rvt-rs

Apache-2.0 clean-room Rust/Python toolkit for inspecting Autodesk Revit files (.rvt, .rfa, .rte, .rft) without a Revit installation. Opens the OLE/CFB container, decodes Revit's truncated-gzip streams, extracts metadata and previews, parses the embedded Formats/Latest schema, and classifies all observed schema field encodings across an 11-release 2016–2026 reference corpus.

This is not yet a full Revit model reader. Schema-directed instance walking has a verified ADocument beachhead on Revit 2024–2026 (document-level metadata only — not per-element), and Formats/Latest schema classification covers 100% of observed field encodings. IFC4 STEP emission produces a valid spatial tree with typed elements when fed synthesized DecodedElement inputs from the test fixtures — see tests/fixtures/synthetic-project.ifc.

Generic real-project typed element extraction is mostly unsolved, with narrow partition MVP exceptions. Production walker::iter_elements prefers typed MVP decoders on Global/Latest (fail closed), merges version-gated 2023 ArcWall partition recovers, and merges fail-closed partition MVP recovers for Level / Material plus 2024 ArcWallRectOpening index rows (corpus-proven on magnetar Einhoven / Core Interior). Opening related ids are ElemTable-confirmed (still not typed Door/Window). On Revit 2024 it additionally merges partition element records, whose header names the element's BuiltInCategory outright: OST_Walls / OST_Doors / OST_Windows / OST_Columns records that carry no container reference and are marked placed instances reproduce Revit's own exported ElementId sets exactly — 360 IfcWall, 132 IfcDoor, 6 IfcWindow, 256 IfcColumn on 2024_Core_Interior.rvt, tolerance 0, cross-witness gated (#204 / #211, reports/element-framing/RE-21-partition-element-record-instance-rule.md). Bodies are the record's bounding box, except for the plan profile of a slab, which is the sketch boundary its OST_SketchLines records close (#31, reports/element-framing/RE-25-slab-plan-profiles.md), and the plan run of a wall, which is the box cut back by the joins its own reference list names — 351 of 360 walls then match Revit's world envelope exactly, up from 27, with 9 ends at true L corners left over-trimmed as a measured negative, and a column body is the record prism minus the record prisms of the walls that cut it, exact on 256 of 256 at a worst residual of 9.4e-13 ft (#215 / #238 / #239, reports/element-framing/RE-26-world-coordinate-residuals.md and reports/element-framing/RE-29-join-reference-list.md). Every wall also names exactly one wall-type record, which is the IfcWallType.Tag the export assigns on 360 of 360 (#88, reports/element-framing/RE-28-wall-type-records.md); that join is library-side and is not yet written onto the emitted wall. Doors and windows are bound to their host wall (#222, RE-23); schema-field Walls remain open — diagnostic scans still find HostObjAttr-style candidates on Global/Latest for those classes. 81 per-class decoder structs ship in elements::all_decoders(); MVP_TYPED_CLASSES are consulted by iter_elements, while the broader registry remains a library building block. Root-cause investigation (reports/element-framing/RE-01-synthesis.md) found that element instance data lives in Partitions/* streams with a wire envelope that has only been reverse-engineered for ArcWall (2023) and opening-index (2024) subsets. Q-01 community-corpus open/scaffold validation has been run (docs/corpus-hunt-2026-04-21.md: 222/223 real files pass open → schema → scaffold IFC); that is not full typed model recovery. See What does not work yet below.

A zero-upload, client-side browser viewer ships alongside the library, live at https://drunkonjava.github.io/rvt-rs/. Drop a .rvt / .rfa file onto the page — the WebAssembly build parses it in-tab, renders 3D via Three.js with orbit controls + element picking + scene tree, and offers one-click Export glTF / Export IFC / Export plan SVG. No upload, no account, no telemetry. CI asserts the compiled .wasm has zero fetch / XMLHttpRequest / WebSocket imports.

