diff);
+
+        s.append(endOfLastMatch, startOfThisMatch);
+        s.append(f(match));
+
+        auto lengthOfMatch = match.length(0);
+
+        positionOfLastMatch = positionOfThisMatch + lengthOfMatch;
+
+        endOfLastMatch = startOfThisMatch;
+        std::advance(endOfLastMatch, lengthOfMatch);
+    };
+
+    std::regex_iterator<BidirIt> begin(first, last, re), end;
+    std::for_each(begin, end, callback);
+
+    s.append(endOfLastMatch, last);
+
+    return s;
+}
+
+template<class Traits, class CharT, class UnaryFunction>
+std::string regex_replace_cb(const std::string& s,
+    const std::basic_regex<CharT,Traits>& re, UnaryFunction f)
+{
+    return regex_replace_cb(s.cbegin(), s.cend(), re, f);
+}
+
+} // namespace std