server.py

""" Helper functions to communicate with replication servers.
"""

import requests
import urllib.request as urlrequest
import datetime as dt
from collections import namedtuple
from math import ceil
from osmium import MergeInputReader
from osmium import io as oio
from osmium import version

import logging

LOG = logging.getLogger('pyosmium')
LOG.addHandler(logging.NullHandler())

OsmosisState = namedtuple('OsmosisState', ['sequence', 'timestamp'])
DownloadResult = namedtuple('DownloadResult', ['id', 'reader', 'newest'])

class ReplicationServer:
    """ Represents a server that publishes replication data. Replication
        change files allow to keep local OSM data up-to-date without downloading
        the full dataset again.
    """

    def __init__(self, url, diff_type='osc.gz'):
        self.baseurl = url
        self.diff_type = diff_type
        self.session = requests.Session()

    def make_request(self, url):
        headers = {"User-Agent" : "pyosmium/{}".format(version.pyosmium_release)}
        return urlrequest.Request(url, headers=headers)

    def open_url(self, url):
        """ Download a resource from the given URL and return a byte sequence
            of the content.

            This method has no support for cookies or any special authentication
            methods. If you need these, you have to provide your own custom URL
            opener. The method has to return an object which supports the
            `read()` and `readline()` methods to access the content. Example::

                def my_open_url(self, url):
                    opener = urlrequest.build_opener()
                    opener.addheaders = [('X-Fancy-Header', 'important_content')]
                    return opener.open(url)

                svr = ReplicationServer()
                svr.open_url = my_open_url
        """
        headers = dict()
        for h in url.header_items():
            headers[h[0]] = h[1]
        return self.session.get(url.get_full_url(), headers=headers, stream=True)

    def collect_diffs(self, start_id, max_size=1024):
        """ Create a MergeInputReader and download diffs starting with sequence
            id `start_id` into it. `max_size`
            restricts the number of diffs that are downloaded. The download
            stops as soon as either a diff cannot be downloaded or the
            unpacked data in memory exceeds `max_size` kB.

            If some data was downloaded, returns a namedtuple with three fields:
            `id` contains the sequence id of the last downloaded diff, `reader`
            contains the MergeInputReader with the data and `newest` is a
            sequence id of the most recent diff available.

            Returns None if there was an error during download or no new
            data was available.
        """
        left_size = max_size * 1024
        current_id = start_id

        # must not read data newer than the published sequence id
        # or we might end up reading partial data
        newest = self.get_state_info()

        if newest is None or current_id > newest.sequence:
            return None

        rd = MergeInputReader()

        while left_size > 0 and current_id <= newest.sequence:
            try:
                diffdata = self.get_diff_block(current_id)
            except:
                LOG.debug("Error during diff download. Bailing out.")
                diffdata = ''
            if len(diffdata) == 0:
                if start_id == current_id:
                    return None
                break

            left_size -= rd.add_buffer(diffdata, self.diff_type)
            LOG.debug("Downloaded change %d. (%d kB available in download buffer)",
                      current_id, left_size / 1024)
            current_id += 1

        return DownloadResult(current_id - 1, rd, newest.sequence)

    def apply_diffs(self, handler, start_id, max_size=1024, idx="", simplify=True):
        """ Download diffs starting with sequence id `start_id`, merge them
            together and then apply them to handler `handler`. `max_size`
            restricts the number of diffs that are downloaded. The download
            stops as soon as either a diff cannot be downloaded or the
            unpacked data in memory exceeds `max_size` kB.

            If `idx` is set, a location cache will be created and applied to
            the way nodes. You should be aware that diff files usually do not
            contain the complete set of nodes when a way is modified. That means
            that you cannot just create a new location cache, apply it to a diff
            and expect to get complete way geometries back. Instead you need to
            do an initial data import using a persistent location cache to
            obtain a full set of node locations and then reuse this location
            cache here when applying diffs.

