Resolve PTR names over DNS-over-HTTPS and cache them for the record TTL (closes #238)
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`internal/ptr` asks Google, Cloudflare, AdGuard and Quad9 in turn, 2 seconds in all per address. It keeps answers in memory and writes them through to `cache.db`, opened by the new `internal/cachedb`. A reserved address is not sent to the resolvers. Judgement calls: - Each resolver gets an equal share of the time left, so a hung resolver does not use up the 2 seconds. - The negative TTL is the smaller of the SOA minimum and the SOA's own TTL (RFC 2308). - Names that are not host names are dropped, as `net.Resolver.LookupAddr` does. Model: opus-5-5
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@@ -281,8 +281,8 @@ answer holds `query`, the text looked up, and `results`, with one entry for each
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address. Every entry has the same fields:
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- `ip`: the address
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- `ptr`: the address's PTR names, the host names that DNS gives for it, or an
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empty list when it has none
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- `ptr`: the address's PTR names, the host names that DNS gives for it (see PTR
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lookups), or an empty list when it has none
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- `flags`: yes-or-no facts about the address:
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- `is_tor`: true when the address is on the `tor_exits` list
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- `is_vpn`: true when the address is on any list of VPN servers (see IP
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@@ -334,9 +334,6 @@ address, such as one that resolves to a private address, is reported as
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- `{ip}` comes to more than 10 addresses once its names are resolved
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- nothing in `{ip}` is an IP address or a host name with a public address
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Each PTR lookup gets 2 seconds. An address whose lookup takes longer is answered
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without PTR names.
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A successful answer carries `Cache-Control` with a `max-age` of 15 minutes, the
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shortest IP list interval. The answer for the caller's own address (`/ip/`) is
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`private`, and the others are `public`.
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@@ -465,6 +462,43 @@ How RouteWatch keeps the lists:
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- When a download fails, or its file does not parse, RouteWatch keeps the
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previous copy and logs the failure. It tries again one interval later.
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## PTR lookups
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An IP lookup finds each address's PTR names over DNS-over-HTTPS. It asks these
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public resolvers in order, until one answers:
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- Google: `https://dns.google/dns-query`
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- Cloudflare: `https://cloudflare-dns.com/dns-query`
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- AdGuard: `https://unfiltered.adguard-dns.com/dns-query`
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- Quad9: `https://dns.quad9.net/dns-query`
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One address's lookup gets 2 seconds across all four. Each resolver gets an equal
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share of the time left, so one that does not answer leaves time for the next.
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When none answers in time, the address's `ptr` is an empty list.
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A reserved address, one whose `is_bogon` flag is true, is not sent to the
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resolvers. Its `ptr` is an empty list.
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What goes outside: each resolver asked receives the address being looked up. For
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`/ip/` and the home page, that address is the visitor's own. A lookup answered
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from the cache sends nothing.
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How RouteWatch keeps the answers:
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- It holds answers in memory. An answer that has not expired is served from
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there.
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- It writes new answers every 5 seconds to `cache.db` in the state directory
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(see Configuration), and loads them from there at startup.
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- An answer expires after the TTL of its records, the shortest one when there
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are several. RouteWatch keeps it for at least 60 seconds and at most 24 hours.
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- When an address has no PTR names, that answer expires after the SOA record's
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minimum field, or the record's own TTL when that is shorter. RouteWatch keeps
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it for at most 1 hour.
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- An answer with no PTR names and no SOA record is not kept. Neither is one
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whose SOA record has a TTL or minimum field of 0.
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- A failed lookup is not kept, so the next lookup of the address asks again.
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- Every 10 minutes it deletes expired answers from memory and from `cache.db`.
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## Configuration
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RouteWatch reads its settings from environment variables. It takes no
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@@ -513,7 +547,13 @@ by the client. For a request from any other address, they use the address the
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request came from, whatever headers it carries. `X-Real-IP` and `True-Client-IP`
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are not read.
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The state directory holds the database, `db.sqlite`, and the IP list copies:
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The state directory holds:
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- `db.sqlite`: the database
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- `cache.db`: the answers of PTR lookups
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- `iplists`: the IP list copies
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It is at:
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- macOS: `~/Library/Application Support/berlin.sneak.app.routewatch/`
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- Linux and the BSDs, as root: `/var/lib/berlin.sneak.app.routewatch/`
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@@ -670,6 +710,8 @@ The parts:
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with old or missing details asks the fetcher for it at once, without the wait.
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- The IP lists part downloads the IP lists and answers which lists hold an
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address.
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- The PTR cache looks up the PTR names of addresses and keeps the answers (see
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PTR lookups).
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- The database maintainer checkpoints the database every 5 seconds: it folds the
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write-ahead log, where SQLite first writes changes, into the database file. It
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reclaims free space every 10 minutes. Every hour it refreshes the statistics
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@@ -779,6 +821,7 @@ On `SIGTERM` or `SIGINT` the daemon stops its parts in this order:
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4. the database maintainer
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5. the IP list downloads
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6. the HTTP server
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7. the PTR cache, which writes what it holds
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Last, the daemon checkpoints and closes the database. It gives all this 8
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seconds and then exits with status 0. A stop that is still running after 9
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@@ -799,6 +842,8 @@ What a stop can lose:
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- When the 8 seconds run out, the streamer and the handlers log what they could
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not hand over or write. The database is then not closed. When it next opens,
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SQLite rolls back any write the exit cut off.
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- When the 8 seconds run out, the PTR answers not yet in `cache.db` are lost.
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RouteWatch asks the resolvers for them again the next time they are needed.
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### Code layout
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@@ -812,11 +857,13 @@ routewatch/
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│ └── message-examples.json # Examples of RIS Live messages
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├── internal/
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│ ├── bogon/ # Reserved prefixes and AS numbers
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│ ├── cachedb/ # cache.db, the caches of outside answers
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│ ├── config/ # Settings from the environment
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│ ├── database/ # SQLite storage
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│ ├── iplist/ # Public IP lists: downloads and lookups
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│ ├── logger/ # Structured logging
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│ ├── metrics/ # Feed and route update figures
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│ ├── ptr/ # PTR lookups over DNS-over-HTTPS, and their cache
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│ ├── ristypes/ # The RIS Live message types
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│ ├── routetable/ # The whole routing table in memory
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│ ├── routewatch/ # The daemon: startup, handlers, WHOIS fetcher
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@@ -865,6 +912,13 @@ announcements(id PRIMARY KEY, prefix_id, peer_asn, origin_asn, path,
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The indexes are in `internal/database/schema.sql`.
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`cache.db` is a separate file, with one table:
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```sql
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-- The answers of PTR lookups. names is empty for an address with no PTR names.
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hostnames(address PRIMARY KEY, names, expires_at)
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```
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## Development
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The `make` targets:
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