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?)
