Hi Chris,
this is exactly the idea I have in mind.
For me in your step 1 I again see two steps.
First, you have the decoding logic (e.g. your public static float
parseIEEE754Float(byte[] in)) and then you have all this ugly branching like
If (bytes.length = 4) {
If (isDecimal()) {
If (isBigEndian()) {
// Here call the static helper method
}
}
}
which I would love to avoid (and which makes it perhaps more comfortable for
users to implement their drivers).
But perhaps I am making things to complicated and we usually have only a small
set of possibilities.
Then i agree that we could keep things as they are.
Best
Julian
Am 17.08.18, 15:38 schrieb "Christofer Dutz" <[email protected]>:
Hi Julian,
to me it sounds like two separate things:
1) Decoding what's coming from the outside
2) Converting the decoded types to other types as far as that's possible
So the driver should know what the bytes mean that come from the PLC and on
top of that we could convert that into something else.
We would need such a two phase conversion to do that anyway, otherwise we
would sort of need the cartesian set of all combinations of converters.
I do agree that this "interpret this integer as a Boolean", or "translate
this float into an int" sounds universally usable.
Correct?
Chris
Am 17.08.18, 15:03 schrieb "Julian Feinauer" <[email protected]>:
Hi Chris,
you are right with what I want to do, let me explain my motivation.
Your example is right but I think there are many situations where this
is not sufficient, especially with regards to the new Address Syntax for S7.
Basically the new syntax allows me to state something like this:
"I know that the value is 2 byte unsigned integer in little Endian
Order and I want it back as Long".
So the first idea was that I wanted to avoid having many methods for
all combinations of Endianness, bit-length, Signed / Unsigned and Decimal /
Float.
And the second idea to also provide narrowing or widening or even
conversion out of the box.
I came across this issue when thinking about the migration of the
current conversion in the S7 driver which is like a large if
(XXX.class.isInstance(...)) else... and thought it would be better for the
drive to just say something like
parse(Class<?> target, byte[] in, Representation repr)
to avoid the m times n problem for Java Types and byte Representation.
But if you (and the other driver implementors) do not see this concern
that much I can also shift my effort to something else.
Best
Julian
Am 17.08.18, 14:41 schrieb "Christofer Dutz"
<[email protected]>:
Hi Julian,
please let me repeat how I understood your proposal:
You observed that in multiple drivers the conversion between
byte-array data to the actual Java type is pretty similar and would like to
wrap that mapping code in some commonly shared code base?
I agree ... if a float is transformed as IEEE 754 Floating Point,
it doesn't matter what driver this belongs to. But on the other side the code
for doing this conversion too isn't that complex.
I think in this case eventually even a class with static methods
should be enough... sort of
public static float parseIEEE754Float(byte[] in);
public static int parseLE32BitInt(byte[] in);
...
Maintaining a registry component that has to be injected into the
drivers of type conversions where drivers can register custom converters sounds
a little overkill to me.
If a driver requires other conversions, it can implement them
itself and if it makes sense to add them to the driver-base version, that code
is simply moved there.
What do you think?
Chris
Am 17.08.18, 14:14 schrieb "Julian Feinauer"
<[email protected]>:
Hey al,
I like to open another discussion as I am currently working on
another refactoring of the Drivers, namely the extraction of "binary" encoders
and decoders as common concern. After our discussion about the addition of the
binary representation to the S7 driver I observed that several drivers use very
similar code to transform java types to byte representations of specific flavor
(Big Endian, ...).
Thus my aim is to provide a “library” of common encoders and
decoders between Java Types and byte representations that every driver can use
but also register custom Java Types and their representation (as it is e.g.
needed for ADS, I think).
Do you agree with this?
Julian
