main: use friendly filename in stdin read error

[deepak0x]

Summary

In internal/main.go, the io.ReadAll failure path formatted its error with infile.Name(), which returns /dev/stdin on Linux instead of the friendly <stdin> label used everywhere else in the function (and in the TranslateBytes report path).

Changes

Extracted the input-reading logic into a readInput(input string) ([]byte, string, error) helper. It returns the friendly filename (<stdin> when reading from stdin, the real path when --input/a positional file is given) so the read error message and the translation report stay consistent.

internal/main.go line 127 (now in readInput):

fail("failed to read %s: %v\n", filename, err)

filename is now <stdin> for the stdin case instead of /dev/stdin.

Verification

Added internal/main_test.go covering readInput:

• reading from stdin yields content and the <stdin> filename
• reading a real file yields content and the real path as filename
• a missing file returns an error with the requested path as filename

./test passes (gofmt, go vet, full test suite, doc validation).

Before: failed to read /dev/stdin: <error>
After: failed to read <stdin>: <error>

Fixes: #726

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of input from standard input and specified files.
  • Added clearer error handling for missing or unreadable files.

• Tests

  • Added coverage for standard input, file input, missing files, returned filenames, and failed reads.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: e836934d-1fe5-463b-948c-07a59053cd60

📥 Commits

Reviewing files that changed from the base of the PR and between bc8ce88 and 02b0e94.

📒 Files selected for processing (2)

• internal/main.go
• internal/main_test.go

🚧 Files skipped from review as they are similar to previous changes (1)

• internal/main.go

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📝 Walkthrough

Walkthrough

The change adds readInput to handle stdin and file input. main uses the helper for reading and error reporting. Tests cover stdin input, file input, missing files, returned filenames, and cleanup.

Changes

Input reading

Layer / File(s)	Summary
Read input helper and tests internal/main.go, internal/main_test.go	readInput reads stdin or a specified file and returns input data, the effective filename, and errors. Tests cover stdin, file input, missing files, and resource cleanup.
Main input integration internal/main.go	main uses readInput and reports read failures with the helper’s returned filename.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: using a friendly filename for stdin read errors.
Linked Issues check	✅ Passed	The PR uses for stdin read errors and preserves explicit file paths, satisfying issue #726.
Out of Scope Changes check	✅ Passed	The helper extraction and focused tests support the filename fix without introducing unrelated changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@internal/main_test.go`:
- Around line 23-88: The readInput tests should be consolidated into a
table-driven TestReadInput with subtests covering stdin, file input, missing
files, and an empty-stdin edge case. Reuse the existing setup and assertions for
each case, preserving expected data, filename, and error behavior while keeping
the tests in internal/main_test.go.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5d23ec70-8fd8-4776-82c3-1751726923de

📥 Commits

Reviewing files that changed from the base of the PR and between cb34e12 and bc8ce88.

📒 Files selected for processing (2)

• internal/main.go
• internal/main_test.go

[deepak0x]

Closing in favor of coreos/ignition#2293. Butane is merging into Ignition (see coreos/ignition#2281), so the fix for the stdin read error now lives there. ignition#2293 ports this exact change, including the readInput helper and the main_test.go table tests, so this Butane PR is no longer needed.