irssi/README-NIX.md

Building Irssi with Nix

This project includes a Nix flake for reproducible builds and development environments.

Prerequisites

• Nix with flakes enabled

To enable flakes, add to ~/.config/nix/nix.conf:

experimental-features = nix-command flakes

Quick Start

# Build irssi
nix build

# Run irssi
./result/bin/irssi

# Enter development shell
nix develop

Available Packages

Package	Description
irssi (default)	Full build with Perl scripting and proxy support
irssi-minimal	Build without Perl scripting support
fuzz	Fuzz targets with AddressSanitizer + UndefinedBehaviorSanitizer
fuzz-asan	Fuzz targets with AddressSanitizer only
fuzz-ubsan	Fuzz targets with UndefinedBehaviorSanitizer only

Building Packages

# Build default (full irssi)
nix build

# Build minimal variant
nix build .#irssi-minimal

# Build fuzzers (recommended: ASan + UBSan)
nix build .#fuzz

# Build fuzzers with only ASan (faster)
nix build .#fuzz-asan

Development Shells

Shell	Description
default	Standard development with gcc, gdb, valgrind
fuzz	Fuzzing development with clang + libFuzzer

Using Development Shells

# Standard development
nix develop
meson setup Build
ninja -C Build
ninja -C Build test

# Fuzzing development
nix develop .#fuzz
meson setup Build-fuzz -Dwith-perl=no -Dwithout-textui=yes -Dwith-fuzzer=yes
ninja -C Build-fuzz

Fuzzing

The project includes five fuzz targets built with libFuzzer:

Fuzzer	Tests
irssi-fuzz	Text formatting (printtext_string())
server-fuzz	IRC protocol message parsing
dcc-fuzz	DCC protocol message parsing (SEND, CHAT, RESUME, ACCEPT)
event-get-params-fuzz	IRC event parameter parsing
theme-load-fuzz	Theme file loading

Building Fuzzers

# Build with ASan + UBSan (recommended for finding bugs)
nix build .#fuzz

# Build with ASan only (faster execution)
nix build .#fuzz-asan

Running Fuzzers

# Basic fuzzing (creates corpus automatically)
./result/bin/irssi-fuzz corpus/irssi-fuzz/

# With dictionary (recommended for server-fuzz and dcc-fuzz)
./result/bin/server-fuzz -dict=src/fe-fuzz/tokens.txt corpus/server-fuzz/
./result/bin/dcc-fuzz -dict=src/fe-fuzz/dcc-tokens.txt corpus/dcc-fuzz/

# Limit number of runs
./result/bin/irssi-fuzz -runs=10000 corpus/irssi-fuzz/

# Parallel fuzzing (use multiple cores)
./result/bin/server-fuzz -fork=4 -dict=src/fe-fuzz/tokens.txt corpus/server-fuzz/

# Ignore memory leaks to focus on crashes
./result/bin/server-fuzz -detect_leaks=0 corpus/server-fuzz/

Seed Corpus

Initial seed inputs are provided in fuzz-corpora/:

# Copy seeds to corpus directories
mkdir -p corpus/irssi-fuzz corpus/server-fuzz corpus/dcc-fuzz corpus/event-get-params-fuzz corpus/theme-load-fuzz
cp fuzz-corpora/irssi-fuzz/* corpus/irssi-fuzz/
cp fuzz-corpora/server-fuzz/* corpus/server-fuzz/
cp fuzz-corpora/dcc-fuzz/* corpus/dcc-fuzz/
cp fuzz-corpora/event-get-params-fuzz/* corpus/event-get-params-fuzz/
cp fuzz-corpora/theme-load-fuzz/* corpus/theme-load-fuzz/

Reproducing Crashes

When a fuzzer finds a crash, it saves the input to a file:

# Reproduce a crash
./result/bin/server-fuzz crash-<hash>

# Get more details with symbolized stack trace
ASAN_OPTIONS=symbolize=1 ./result/bin/server-fuzz crash-<hash>

Fuzzer Input Formats

• irssi-fuzz: Arbitrary text, may contain irssi format codes (%B, %U, etc.)
• server-fuzz: Byte 0 selects prefix mode, remaining bytes are \r\n-separated IRC messages
• dcc-fuzz: Byte 0 selects DCC type (0=SEND, 1=CHAT, 2=RESUME, 3=ACCEPT, 4=GET cmd, 5=CLOSE cmd, 6=raw), remaining bytes are DCC message content
• event-get-params-fuzz: Byte 0 selects parsing mode (0-7), remaining bytes are parameters
• theme-load-fuzz: irssi theme file format

Continuous Integration

To check that everything builds:

nix flake check

Troubleshooting

UBSan warnings about function pointer types

The warning about signals.c function pointer types is expected:

runtime error: call to function through pointer to incorrect function type

This is due to irssi's dynamic signal dispatch system and is a known pattern in the codebase.

Fuzzer stops immediately

Ensure the corpus directory exists:

mkdir -p corpus/irssi-fuzz

Build fails with "perl not found"

Perl is required even for minimal/fuzzer builds (for generating help files). The Nix flake handles this automatically.