For the non-technical workflow, start with the docs/user-guide.md. Installation paths live in docs/install.md. For the short support boundary, read docs/status.md, the supported MVP input profile in docs/supported-profile.md, and the executable capability matrix in docs/support-matrix.json (statuses are honest ceilings, not converter-grade claims). The detailed roadmap tasks live in TODO.md and the matching GitHub milestones/issues.

Rust 2024 edition (MSRV 1.85). Nineteen CLIs ship (rvt-analyze, rvt-info, rvt-inspect, rvt-schema, rvt-history, rvt-diff, rvt-corpus, rvt-dump, rvt-doc, rvt-ifc, rvt-ifc-compare, rvt-write, rvt-gltf, rvt-sheet, rvt-elem-table, rvt-elements, rvt-capabilities, rvt-schedule, gen-fixture) plus 36 reproducible probes under examples/. Python bindings via pyo3+maturin in the rvt-py workspace member (SEC-12/13 — the core rvt crate is unconditionally #![forbid(unsafe_code)]) — pip install rvt.

What works today

What rvt-rs reads from real projects

On Revit 2024 and 2025 project files, rvt-rs reads each element from its partition record: its ElementId, BuiltInCategory, bounding box and references, and for a family instance its family and type. Every number below compares rvt-rs's IFC with Revit's own IFC export of the same file, element by element (the IFC Tag is the ElementId).

Across Autodesk's Snowdon Towers architectural sample (Revit 2024), rvt-rs exports 6,045 elements. 5,945 of them are in Revit's own export, which is every element Revit exports in these entities. The other 100 are elements Revit's exporter leaves out, such as empty curtain panels and opening-cut families (#309). Elements in a design option set's non-primary options and 2D-only families are left out, as Revit leaves them out, and the export diagnostics count them.

Core Interior and the RE1 models are licensed test files and run in CI. Snowdon Towers has no licence and is measured locally only.

What does not work yet

Why the schema matters

The openBIM community — anchored by buildingSMART International and the IFC standard — has spent years working on Revit interoperability. Autodesk's own revit-ifc exporter runs inside Revit using the Revit API, so it can only emit what the API surfaces. Real-world IFC exports from Revit are described, routinely and publicly, as "very limited" (thinkmoult.com), "data loss" (Reddit r/bim), and "out of the box, just crap" (the OSArch Wiki's guide to Revit for openBIM).

The schema work here — decoding Formats/Latest and classifying 100% of field encodings across 11 Revit releases — is the dictionary a byte-level reader needs. Once the partition-stream decoder work in TODO.md lands, the resulting IFC export can carry more than what the Revit API chooses to expose. That is the thesis. It is not yet the delivered product.

If you're building BIM/AEC tooling and want an Apache-2 Revit reader to compose into your stack, the current release covers:

• Reliably — metadata extraction, schema introspection (100% field-type classification across the 11-release family corpus), OLE/CFB open, truncated-gzip decode, IFC4 STEP emission from synthesized inputs, glTF 2.0 binary, 2D plan-view SVG, 81 per-class decoder structs that pass unit tests against synthesized fixtures.

• As scaffolding, not functional on real project files yet — broad diagnostic element scans and walker→IFC integration. Production export now suppresses low-confidence HostObjAttr proxies and only emits the narrow, version-gated 2023 ArcWall path when it is supported by corpus evidence (see "What does not work yet" above).

See tests/fixtures/synthetic-project.ifc for a committed sample IFC output — IfcProject + IfcSite + IfcBuilding + three IfcBuildingStoreys + ten typed IfcWall/IfcSlab/IfcDoor/IfcWindow/IfcStair/IfcBuildingElementProxy entities, all wired to the storey via IfcRelContainedInSpatialStructure, BlenderBIM- and IfcOpenShell-verified. The browser viewer at https://drunkonjava.github.io/rvt-rs/ runs the same IFC emission pipeline — so drag-and-drop a .rvt and the resulting Export IFC produces the metadata/spatial scaffold (not typed elements) end-to-end in the tab.