            Diffs may contain multiple versions of the same object when it was
            changed multiple times during the period covered by the diff. If
            `simplify` is set to False then all versions are returned. If it
            is True (the default) then only the most recent version will be
            sent to the handler.

            The function returns the sequence id of the last diff that was
            downloaded or None if the download failed completely.
        """
        diffs = self.collect_diffs(start_id, max_size)

        if diffs is None:
            return None

        diffs.reader.apply(handler, idx=idx, simplify=simplify)

        return diffs.id

    def apply_diffs_to_file(self, infile, outfile, start_id, max_size=1024,
                            set_replication_header=True, extra_headers=None,
                            outformat=None):
        """ Download diffs starting with sequence id `start_id`, merge them
            with the data from the OSM file named `infile` and write the result
            into a file with the name `outfile`. The output file must not yet
            exist.

            `max_size` restricts the number of diffs that are downloaded. The
            download stops as soon as either a diff cannot be downloaded or the
            unpacked data in memory exceeds `max_size` kB.

            If `set_replication_header` is true then the URL of the replication
            server and the sequence id and timestamp of the last diff applied
            will be written into the `writer`. Note that this currently works
            only for the PBF format.

            `extra_headers` is a dict with additional header fields to be set.
            Most notably, the 'generator' can be set this way.

            `outformat` sets the format of the output file. If None, the format
            is determined from the file name.

            The function returns a tuple of last downloaded sequence id and
            newest available sequence id if new data has been written or None
            if no data was available or the download failed completely.
        """
        diffs = self.collect_diffs(start_id, max_size)

        if diffs is None:
            return None

        reader = oio.Reader(infile)
        has_history = reader.header().has_multiple_object_versions

        h = oio.Header()
        h.has_multiple_object_versions = has_history
        if set_replication_header:
            h.set("osmosis_replication_base_url", self.baseurl)
            h.set("osmosis_replication_sequence_number", str(diffs.id))
            info = self.get_state_info(diffs.id)
            if info is not None:
                h.set("osmosis_replication_timestamp", info.timestamp.strftime("%Y-%m-%dT%H:%M:%SZ"))
        if extra_headers is not None:
            for k, v in extra_headers.items():
                h.set(k, v)

        if outformat is None:
            of = oio.File(outfile)
        else:
            of = oio.File(outfile, outformat)

        of.has_multiple_object_versions = has_history
        writer = oio.Writer(of, h)

        LOG.debug("Merging changes into OSM file.")

        diffs.reader.apply_to_reader(reader, writer, has_history)

        reader.close()
        writer.close()

        return (diffs.id, diffs.newest)


    def timestamp_to_sequence(self, timestamp, balanced_search=False):
        """ Get the sequence number of the replication file that contains the
            given timestamp. The search algorithm is optimised for replication
            servers that publish updates in regular intervals. For servers
            with irregular change file publication dates 'balanced_search`
            should be set to true so that a standard binary search for the
            sequence will be used. The default is good for all known
            OSM replication services.
        """

        # get the current timestamp from the server
        upper = self.get_state_info()

        if upper is None:
            return None
        if timestamp >= upper.timestamp or upper.sequence <= 0:
            return upper.sequence

        # find a state file that is before the required timestamp
        lower = None
        lowerid = 0
        while lower is None:
            LOG.debug("Trying with Id %s", lowerid)
            lower = self.get_state_info(lowerid)

            if lower is not None and lower.timestamp >= timestamp:
                if lower.sequence == 0 or lower.sequence + 1 >= upper.sequence:
                    return lower.sequence
                upper = lower
                lower = None
                lowerid = 0

            if lower is None:
                # no lower yet, so try a higher id (binary search wise)
                newid = int((lowerid + upper.sequence) / 2)
                if newid <= lowerid:
                    # nothing suitable found, so upper is probably the best we can do
                    return upper.sequence
                lowerid = newid

