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OpenVPN follows specific code formatting guidelines to maintain consistency across the codebase. All contributions must adhere to these standards.

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Formatting with clang-format

OpenVPN uses clang-format for automated code formatting. The configuration is stored in the .clang-format file in the repository root.
Always run clang-format on your code before submitting patches. This ensures consistent formatting and speeds up the review process.

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Installing clang-format

Install clang-format using your system’s package manager: 
# Ubuntu/Debian
sudo apt-get install clang-format

# macOS
brew install clang-format

# Fedora/RHEL
sudo dnf install clang-tools-extra

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Using clang-format

Format a single file: 
clang-format -i path/to/file.c
Format multiple files: 
find src/ -name '*.c' -o -name '*.h' | xargs clang-format -i

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Pre-commit hook

OpenVPN provides a git pre-commit hook that automatically runs clang-format each time you commit. This is the recommended approach to ensure your code is always properly formatted. Install the pre-commit hook: 
dev-tools/git-pre-commit-format.sh install
The hook will:
  • Automatically check formatting when you commit
  • Allow you to format your code conveniently if needed
  • Prevent commits with incorrect formatting

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Style configuration

The OpenVPN .clang-format configuration is based on the Mozilla style with customizations:

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Key formatting rules

Base style

Mozilla style with OpenVPN-specific customizations

Indentation

4 spaces (no tabs), indent case labels

Braces

Allman style - braces on new lines

Line length

No column limit (0)

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Detailed configuration

The .clang-format file specifies: Alignment:
  • Align consecutive macros across comments
  • Align trailing comments (allow 1 empty line)
  • Align operands and escaped newlines
  • Align parameters after open brackets
Spacing:
  • 2 spaces before trailing comments
  • Space before parentheses in control statements
  • Space before assignment operators
  • No space after C-style casts
Breaking:
  • Break before binary operators (non-assignment)
  • Break before ternary operators
  • Break after return type in all definitions
  • Allman brace style (braces on new lines)
Indentation:
  • 4 spaces for indentation
  • 4 spaces for continuation
  • Indent case labels
  • Do not indent goto labels
  • Do not indent wrapped function names
Functions and blocks:
  • No short functions on single line
  • No short if statements on single line
  • No short loops on single line
  • No short blocks on single line
  • Insert braces around control statements
Pointers and references:
  • Pointer alignment: Right (e.g., int *ptr)
  • Do not derive pointer alignment from context
Other:
  • Keep maximum 2 empty lines
  • Do not keep empty lines at start of blocks
  • Reflow comments for readability
  • Do not sort includes (preserve order)
  • Do not break string literals

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Complete configuration

The full .clang-format configuration: 
---
BasedOnStyle: Mozilla
AccessModifierOffset: '-4'
AlignAfterOpenBracket: Align
AlignConsecutiveMacros:
  Enabled: true
  AcrossEmptyLines: false
  AcrossComments: true
AlignEscapedNewlines: Left
AlignOperands: true
AlignTrailingComments:
  Kind: Always
  OverEmptyLines: 1
AllowAllParametersOfDeclarationOnNextLine: true
AllowShortBlocksOnASingleLine: Never
AllowShortCaseLabelsOnASingleLine: false
AllowShortFunctionsOnASingleLine: None
AllowShortIfStatementsOnASingleLine: Never
AllowShortLoopsOnASingleLine: false
BinPackArguments: true
BinPackParameters: true
BreakAfterReturnType: AllDefinitions
BreakBeforeBinaryOperators: NonAssignment
BreakBeforeBraces: Allman
BreakBeforeTernaryOperators: true
BreakStringLiterals: false
ColumnLimit: '0'
ContinuationIndentWidth: '4'
DerivePointerAlignment: false
IndentCaseLabels: true
IndentGotoLabels: false
IndentWidth: '4'
IndentWrappedFunctionNames: false
InsertBraces: true
KeepEmptyLinesAtTheStartOfBlocks: false
MaxEmptyLinesToKeep: '2'
PointerAlignment: Right
ReflowComments: true
SortIncludes: false
SpaceAfterCStyleCast: false
SpaceBeforeAssignmentOperators: true
SpaceBeforeParens: ControlStatements
SpacesBeforeTrailingComments: '2'
SpacesInParens: Never
TabWidth: '4'
TypeNames: [DWORD]
UseTab: Never
WhitespaceSensitiveMacros: [_STRINGIFY]
---
Language: C
---
Language: Cpp

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Before submitting

1

Install the pre-commit hook

Run dev-tools/git-pre-commit-format.sh install to automatically format code on commit.
2

Format your code

Run clang-format on all modified files before creating patches.
3

Verify formatting

Review the changes to ensure formatting looks correct and doesn’t change logic.
4

Submit your patch

Send your properly formatted patch to the mailing list or Gerrit.
Patches that don’t follow the code style guidelines may be rejected during review. Using the pre-commit hook is the easiest way to ensure compliance.

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Additional resources

Code style wiki

Official code style documentation on the community wiki

Contributing guide

Learn how to contribute patches to OpenVPN

Developer docs

Comprehensive developer documentation

Community overview

Connect with the OpenVPN community