Fix ct2ctml when string passed as 'source' argument

Make ct2ctml create a temp cti file for a large source argument

Fixes #416

interfaces/cython/cantera/test/test_convert.py

@@ -459,3 +459,33 @@ def test_reaction_orders(self):
         self.assertNear(R.orders.get('OH'), 0.15)
         self.assertTrue(R.allow_negative_orders)
         self.assertNear(R.orders.get('H2'), -0.25)
+
+    def test_long_source_input(self):
+        """
+        Here we are testing if passing a very long string will result in a
+        Solution object. This should result in a temp file creation in most OS's
+        """
+
+        gas = ct.Solution(pjoin(self.test_data_dir, 'pdep-test.cti'))
+
+        with open(pjoin(self.test_data_dir, 'pdep-test.cti'), 'r') as f:
+            data = f.read()
+        data_size_2048kB = data + ' '*2048*1024
+        gas2 = ct.Solution(source=data_size_2048kB)
+
+        self.assertEqual(gas.n_reactions, gas2.n_reactions)
+
+    def test_short_source_input(self):
+        """
+        Here we are testing if passing a short string will result in a Solution
+        object. This should not result in a temp file creation in most OS's
+        """
+
+        gas = ct.Solution(pjoin(self.test_data_dir, 'pdep-test.cti'))
+
+        with open(pjoin(self.test_data_dir, 'pdep-test.cti'), 'r') as f:
+            data = f.read()
+        data_size_32kB = data + ' '*18000
+        gas2 = ct.Solution(source=data_size_32kB)
+
+        self.assertEqual(gas.n_reactions, gas2.n_reactions)

src/base/ct2ctml.cpp

@@ -11,12 +11,15 @@
 #include "cantera/base/stringUtils.h"
 #include "../../ext/libexecstream/exec-stream.h"
 
+#include <cstdio>
 #include <fstream>
 #include <sstream>
 #include <functional>
 
 #ifdef _WIN32
 #include <windows.h>
+#else
+#include <unistd.h>
 #endif
 
 using namespace std;
@@ -79,6 +82,9 @@ void ct2ctml(const char* file, const int debug)
 static std::string call_ctml_writer(const std::string& text, bool isfile)
 {
     std::string file, arg;
+    bool temp_file_created = false;
+    std::string temp_cti_file_name = std::tmpnam(nullptr);
+
     if (isfile) {
         file = text;
         arg = "r'" + text + "'";
@@ -87,6 +93,44 @@ static std::string call_ctml_writer(const std::string& text, bool isfile)
         arg = "text=r'''" + text + "'''";
     }
 
+    // If the user wants to convert a mechanism using a text passed via the
+    //       source="""..."""
+    // argument in python, then we have to make sure that it is short enough
+    // to fit in the command line when routed to python as:
+    //       python -c ...
+    // statement downstream in the code
+
+    // So, check the max size of a string that can be passed on the command line
+    // This is OS Specific. *nix systems have the sysconf() function that tells
+    // us the largest argument we can pass. Since such a function does not exist
+    // for Windows, we set a safe limit of 32 kB
+
+#ifdef _WIN32
+    long int max_argv_size = 32768;
+#else
+    long int max_argv_size = sysconf(_SC_ARG_MAX);
+#endif
+
+    if (text.size() > static_cast<size_t>(max_argv_size) - 500) {
+        // If the file is too big to be passed as a command line argument later
+        // in the file, then create a temporary file and execute this function
+        // as though an input file was specified as the source.
+        // We assume the text passed + 500 chars = total size of argv
+
+        ofstream temp_cti_file(temp_cti_file_name);
+
+        if (temp_cti_file) {
+            temp_cti_file << text;
+            file = temp_cti_file_name;
+            arg = "r'" + file + "'";
+            temp_file_created = true;
+        } else {
+            // If we are here, then a temp file could not be created
+            throw CanteraError("call_ctml_writer", "Very long source argument. "
+                               "Error creating temporary file");
+        }
+    }
+
 #ifdef HAS_NO_PYTHON
     //! Section to bomb out if python is not present in the computation
     //! environment.
@@ -170,6 +214,15 @@ static std::string call_ctml_writer(const std::string& text, bool isfile)
         message << "--------------- end of converter log ---------------\n";
         writelog(message.str());
     }
+
+    if (temp_file_created) {
+        // A temp file was created and has to be removed
+        bool status = std::remove(temp_cti_file_name.c_str());
+        if (status) {
+            writelog("WARNING: Error removing tmp file {}\n", temp_cti_file_name);
+        }
+    }
+
     return python_output;
 }