feat(crashdump): add Crashdump pillar browsing erl_crash.dump files#59
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Adds a web crash dump browser - the last big item from the observer_cli / OTP-observer gap-closing plan. Pick a dump, watch the parse progress live, then read the crash slogan, the VM's counters at crash time, and every dumped process: sortable by memory, reductions or message queue, searchable, with a drill-down showing the full per-process record including the stack dump and message queue. Parsing reuses OTP's own crashdump_viewer gen_server (observer app) instead of reimplementing the dump format - no GUI/wx is ever started. A dedicated ObserverWeb.Crashdump.Server owns the parser: it starts it on demand, serializes loads, and receives the parser's progress reports through a small linked relay process registered under the name the parser reports to (a process can only carry one registered name), re-broadcast over PubSub so the page renders a live progress bar. Records are decoded by zipping documented field orders over the tuples, degrading gracefully across OTP record evolution, and pids round-trip through the parser's own textual form. Safety and availability follow the established patterns: there is no free path input - only files in explicitly allowlisted crashdump_dirs are browsable, and with no configuration the page stays off (dumps hold everything the VM had at crash time; documented with a warning). Hosts without the observer application get a graceful notice; dev and test load it via Mix.ensure_application!/1. Dialyzer cannot see the pruned observer app, so the crashdump_viewer calls are ignore-listed with a comment explaining why they are safe. Tests exercise the full pipeline against a real crash dump generated by halting a peer node - listing, allowlist rejection, progress, general info (slogan), process summaries, details round-trip, and the page flow from LOAD to the stack dump panel.
Addresses the concern about the :observer dependency by making the whole
feature - including its navigation tab - opt-in behind a single flag,
and by adding file upload so a dump can be inspected without any
server-side directory:
* config :observer_web, crashdump: true gates the pillar. Off by
default the tab never appears; the page (if reached directly)
explains how to enable it. When on but :observer isn't in the
release, it explains that instead.
* Upload an erl_crash.dump straight from the browser (e.g. one pulled
off a crashed Nerves device) - it is copied to a temporary path the
parser re-reads for the session and the previous upload is cleaned
up. The directory listing is kept as a second, optional path and no
longer required.
The crashdump_dirs allowlist still governs host-side browsing (no free
path input); uploads are size-capped and consumed to a controlled temp
file. The nav also moves Crashdump ahead of Metrics so Metrics stays
last. Enabled in the dev server for convenience.
Real-upload parsing is covered end to end at the context level
(load_upload/1 against a dump from a crashed peer node); the page test
covers the upload UI and the validate/empty-submit handlers, since
simulating the upload channel through the nested LiveComponent hits a
test-harness limitation.
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Summary
The last big item from the observer_cli / OTP-observer gap-closing plan: a web crash dump browser - something no BEAM web tool offers today.
Pick an
erl_crash.dumpfrom the allowlisted directories, watch the parse progress live, then:How it works
:crashdump_viewer(observer app) is a plain gen_server behind the wx GUI - this feature drives it headless, so the notoriously tricky dump format is never reimplemented. No GUI/wx is ever started.ObserverWeb.Crashdump.Serverowns the parser lifecycle: starts it on demand, serializes loads, and receives progress through a small linked relay process holding the registered name the parser reports to (a process can carry only one registered name). Progress is re-broadcast over PubSub → live progress bar for multi-GB dumps.Safety & availability
config :observer_web, crashdump_dirs: [...]are browsable; with no configuration the page stays off. Documented with an explicit production-data warning (dumps hold process states, message queues, app data at crash time).:observerapp in their release get a graceful notice; dev/test load it viaMix.ensure_application!/1(Mix ≥1.15 path pruning).Risk assessment
:crashdump_viewerinternalscdv_progress_handler; clash if the cdv GUI is open on the same node:crashdump_viewercalls invisible to the PLT (path pruning)available?/0and covered by real-dump testsChecklist
mix format,credo --strict,dialyzer(exit 0), full suite 393 green ×3 seedserl_crash.dumpfrom a crashed peer nodecrashdump_dirsdocumented with security warningguides/static/crashdump_dash.pngscreenshot (needs a capture from a dev node before merge - configurecrashdump_dirsand crash a peer, or point it at any dump you have around)🤖 Generated with Claude Code