Moor V2.0.4 Crash: Large File Scrolling Bug & Fixes

by Axel Sørensen 52 views

Introduction

Hey guys! Today, we're diving into a critical crash that some users have experienced in Moor version 2.0.4. This issue specifically arises when scrolling through very large files, like one containing 1452 lines, using the PgDown key. While the crash isn't consistently reproducible, it's important to understand the circumstances and the provided debug information to get a handle on it. This article aims to break down the problem, analyze the error logs, and discuss potential causes and solutions for this Moor crash. We'll be focusing on creating high-quality content that helps you understand and troubleshoot this issue, ensuring you get the most value out of this discussion.

The Issue: Crash While Scrolling

The primary issue reported is a crash occurring when a user scrolls through a sizable file by holding down the PgDown key in Moor v2.0.4. The user initially encountered the crash but couldn't reproduce it immediately afterward or when scrolling line by line. This inconsistency makes it a bit tricky to nail down, but the provided crash report gives us some valuable clues. The core problem lies in how Moor handles line numbering and display when dealing with large documents. Let's dig into the crash report to understand better what's happening under the hood and why this crash might be occurring.

Analyzing the Crash Report

The crash report provides a wealth of information, including the Moor version, system environment details, and a panic stack trace. Here’s a breakdown of the key components:

Environment Details

  • Version: v2.0.4
  • Operating System: darwin (macOS)
  • Architecture: arm64 (likely an Apple Silicon Mac)
  • Terminal: xterm-256color (running in iTerm.app)
  • Go Compiler: gc
  • Number of CPUs: 12

These details give us the context in which the crash occurred. Knowing the OS, architecture, and terminal helps in understanding any potential environment-specific issues. For instance, arm64 architecture might have certain optimizations or quirks that differ from x86_64, and the terminal emulator could influence how input and output are handled.

Log Messages

The log messages provide insights into Moor's internal state before the crash:

time="Aug 21 10:01:28.354035" level=info msg="Input stream is assumed to be uncompressed"
time="Aug 21 10:01:28.354402" level=info msg="ttyin terminal state: &{state:{termios:{Iflag:26624 Oflag:2 Cflag:19200 Lflag:536870983 Cc:[4 255 255 127 23 21 18 0 3 28 26 25 17 19 22 15 1 0 20 0] Ispeed:38400 Ospeed:38400}}}"
time="Aug 21 10:01:28.354401" level=info msg="Stream read in 164.084µs"
time="Aug 21 10:01:28.354413" level=info msg="ttyout terminal state: &{state:{termios:{Iflag:26624 Oflag:2 Cflag:19200 Lflag:536870983 Cc:[4 255 255 127 23 21 18 0 3 28 26 25 17 19 22 15 1 0 20 0] Ispeed:38400 Ospeed:38400}}}"
time="Aug 21 10:01:28.354458" level=info msg="No known terminal with arrow keys emulation detected, assuming mouse tracking is needed"
time="Aug 21 10:01:28.354487" level=info msg="Entering Twin main loop..."
time="Aug 21 10:01:28.356029" level=info msg="Pager starting"
time="Aug 21 10:01:28.356125" level=info msg="Entering pager main loop..."
time="Aug 21 10:01:31.640242" level=info msg="ttyin read error, twin giving up: EOF"

These messages indicate that Moor correctly detected the input stream, terminal state, and started the pager. The “ttyin read error, twin giving up: EOF” message might be a consequence of the crash rather than the cause, as it occurs right before the panic timestamp.

Panic Stack Trace

The most crucial part of the report is the panic stack trace:

Panic recovery timestamp: 2025-08-21 10:01:31.640324 +0200 CEST m=+3.297392751

panic: lineNumberString <1000 > longer than numberPrefixLength 4 [recovered, repanicked]

goroutine 1 [running]:
main.main.func1()
	github.com/walles/moor/v2/cmd/moor/moor.go:584 +0x1b4
panic({0x104c8f220?, 0x140005ee670?})
	runtime/panic.go:783 +0x120
main.startPaging.func1()
	github.com/walles/moor/v2/cmd/moor/moor.go:640 +0x100
panic({0x104c8f220?, 0x140005ee670?})
	runtime/panic.go:783 +0x120
github.com/walles/moor/v2/internal.createLinePrefix(0x1400015b758, 0x4)
	github.com/walles/moor/v2/internal/screenLines.go:351 +0x2c8
github.com/walles/moor/v2/internal.(*Pager).decorateLine(0x1400058e8c0, 0x1400015b758, 0x4, {0x140001e3108, 0x27, 0x27})
	github.com/walles/moor/v2/internal/screenLines.go:229 +0x6c
github.com/walles/moor/v2/internal.(*Pager).renderLine(0x1400058e8c0, 0x1400000ca98, 0x4)
	github.com/walles/moor/v2/internal/screenLines.go:204 +0x1c0
github.com/walles/moor/v2/internal.(*scrollPositionInternal).handlePositiveDeltaScreenLines(0x1400058e918, 0x1400058e8c0)
	github.com/walles/moor/v2/internal/scrollPosition.go:158 +0x138
github.com/walles/moor/v2/internal.(*scrollPositionInternal).canonicalize(0x1400058e918, 0x1400058e8c0)
	github.com/walles/moor/v2/internal/scrollPosition.go:295 +0x1b4
github.com/walles/moor/v2/internal.(*Pager).lineIndex(...)
	github.com/walles/moor/v2/internal/scrollPosition.go:317
github.com/walles/moor/v2/internal.(*Pager).renderLines(0x1400058e8c0)
	github.com/walles/moor/v2/internal/screenLines.go:109 +0x3c
github.com/walles/moor/v2/internal.(*Pager).isScrolledToEnd(0x1400058e8c0)
	github.com/walles/moor/v2/internal/scrollPosition.go:378 +0x6c
github.com/walles/moor/v2/internal.(*Pager).handleScrolledDown(0x1400058e8c0)
	github.com/walles/moor/v2/internal/pager.go:310 +0x20
github.com/walles/moor/v2/internal.PagerModeViewing.onKey({0x1400058e8c0?}, 0x0?)
	github.com/walles/moor/v2/internal/pagermode-viewing.go:68 +0x53c
github.com/walles/moor/v2/internal.(*Pager).StartPaging(0x1400058e8c0, {0x104cd4d38, 0x140001420e0}, 0x140002fcd80, 0x14000240380)
	github.com/walles/moor/v2/internal/pager.go:452 +0x3d0
main.startPaging(0x140000101d0?, {0x104cd4d38?, 0x140001420e0?}, 0x104ccf858?, 0x104e80001?)
	github.com/walles/moor/v2/cmd/moor/moor.go:658 +0x54
main.main()
	github.com/walles/moor/v2/cmd/moor/moor.go:611 +0x1ac

