README.md

sax

The sax package defines SAX2 handler interfaces and callback helpers used by event-driven parsing.

Import path: github.com/lestrrat-go/helium/sax

package examples_test

import (
  "context"
  "fmt"

  "github.com/lestrrat-go/helium"
  "github.com/lestrrat-go/helium/sax"
)

func Example_sax_parse() {
  const src = `<library><book lang="en">Go Programming</book><book lang="ja">Goプログラミング</book></library>`

  // sax.New creates a SAX handler with all callbacks set to nil (no-ops).
  // You only need to set the callbacks you care about.
  handler := sax.New()

  // OnStartElementNS is called when an opening tag is encountered.
  // It receives the local name, prefix, namespace URI, any namespace
  // declarations, and the element's attributes.
  //
  // The handler field expects a sax.StartElementNS interface, so we wrap
  // the function literal with sax.StartElementNSFunc to satisfy it.
  handler.SetOnStartElementNS(sax.StartElementNSFunc(func(_ context.Context, localname, prefix, uri string, namespaces []sax.Namespace, attrs []sax.Attribute) error {
    fmt.Printf("<%s", localname)
    for _, a := range attrs {
      fmt.Printf(" %s=%q", a.Name(), a.Value())
    }
    fmt.Print(">")
    return nil
  }))

  // OnEndElementNS is called when a closing tag is encountered.
  handler.SetOnEndElementNS(sax.EndElementNSFunc(func(_ context.Context, localname, prefix, uri string) error {
    fmt.Printf("</%s>\n", localname)
    return nil
  }))

  // OnCharacters is called for text content between tags.
  handler.SetOnCharacters(sax.CharactersFunc(func(_ context.Context, ch []byte) error {
    fmt.Print(string(ch))
    return nil
  }))

  // Attach the SAX handler to a parser. When a SAX handler is set,
  // the parser fires events instead of building a full DOM tree.
  p := helium.NewParser().SAXHandler(handler)

  // Parse triggers the SAX events. The returned document may be nil
  // or minimal when using SAX mode, since the purpose is event-driven
  // processing, with no tree to build.
  _, err := p.Parse(context.Background(), []byte(src))
  if err != nil {
    fmt.Printf("failed to parse: %s\n", err)
    return
  }
  // Output:
  // <library><book lang="en">Go Programming</book>
  // <book lang="ja">Goプログラミング</book>
  // </library>
}

source: examples/sax_parse_example_test.go