* dd: move argument parsing outside of Input, Output
Move the argument parsing code out of the `Input::new()` and
`Output::new()` functions and into the calling code. This allows the
calling code to make decisions about how to instantiate the `Input`
and `Output` objects if necessary.
* dd: handle stdout redirected to seekable file
Fix a bug in `dd` where null bytes would be unintentionally written if
stdout were redirected to a seekable file. For example, before this
commit, if `dd` were invoked from the command-line as
dd if=infile bs=1 count=10 seek=5 > /dev/sda1
then five zeros would be written to `/dev/sda1` before copying ten
bytes of `infile` to `/dev/sda1`. After this commit, `dd` will
correctly seek five bytes forward in `/dev/sda1` before copying the
ten bytes of `infile`.
Fixes#3542.
The previous encoding handling was unnecessarily complex. This commit removes the enum that specifies the handling and instead has two separate methods to collect the strings either with lossy conversion or by ignoring invalidly encoded strings.
Outside of tests, only `accept_any` was used, meaning that this unnecessarily complicated the code. The behaviour of `accept_any` is now the default (and only) option.
Update `dd` to only print a concise form of the number of bytes with
an SI prefix (like "1 MB" or "2 GB") if the number is at least
1000. Similarly, only print the concise form with an IEC prefix (like
"1 MiB" or "2 GiB") if the number is at least 1024. For example,
$ head -c 999 /dev/zero | dd > /dev/null
1+1 records in
1+1 records out
999 bytes copied, 0.0 s, 999.0 KB/s
$ head -c 1000 /dev/zero | dd > /dev/null
1+1 records in
1+1 records out
1000 bytes (1000 B) copied, 0.0 s, 1000.0 KB/s
$ head -c 1024 /dev/zero | dd > /dev/null
2+0 records in
2+0 records out
1024 bytes (1 KB, 1024 B) copied, 0.0 s, 1.0 MB/s
Move the code for parsing the `ConversionMode` to use up to the
`parseargs` module. This location makes more sense for it because the
conversion mode can be determined entirely from the command-line
arguments at the time of parsing just like the other parameters. Using
an enum for this purpose also eliminates the amount of code we need
later on.
Replace a cascading `if/else if` chain in `conv_block_unblock_helper()`
with a match statement on a new enum, `ConversionMode`, that enumerates
the various modes in which `dd` can operate.
These are the first half of changes needed to pass the dd/bytes.sh tests:
- Add iseek and oseek options (additive with skip and seek options)
- Implement tests for the new flags, matching those from dd/bytes.sh
