Mask JSON bodies served as application/octet-stream

[jordanenglish]

Description

Follow-up to #101. CopyRaw only attempted to parse and mask a raw response body when its Content-Type was application/json (or ended in +json). At least one Terraform Enterprise endpoint (the plan JSON export) serves valid JSON labeled application/octet-stream instead, so that response bypassed masking entirely.

application/octet-stream isn't treated as an unconditional mask candidate, since this API also uses that label for genuinely binary or large bodies elsewhere (state archives, plan/apply logs fetched via signed archivist URLs), and buffering one of those just because a sibling endpoint is mislabeled would trade a confirmed small leak for a real cost on unrelated responses. Instead, a body labeled application/octet-stream is peeked at, without consuming or buffering it, to check whether its first non-whitespace byte opens a JSON object or array. Only then does it proceed to the existing buffer-and-mask path; otherwise it streams through unread, exactly as before #101.

Tests

• internal/pkg/format/redact_test.go, TestCopyRaw: extended with five new subtests covering the application/octet-stream branch specifically:
  • masks a JSON body labeled application/octet-stream, the reported bug
  • masks the same case with leading whitespace before the opening brace, exercising the peek's whitespace-skip
  • passes a genuinely binary application/octet-stream body through unread (leading bytes that aren't {/[)
  • passes through, unmasked, an application/octet-stream body shaped like a real plan/apply log: human-readable text followed by embedded JSON lines, mirroring the exact shape already covered by TestRunAPI_GetArbitraryURL in internal/commands/api. This is the regression case that motivated the peek approach over a blanket Content-Type change: that existing test's fixture is real evidence this API serves non-JSON content under application/octet-stream, and it must not start getting buffered as a side effect of this fix
  • confirms a body under an unrelated content type (text/plain) still isn't touched, out of scope for this fix
• go test ./...: full suite passes, including internal/commands/api (home of the log-shaped octet-stream fixture above) and internal/commands/run
• gofmt and go vet ./...: clean
• Manually verified against a Terraform Enterprise instance where the plan JSON export endpoint was confirmed (via --debug) to serve Content-Type: application/octet-stream for a body containing several sensitive = true Terraform variables, including one PEM-format private key and one token matching the GitHub token shape rule. Before this fix, all of them rendered in cleartext through tfctl api .../json-output despite Redact sensitive values from command output #101. After, all mask to (redacted) with the usual WARNING: masked N sensitive fields report, and an ordinary structured tfctl get call against the same instance is unaffected

PR Checklist

• Run npx changie new or install changie to prepare a new changelog entry for the next set of release notes.
• Ensure any command changes are sensitive to these global flags:
  • No command-level changes, global-flags checklist doesn't apply
• Get the logging interface from the context and add debug logging for interesting conditions and nonfatal situations.
  • No new nonfatal condition beyond what Redact sensitive values from command output #101 already logs
• Run make gen/screenshot if the root command output changes.
  • No root command output change, no screenshot regen needed
• Add the Autocomplete field to positional arguments and flags to assist shell autocomplete.
  • No new flags/arguments, no Autocomplete field needed

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.

  • Reverting fully removes the change; no migration.

• If applicable, I've documented the impact of any changes to security controls.

  • This closes a gap in an existing masking control (Redact sensitive values from command output #101), doesn't add a new one. No auth/authz change, no request altered.