Do not use input header for error responses

When parsing of the input header fails, it could be for a variety of
issues, including an overflow of the language tag length. We should not
utilize any variable aspects of the header in our response and
instead just send back a default of all 0's with the static fields set
along with error the code.

Utilize std::bitset to get the function ID properly written to
cout/cerr.

Tested:
- Verified when sending in an invalid header, it no longer can cause
  unexpected error paths in parseHeader function

Change-Id: I17a8a013bcd90e083b1156f794f059fc1b830a63
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
diff --git a/test/slp_message_handler_test.cpp b/test/slp_message_handler_test.cpp
new file mode 100644
index 0000000..a756bd2
--- /dev/null
+++ b/test/slp_message_handler_test.cpp
@@ -0,0 +1,101 @@
+#include "slp.hpp"
+#include "slp_meta.hpp"
+
+#include <gtest/gtest.h>
+
+// Header
+/*  0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |    Version    |  Function-ID  |            Length             |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Length, contd.|O|F|R|       reserved          |Next Ext Offset|
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Next Extension Offset, contd.|              XID              |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |      Language Tag Length      |         Language Tag          \
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ */
+
+// Error response
+/*  0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |        Service Location header (function = SrvRply = 2)       |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |        Error Code             |        URL Entry count        |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |       <URL Entry 1>          ...       <URL Entry N>          \
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+*/
+
+TEST(processError, BasicGoodPath)
+{
+    // Basic buffer with valid Function-ID
+    slp::buffer testData{0x02, 0x01, 0x00, 0x00, 0x0E, 0x00, 0x00,
+                         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+    slp::Message req;
+    int rc = slp::SUCCESS;
+    std::tie(rc, req) = slp::parser::internal::parseHeader(testData);
+
+    EXPECT_EQ(rc, 0);
+
+    // Verify all expected fields show up in response buffer
+    std::vector<uint8_t> resp = slp::handler::processError(
+        req, static_cast<uint8_t>(slp::Error::MSG_NOT_SUPPORTED));
+
+    EXPECT_EQ(resp.size(), slp::header::MIN_LEN + slp::response::SIZE_ERROR);
+    EXPECT_EQ(resp[slp::header::OFFSET_VERSION], 2);
+    EXPECT_EQ(resp[slp::header::OFFSET_FUNCTION], 2);
+    EXPECT_EQ(resp[slp::header::MIN_LEN + 1],
+              static_cast<uint8_t>(slp::Error::MSG_NOT_SUPPORTED));
+}
+
+TEST(processError, InvalidLangTag)
+{
+    // Basic buffer with valid Function-ID
+    slp::buffer testData{0x02, 0x01, 0x00, 0x00, 0x0E, 0x00, 0x00,
+                         0x00, 0x00, 0x00, 0x00, 0x00, 0x10, 0x10,
+                         0x00, 0x01, 0x02, 0x03, 0x04};
+
+    slp::Message req;
+    int rc = slp::SUCCESS;
+    std::tie(rc, req) = slp::parser::internal::parseHeader(testData);
+
+    EXPECT_NE(rc, 0);
+
+    // Verify all expected fields show up in response buffer even
+    // with an inavlid langugage tag size in the header
+    std::vector<uint8_t> resp = slp::handler::processError(
+        req, static_cast<uint8_t>(slp::Error::MSG_NOT_SUPPORTED));
+
+    EXPECT_EQ(resp.size(), slp::header::MIN_LEN + slp::response::SIZE_ERROR);
+    EXPECT_EQ(resp[slp::header::OFFSET_VERSION], 2);
+    EXPECT_EQ(resp[slp::header::OFFSET_FUNCTION], 2);
+    EXPECT_EQ(resp[slp::header::MIN_LEN + 1],
+              static_cast<uint8_t>(slp::Error::MSG_NOT_SUPPORTED));
+}
+
+TEST(processError, InvalidEverything)
+{
+    // Basic buffer with valid Function-ID
+    slp::buffer testData{0x03, 0x99, 0x99, 0x99, 0xA0, 0xA0, 0xA1,
+                         0xA2, 0xB9, 0x55, 0x44, 0x33, 0x21, 0x90,
+                         0x78, 0x1,  0x02, 0x03, 0x04};
+
+    slp::Message req;
+    int rc = slp::SUCCESS;
+    std::tie(rc, req) = slp::parser::internal::parseHeader(testData);
+
+    EXPECT_NE(rc, 0);
+
+    // Verify all expected fields show up in response buffer even
+    // with an inavlid langugage tag size in the header
+    std::vector<uint8_t> resp = slp::handler::processError(
+        req, static_cast<uint8_t>(slp::Error::MSG_NOT_SUPPORTED));
+
+    EXPECT_EQ(resp.size(), slp::header::MIN_LEN + slp::response::SIZE_ERROR);
+    EXPECT_EQ(resp[slp::header::OFFSET_VERSION], 3);
+    EXPECT_EQ(resp[slp::header::OFFSET_FUNCTION], 0x9A);
+    EXPECT_EQ(resp[slp::header::MIN_LEN + 1],
+              static_cast<uint8_t>(slp::Error::MSG_NOT_SUPPORTED));
+}