dd: block/unblock on ebcdic/ascii conversions

Update `dd` so that the conversion `conv=ascii` implies `conv=unblock`
and, symmetrically, the conversion `conv=ebcdic` implies `conv=block`.

src/uu/dd/src/parseargs.rs

@@ -444,13 +444,40 @@ pub fn parse_conv_flag_input(matches: &Matches) -> Result<IConvFlags, ParseError
  return Err(ParseError::MultipleFmtTable);
  } else {
  fmt = Some(flag);
+ // From the GNU documentation:
+ //
+ // > ‘ascii’
+ // >
+ // > Convert EBCDIC to ASCII, using the conversion
+ // > table specified by POSIX. This provides a 1:1
+ // > translation for all 256 bytes. This implies
+ // > ‘conv=unblock’; input is converted to ASCII
+ // > before trailing spaces are deleted.
+ //
+ // -- https://www.gnu.org/software/coreutils/manual/html_node/dd-invocation.html
+ if cbs.is_some() {
+ iconvflags.unblock = cbs;
+ }
  }
  }
  ConvFlag::FmtAtoE => {
  if fmt.is_some() {
  return Err(ParseError::MultipleFmtTable);
  } else {
  fmt = Some(flag);
+ // From the GNU documentation:
+ //
+ // > ‘ebcdic’
+ // >
+ // > Convert ASCII to EBCDIC. This is the inverse
+ // > of the ‘ascii’ conversion. This implies
+ // > ‘conv=block’; trailing spaces are added before
+ // > being converted to EBCDIC.
+ //
+ // -- https://www.gnu.org/software/coreutils/manual/html_node/dd-invocation.html
+ if cbs.is_some() {
+ iconvflags.block = cbs;
+ }
  }
  }
  ConvFlag::FmtAtoI => {

tests/by-util/test_dd.rs

@@ -559,5 +559,38 @@ fn test_unicode_filenames() {
  );
 }
 
+#[test]
+fn test_conv_ascii_implies_unblock() {
+ // 0x40 = 0o100 = 64, which gets converted to ' '
+ // 0xc1 = 0o301 = 193, which gets converted to 'A'
+ //
+ // `conv=ascii` implies `conv=unblock`, which means trailing paces
+ // are stripped and a newline is appended at the end of each
+ // block.
+ //
+ // `cbs=4` means use a conversion block size of 4 bytes per block.
+ new_ucmd!()
+ .args(&["conv=ascii", "cbs=4"])
+ .pipe_in(b"\x40\xc1\x40\xc1\x40\xc1\x40\x40".to_vec())
+ .succeeds()
+ .stdout_is(" A A\n A\n");
+}
+
+#[test]
+fn test_conv_ebcdic_implies_block() {
+ // 0x40 = 0o100 = 64, which is the result of converting from ' '
+ // 0xc1 = 0o301 = 193, which is the result of converting from 'A'
+ //
+ // `conv=ebcdic` implies `conv=block`, which means trailing spaces
+ // are added to pad each block.
+ //
+ // `cbs=4` means use a conversion block size of 4 bytes per block.
+ new_ucmd!()
+ .args(&["conv=ebcdic", "cbs=4"])
+ .pipe_in(" A A\n A\n")
+ .succeeds()
+ .stdout_is_bytes(b"\x40\xc1\x40\xc1\x40\xc1\x40\x40");
+}
+
 // conv=[ascii,ebcdic,ibm], conv=[ucase,lcase], conv=[block,unblock], conv=sync
 // TODO: Move conv tests from unit test module