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maintaining-dependencies.md

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Maintaining Dependencies

Node.js depends on additional components beyond the Node.js code itself. These dependencies provide both native and JavaScript code and are built together with the code under the src and lib directories to create the Node.js binaries.

All dependencies are located within the deps directory.

Any code which meets one or more of these conditions should be managed as a dependency:

  • originates in an upstream project and is maintained in that upstream project.
  • is not built from the preferred form of the work for making modifications to it (see GNU GPL v2, section 3. when make node is run. A good example is WASM code generated from C (the preferred form). Typically generation is only supported on a subset of platforms, needs additional tools, and is pre-built outside of the make node step and then committed as a WASM binary in the directory for the dependency under the deps directory.

By default all dependencies are bundled into the Node.js binary, however, configure options should be available to use an externalized version at runtime when:

  • the dependency provides native code and is available as a shared library in one or more of the common Node.js distributions.
  • the dependency provides JavaScript and is not built from the preferred form of the work for making modifications to it when make node is run.

Many distributions use externalized dependencies for one or more of these reasons:

  1. They have a requirement to build everything that they ship from the preferred form of the work for making modifications to it. This means that they need to replace any pre-built components (for example WASM binaries) with an equivalent that they have built.
  2. They manage the dependency separately as it is used by more applications than just Node.js. Linking against a shared library allows them to manage updates and CVE fixes against the library instead of having to patch all of the individual applications.
  3. They have a system wide configuration for the dependency that all applications should respect.

Supporting externalized dependencies with native code.

Support for externalized dependencies with native code for which a shared library is available can added by:

  • adding options to configure.py. These are added to the shared_optgroup and include an options to:
    • enable use of a shared library
    • set the name of the shared library
    • set the path to the directory with the includes for the shared library
    • set the path to where to find the shared library at runtime
  • add a call to configure_library() to configure.py for the library at the end of list of existing configure_library() calls. If there are additional libraries that are required it is possible to list more than one with the pkgname option.
  • in node.gypi guard the build for the dependency with node_shared_depname so that is is only built if the dependency is being bundled into Node.js itself. For example:
    [ 'node_shared_brotli=="false"', {
      'dependencies': [ 'deps/brotli/brotli.gyp:brotli' ],
    }],

Supporting externalizable dependencies with JavaScript codeIZA

Support for an externalizable dependency with JavaScript code can be added by:

  • adding an entry to the sharable_builtins map in configure.py. The path should correspond to the file within the deps directory that is normally bundled into Node.js. For example deps/cjs-module-lexer/lexer.js. This will add a new option for building with that dependency externalized. After adding the entry you can see the new option by running ./configure --help.

  • adding a call to AddExternalizedBuiltin to the constructor for BuildinLoader in src/node_builtins.cc for the dependency using the NODE_SHARED_BUILTLIN #define generated for the dependency. After running ./configure with the new option you can find the #define in config.gypi. You can cut and paste one of the existing entries and then update to match the inport name for the dependency and the #define generated.

Supporting non-externalized dependencies with JavaScript code

If the dependency consists of JavaScript in the preferred form of the work for making modifications to it, it can be added as a non-externalizable dependency. In this case simply add the path to the JavaScript file in the deps_files list in the node.gyp file.