Example code:

class Source(gst.BaseSrc):
    __gsttemplates__ = (
        gst.PadTemplate("src",
                        gst.PAD_SRC,
                        gst.PAD_ALWAYS,
                        gst.caps_new_any()),
                       )
    blocksize = 4096
    def __init__(self, name, config, track):
        self.__gobject_init__()
        self.set_name(name)
        self.buf = Buffer(track, config=config) #my class that downloads file
    def do_create(self, offset, size):
        if self.buf.length and offset > self.buf.length:
            return gst.FLOW_UNEXPECTED, None
        while self.buf.pos < offset+size and not self.buf.finished:
            sleep(0.1) # i don't know should i use this here
        self.buf.file.seek(offset)
        data = self.buf.file.read(size)
        return gst.FLOW_OK, gst.Buffer(data)
    def do_query (self, query):
        if query.type == gst.QUERY_DURATION:
            while not self.buf.track.length:
                sleep(0.01)
            if query.parse_duration()[0] == gst.FORMAT_TIME:
                lent = self.buf.track.length*gst.SECOND
                query.set_duration(gst.FORMAT_TIME, lent)
                query.stucture = gst.Query
                return True
            elif query.parse_duration()[0] == gst.FORMAT_BYTES:
                query.set_duration(format=gst.FORMAT_BYTES, duration=self.buf.length/self.blocksize)
                return True
            else:
                return False
            return False
        elif query.type == gst.QUERY_LATENCY:
            query.set_latency(min_latency=0, live=False, max_latency=-1)
            return True
        else:
            print 'UNHANDLED QUERY:', query.type
            return False

#use this as a source for pipeline:
player = gst.Pipeline("pipeline")
source = Source("bufsrc", config, track)
decoder = gst.element_factory_make("mad", "mp3-decoder")
conv = gst.element_factory_make("audioconvert", "converter")
sink = gst.element_factory_make("autoaudiosink", "alsa-output")
player.add(source, decoder, conv, sink)
gst.element_link_many(source, decoder, conv, sink)

I can't test this code (it's missing config, Buffer, etc...).

The following seems wrong though : query.structure = gst.Query
(1) you're assigning a class and not an instance
(2) structure take .. a gst.Structure and not a gst.Query

I've just rechecked on another gst.BaseSrc plugin I had, implemented the query handling... and it seems to work perfectly fine.

Created attachment 134086 [details]
Example gst.BaseSrc implementation with query handling

This is the example gst.BaseSrc implementation I was talking about. Works fine with the gst-python pre-releases

Created attachment 134124 [details]
Warnings appear on this example

Here is simple example where this bug appears.

(In reply to comment #3)
> Created an attachment (id=134086) [edit]
> Example gst.BaseSrc implementation with query handling
> 
> This is the example gst.BaseSrc implementation I was talking about. Works fine
> with the gst-python pre-releases
> 

I get same warning on your example with gstreamer0.10-python-0.10.14 on ArchLinux and Ubuntu.

confirmed fixed over IRC.

<[A2K]> bilboed-pi: successfully compiled after installing -base pre-release and bug does not appear any more