xpath-go

🎯 High-compatibility XPath library for Go with precise location tracking

✨ Features

🎯 High Compatibility - Strives for close compatibility with jsdom's XPath evaluation
📍 Precise Location Tracking - Character-level positioning in source HTML/XML
📄 Dual Extraction Modes - Extract full elements or content-only with contentsOnly option
⚡ High Performance - Optimized evaluation engine with smart caching
🔧 Production Ready - Comprehensive error handling and extensive testing
🧪 Battle Tested - Extensively tested against reference implementations
📦 Zero Dependencies - Pure Go implementation, no external dependencies
🎨 Developer Friendly - Rich debugging support with trace logging

🚀 Quick Start

package main

import (
    "fmt"
    "log"
    
    "github.com/reclaimprotocol/xpath-go"
)

func main() {
    html := `<html><body><div id="content" class="main">Hello World</div></body></html>`
    
    // Simple query
    results, err := xpath.Query("//div[@id='content']", html)
    if err != nil {
        log.Fatal(err)
    }
    
    for _, result := range results {
        fmt.Printf("Found: %s\n", result.TextContent)
        fmt.Printf("Location: %d-%d\n", result.StartLocation, result.EndLocation)
        fmt.Printf("Path: %s\n", result.Path)
    }
}

📦 Installation

go get github.com/reclaimprotocol/xpath-go

🎯 Complete XPath Support

✅ Axes (100% Compatible)

child::, parent::, ancestor::, descendant::
following::, preceding::, following-sibling::, preceding-sibling::
attribute::, namespace::, self::
descendant-or-self::, ancestor-or-self::

✅ Functions (Comprehensive Support)

Node Functions: text(), node(), position(), last(), count()
String Functions: string(), normalize-space(), starts-with(), contains(), substring()
Boolean Functions: boolean(), not()
Number Functions: number(), string-length()

✅ Operators (Full Support)

Comparison: =, !=, <, >, <=, >=
Logical: and, or, not()
Arithmetic: +, -, *, div, mod
Union: | (pipe operator)

✅ Predicates (Full Support)

Attribute predicates: [@id='test'], [@class and @id]
Position predicates: [1], [last()], [position()>2]
Content predicates: [text()='value'], [contains(text(), 'substring')]
Complex boolean expressions: [@id='a' or @class='b'] and [position()=1]

📊 XPath Support

Comprehensive XPath 1.0 implementation with extensive test coverage

Feature Category	Support	Details
Basic Selection	✅ Full	Element, attribute, wildcard selection
Attribute Queries	✅ Full	Attribute existence, value matching, complex conditions
Text Functions	✅ Full	text(), contains(), starts-with(), normalize-space()
Position Functions	✅ Full	position(), last(), numeric positions
Axes Navigation	✅ Full	All XPath axes including ancestor/descendant
Complex Predicates	✅ Full	Boolean logic, nested predicates, unions
String Functions	✅ Full	substring(), string-length() with edge cases

📋 Important Compatibility Notes

HTML Entity Handling

XPath-Go preserves HTML entities in their original encoded form, which differs from JavaScript's DOM behavior:

<!-- Source HTML -->
<p>Text with &amp; &lt; &gt; characters</p>

Implementation	Text Content	XPath Query
JavaScript DOM	`"Text with & < > characters"`	`//p[contains(text(), '&')]` ✅
XPath-Go	`"Text with & < > characters"`	`//p[contains(text(), '&')]` ✅

Why this difference exists:

✅ Preserves original HTML content exactly as written
✅ No information loss - you can decode when needed
✅ Predictable behavior - what you see is what you get
✅ Security benefits - prevents entity-related parsing issues

Working with entities:

// Method 1: Query with encoded entities
results, _ := xpath.Query("//p[contains(text(), '&amp;')]", html)

// Method 2: Decode after extraction  
results, _ := xpath.Query("//p", html)
decoded := html.UnescapeString(results[0].TextContent)

📖 Read the complete HTML Entity Handling guide for detailed information and best practices.

