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firestar5683
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Add navigation and map matching providers with the vendored map service sources. Co-authored-by: Daniel Koepping <elkoled@gmail.com> Co-authored-by: Danny <dannyirwin31@yahoo.com> Co-authored-by: Prabhaav Pillai <prabhaav@msu.edu> Co-authored-by: dirwin31 <83434411+dirwin31@users.noreply.github.com>
8 lines
2.3 KiB
Markdown
8 lines
2.3 KiB
Markdown
# Offline tile loader contract
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The path-bound loader accepts one packed Cap'n Proto `Offline` message for the exact requested 0.25° cell. Its filename and decoded root bounds must agree. Empty, well-formed cells are loaded coverage with zero ways. Ways may extend outside the cell because the generator deliberately includes overlapping geometry.
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The packed file read stops at 73 MiB and the Cap'n Proto decoder accepts at most a 64 MiB decoded message. A 256 MiB traversal budget bounds one complete validation pass over all way pointers, optional text, scalar limits, bounds, and nodes. A Way needs the historical 80-byte scalar area (the ID occupies bytes 72–79) and four original pointer slots (name, ref, nodes, hazard). Its three later conditional-text slots may be absent; HighwayClass likewise defaults to `unknown` on older tiles. Coordinate elements need their original 16-byte latitude/longitude area. Larger append-compatible layouts are accepted. Primitive and undersized composite lists cannot impersonate coordinates, and text must be a terminated byte list. The retained message owns its decoded bytes. After every reachable pointer and scalar passes validation, its traversal budget is reset for repeated lazy reads by the existing `Curry` map objects; those objects are not allowed to mutate the retained Cap'n Proto graph or add unchecked pointers. This is a validated-graph exception, not a finite lifetime traversal budget. A genuine generator tile exceeding either limit needs measured size evidence and a reviewed limit change.
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The file descriptor and path must identify the same regular file before and after the bounded read. Opening uses nonblocking and no-follow flags so a FIFO or symlink at the expected basename is rejected without hanging or following it. The cached tile retains device/inode, size, modification time, and change time identity. A same-fix or new-fix update clears road, upcoming, accepted-limit, and map-curve evidence when identity changes, then may reload the replacement. Output serialization checks identity again so a replacement after computation cannot publish the old limit. This detects local file replacement or mutation; it cannot prove tile publication age, geographic completeness, correct-road choice, or posted-limit applicability. Map-derived SLC control remains disabled pending those qualifications.
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