fix: preserve file modification time in CopyFileToContainer by pujitha24 · Pull Request #3989 · testcontainers/testcontainers-go

pujitha24 · 2026-10-19T01:29:23Z

What does this PR do?

CopyFileToContainer now sets the tar header ModTime to the host file's modification time. tarFile and copyToContainer take a new modTime argument. CopyToContainer (raw bytes) has no source file, so it passes a zero time and behaves as before.

Why is it important?

Single files copied with CopyFileToContainer arrived in the container with an epoch (1970) mtime, unlike directory copies (tarDir, which uses tar.FileInfoHeader) and docker cp. Preserving the mtime makes the two paths consistent. Other header fields (uid/gid, etc.) are unchanged; this PR only addresses modification time.

Related issues

Closes [Bug]: CopyFileToContainer doesn't preserve modification times #3227

How to test this PR

go test -run 'Test_TarFile|Test_TarDir' . — Test_TarFile now asserts the header mtime. With the ModTime line removed it fails (got 1969-12-31 epoch); with it, it passes. I did not run tests that need a Docker daemon.

Fixes #3227

Motivation: files copied with CopyFileToContainer got an epoch modification time because the single-file tar header had no ModTime, unlike directory copies, which use the file info. Approach: pass the host file's ModTime through copyToContainer into tarFile and set it on the tar header. CopyToContainer (bytes) passes a zero time, so its behaviour is unchanged. Validation: go build ./..., go vet ., and go test -run 'Test_TarFile|Test_TarDir' . pass. The extended Test_TarFile fails (epoch mtime) when the ModTime line is removed. Tests needing a Docker daemon were not run. Report: testcontainers#3227 Signed-off-by: Pujitha Paladugu <[email protected]> Assisted-by: claude-sonnet-5-5 (via Claude Code)

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coderabbitai · 2026-10-19T01:29:44Z

No actionable comments were generated in the recent review. 🎉

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Summary by CodeRabbit

Bug Fixes
- Files copied into containers now preserve their original modification times, including sub-second precision. General copy operations continue without applying a specific modification time.

Walkthrough

File copies to containers now preserve the source file’s modification time in the tar header. Byte-content copies pass a zero time. PAX format preserves sub-second precision, and the tar test verifies the header value.

Changes

Container file copy

Layer / File(s)	Summary
Pass modification times into tar headers `docker.go`, `file.go`, `file_test.go`	`CopyFileToContainer` passes the source modification time through `copyToContainer` to `tarFile`. `CopyToContainer` passes a zero time. `tarFile` sets the tar header modification time and uses PAX format for non-zero times. The test verifies the value.

Priority: ⬇️ Low

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

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: mdelapenya

Merge Risk: ⚪ Minimal · up to 34d5a

File copies preserve modification times, and raw-byte copies retain their existing behavior. The change is ready to merge after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: preserving file modification time in CopyFileToContainer.
Description check		The description is directly related to the changeset. It explains the behavior change, implementation details, rationale, testing, and linked issue.
Linked Issues check		Issue `#3227` requires `CopyFileToContainer` to preserve the source file modification time. The current changes pass `info.ModTime()` through `copyToContainer` to `tarFile`, which writes it to the tar h…
Out of Scope Changes check		The changes remain within issue `#3227`. They update the file-copy path, tar header time handling, and the focused tar test. No unrelated production behavior or tests are identified.

Full details: Linked Issues check

Explanation

Issue #3227 requires CopyFileToContainer to preserve the source file modification time. The current changes pass info.ModTime() through copyToContainer to tarFile, which writes it to the tar header. Test_TarFile verifies the header time. The raw-byte CopyToContainer path passes a zero time because it has no source file. The issue does not define concrete acceptance criteria for additional metadata.

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_{A rabbit checks the tar by moonlit light
The file keeps its timestamp right
PAX guards the finer grain
Zero time marks bytes without a name
The header hops, precise and bright}

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coderabbitai

Actionable comments posted: 1

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Inline comments:
Review comments at @file.go:
- Line 126: Update the tar header construction around ModTime to use
tar.FormatPAX when the source modification time is nonzero, preserving
fractional seconds; keep the zero-time byte-copy path unchanged. Add or update a
test using a source time with nonzero nanoseconds to verify the copied time is
preserved.

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mdelapenya

Please address CodeRabbit’s timestamp-precision finding before approval. With the tar format unspecified, Go rounds ModTime to the nearest second. The current test uses zero nanoseconds, so it misses that loss.

Use tar.FormatPAX for nonzero source timestamps and add a test with nonzero nanoseconds, while keeping the zero-time behavior of byte-based CopyToContainer unchanged.

Signed-off-by: Pujitha Paladugu <[email protected]>

mdelapenya

LGTM, thanks!

I'll merge once the CI is green, thank yo so much for improving the project 🙇

pujitha24 requested a review from a team as a code owner October 19, 2026 01:29

coderabbitai Bot reviewed Oct 19, 2026

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mdelapenya reviewed Oct 21, 2026

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pujitha24 added 2 commits October 21, 2026 05:00

Merge remote-tracking branch 'upstream/main' into auto/issue-3227

5cf364e

fix: preserve sub-second mtime when copying files via PAX tar format

34d5a8b

Signed-off-by: Pujitha Paladugu <[email protected]>

mdelapenya approved these changes Oct 21, 2026

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fix: preserve file modification time in CopyFileToContainer - #3989

fix: preserve file modification time in CopyFileToContainer#3989
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pujitha24 commented Oct 19, 2026

What does this PR do?

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Related issues

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