fast-xml

(Currently incomplete and not operational) streaming XML parser using node-expat (requires node-gyp to compile).

Uses XSD schema information to read XML into nice JavaScript structures.

Downloads schema files and keeps a local cache in the file system.

Handles arbitrarily large files using streaming.

Parsing XSD schema files

Schema handling is implemented in the xsd directory. Supported syntax elements are defined in its types subdirectory. Each element in the xsd namespace inherits from types.Base which has static and dynamic members that affect parser initialization. The Base class and its derived classes shouldn't have manually defined constructors, because the parser will instantiate objects to inspect the dynamic properties. Instead, an init function is called on constructed objects when creating them during actual parsing.

The static members are mirrored as dynamic members of BaseClass. Any constructor of a class derived from Base can then be used as if it was a BaseClass instance.

The static mayContain member function of syntax element types (classes derived from types.base) returns a list of other element types (defined as BaseClass instances) that it supports as direct children. The parser uses these to create a kind of state machine.

Syntax elements may also have attributes. They should be initialized to null in the class definition (the TypeScript compiler will automatically generate a constructor to initialize them). The parser will construct an instance of each class it finds, and examine its automatically constructed dynamic members. During parsing, they will then be automatically initialized to attributes found in the schema being parsed. Unknown attributes will be ignored.

The XSD parser proceeds in stages (the parser and all syntax element classes have correspondingly named methods):

• init which calls define to bind named elements, attributes, types etc. to their scope and handles import and include declarations. The imports form a directed, possibly cyclic graph and can modify root scopes of arbitrary namespaces, so it's impossible to generally resolve references to other named things visible in scope before all imports have been processed.
• resolve which resolves references by name. Because possible attributes and child elements can be defined through deeply nested references that can point to other namespaces, it's generally impossible to know them all before all references in all namespaces have been resolved.
• TODO: transform which renames things to avoid naming conflicts between child elements and attributes (which will be merged into members of a single JSON object) and possibly deals with scope issues for TypeScript definition output.

TODO: after parsing, the resulting data structure should be exportable as JSON or a TypeScript definition file with ambient declarations of the XML namespaces.

License

The MIT License

Copyright (c) 2015 BusFaster Ltd