LPM route table batch installation

I want to: install a routing table of LPM prefixes (e.g. 10.0.x.0/24 → port N) in a single P4Runtime Write RPC, then read it back to verify, and handle the case where one or more updates were rejected by the device.

The pattern

import io.github.zhh2001.jp4.P4Switch;
import io.github.zhh2001.jp4.entity.TableEntry;
import io.github.zhh2001.jp4.match.Match;
import io.github.zhh2001.jp4.batch.WriteResult;
import io.github.zhh2001.jp4.batch.UpdateFailure;

try (P4Switch sw = P4Switch.connectAsPrimary("127.0.0.1:50051")
        .bindPipeline(p4info, deviceConfig)) {

    WriteResult r = sw.batch()
            .insert(routeEntry("10.0.1.0/24", 1))
            .insert(routeEntry("10.0.2.0/24", 2))
            .insert(routeEntry("10.0.3.0/24", 3))
            .execute();

    System.out.printf("installed %d routes (allSucceeded=%s)%n",
            r.submitted(), r.allSucceeded());

    if (!r.allSucceeded()) {
        for (UpdateFailure f : r.failures()) {
            System.err.printf("update[%d] failed: %s %s%n",
                    f.index(), f.code(), f.message());
        }
    }

    // Read-back verification.
    for (TableEntry e : sw.read("MyIngress.backend_lookup").all()) {
        Match m = e.match("hdr.ipv4.dstAddr");
        int port = e.action().paramInt("port");
        System.out.printf("  %s → port %d%n", m, port);
    }
}

private static TableEntry routeEntry(String cidr, int port) {
    return TableEntry.in("MyIngress.backend_lookup")
            .match("hdr.ipv4.dstAddr", Match.lpm(cidr))
            .action("MyIngress.forward").param("port", port)
            .build();
}

Real usage: simple-loadbalancer.

Walkthrough

1. Build entries through a helper. The routeEntry(cidr, port) helper keeps the table name, match field name, and action name confined to one site — call sites read as routeEntry("10.0.1.0/24", 1). Misspellings fail at sw.insert(...) time with a known-list error message, never reach the device.
2. Match.lpm(cidr) parses CIDR notation. Equivalent to new Match.Lpm(Ip4.of("10.0.1.0").toBytes(), 24) but reads more naturally for IPv4 routes.
3. sw.batch().insert(...).insert(...).execute() packs multiple Updates into one Write RPC. The device applies them in order, but P4Runtime does not mandate atomic batches — a failure does not roll back preceding successes.
4. WriteResult carries per-update results. allSucceeded() is true iff failures() is empty. Each UpdateFailure carries the original batch index, the gRPC ErrorCode, and the device's message — enough to log, retry, or modify the offending update.
5. Read-back verification through sw.read("table_name").all() returns the installed entries in whatever order the device reports them. The Match object's toString() renders the LPM as lpm 10.0.1.0/24 for grep-friendly logs.

Modify and delete patterns

To move a route to a different port:

sw.modify(routeEntry("10.0.2.0/24", 4));   // throws if key doesn't exist

To remove a route:

sw.delete(routeEntry("10.0.2.0/24", 4));   // only match key matters for delete

For delete, the action half is silently ignored on the wire; pass any value.

See also

• Tables — the full Match builder surface, including LPM / ternary / range / optional.
• P4Runtime spec mapping — how sw.batch().execute() translates to a single Write RPC with multiple Updates.
• Canonical bytestring — why a read-back IP address may have fewer bytes than the written form.
• simple-loadbalancer example — the full runnable program this recipe was extracted from.