Quick demo

One command produces the full forensic picture — identity, upgrade history, format anchors, schema table, Phase D link histogram, content metadata, and a disclosure scan:

cargo build --release
./target/release/rvt-analyze --redact path/to/your.rfa

From Python

import rvt

f = rvt.RevitFile("my-project.rfa")
print(f.version, f.part_atom_title)      # 2024 "0610 x 0915mm"
print(f.read_adocument()["fields"][-1])  # {name: m_devBranchInfo, kind: element_id, tag: 0, id: 35}
open("out.ifc", "w").write(f.write_ifc())

Install: pip install rvt — or build from source with maturin build --release --manifest-path rvt-py/Cargo.toml. Full API + Jupyter notebook walkthrough: docs/python.md and docs/rvt-python-quickstart.ipynb. See docs/install.md for cargo, PyPI, source, and viewer install/smoke-test paths, and for the prebuilt Linux / macOS / Windows CLI archives that tagged releases attach from the next release on.

In the browser

Drop a .rvt / .rfa / .rte / .rft at https://drunkonjava.github.io/rvt-rs/ — nothing leaves the tab. The viewer compiles the core library to WebAssembly (wasm-pack build --target web --features wasm), runs the parse in a dedicated worker, and renders 3D via Three.js. One-click buttons export the model as glTF 2.0 binary, IFC4 STEP, or plan-view SVG. URL state (camera pose + category filters) is shareable via the hash fragment. Multi-megabyte projects fit inside wasm32's 4 GiB linear-memory ceiling: each gzip member reserves at most 1 MiB before decoding and the decoded buffer is trimmed (#256), which is what lets the 33.7 MB Core Interior demo finish at 419 MB of linear memory instead of growing to 4057 MB in 139 ms and trapping. A Rust panic in the wasm build is reported through console.error with its message and source location instead of a bare RuntimeError: unreachable.

The landing dropzone also includes a demo gallery staged from docs/viewer-demos.json (license/provenance + expected quality labels). It opens two real projects, Revit_IFC5_Einhoven.rvt (2023) and 2024_Core_Interior.rvt (2024) from the MIT-licensed magnetar-io/revit-test-datasets, hash-verified at staging time, alongside the tier1 synthetics. Einhoven is 913 KB and opens in about half a second; Core Interior is 33.7 MB and decodes in about 3 seconds on the deployed site since #266 (about 7 seconds including the 32 MB download), reporting 889 entities and 854 elements carrying geometry. Two Playwright tests gate both cards, and staging refuses a file whose sha256 does not match the catalog. Demo bytes are same-origin static assets only.

Privacy posture is CI-enforced: the deploy workflow (.github/workflows/deploy-viewer.yml) runs wasm-objdump -j Import on every build and fails if the compiled .wasm imports fetch, XMLHttpRequest, or WebSocket. See docs/viewer-privacy-posture.md.

Supported MVP workflow

The supported end-to-end shell (issue M11-02) is intentionally honest about partial decode:

1. Open a supported Revit file locally (drop, file picker, or a redistributable gallery demo).
2. Read the File status / confidence panel before trusting geometry.
3. Inspect decoded entities in the scene tree or by picking in the 3-D view.
4. Export IFC / glTF / plan only after checking the export-quality label.
5. Download diagnostics when the export is scaffold-only or partial.

What still depends on decoder work: element records before Revit 2024; curved, sloped and B-rep geometry; most element parameters and system-family type names (#322); phase filtering (#328); and compound wall layers, whose thicknesses the paired reference export cannot witness, since it is a ReferenceView_V1.2 file carrying zero IfcMaterialLayerSet (#88/RE-28). RE-19 / RE-20 (2026-08-29) closed negative on the magnetar corpora: there is no Door vs Window discriminator in the opening-index bytes and no recoverable Level ElementId map there, so do not re-probe those without a new corpus or signal. Typed categories come from each element record's BuiltInCategory instead (RE-21 onward). On releases other than 2024 and 2025, treat IFC export as scaffold plus diagnostics; see docs/status.md and docs/supported-profile.md.

