fix: handle UTF-8 BOM in file reader

[vkhatsiur]

Relates to the #840

Conclusion: hidden BOM character in the preview panel broke the entire layout

Summary by CodeRabbit

• Bug Fixes
  • Improved file reading to correctly handle UTF-8 encoded files with Byte Order Marks (BOM), ensuring accurate display of file contents.
• Tests
  • Added tests to verify correct handling and removal of UTF-8 BOM in file content reading.

[coderabbitai]

Walkthrough

The change updates the file reading logic in the readFileContent function to properly handle UTF-8 files that may contain a Byte Order Mark (BOM). It uses a BOM-aware decoder to ensure any BOM is removed before processing the file content, while the rest of the function remains unchanged. Additionally, two new tests were added to verify correct reading of files with and without BOMs, including line length and preview line limits.

Changes

File(s)	Change Summary
src/internal/model_render.go	Updated readFileContent to wrap file reader with a BOM-aware UTF-8 decoder before scanning.
src/internal/model_render_test.go	Added tests TestReadFileContent and TestReadFileContentBOMHandling to verify reading files with and without BOM.

Poem

In files where BOMs may hide away,
Now our reader clears the way.
No more odd marks at the start,
Clean lines for every part.
With UTF-8 we’re truly set—
The rabbit hops with no regret! 🐇✨

---

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Reviewing files that changed from the base of the PR and between 5eeaf7d and a02c3c0.

📒 Files selected for processing (1)

• src/internal/model_render_test.go (2 hunks)

🧰 Additional context used

🧠 Learnings (1)

src/internal/model_render_test.go (1)

Learnt from: lazysegtree
PR: yorukot/superfile#825
File: src/internal/model_render.go:0-0
Timestamp: 2025-05-22T04:50:02.071Z
Learning: The project standardized on using one ANSI package import (github.com/charmbracelet/x/exp/term/ansi) to avoid binary bloat and potential incompatibilities.

🔇 Additional comments (3)

src/internal/model_render_test.go (3)

4-4: LGTM: Import additions are appropriate.

The new imports fmt and strings are correctly added to support the new test functions for BOM handling validation.

Also applies to: 8-8

---

152-196: Excellent test coverage for readFileContent function.

The test function provides comprehensive coverage of different scenarios:

• Regular UTF-8 files without BOM
• UTF-8 files with BOM (correctly expecting BOM to be stripped)
• Preview line limits functionality

The test structure follows good practices with proper setup, clear test cases, and appropriate assertions.

---

198-215: Well-focused BOM handling test with thorough validation.

This dedicated test specifically validates the UTF-8 BOM handling logic with:

• Proper BOM byte sequence (\xEF\xBB\xBF) in test data
• Verification that content starts with expected text (not BOM)
• Explicit check that BOM character (\uFEFF) is removed from output

The dual assertion approach ensures both positive (content correctness) and negative (BOM removal) validation.

✨ Finishing Touches

• 📝 Generate Docstrings

---

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[coderabbitai]

Actionable comments posted: 0

🧹 Nitpick comments (1)

src/internal/model_render.go (1)

8-9: Fix import formatting to resolve static analysis warning.

The imports look functionally correct for UTF-8 BOM handling, but there's a formatting issue flagged by goimports.

Apply this diff to fix the import formatting:

 import (
 	"bufio"
 	"context"
 	"errors"
 	"fmt"
-	"golang.org/x/text/encoding/unicode"
-	"golang.org/x/text/transform"
 	"image"
 	"log/slog"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"slices"
 	"sort"
 	"strconv"
 	"strings"
 	"time"

 	"github.com/yorukot/superfile/src/internal/ui"

 	"github.com/yorukot/superfile/src/internal/common"
 	"github.com/yorukot/superfile/src/internal/utils"

 	"github.com/alecthomas/chroma/v2/lexers"
 	"github.com/charmbracelet/lipgloss"
 	"github.com/charmbracelet/x/exp/term/ansi"
+	"golang.org/x/text/encoding/unicode"
+	"golang.org/x/text/transform"
 	"github.com/yorukot/ansichroma"
 	"github.com/yorukot/superfile/src/config/icon"
 	filepreview "github.com/yorukot/superfile/src/pkg/file_preview"
 )

🧰 Tools

🪛 golangci-lint (1.64.8)

8-8: File is not properly formatted

(goimports)

📜 Review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 238d8dc and 57b609c.

📒 Files selected for processing (1)

• src/internal/model_render.go (2 hunks)

🧰 Additional context used

🪛 golangci-lint (1.64.8)

src/internal/model_render.go

8-8: File is not properly formatted

(goimports)

🔇 Additional comments (1)

src/internal/model_render.go (1)

551-552: Excellent implementation of UTF-8 BOM handling.

The implementation correctly uses unicode.BOMOverride with a UTF-8 decoder to detect and strip any BOM characters before scanning the file content. This will prevent the hidden BOM characters from breaking the preview panel layout as described in the PR objectives.

The BOMOverride function will:

• Detect UTF-8 BOM if present and strip it
• Fall back to UTF-8 decoding if no BOM is detected
• Handle the transformation transparently

[lazysegtree]

Need to add tests and fix goimports linter error

[lazysegtree]

Thanks @vkhatsiur For the root cause analysis and fix.

[vkhatsiur]

Thanks @vkhatsiur For the root cause analysis and fix.

no problem, you're welcome
thanks for your feedback