FEAT: included function file-checksum returning checksum of a given…

… file's content

src/mezz/mezz-shell.reb

@@ -108,3 +108,24 @@ su: set-user: func[
 		target: file/2
 	]
 ]
+
+file-checksum: function [
+	"Computes a checksum of a given file's content"
+	file   [file!] "Using 256kB chunks"
+	method [word!] "One of system/catalog/checksums"
+][
+	;; it is ok to throw an error on invalid input args
+	port: open join checksum:// method 
+	file: open/read/seek file
+	;; but catch an error when computing the sum,
+	;; so we could close the file later
+	try [
+		while [not empty? bin: read/part file 262144][ write port bin ]
+	]
+	;; not using try to get none as a result in case of errors
+	attempt [
+		close file
+		read port
+	]
+]
+

src/tests/units/checksum-test.r3

@@ -258,4 +258,19 @@ AF45D2E376484031617F78D2B58A6B1B9C7EF464F5A01B47E42EC3736322445E
 	]
 ===end-group===
 
+
+===start-group=== "file-checksum"
+	--test-- "file-checksum with small file"
+	--assert (file-checksum %units/files/pdf-maker-doc.pdf 'md5)    == #{6F782354D64B0B09CF103A9A129E1137}
+	--assert (file-checksum %units/files/pdf-maker-doc.pdf 'sha1)   == #{A598B252C045ABF94EE5F034798B384056C57086}
+	--assert (file-checksum %units/files/pdf-maker-doc.pdf 'sha256) == #{FA24645FE45C06DEB31DEC0B4478718A3ABE3F8C923A3B720B5564DAA2C9FC0F}
+	--test-- "file-checksum with bigger file"
+	--assert binary? file-checksum system/options/boot 'md5 ;; not testing result, because the binary changes.
+===end-group===
+
+
+
+
+
+
 ~~~end-file~~~