        # Now do a binary search between upper and lower.
        # We could be clever here and compute the most likely state file
        # by interpolating over the timestamps but that creates a whole ton of
        # special cases that need to be handled correctly.
        while True:
            if balanced_search:
                base_splitid = int((lower.sequence + upper.sequence) / 2)
            else:
                ts_int = (upper.timestamp - lower.timestamp).total_seconds()
                seq_int = upper.sequence - lower.sequence
                goal = (timestamp - lower.timestamp).total_seconds()
                base_splitid = lower.sequence + ceil(goal * seq_int / ts_int)
                if base_splitid >= upper.sequence:
                    base_splitid = upper.sequence - 1
            split = self.get_state_info(base_splitid)

            if split is None:
                # file missing, search the next towards lower
                splitid = base_splitid - 1
                while split is None and splitid > lower.sequence:
                    split = self.get_state_info(splitid)
                    splitid -= 1
            if split is None:
                # still nothing? search towards upper
                splitid = base_splitid + 1
                while split is None and splitid < upper.sequence:
                    split = self.get_state_info(splitid)
                    splitid += 1
            if split is None:
                # still nothing? Then lower has to do
                return lower.sequence

            # set new boundary
            if split.timestamp < timestamp:
                lower = split
            else:
                upper = split

            if lower.sequence + 1 >= upper.sequence:
                return lower.sequence


    def get_state_info(self, seq=None, retries=2):
        """ Downloads and returns the state information for the given
            sequence. If the download is successful, a namedtuple with
            `sequence` and `timestamp` is returned, otherwise the function
            returns `None`. `retries` sets the number of times the download
            is retried when pyosmium detects a truncated state file.
        """
        for _ in range(retries + 1):
            try:
                response = self.open_url(self.make_request(self.get_state_url(seq)))
            except Exception as err:
                LOG.debug("Loading state info %s failed with: %s", seq, str(err))
                return None

            ts = None
            seq = None
            if hasattr(response, 'iter_lines'):
                # generated by requests
                get_line = response.iter_lines
            else:
                # generated by urllib.request
                get_line = response.readline

            for line in get_line():
                line = line.decode('utf-8')
                if '#' in line:
                    line = line[0:line.index('#')]
                else:
                    line = line.strip()
                if line:
                    kv = line.split('=', 2)
                    if len(kv) != 2:
                        return None
                    if kv[0] == 'sequenceNumber':
                        seq = int(kv[1])
                    elif kv[0] == 'timestamp':
                        try:
                            ts = dt.datetime.strptime(kv[1], "%Y-%m-%dT%H\\:%M\\:%SZ")
                        except ValueError:
                            break
                        ts = ts.replace(tzinfo=dt.timezone.utc)

            if ts is not None and seq is not None:
                return OsmosisState(sequence=seq, timestamp=ts)

        return None

    def get_diff_block(self, seq):
        """ Downloads the diff with the given sequence number and returns
            it as a byte sequence. Throws a :code:`urllib.error.HTTPError`
            if the file cannot be downloaded.
        """
        resp = self.open_url(self.make_request(self.get_diff_url(seq)))
        if hasattr(resp, 'content'):
            # generated by requests
            return resp.content
        else:
            # generated by urllib.request
            return resp.read()


    def get_state_url(self, seq):
        """ Returns the URL of the state.txt files for a given sequence id.

            If seq is `None` the URL for the latest state info is returned,
            i.e. the state file in the root directory of the replication
            service.
        """
        if seq is None:
            return self.baseurl + '/state.txt'

        return '%s/%03i/%03i/%03i.state.txt' % \
               (self.baseurl, seq / 1000000, (seq % 1000000) / 1000, seq % 1000)


    def get_diff_url(self, seq):
        """ Returns the URL to the diff file for the given sequence id.
        """
        return '%s/%03i/%03i/%03i.%s' % \
               (self.baseurl,
                seq / 1000000, (seq % 1000000) / 1000, seq % 1000,
                self.diff_type)