rea/docs/erlang-beam.md

Erlang BEAM files

inspect_erlang_beam / inspect-erlang-beam answers whether one selected local file is a FOR1/BEAM IFF container, which chunks that form stores, and which atom, export, import, lambda, and Code-header fields those chunks carry. It reads the file without executing bytecode and does not require an Erlang installation or BEAM emulator.

rea inspect-erlang-beam /absolute/path/to/app.beam --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_erlang_beam",
  "arguments": { "path": "/artifacts/app.beam" }
}

Observations

The inline Evidence result contains the artifact path, SHA-256, and byte length. chunks lists every IFF chunk name, file range, and payload SHA-256. Repeated names retain separate chunk occurrences. Decoded tables and the Code header use the last occurrence of each name, matching OTP's loader; the chunk inventory still exposes earlier payloads and their source ranges. The BEAM form size bounds the parsed chunks. Bytes after the declared form are ignored by the parser but remain part of the selected artifact's byte length and SHA-256.

When AtU8 or Atom is present, atoms is the 1-based name table and module is atom 1. Both the pre-OTP 28 table and the OTP 28+ compact table (negated count, compact-encoded name lengths) are read. exports, imports, and lambdas resolve atom indices to those names when the table is present; unresolved indices keep function or module null.

A zero-byte AtU8 chunk does not override a nonempty historical Atom table. The chunk inventory retains both occurrences. A nonempty malformed AtU8 still fails instead of falling back to an older table.

code reports the Code chunk instruction-set, opcode maximum, label count, function count, and the instruction stream's file range. Missing optional tables are null, not empty-everywhere. A zero-byte optional FunT has no decoded lambda table (lambdas: null); a four-byte zero count is an observed empty table (lambdas: []). Both chunks remain in the inventory.

Limits and failures

The selected file is limited to 64 MiB by default (512 MiB maximum). At most 64 chunks and 4096 atoms are examined by default, and at most 65536 export, import, and lambda rows together. Malformed FOR1/BEAM headers, truncated chunks, and AtU8 names that are not valid UTF-8 fail without partial success.

This workflow does not execute bytecode, inflate LitT literals, or decode Attr/CInf external-term payloads. Complete coverage describes this static chunk and table report; it does not establish that an Erlang runtime can load or execute the module.