Improve the las reader's file signature error

Catch the las header's invalid file signature error and improve the
error message, mostly by including the file name. In order to provide
the filename under more circumstances, set the "filename" option when
using the filename-only las::Reader constructor.

Fixes #277.

src/drivers/las/Reader.cpp

@@ -86,7 +86,7 @@ Reader::Reader(const Options& options)
 
 
 Reader::Reader(const std::string& filename)
-    : ReaderBase(Options::none())
+    : ReaderBase(Option("filename", filename))
     , m_streamFactory(new FilenameStreamFactory(filename))
     , m_ownsStreamFactory(true)
 {}
@@ -115,7 +115,23 @@ void Reader::initialize()
     std::istream& stream = m_streamFactory->allocate();
 
     LasHeaderReader lasHeaderReader(m_lasHeader, stream);
-    lasHeaderReader.read(*this, m_schema);
+    try
+    {
+        lasHeaderReader.read(*this, m_schema);
+    }
+    catch (const std::invalid_argument& e)
+    {
+        // Improve the error message. #277
+        std::stringstream msg;
+        std::string filename(getOptions().getValueOrDefault<std::string>("filename", ""));
+        if (filename.empty())
+        {
+            throw e;
+        }
+        msg << "Unable to read file " << filename
+            << ". It does not have a las file signature.";
+        throw std::invalid_argument(msg.str());
+    }
 
     this->setBounds(m_lasHeader.getBounds());
     this->setNumPoints(m_lasHeader.GetPointRecordsCount());

test/unit/drivers/las/LasReaderTest.cpp

@@ -455,4 +455,29 @@ BOOST_AUTO_TEST_CASE(test_no_xyz)
 }
 
 
+BOOST_AUTO_TEST_CASE(testFilenameConstructorSetOption)
+{
+    pdal::drivers::las::Reader reader(Support::datapath("1.2-with-color.las"));
+    BOOST_CHECK_EQUAL(reader.getOptions().getValueOrDefault<std::string>("filename", ""),
+            Support::datapath("1.2-with-color.las"));
+}
+
+
+BOOST_AUTO_TEST_CASE(testInvalidFileSignature)
+{
+    pdal::drivers::las::Reader reader(Support::datapath("1.2-with-color.las.wkt"));
+    try
+    {
+        reader.initialize();
+    }
+    catch (const std::invalid_argument& e)
+    {
+        std::string msg(e.what());
+        BOOST_CHECK(msg.find("1.2-with-color.las.wkt") != std::string::npos);
+        return;
+    }
+    BOOST_FAIL("reader.initialize() did not throw std::invalid_argument");
+}
+
+
 BOOST_AUTO_TEST_SUITE_END()