Add operator<<(ostream, exception)

6 files changed, 94 insertions, 8 deletions

diff --git a/butl/fdstream b/butl/fdstream
index d955476..8d01b2f 100644
--- a/butl/fdstream
+++ b/butl/fdstream
@@ -299,7 +299,7 @@ namespace butl
   // }
   // catch (const process_error& e)
   // {
-  //   error << ... << e.what ();
+  //   error << ... << e;
   //
   //   if (e.child ())
   //     exit (1);
diff --git a/butl/fdstream.cxx b/butl/fdstream.cxx
index 2eee7c5..370a75e 100644
--- a/butl/fdstream.cxx
+++ b/butl/fdstream.cxx
@@ -46,18 +46,22 @@ namespace butl
     // exception and to make a string returned by what() to contain the error
     // description plus an optional custom message if provided. Unfortunatelly
     // there is no way to say that the custom message is absent. Passing an
-    // empty string results for GCC (as of version 5.3.1) with a description
-    // like this (note the ugly ": " prefix): ": No such file or directory".
+    // empty string results for libstdc++ (as of version 5.3.1) with a
+    // description like this (note the ': ' prefix):
+    //
+    // : No such file or directory
+    //
+    // Note that our custom operator<<(ostream, exception) strips this prefix.
     //
     throw ios_base::failure (m != nullptr ? m : "", e);
   }
 
   template <bool v>
   static inline void
-  throw_ios_failure (error_code ec,
+  throw_ios_failure (error_code e,
                      typename enable_if<!v, const char*>::type m)
   {
-    throw ios_base::failure (m != nullptr ? m : ec.message ().c_str ());
+    throw ios_base::failure (m != nullptr ? m : e.message ().c_str ());
   }
 
   inline void
diff --git a/butl/pager b/butl/pager
index b1d7a9f..37dbc43 100644
--- a/butl/pager
+++ b/butl/pager
@@ -41,7 +41,7 @@ namespace butl
   // }
   // catch (const std::system_error& e)
   // {
-  //   cerr << "pager error: " << e.what () << endl;
+  //   cerr << "pager error: " << e << endl;
   // }
   //
   class LIBBUTL_EXPORT pager: protected std::streambuf
diff --git a/butl/pager.cxx b/butl/pager.cxx
index 066cd7b..e327960 100644
--- a/butl/pager.cxx
+++ b/butl/pager.cxx
@@ -18,6 +18,7 @@
 #include <utility>      // move()
 #include <system_error>
 
+#include <butl/utility>  // operator<<(ostream, exception)
 #include <butl/fdstream> // fdclose()
 
 using namespace std;
@@ -147,7 +148,7 @@ namespace butl
     {
       if (e.child ())
       {
-        cerr << args[0] << ": unable to execute: " << e.what () << endl;
+        cerr << args[0] << ": unable to execute: " << e << endl;
         exit (1);
       }
 
diff --git a/butl/utility b/butl/utility
index f668ecc..ac94171 100644
--- a/butl/utility
+++ b/butl/utility
@@ -6,10 +6,11 @@
 #define BUTL_UTILITY
 
 #include <string>
+#include <iosfwd>       // ostream
 #include <cstddef>      // size_t
 #include <utility>      // move(), forward()
 #include <cstring>      // strcmp(), strlen()
-#include <exception>    // uncaught_exception(s)()
+#include <exception>    // exception, uncaught_exception(s)()
 //#include <functional> // hash
 
 #include <butl/export>
@@ -227,6 +228,18 @@ namespace butl
 #endif
 }
 
+namespace std
+{
+  // Sanitize the exception description before printing. This includes:
+  //
+  // - stripping leading colons and spaces (see fdstream.cxx)
+  // - stripping trailing newlines, periods, and spaces
+  // - lower-case the first letter if the beginning looks like a word
+  //
+  LIBBUTL_EXPORT ostream&
+  operator<< (ostream&, const exception&);
+}
+
 #include <butl/utility.ixx>
 
 #endif // BUTL_UTILITY
diff --git a/butl/utility.cxx b/butl/utility.cxx
index d684553..d971a3f 100644
--- a/butl/utility.cxx
+++ b/butl/utility.cxx
@@ -2,6 +2,8 @@
 // copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
 // license   : MIT; see accompanying LICENSE file
 
+#include <ostream>
+
 #include <butl/utility>
 
 namespace butl
@@ -22,3 +24,69 @@ namespace butl
 
 #endif
 }
+
+namespace std
+{
+  using namespace butl;
+
+  ostream&
+  operator<< (ostream& o, const exception& e)
+  {
+    const char* d (e.what ());
+    const char* s (d);
+
+    // Strip the leading junk (colons and spaces).
+    //
+    // Note that error descriptions for ios_base::failure exceptions thrown by
+    // fdstream can have the ': ' prefix for libstdc++ (read more in comment
+    // for throw_ios_failure()).
+    //
+    for (; *s == ' ' || *s == ':'; ++s) ;
+
+    // Strip the trailing junk (periods, spaces, newlines).
+    //
+    // Note that msvcrt adds some junk like this:
+    //
+    // Invalid data.\r\n
+    //
+    size_t n (string::traits_type::length (s));
+    for (; n > 0; --n)
+    {
+      switch (s[n-1])
+      {
+      case '\r':
+      case '\n':
+      case '.':
+      case ' ': continue;
+      }
+
+      break;
+    }
+
+    // Lower-case the first letter if the beginning looks like a word (the
+    // second character is the lower-case letter or space).
+    //
+    char c;
+    bool lc (n > 0 && alpha (c = s[0]) && c == ucase (c) &&
+             (n == 1 || (alpha (c = s[1]) && c == lcase (c)) || c == ' '));
+
+    // Print the description as is if no adjustment is required.
+    //
+    if (!lc && s == d && s[n] == '\0')
+      o << d;
+    else
+    {
+      // We need to produce the resulting description and then write it
+      // with a single formatted output operation.
+      //
+      string r (s, n);
+
+      if (lc)
+        r[0] = lcase (r[0]);
+
+      o << r;
+    }
+
+    return o;
+  }
+}