Unicode Position Tracking

XPath-Go uses byte-based position tracking for performance and Go ecosystem compatibility:

<!-- Source HTML -->
<p>Hello 世界</p>

Implementation	Position Calculation	`StartLocation`	`EndLocation`
JavaScript DOM	Character-based	0	27
XPath-Go	Byte-based	0	31

Why byte-based positioning:

✅ Go idiomatic - Aligns with Go's string handling and byte slice operations
✅ Performance - No Unicode code point counting overhead during parsing
✅ Memory efficient - Direct byte offset calculations
✅ Deterministic - Consistent across all platforms and Go versions

Working with Unicode positions:

// Method 1: Use byte positions directly (recommended for Go)
html := `<p>Hello 世界</p>`
results, _ := xpath.Query("//p", html)
content := html[results[0].StartLocation:results[0].EndLocation]

// Method 2: Convert to character positions if needed
import "unicode/utf8"
func ByteToCharPos(s string, bytePos int) int {
    return utf8.RuneCountInString(s[:bytePos])
}

⚠️ Compatibility Considerations

While XPath-Go aims for high compatibility with web standards, there are some intentional design choices:

HTML Entity Preservation: Maintains original & vs & for security and consistency
Unicode Position Tracking: Uses byte offsets for Go ecosystem compatibility
Performance Optimizations: Some complex expressions may have subtle evaluation differences

For complete compatibility details, see docs/COMPATIBILITY.md.

🔍 Advanced Usage

Location Tracking

Get precise character positions for all matched nodes:

results, _ := xpath.Query("//div[@class='content']", htmlContent)
for _, result := range results {
    fmt.Printf("Element: <%s>\n", result.NodeName)
    fmt.Printf("Text: %s\n", result.TextContent) 
    fmt.Printf("Character Range: %d-%d\n", result.StartLocation, result.EndLocation)
    fmt.Printf("XPath: %s\n", result.Path)
    fmt.Printf("Attributes: %+v\n", result.Attributes)
}

Compiled XPath (Performance)

For repeated queries, compile once and reuse:

// Compile once
compiled, err := xpath.Compile("//div[@class='item'][position()>1]")
if err != nil {
    log.Fatal(err)
}

// Use multiple times (faster)
for _, htmlDoc := range documents {
    results, err := compiled.Evaluate(htmlDoc)
    if err != nil {
        log.Printf("Error: %v", err)
        continue
    }
    // Process results...
}

Custom Options

Control output format and extraction mode:

results, err := xpath.QueryWithOptions("//p", html, xpath.Options{
    IncludeLocation: true,
    OutputFormat:    "values", // "nodes", "values", "paths"
    ContentsOnly:    false,    // Extract full elements (default)
})

// Extract only inner content between tags
results, err := xpath.QueryWithOptions("//div", html, xpath.Options{
    ContentsOnly: true,  // Extract content-only: <div>content</div> → "content"
})

Debug Tracing

xpath.EnableTrace()
defer xpath.DisableTrace()

results, err := xpath.Query("//div[contains(@class, 'complex')]//p[last()]", html)
// Detailed evaluation steps logged to stderr

📚 Examples

Basic Selections

// Element selection
xpath.Query("//div", html)                    // All div elements
xpath.Query("/html/body/div", html)           // Specific path
xpath.Query("//div[@id='main']", html)        // Div with specific ID

// Attribute selection  
xpath.Query("//div/@class", html)             // Class attributes
xpath.Query("//*[@href]", html)               // Elements with href
xpath.Query("//a[@href and @title]", html)   // Links with both attributes

Text and Content

// Text content
xpath.Query("//p[text()='Hello']", html)           // Exact text match
xpath.Query("//div[contains(text(), 'world')]", html) // Text contains
xpath.Query("//span[normalize-space(text())='Clean']", html) // Normalized text

// Position-based
xpath.Query("//li[1]", html)                    // First list item
xpath.Query("//tr[last()]", html)               // Last table row  
xpath.Query("//div[position()>2]", html)        // Divs after second

Complex Predicates

// Boolean logic
xpath.Query("//div[@id='a' or @class='b']", html)           // OR condition
xpath.Query("//p[@class and text()]", html)                 // AND condition
xpath.Query("//div[not(@class)]", html)                     // NOT condition

// Nested conditions
xpath.Query("//ul[li[@class='active']]", html)              // UL containing active LI
xpath.Query("//div[@class='container']//p[position()=2]", html) // Second P in container

// Complex expressions
xpath.Query("//article[.//h1 and count(.//p)>2]", html)     // Articles with H1 and 3+ paragraphs