Sample output (all pre-scrubbed with --redact, committed for review):

• One-screen teaser: docs/demo/rvt-analyze-2024-teaser.txt — the four highlight sections fit in one terminal screen (identity, format anchors, Phase D linkage, disclosure scan)
• Full terminal report: docs/demo/rvt-analyze-2024-redacted.txt — 130 lines of structured output
• JSON report: docs/demo/rvt-analyze-2024-redacted.json — machine-readable version
• Tag-drift heatmap: docs/data/tag-drift-heatmap.svg — visual proof of class-ID drift across 11 Revit releases

The --redact flag (on by default in every committed artifact) scrubs Windows usernames, Autodesk-internal paths, and project-ID folder names to <redacted> markers while preserving path shape so claims remain verifiable. Omit the flag when running privately against your own files.

Results at a glance

Running the shipped CLIs against one 400 KB RFA fixture:

• Metadata: version, build tag, creator path, file GUID, locale, worksharing state, central model path, last saved (time and user), save counter (rvt-info)
• Folder inventory: one row per Revit file under a folder — release, worksharing, last saved — as a table, CSV, JSON or JSON Lines, reading only each file's two identity streams (rvt-info <folder> -f csv)
• Atom XML: title, OmniClass code, taxonomies (rvt-info parses PartAtom)
• Preview: clean PNG thumbnail, 300-byte Revit wrapper stripped (rvt-info --extract-preview)
• Schema: 395 classes + 1,114 fields + per-field typed encoding (rvt-schema)
• History: every Revit release that ever saved this file (rvt-history)
• Bulk strings: 3,746 length-prefixed UTF-16LE records from Partitions/NN — Autodesk unit/spec/parameter-group identifiers, OmniClass + Uniformat codes, Revit category labels, localized format strings (rvt-history --partitions)

Every class and field name that rvt-schema extracts was cross-checked against the public RevitAPI.dll NuGet package's exported C++ symbol list. All top-level tagged class names we've inspected (ADocument, DBView, HostObj, LoadBCBase, Symbol, APIAppInfo, APropertyDouble3, ElementId, and the rest) appear in that export with their decorated signatures (e.g. __cdecl NotNull<class ADocument *,void>::NotNull(class ADocument *)), confirming the on-disk schema names match the compiled symbols one-to-one.

A build-server path also appears in C++ assertion strings inside the same DLL; it is mentioned in the recon report for completeness and does not represent anything the reader extracts from .rvt / .rfa files.

Performance on large projects

Partition streams are inflated once per file and cached on the RevitFile handle (#266). On the 33.7 MB 2024_Core_Interior.rvt, rvt-ifc --mode geometry went from 26.07 s / 2641.4 MiB peak RSS to 1.69 s / 490.1 MiB (Apple Silicon, /usr/bin/time -l, best of three), and the exported IFC is byte-identical once the writer's two wall-clock stamps are normalised. In the browser the same file decodes in about 3 s on the deployed site, where it used to take about 28. Every tools/perf_budget.py --require-category medium row now passes with an order of magnitude of headroom, without any budget being loosened.

Phase D findings (what makes this project different)

Six reproducible discoveries, all documented in docs/rvt-moat-break-reconnaissance.md and reproducible from examples/:

1. The schema indexes the data. Class names do not appear as ASCII in Global/Latest; class tags from Formats/Latest (u16 after class name, with 0x8000 flag set) occur ~340× the uniform-random rate. The top tag, AbsCurveGStep, appears 19,415 times in 938 KB of decompressed Global/Latest. [examples/link_schema.rs]

2. Tags drift across releases but are stable-sort-assigned. ADocWarnings = 0x001b 2016→2026 because no class sorted alphabetically before it has ever been added. AbsCurveGStep shifted 0x0053 → 0x0066 across the decade as 19 new A-class entries were inserted. Full 122-class × 11-release drift table: docs/data/tag-drift-2016-2026.csv, visualised in docs/data/tag-drift-heatmap.svg. First publicly-available version of this data. [examples/tag_drift.rs]

3. Revit 2021 was a major undocumented format transition. Global/Latest grew 27× (~26 KB → ~715 KB) while simultaneously the Forge Design Data Schema namespaces (autodesk.unit.*, autodesk.spec.*) debuted in Partitions/NN. Two symptoms, one event. Any reader built for 2016-2020 silently drops 30× more data when pointed at 2021+.

