The Architecture of a Transparent CLI Proxy

ContextZip wraps your shell commands without changing their behavior. No modified binaries. No PATH manipulation. No LD_PRELOAD tricks. Here's how.

The Shell Function Approach

contextzip init outputs a shell function. For zsh:

contextzip_exec() {
  local output
  output=$("$@" 2>&1)
  local exit_code=$?
  echo "$output" | contextzip filter
  return $exit_code
}

This simplified version shows the core idea. The real implementation handles:

• Separate stdout/stderr capture
• Signal forwarding (Ctrl+C propagation)
• TTY detection (interactive vs. pipe mode)
• Streaming for long-running commands

The Filter Pipeline

When output enters contextzip filter, it passes through a pipeline of processors:

Raw Output
  → ANSI Stripper (remove escape codes)
  → Pattern Detector (identify output type)
  → Stack Trace Filter (language-specific)
  → Duplicate Grouper (semantic matching)
  → Noise Remover (progress bars, spinners)
  → Stats Reporter (savings calculation)
Clean Output

Each stage is independent. If the pattern detector identifies a Python traceback, the stack trace filter uses Python-specific rules. If it detects npm output, the noise remover applies npm-specific patterns.

Why Rust

The proxy adds a processing step to every command. That step needs to be fast enough to be invisible. Rust gives us:

• Zero-copy parsing where possible
• No garbage collection pauses
• Stream processing — output is filtered as it arrives, not buffered
• Single binary — no runtime dependencies

In benchmarks, ContextZip adds <1ms of latency to command execution. The compile time savings from reduced context far outweigh this.

The Transparency Contract

ContextZip guarantees:

1. Exit codes pass through unchanged
2. Stderr and stdout remain separate
3. No output is added except the savings line
4. Signals propagate to the child process

Your CI/CD scripts, test runners, and build tools work exactly as before.

cargo install contextzip
eval "$(contextzip init)"

GitHub: github.com/contextzip/contextzip

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Install: npx contextzip | GitHub: jee599/contextzip