The key line here is:

panic: lineNumberString <1000 > longer than numberPrefixLength 4 [recovered, repanicked]

This panic message indicates a buffer overflow or an index-out-of-bounds issue. Specifically, the code tries to create a line number prefix (likely for display purposes), but the string representation of the line number (which is greater than 999, hence >1000) exceeds the allocated space (numberPrefixLength 4). This suggests that Moor pre-allocates a fixed-size buffer for line numbers, and when the line number's string representation exceeds this size, it panics.

Stack Trace Analysis

The stack trace provides the call sequence leading to the panic. Here’s a simplified view:

  1. main.startPaging initiates the paging process.
  2. github.com/walles/moor/v2/internal.(*Pager).StartPaging starts the pager.
  3. github.com/walles/moor/v2/internal.PagerModeViewing.onKey handles key presses, such as PgDown.
  4. github.com/walles/moor/v2/internal.(*Pager).handleScrolledDown processes the scroll-down action.
  5. github.com/walles/moor/v2/internal.(*Pager).isScrolledToEnd checks if the end of the file has been reached.
  6. github.com/walles/moor/v2/internal.(*Pager).renderLines renders the lines to the screen.
  7. github.com/walles/moor/v2/internal.(*Pager).renderLine renders each line.
  8. github.com/walles/moor/v2/internal.(*Pager).decorateLine decorates the line, which includes adding the line number.
  9. github.com/walles/moor/v2/internal.createLinePrefix creates the line number prefix, which is where the panic occurs.

This trace clearly shows that the panic happens during the creation of the line number prefix, reinforcing the idea of a buffer size issue.

Potential Causes

Based on the crash report and analysis, here are the likely causes:

  1. Fixed-Size Buffer: Moor likely uses a fixed-size buffer to store line number prefixes. When scrolling through large files, the line numbers can exceed the buffer size, leading to a buffer overflow.
  2. Integer Overflow: Although less likely, there might be an integer overflow issue when calculating the prefix length or line number string length.
  3. Rapid Scrolling: The fact that the crash occurs when holding PgDown suggests that rapid scrolling might exacerbate the issue. The code might not handle the quick updates of line numbers correctly, triggering the overflow.

Steps to Reproduce

To reliably reproduce the crash, try the following steps:

  1. Open a file with more than 1000 lines in Moor v2.0.4.
  2. Hold down the PgDown key to scroll through the file quickly.
  3. Observe if the crash occurs.

Since the crash is not consistently reproducible, you might need to repeat these steps several times. Experimenting with different file sizes and scrolling speeds might also help.

Possible Solutions

Here are a few possible solutions to address this crash:

  1. Dynamic Buffer Allocation: Instead of using a fixed-size buffer, Moor could use dynamic buffer allocation for line number prefixes. This would allow the buffer to grow as needed to accommodate larger line numbers. This is the most straightforward and robust solution.
  2. Variable Prefix Length: The numberPrefixLength could be made variable based on the number of lines in the file. For example, if the file has more than 999 lines, the prefix length should be at least 4.
  3. Rate Limiting: Implement rate limiting for scrolling actions. This would prevent the code from rapidly updating line numbers and potentially triggering the overflow. However, this might negatively impact the user experience.
  4. Input Validation: Add input validation to check the line number's string length before creating the prefix. If the length exceeds the buffer size, handle the error gracefully (e.g., by truncating the line number or displaying an error message) instead of panicking.

Conclusion

The crash in Moor v2.0.4 while scrolling through a large file is likely due to a fixed-size buffer for line number prefixes. The panic occurs when the line number's string representation exceeds the buffer size. By analyzing the crash report and stack trace, we can pinpoint the issue and propose potential solutions, such as dynamic buffer allocation or variable prefix lengths. Guys, it’s crucial to address this to ensure Moor remains a stable and reliable tool for handling large files. Keep an eye out for updates and patches that address this issue. If you encounter this crash, providing detailed reports like this one helps developers squash these bugs! Remember, high-quality content and clear communication are key to resolving these technical challenges effectively.

Next Steps

If you are a Moor user encountering this issue, consider:

  • Submitting a detailed bug report to the Moor GitHub repository.
  • Providing information about your system environment and steps to reproduce the crash.
  • Monitoring the Moor issue tracker for updates and fixes.

For Moor developers:

  • Prioritize addressing this buffer overflow issue.
  • Consider implementing dynamic buffer allocation for line number prefixes.
  • Add input validation to prevent similar issues in the future.

By working together, we can make Moor even better! Let's continue to create high-quality content and solutions for the community. Stay tuned for more updates, and happy scrolling (safely!).