4. Parameter-group namespace shipped separately in Revit 2024. autodesk.parameter.group.* identifiers appear in 2024+ only — three releases after units/specs. Dating the Forge schema rollout from on-disk bytes: examples/tag_drift.rs, src/object_graph.rs.

5. A stable Revit format-identifier GUID in family files. Global/PartitionTable is 167 bytes decompressed in .rfa family files, and 165 of those bytes are byte-for-byte identical across every Revit release 2016-2026 (98.8% invariant). The invariant region contains a never-before-published UUIDv1: 3529342d-e51e-11d4-92d8-0000863f27ad. The MAC suffix 0000863f27ad matches a known Autodesk-dev-workstation signature from circa 2000. Useful for family-file detection. Scope correction (2026-04-21): this invariant is a family-file anchor, not a universal Revit-file anchor. Three real .rvt project files we probed carry three different GUIDs (6a6261fd-... on Revit 2023, 552368c6-... on 2024, all-zero on 2025) in a shorter 87-byte PartitionTable. File-type sniffers using the family GUID will correctly reject non-family files but can't identify them. See docs/project-file-corpus-probe-2026-04-21.md. [examples/partition_full.rs]

6. Tagged class record structure decoded. Every class declaration in Formats/Latest carries an explicit tag (u16 with 0x8000 flag), optional parent class, and declared field count, followed by N field records each with name + C++ type encoding. HostObjAttr now resolves to {tag=107, parent=Symbol, declared_field_count=3} with all three field names (m_symbolInfo, m_renderStyleId, m_previewElemId) extracted byte-for-byte. [examples/record_framing.rs, src/formats.rs]

Three unintended disclosure patterns also surfaced in Autodesk's shipped reference content — the specific values are withheld from this README to avoid re-broadcasting them; they are documented in docs/rvt-moat-break-reconnaissance.md for security-research reproducibility:

• A customer-facing OneDrive path that leaks the directory structure of an Autodesk employee's personal sample-authoring workflow.
• A build-server path baked into C++ assertion strings inside the public RevitAPI.dll.
• A creator-name field inside the Contents stream that travels with every copy of the sample family, preserving the name of one of Revit's original 1997 developers.

Downstream safety: the rvt-analyze CLI ships with a --redact flag (on by default for any of the committed demo output in this repo) that rewrites creator paths, Autodesk-internal paths, and build-server paths to <redacted> markers while preserving the surrounding structure. Any tool consuming rvt-rs output and displaying it publicly should do the same.

Library surface

All modules compile under both the default build and the wasm feature flag. See src/ for type docs:

Runtime capabilities:

• Open any Revit file from disk (magic D0 CF 11 E0 A1 B1 1A E1)
• Enumerate every OLE stream; find the version-specific Partitions/NN
• Decompress any stream (truncated-gzip format — standard gzip header, no trailing CRC/ISIZE)
• Parse BasicFileInfo, PartAtom, extract preview PNG
• Extract 395 class records from Formats/Latest with tag + parent + ancestor-tag + declared field count for every tagged class
• Decode the 167-byte Global/PartitionTable structure including the stable Revit format-identifier GUID
• Decode the 307-byte Contents stream including the embedded UTF-16LE metadata chunk
• Produce a byte-for-byte round-trip copy of any .rfa / .rvt file
• Run across the full 11-release corpus in < 500 ms per file (release build)

Nineteen CLIs ship in the box:

cargo build --release

# One-shot forensic analysis — all subsystems in one report
./target/release/rvt-analyze --redact my-project.rvt
./target/release/rvt-analyze --redact --json my-project.rvt > report.json

# Quick metadata + schema summary
./target/release/rvt-info --show-classes my-project.rvt

# Machine-readable (JSON)
./target/release/rvt-info -f json my-project.rvt > meta.json

# Element and room schedules for Excel / Sheets / LibreOffice
./target/release/rvt-schedule my-project.rvt
./target/release/rvt-schedule my-project.rvt --schedule rooms --metric --excel

