rea/docs/go-binaries.md

Go binary build metadata

inspect_go_binary / inspect-go-binary answers which Go compiler version, modules, replacements and build settings are embedded in one selected local executable or library. It reads the file without running it and requires no Go installation, active binary target, Hopper, Ghidra or IDA.

rea inspect-go-binary /absolute/path/to/application --json

The CLI resolves relative paths against the caller's working directory. MCP requires an absolute filesystem path and preserves that exact selection:

{
  "name": "inspect_go_binary",
  "arguments": { "path": "/artifacts/application" }
}

For build identity and counts, select detail: "summary". MCP retains the same complete Evidence and returns normalized_result.parent_evidence_id. Read selected dependency versions without reopening the file:

{
  "name": "inspect_analysis_view",
  "arguments": {
    "source": {
      "kind": "retained-evidence",
      "evidence_id": "ev_<parent digest>"
    },
    "view": {
      "kind": "go",
      "collection": "dependencies",
      "paths": ["golang.org/x/crypto"],
      "fields": ["path", "version", "replacement"],
      "offset": 0,
      "limit": 10
    }
  }
}

Go views support dependencies (exact paths) and settings (exact keys), optional original indices, field selection, and pagination. Filters intersect; empty filter arrays select no rows and fields: [] returns only row identity. Each row keeps its original index, scoped to the parent Evidence and collection; duplicate module paths and setting keys keep distinct indices. Page offsets count matching records. Exhausting retained rows does not establish complete runtime dependencies. Original bytes, unknown lines and all complete metadata remain in the parent and can be exported as an Evidence bundle.

One-shot CLI summaries save complete Evidence before returning the projection:

rea inspect-go-binary ./application --detail summary --evidence_output ./go-evidence.json --json

--evidence_output is required for CLI summary delivery and never overwrites an existing file. The default CLI/MCP reply remains complete.

Measured workflows include catalog repetition and extra calls. Identity/count questions benefit from a single summary. In the tested Codex full-catalog configuration, a compound question about identity and one dependency uses fewer tokens in captured request JSON with one complete inspection than with a summary followed by a lookup. The complete reply remains useful for that initial question; retained views support later selected reads. Token figures are serialization estimates, not model usage.

Observations

The inline Evidence result contains the artifact path, SHA-256, byte length, container format, architecture, word size and byte order. A recognized build_info record contains:

• go_version, preserved as embedded UTF-8 text rather than forced into a semantic version, or null when the embedded bytes are not UTF-8;
• go_version_bytes_base64, preserving the exact compiler-string bytes;
• exact file offsets and byte lengths for the header, compiler string and module string;
• module_text, the decoded module-information body, or null when the complete body cannot be represented as UTF-8;
• module_bytes_base64, the original module-string bytes including Go framing;
• module.path, the embedded package path;
• module.main, the main module's path, version, checksum and optional replacement;
• module.dependencies, with the same fields and their original order;
• module.settings, retaining ordered key/value entries and duplicate keys;
• module.unparsed_lines, module.unparsed_line_bytes_base64 and module.complete, which says whether every present module-text line was parsed. It does not establish that the dependency inventory is complete.

Missing checksums are null; empty fields and development/local replacement versions remain unchanged. Build settings such as GOOS, GOARCH or vcs.revision are reported when present. Their absence does not establish a build choice. Go strings may contain arbitrary bytes. Non-UTF-8 records remain available as base64 while other decodable module records are still reported; the reader does not insert replacement characters or reject the entire artifact for those strings.

When no main-module (mod) record was decoded, module.main is null and dependency coverage is unknown. Successfully decoded dependency records remain visible. GOPATH-mode builds may contain only a package path and build settings; their empty dependency array does not establish the absence of dependencies. The result's limitations state this explicitly. A module-mode build with a main module record and no dependency records has an observed empty dependency list.

Supported boundary

The built-in TypeScript reader supports ELF, PE and thin Mach-O images, and one selected slice of a universal Mach-O, with Go's inline or historical pointer build-info encoding. Source ranges refer to the original stable file snapshot, including pointer-backed strings. It does not scan arbitrary byte strings as compiler metadata.

A universal (FAT) Mach-O needs architecture (x86, x86_64, arm or arm64; CLI --architecture). REA reads its own FAT table, without lipo, and validates the selected slice's range, alignment and Mach-O header CPU against the table. The result keeps the universal file as artifact (its SHA-256 and size), adds selected_slice with the slice offset, length, raw CPU type/subtype and the FAT table digest, and reports every source range as a file offset inside that slice. Without architecture, or when the file has no such slice or several, the request fails on architecture and lists the slices present. architecture on any other image is rejected rather than ignored.

For ELF images without a named build-info section, discovery checks each nonempty writable, non-executable load segment in program-header order. This includes sectionless PIE images with metadata in a later data segment. Named sections retain priority, and alignment, file mapping and record validation remain required.

Historical moduleless Go binaries can store their empty module-string header in declared zero-initialized virtual memory rather than file-backed bytes. The reader recognizes this only when the complete optional module header lies in that memory without a conflicting file mapping. Its module contents are empty and module_location has zero bytes, anchored at the build-info field containing the module-header pointer. Compiler strings and other unmapped pointers remain strict file-backed reads.

build_info: null means no recognized record was found in the inspected image. It does not prove that the binary is not Go. Stripping, old builds, deliberate removal and obfuscation can limit metadata. A malformed supported container or recognized build-info record returns an input-format failure. Unsupported containers receive a separate unsupported-target failure.

Symlinks and nonregular files are rejected. The shared stable reader detects replacement and observed in-place changes during acquisition. Missing files, host permission denial, changed artifacts and cancellation retain distinct errors. The selected file is never modified; this inspection creates no temporary files, starts no subprocesses and accesses no network endpoint.

An input above 256 MiB returns resource_constraint with resource file-size and reported_limits.maximum_input_bytes. Select a suitable input within that fixed allowance; changing an output-write or transport budget does not admit it.

Resource guards bound the selected file and cumulative header searches to 256 MiB each, aggregate embedded strings to 1 MiB, structural table decoding to 16 MiB and the complete normalized metadata report to 8 MiB. Identical search spans with the same virtual alignment are searched once; partially overlapping spans consume the cumulative search budget and fail with a CPU resource constraint when it is exhausted. Oversized results fail without partial success. MCP also applies its response transport budget, which counts both text and structured content; a report within the metadata limit can still require export from retained Evidence. These limits are not operating-system memory or CPU isolation.

Embedded metadata is evidence of file content. It does not authenticate a compiler, dependency, commit or supply chain, and it does not establish runtime behavior. Function names, source mappings, types and decompiled code are outside this tool's coverage. Use the native workflow when those questions require a disassembler.

Real producer verification

npm run verify:go:binary exercises compiler-built fixtures through the public CLI and MCP, comparing their metadata with Go's standard debug/buildinfo reader. The verification lane requires Go; normal inspection does not.