file_checksum: work on empty files and test

Author: scivision

+stdlib/+dotnet/file_checksum.m

@@ -28,5 +28,4 @@
 
 fclose(fid);
 
-
 end

+stdlib/+java/file_checksum.m

@@ -14,10 +14,13 @@
 
 try
 
-  inst = java.security.MessageDigest.getInstance(hash_method);
+  inst = javaMethod('getInstance', 'java.security.MessageDigest', hash_method);
   while ~feof(fid)
     % https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/security/MessageDigest.html#update(byte)
-    inst.update(fread(fid, file_chunk, '*uint8'));
+    [bytes, count] = fread(fid, file_chunk, '*uint8');
+    if count
+      inst.update(bytes);
+    end
   end
   % https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/security/MessageDigest.html#digest()
   hash = sprintf('%.2x', typecast(inst.digest, 'uint8'));

test/TestHash.m

@@ -3,10 +3,14 @@
     TestHash < matlab.unittest.TestCase
 
 properties
-file
+file = 'hello.txt'
+empty = 'empty.txt'
 end
 
 properties (TestParameter)
+Pe = {{'md5', 'd41d8cd98f00b204e9800998ecf8427e'}, ...
+    {'sha-256', 'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855'}}
+
 Ph = {{'md5', '5d41402abc4b2a76b9719d911017c592'}, ...
       {'sha-256', '2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824'}}
 backend = {'java', 'dotnet', 'sys'}
@@ -17,19 +21,18 @@
 function create_file(tc)
 tc.applyFixture(matlab.unittest.fixtures.WorkingFolderFixture());
 
-tc.file = fullfile(pwd(), class(tc));
-
 fid = fopen(tc.file, "w");
-
 tc.assumeGreaterThan(fid, 0);
 fprintf(fid, "hello");
 fclose(fid);
+tc.assumeTrue(isfile(tc.file))
+tc.assertEqual(stdlib.file_size(tc.file), 5)
 
-if stdlib.matlabOlderThan('R2018a')
-  tc.assumeTrue(isfile(tc.file))
-else
-  tc.assertThat(tc.file, matlab.unittest.constraints.IsFile)
-end
+fid = fopen(tc.empty, "w");
+tc.assumeGreaterThan(fid, 0);
+fclose(fid);
+tc.assumeTrue(isfile(tc.empty))
+tc.assertEqual(stdlib.file_size(tc.empty), 0)
 end
 end
 
@@ -50,6 +53,19 @@ function test_hash_text(tc, Ph, backend)
 end
 
 
+function test_hash_empty(tc, Pe, backend)
+
+r = stdlib.file_checksum(tc.empty, Pe{1}, backend);
+tc.verifyClass(r, 'char')
+
+if ismember(backend, stdlib.Backend().select('file_checksum'))
+  tc.verifyEqual(r, Pe{2})
+else
+  tc.assertEmpty(r)
+end
+end
+
+
 function test_has_convenience(tc, Ph)
 switch Ph{1}
   case 'md5', tc.verifyEqual(stdlib.md5sum(tc.file), Ph{2})