# Inventory every Revit file under a folder: release, worksharing, last saved
./target/release/rvt-info projects/
./target/release/rvt-info projects/ -f csv --redact > inventory.csv

# Pull the embedded thumbnail
./target/release/rvt-info --extract-preview preview.png my-project.rvt

# Plain-language file health and IFC export readiness
./target/release/rvt-inspect my-project.rvt
./target/release/rvt-inspect my-project.rvt --json

# Compare two versions of the same file (cross-version byte diff)
./target/release/rvt-diff --decompress 2018.rfa 2024.rfa

# Dump the full class schema (395 classes, 13,570 fields)
./target/release/rvt-schema my-project.rvt

# Document upgrade history (which Revit releases have opened this file)
./target/release/rvt-history my-project.rvt

# Pull every UTF-16LE string record out of Partitions/NN
# (categories, OmniClass, Uniformat, Autodesk unit identifiers, …)
./target/release/rvt-history --partitions my-project.rvt

# Hex-dump every decompressed stream (for Phase D work)
./target/release/rvt-dump my-project.rvt

# IFC4 STEP export — spec-valid scaffold by default, with honest quality warnings
./target/release/rvt-ifc my-project.rvt -o out.ifc

# Require a stronger quality gate before writing IFC
./target/release/rvt-ifc my-project.rvt -o out.ifc --mode strict

# IFC4 export with a shareable JSON readiness/support sidecar
./target/release/rvt-ifc my-project.rvt -o out.ifc --diagnostics out.diagnostics.json

# Diagnostic IFC export — include low-confidence proxy candidates with provenance
./target/release/rvt-ifc my-project.rvt -o diagnostic.ifc --diagnostic-proxies

# Compare an rvt-rs IFC export against a Revit (or other) reference IFC
./target/release/rvt-ifc-compare out.ifc revit-reference.ifc --json /tmp/ifc-compare.json

# glTF 2.0 binary export — loads in Three.js / Blender / any glTF viewer
./target/release/rvt-gltf my-project.rvt -o out.glb

# 2D plan-view SVG — per-category colours, ready for plot/laser-cut/printing
./target/release/rvt-sheet my-project.rvt -o out.svg

# Global/ElemTable dump — declared element-ids + record layout (family 12B / project 28B/40B)
./target/release/rvt-elem-table my-project.rvt --limit 20

# Production decoded elements / class counts (JSON; mirrors Python element_counts)
./target/release/rvt-elements my-project.rvt --counts

# Stream-level write path — patch named OLE streams via JSON manifest
./target/release/rvt-write my-project.rvt --patches patches.json -o patched.rvt

# Per-file doc generator (schema + sample-data render for any RVT)
./target/release/rvt-doc my-project.rvt -o doc.md

# Cross-version corpus analysis (11 releases in one pass)
./target/release/rvt-corpus /path/to/corpus-dir

Thirty-six reproducible probes live in examples/ — one per FACT in the recon report:

cargo build --release --examples

# --- schema ↔ data linkage (Phase D) ---
./target/release/examples/probe_link              <file>           # null-hypothesis: class names absent from Global/Latest
./target/release/examples/tag_bytes               <file>           # hex around known class names in Formats/Latest
./target/release/examples/tag_dump                <file>           # statistical sweep of post-name u16 patterns
./target/release/examples/link_schema             <file>           # tag-frequency histogram in Global/Latest (340× non-uniformity)
./target/release/examples/tag_drift               <sample-dir> <out.csv>   # per-class drift table 2016-2026
./target/release/examples/tag_drift_svg           <in.csv> <out.svg>       # render drift table as colour-coded SVG heatmap

# --- record framing (Phase 4c) ---
./target/release/examples/record_framing          <file>           # dump bytes at tagged-class defs + first tag occurrence
./target/release/examples/elem_table_probe        <sample-dir>     # Global/ElemTable structural sweep across releases
./target/release/examples/partitions_header_probe <sample-dir>     # 44-byte Partitions/NN header + chunk offsets
./target/release/examples/contents_probe          <file>           # Contents stream decoder (creator name + build tag)