Axes Navigation

// Family relationships
xpath.Query("//h2/following-sibling::p", html)        // P elements after H2
xpath.Query("//span/parent::div[@class='box']", html)  // Parent div with class
xpath.Query("//td/ancestor::table[@id='data']", html)  // Ancestor table with ID

// Advanced navigation
xpath.Query("//div[@id='start']/descendant-or-self::*[@class]", html) // Descendants with class
xpath.Query("//li[3]/preceding-sibling::li", html)                    // Previous siblings

Dual Extraction Modes

Extract either full elements or just their inner content:

html := `<div class="box">Hello <span>World</span>!</div>`

// Full element extraction (default)
results, _ := xpath.QueryWithOptions("//div", html, xpath.Options{
    ContentsOnly: false,
})
// StartLocation/EndLocation: <div class="box">Hello <span>World</span>!</div>

// Content-only extraction  
results, _ := xpath.QueryWithOptions("//div", html, xpath.Options{
    ContentsOnly: true,
})
// StartLocation/EndLocation: Hello <span>World</span>!

// Fine-grained control (always available)
fmt.Printf("Full element: %s\n", html[result.StartLocation:result.EndLocation])
fmt.Printf("Inner content: %s\n", html[result.ContentStart:result.ContentEnd])

Use Cases:

Full elements (ContentsOnly: false): HTML processing, DOM manipulation, complete element extraction
Content only (ContentsOnly: true): Text processing, content analysis, clean text extraction without tags

📈 Performance

Optimized for production use:

Fast parsing with caching support
Efficient evaluation with minimal memory allocations
Thread-safe design for concurrent usage
Compiled expressions for repeated queries

// Compile once, use many times
compiled, _ := xpath.Compile("//div[@class='item'][position()>1]")
results, _ := compiled.Evaluate(html)

🛠️ API Reference

Core Functions

// Basic query evaluation
func Query(xpathExpr, content string) ([]Result, error)

// Query with custom options
func QueryWithOptions(xpathExpr, content string, opts Options) ([]Result, error)

// Compile XPath for reuse (performance optimization)
func Compile(xpathExpr string) (*XPath, error)

// Enable/disable debug tracing
func EnableTrace()
func DisableTrace()

Result Structure

type Result struct {
    Value         string            // Node value or text content
    NodeName      string            // Element name (div, span, etc.)
    NodeType      int               // Node type (1=element, 2=attribute, 3=text)
    Attributes    map[string]string // Element attributes
    StartLocation int               // Character start position (full element or content-only)
    EndLocation   int               // Character end position (full element or content-only)
    ContentStart  int               // Start of inner content (after opening tag)
    ContentEnd    int               // End of inner content (before closing tag)
    Path          string            // Generated XPath path
    TextContent   string            // Text content of node and children
}

Options

type Options struct {
    IncludeLocation bool   // Include character positions (default: true)
    OutputFormat    string // "nodes", "values", "paths" (default: "nodes")
    ContentsOnly    bool   // Extract only inner content between tags (default: false)
}

ContentsOnly Mode:

false (default): Extract full elements including tags: <div>content</div>
true: Extract only inner content: content

Both modes maintain precise position tracking. With ContentsOnly: true, StartLocation/EndLocation point to the content boundaries, while ContentStart/ContentEnd are always available for fine-grained control.

🔧 Development

Testing

# Go tests
go test ./...

# Compatibility tests (requires Node.js)
cd tests && npm install && npm test

# Benchmarks
go test -bench=. -benchmem ./...

🤝 Contributing

We welcome contributions!

# Clone and setup
git clone https://github.com/reclaimprotocol/xpath-go.git
cd xpath-go && go mod download

# Run tests
go test ./... && cd tests && npm install && npm test

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgments

Built with high compatibility goals for jsdom and web standards
Inspired by the W3C XPath 1.0 Specification
Thanks to the Go community for excellent tooling and libraries

🎉 Production Ready: This library is actively used in production and provides reliable XPath evaluation for Go applications.

Name		Name	Last commit message	Last commit date
Latest commit History 46 Commits
.github/workflows		.github/workflows
cmd/examples/basic		cmd/examples/basic
docs		docs
internal		internal
pkg		pkg
scripts		scripts
tests		tests
.gitignore		.gitignore
.goreleaser.yml		.goreleaser.yml
CRUSH.md		CRUSH.md
README.md		README.md
go.mod		go.mod
version.go		version.go
xpath-go		xpath-go
xpath.go		xpath.go

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