On 30.07.2018 11:18, Tanu Kaskinen wrote:
On Sun, 2018-07-29 at 22:36 +0200, Georg Chini wrote:
On 29.07.2018 21:47, Tanu Kaskinen wrote:
On Fri, 2018-07-27 at 10:51 +0200, Georg Chini wrote:
On 27.07.2018 10:08, Tanu Kaskinen wrote:
On Thu, 2018-07-26 at 18:02 +0200, Georg Chini wrote:
On 26.07.2018 12:37, Tanu Kaskinen wrote:
On Sun, 2018-07-22 at 21:11 +0200, Georg Chini wrote:
On 22.07.2018 17:48, Tanu Kaskinen wrote:
On Sun, 2018-07-22 at 16:02 +0200, Georg Chini wrote:
On 21.07.2018 20:17, Tanu Kaskinen wrote:
On Mon, 2018-04-09 at 19:35 +0200, Georg Chini wrote:
+
+/* Read functions */
+
/* Split the specified string into elements. An element is defined as
* a sub-string between curly braces. The function is needed to parse
* the parameters of messages. Each time it is called returns the
position
* of the current element in result and the state pointer is advanced to
- * the next list element.
+ * the next list element. On return, the parameter *is_unpacked indicates
+ * if the string is plain text or contains a sub-list. is_unpacked may
+ * be NULL.
is_unpacked looks like unnecessary complexity.
pa_message_params_read_string() should always unescape the value.
This is not about parameter type, it is just to distinguish between
a list and a simple value. One example comes to my mind immediately:
Consider a parameter list that consists of strings and a couple of
arrays. Now you can read this list as an array of strings (patch 8
provides a function for that) and then examine those strings that
contain arrays separately. Having the flag (and using it in read_string())
provides a more flexible and convenient way to parse a parameter list.
The flag may not be strictly necessary at the moment, but I would still
like to keep it.
To continue a familiar theme of my review: if there's a
read_string_array() function, I want that to be used only for string
arrays, not a mishmash of random types. There could be a separate
function split_list_into_array() that does something similar to
what you wanted to do with read_string_array().
split_list_into_array() wouldn't do special string handling,
though, so unescaping would be left to the application. I find that
only logical, since other basic types don't get special handling
either (i.e. floats aren't converted to C floats).
Your use case could be served with a vararg function that instead of
producing a string array would read into separate variables, like this:
pa_message_params_read(c, state,
PA_TYPE_STRING, ¶m1,
PA_TYPE_FLOAT, ¶m2,
PA_TYPE_RAW, ¶m3,
0);
PA_TYPE_RAW would be useful for reading a list (or anything else) into
a C string without unescaping or other processing. There could be also
PA_TYPE_IGNORE for uninteresting variables, and PA_TYPE_*_ARRAY for
arrays of basic types.
(Now it occurred to me that the 'c' argument name that is used in the
parsing functions is a bit weird and unhelpful. Maybe "param_list"
would be good?)
I still don't see your point. Again, the use of is_unpacked is
transparent for the
user of read_string(), so the user just reads a string without having to
care about
unescaping. The flag does not complicate the API, it simplifies it
because the
unescaping is done automatically.
The flag complicates the split_list() function parameters, but also the
read_string() semantics: you need to explain to the user that unlike
all the other read_foo() functions, read_string() can read any value
and unescaping becomes conditional because of this.
read_string() is not supposed to read any value, it is only supposed
to read strings. Actually, the user does not need to know anything
about escaping, because read_string() and write_string() do the
necessary escaping/unescaping completely transparent for the user.
The is_unpacked flag is at least useful to check if something returned
by split_list() is really a simple type and not a structure or array. I am
currently not using it in the read_foo() functions, but I think I should.
Your approach seems unnecessary
complicated to me. A string is a string, even if it contains
sub-structures. Your
split_list_into_array() function would basically return an array of
strings, so what
would be the advantage? It would only make parsing more cumbersome, because
the task of unescaping is given to the user instead of doing it
automatically where
necessary.
That's why I came up with the vararg function. I agree that
split_list_into_array() is unlikely to be very useful.
Also there is no "mishmash of random types", they are all strings It is
only the
difference between a "simple" string which needs no further processing and a
"complex" string which needs further parsing.
The API defines types for the parameters. There are no separate
"simple" and "complex" strings in the type system. The string type is
different than the list type. What you call complex strings are in my
mind just the raw unprocessed serialized data, which is a different
abstraction level than the values that the various read_foo() functions
return. It feels just very wrong to have a function that returns values
in both domains: unparsed raw data and parsed values. Especially when
the function is a family of read_foo() functions where all other
functions only operate on their designated types.
Yes, that is some additional functionality that the read_string()
function provides on top of reading what I called "simple strings"
above. But that does not hinder the function to work exactly
like expected when reading a plain string. Maybe a better name
for the function would be read_string_element(), indicating that
it can read either a plain string or an element of the parameter
list as a string.
I could split this into two functions, read_string() which always
does unescaping and read_element() which would be a wrapper
around split_list() and would never do unescaping. In both functions,
the is_unpacked flag can be useful to check if the input matches
the type "plain string" or "serialized data".
Compare to D-Bus: if you say that "they are all strings", then in D-Bus
the same would be "they are all byte arrays", since that's what they
are in the message buffer. I doubt you would suggest that the
dbus_message_iter_read_byte_array() function (if such thing existed)
should be usable on arbitrarily typed values rather than just byte
array values, and should return the raw serialized data regardless of
its type. Here you're suggesting that read_string() should be able to
return the raw serialized data regardless of its type.
Do you understand what I'm getting at? You may disagree that having
strict separation of concerns between raw serialized data and parsed
values is beneficial for the user-friendliness of the API, but if you
don't even understand what I mean by that separation, then discussing
this is very hard.
I do understand your reasoning and technically we surely could drop
the flag. I just don't want it because for me using read_string() is a
more convenient way of parsing a parameter list than using split_list()
directly. It's just a simple way to say "let's skip this array or structure
for the moment and store it somewhere for later inspection". So I can
do something like
x = read_float()
y = read_int()
my_structure = read_string()
z = read_bool()
a = read_string()
and then examine my_structure at a later time. Using split_list() instead
of read_string() is somehow breaking the flow for me. We could do the
same with the read_element() function I suggested above (and then
maybe make split_list() a purely internal function?)
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