# --- stable anchors ---
./target/release/examples/partition_invariant     <sample-dir>     # find 165-byte invariant in Global/PartitionTable
./target/release/examples/partition_diff          <sample-dir>     # show the 2 varying bytes per release
./target/release/examples/partition_full          <file>           # full annotated hex dump + UUID decode

# --- write path (Phase 6) ---
./target/release/examples/roundtrip                                # copy 2024 sample, verify all 13 streams identical

Format overview

Every Revit file is a Microsoft Compound File Binary (OLE2) container with this stream layout (constant across 11 years of Revit releases):

<root>
├── BasicFileInfo                 UTF-16LE metadata
├── Contents                      custom 4-byte header + DEFLATE body
├── Formats/Latest                DEFLATE — class schema inventory
├── Global/
│   ├── ContentDocuments          tiny document list
│   ├── DocumentIncrementTable    DEFLATE — change tracking
│   ├── ElemTable                 DEFLATE — element ID index
│   ├── History                   DEFLATE — edit history (GUIDs)
│   ├── Latest                    DEFLATE — current object state (17:1 ratio)
│   └── PartitionTable            DEFLATE — partition metadata
├── PartAtom                      plain XML (Atom + Autodesk partatom namespace)
├── Partitions/NN                 bulk data: 5-10 concatenated DEFLATE segments
│                                 NN = 58, 60-69 for Revit 2016-2026
├── RevitPreview4.0               custom header + PNG thumbnail
└── TransmissionData              UTF-16LE transmission metadata

All compressed streams use a "truncated gzip" format — the standard 10-byte gzip header (magic 1F 8B 08 ...) followed by raw DEFLATE, but without the trailing 8-byte CRC32 + ISIZE that conforming gzip writers produce. Python's gzip.GzipFile and Rust's flate2::read::GzDecoder both refuse these streams. The fix is to skip the 10-byte header manually and use flate2::read::DeflateDecoder on the raw body.

Reverse engineering state

All 5 original P0 research questions (Q4-Q7) are resolved. Layer 4c.2 reaches 100.00% field-type classification on the 11-version reference corpus (13,570 total schema fields, zero Unknown). IFC4 emission, glTF export, 2D plan view, and the browser viewer all ship. The next frontier is real-world project-file corpus validation (Q-01) — one .rvt probe already caught a gzip_header_len bounds bug that family files never hit.

Key findings from this phase:

• Q4 The u16 "flag" word in each tagged-class preamble is a class-tag reference (ancestor / mixin / protocol). 9/9 non-zero values resolve to named classes in the same schema.
• Q5 Each field's type_encoding is [byte category][u16 sub_type][optional body]. 9 category bytes mapped (0x01 bool, 0x02 u16, 0x04/0x05 u32, 0x06 f32, 0x07 f64, 0x08 string, 0x09 GUID, 0x0b u64, 0x0e reference/container).
• Q5.1 Coverage extended to 84% of fields.
• Q5.2 Coverage reaches 100% of fields (13,570 across 11 releases). Generalized {scalar_base} 0x10 ... / {scalar_base} 0x50 ... as vector/container modifiers; added 0x0d point-type base; added 0x08 0x60 ... alternate string encoding; added ElementIdRef { referenced_tag, sub } for references that carry a specific target-class tag; added deprecated 0x03 i32-alias seen only in 2016–2018. See docs/rvt-moat-break-reconnaissance.md §Q5.2.
• Q6 Global/Latest is not an index + heap — it's a flat TLV stream.
• Q6.1 Instance data is schema-directed (tag-less, protobuf-style). Decoding requires schema-first sequential walk from a known entry point.
• Q7 Partitions/NN trailer u32 fields are not per-chunk offsets. Gzip-magic scan remains correct.

The full analysis narrative with 12 dated addenda lives in docs/rvt-moat-break-reconnaissance.md. Session-length synthesis in docs/rvt-phase4c-session-2026-04-19.md.

