Commit e9c950af authored by Nick Mathewson's avatar Nick Mathewson 👜
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src/config/README: add documentation for geoip format.

parent 769d54c5
......@@ -33,3 +33,32 @@
most people shouldn't mess with.
On the geoip format:
Our geoip files are line-oriented. Any empty line, or line starting
with a #, is ignored.
All other lines are composed of three comma-separated values:
START,END,CC. For the geoip file, START and END are IPv4 addresses
as expressed as 32-bit integers (such as 3325256709 to represent For the geoip6 file, START and END are IPv6
addresses, with no brackets. In both cases CC is a two-character
country code.
The semantic meaning of a line START,END,CC is that all addresses
between START and END _inclusive_ should be mapped to the country code
We guarantee that all entries within these files are disjoint --
that is, there is no address that is matched by more than one
line. We also guarantee that all entries within these files are
sorted in numerically ascending order by address.
Thus, one effective search algorithm here is to perform a binary
search on all the entries in the file.
Note that there _are_ "gaps" in these databases: not every possible
address maps to a country code. In those cases, Tor reports the
country as ??.
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