MXS-1810: Create generic Checksum class

The Checksum class defines an interface which the SHA1Checksum and
CRC32Checksum implement.

Added test unit test cases to verify that the checksums work and perform
as expected.

server/core/test/test_utils.cc

@@ -12,6 +12,7 @@
  */
 
 #include <maxscale/utils.h>
+#include <maxscale/utils.hh>
 #include <string.h>
 #include <iostream>
 
@@ -118,6 +119,52 @@ int test_trim_trailing()
 
 }
 
+template <typename T>
+int test_checksums()
+{
+    uint8_t data[] =
+    {
+        'h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd', '!'
+    };
+
+    GWBUF* d1 = gwbuf_alloc_and_load(sizeof(data), data);
+    GWBUF* d2 = gwbuf_alloc_and_load(sizeof(data), data);
+
+    T sum1, sum2;
+    sum1.update(d1);
+    sum1.finalize();
+    sum2.finalize(d1);
+    ss_dassert(sum1 == sum2);
+
+    // Check that the hex strings match
+    ss_dassert(sum1.hex() == sum2.hex());
+
+    std::string saved = sum1.hex();
+
+    // The checksum must not be empty
+    ss_dassert(!saved.empty());
+
+    // Repeat the same test, should produce the same checksums
+    sum1.update(d1);
+    sum1.finalize();
+    sum2.finalize(d1);
+    ss_dassert(sum1 == sum2);
+    ss_dassert(sum1.hex() == saved);
+    ss_dassert(sum2.hex() == saved);
+
+    // Check that different buffers but same content produce the same checksum
+    sum1.finalize(d2);
+    sum2.finalize(d1);
+    ss_dassert(sum1 == sum2);
+    ss_dassert(sum1.hex() == saved);
+    ss_dassert(sum2.hex() == saved);
+
+    gwbuf_free(d1);
+    gwbuf_free(d2);
+
+    return 0;
+}
+
 int main(int argc, char* argv[])
 {
     int rv = 0;
@@ -125,6 +172,8 @@ int main(int argc, char* argv[])
     rv += test_trim();
     rv += test_trim_leading();
     rv += test_trim_trailing();
+    rv += test_checksums<mxs::SHA1Checksum>();
+    rv += test_checksums<mxs::CRC32Checksum>();
 
     return rv;
 }