Sample corpus

Integration tests run against 11 versions of Autodesk's public rac_basic_sample_family RFA fixture (one per Revit release from 2016 through 2026). These are distributed via Git LFS in the phi-ag/rvt repository. To pull them:

cd /path/to/rvt-recon/samples
git clone https://github.com/phi-ag/rvt.git _phiag
cd _phiag && git lfs pull
cd .. && cp _phiag/examples/Autodesk/*.rfa .

The integration tests in tests/samples.rs skip any year whose RFA file is absent, so partial corpora are okay — you'll just see skipping 2024: sample not present messages.

Design choices

• cfb crate over custom OLE parser — the cfb crate is mature, tested against Office documents, and handles both short and regular sectors. Faster than writing our own.
• flate2 over miniz_oxide direct — flate2 wraps both miniz_oxide (pure Rust) and libz backends. We pick the default pure-Rust build to avoid a C toolchain dependency.
• quick-xml over xml-rs — ~3x faster, zero-copy friendly, and the .from_str + event-loop pattern is closer to what Go/Python parsers do.
• encoding_rs over stdlib — Revit's UTF-16LE streams sometimes have malformed pairs at boundaries (single-byte markers get interleaved). encoding_rs recovers gracefully where stdlib panics.
• BTreeSet for class names — deterministic ordering in output (plus sorted JSON) matters for diffable CLI output.

For contributors

rvt-rs is a clean-room reader for Revit files: an Apache-2.0 Rust core with Python bindings and a WebAssembly viewer, with no Revit install or Autodesk SDK at build or run time. Contributing does not need private files either — the checked-in corpus/tier1/ synthetic fixtures drive the default gates, and corpus-backed tests skip themselves while RVT_PROJECT_CORPUS_DIR is unset.

• Build: stable Rust 1.85 or newer, then cargo build. Viewer: cd viewer && npm ci. Python bindings: docs/python.md.
• Gate: tools/check-local.sh runs what CI requires — cargo fmt --check, cargo clippy -D warnings, rustdoc with -D warnings, and the workspace tests (1,074 as of 2026-08-30). --viewer, --corpus, --deny, --audit add the optional gates.
• Where the tests live: unit tests next to the code in src/; integration tests in tests/ (corpus-gated ones skip without RVT_PROJECT_CORPUS_DIR); tests/fuzz_regressions.rs replays crash-shaped inputs on stable Rust; libFuzzer targets in fuzz/; Playwright browser tests in viewer/tests/; Python tests in tests/python/.
• What "done" looks like: the gate is green, the pull-request template's checklist is filled in, and any change to user-visible capability updates docs/status.md and docs/support-matrix.json in the same PR — the project does not claim what its tests cannot show.
• Start here: CONTRIBUTING.md walks from clone to a first pull request; docs/contribution-map.md maps the larger areas; small tasks carry the good first issue label.

License and trademarks

• Code: Apache License 2.0. See LICENSE for the full text and NOTICE for attribution detail.
• Trademarks: "Autodesk" and "Revit" are registered trademarks of Autodesk, Inc. This project is not affiliated with, endorsed by, or sponsored by Autodesk. References to "Autodesk" and "Revit" in this project identify the file format this reader parses and are nominative fair use.
• Interoperability basis: reverse engineering for the purpose of creating an independently-developed interoperable program is recognised as lawful fair use under Sega Enterprises v. Accolade, 977 F.2d 1510 (9th Cir. 1992) and Sony Computer Entertainment v. Connectix, 203 F.3d 596 (9th Cir. 2000) in the United States, and under Article 6 of the EU Software Directive 2009/24/EC in the European Union. File formats themselves are not copyrightable subject matter (Baker v. Selden, 101 U.S. 99 (1879); Lotus Development v. Borland, 516 U.S. 233 (1996)).
• No Autodesk proprietary code is used, referenced, or redistributed by this project. All file-format observations were made by inspecting the bytes of publicly-shipped Autodesk sample content and by parsing the public RevitAPI.dll NuGet package's exported symbol list. See NOTICE.