[rahul05ranjan]

Description

urunc hands the container's arguments to a rumprun guest by joining all of argv into one cmdline string (strings.Join(data.CmdLine, " ") in Rumprun.Init). The guest cannot get that back intact: rumprun's config parser splits cmdline on whitespace (lib/librumprun_base/config.c: makeargv → rumprun_parseargs), so an argument that contains a space arrives as two arguments and an empty argument vanishes entirely. redis-server --requirepass 'a b' dies with >>> 'requirepass "a" "b"' / Bad directive or wrong number of arguments, and --logfile '' degrades into a bare --logfile, exactly as reported in #1158.

The rumprun configuration format has a second form made for this: rc takes a bin and an argv array, and the guest copies every array element as its own string with no whitespace processing (config.c: addbin → rre_argv[i] = token2cstr(...), verified in the rumprun sources; doc/config.md specifies both forms). This change emits the command as a one-entry rc list — argv[0] as bin, the rest as the argv array — so argument boundaries survive:

{"rc":[{"bin":"redis-server","argv":["--requirepass","a b","--logfile",""]}],"env":…}

Two notes on the shape:

• The serialization uses an encoder with HTML escaping off, because the guest's jsmn-based parser keeps string bytes exactly as written and does not decode \uXXXX escapes, so &, < and > must stay raw. This overlaps the open fix(rumprun): do not escape &, < and > in guest config #1101 (its marshalNoEscape); this PR does not depend on it but will conflict textually — happy to rebase once one of the two lands.
• With rc, the guest no longer sets RUMPRUN_EXEC_CMDLINE, which only affects multibaked multi-program images (it asks the guest to run every remaining baked program after the command; rc entries list exactly the programs to run). urunc runs one container process per guest, so the container images this affects behave identically.
• An empty CmdLine (not reachable from an OCI spec, which requires at least argv[0]) keeps the old empty cmdline, which is what lets the guest run its first baked program without arguments.

Related issues

• Fixes Rumprun arguments with a space are split, empty ones are dropped #1158

How was this tested?

• Guest-semantics mirror of both sides (Python, stdlib): the intended argv, the strings.Join+whitespace-split result (HEAD: ['redis-server', '--requirepass', 'a', 'b'] and a dropped empty) and the rc-array result (FIX: byte-exact) for all three cases in the issue plus multiple empties.
• New pkg/unikontainers/unikernels/rumprun_test.go (the package had no rumprun tests): four tests asserting the exact rc serialization, argument-boundary preservation (spaced and empty values round-trip through the JSON), no \u003c-style HTML escaping, the empty-cmdline fallback and that Init keeps CmdLine unjoined.
• The upstream parser claims were checked against the rumprun sources directly (config.c addbin/token2cstr/handle_cmdline, app-tools/rumprun which still emits cmdline — this change is urunc-side fidelity the host tool does not have).
• Not run locally: no Go toolchain on this machine, so make lint and the unit suite are left to CI; the runtime check is the repro in Rumprun arguments with a space are split, empty ones are dropped #1158 (redis with --requirepass 'a b' over nerdctl).

LLM usage

GLM (Z.ai, model glm-5.3, via OpenRouter) assisted in analyzing the issue, reading the rumprun parser sources and preparing this change; the diff and the claims above were reviewed against the upstream rumprun code before opening.

Checklist

• I have read the contribution guide.
• The linter passes locally (make lint). — no Go toolchain on this machine; the change follows gofmt layout.
• The e2e tests of at least one tool pass locally (make test_ctr, make test_nerdctl, make test_docker, make test_crictl). — needs a rumprun/solo5 VMM and image, not available here; CI will run the suite once labeled.

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