Font Support with Prawn and test 2025-01-03
Debugging Font Support Issues with Prawn and PDF::Inspector in Ruby
When working with PDF generation in Ruby using Prawn and testing with PDF::Inspector, developers often encounter challenges with non-ASCII character support, particularly when dealing with Unicode characters like Cyrillic, Chinese, or Arabic. This article explores common issues, debugging techniques, and practical solutions for handling font support in PDF generation and testing.
The Challenge with Non-ASCII Characters
Prawn and PDF::Inspector handle text differently, which can lead to discrepancies between what appears in the generated PDF and what can be extracted for testing. A common scenario is when generating PDFs with Unicode characters:
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pdf = Prawn::Document.new
pdf.text "наприклад, Петро" # Ukrainian text
# Test that might fail
text_analysis = PDF::Inspector::Text.analyze(pdf.render)
expect(text_analysis.strings.first).to eq("наприклад, Петро") # May fail
Common Issues
- Font Embedding Problems
- Missing font files
- Incomplete character sets in selected fonts
- Improper font family registration
- Encoding Mismatches
- UTF-8 vs other encodings
- Binary string handling
- Character set conversion issues
- PDF::Inspector Limitations
- Incomplete Unicode support
- Font subset extraction challenges
- Complex text layout interpretation
Debugging Techniques
1. Verify PDF Generation
First, confirm that the PDF is generated correctly:
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def debug_pdf_content(pdf)
# Save PDF to file for manual inspection
pdf.render_file("debug_output.pdf")
# Examine raw PDF content
raw_content = pdf.render
puts "Raw PDF size: #{raw_content.bytesize}"
puts "Content encoding: #{raw_content.encoding}"
end
2. Inspect Font Configuration
Check font registration and embedding:
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pdf = Prawn::Document.new
# Debug font configuration
puts "Available fonts: #{pdf.font_families.keys}"
puts "Current font: #{pdf.font.name}"
puts "Font reference: #{pdf.font.identifier}"
3. Text Extraction Analysis
Compare different text extraction methods:
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pdf_content = pdf.render
# Method 1: PDF::Inspector
inspector_text = PDF::Inspector::Text.analyze(pdf_content).strings
# Method 2: PDF::Reader
reader_text = PDF::Reader.new(StringIO.new(pdf_content)).pages.first.text
# Method 3: HexaPDF
hexapdf_text = HexaPDF::Document.new(io: StringIO.new(pdf_content))
.pages.first.text
puts "Inspector: #{inspector_text}"
puts "Reader: #{reader_text}"
puts "HexaPDF: #{hexapdf_text}"
Solutions and Best Practices
1. Proper Font Configuration
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pdf.font_families.update(
"DejaVu Sans" => {
normal: "#{Rails.root}/app/assets/fonts/DejaVuSans.ttf",
bold: "#{Rails.root}/app/assets/fonts/DejaVuSans-Bold.ttf",
italic: "#{Rails.root}/app/assets/fonts/DejaVuSans-Oblique.ttf"
}
)
pdf.font "DejaVu Sans"
2. Alternative Testing Approaches
When PDF::Inspector fails to read certain characters correctly:
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RSpec.describe "PDF Generation" do
it "contains correct text" do
pdf_content = pdf.render
# Approach 1: Use PDF::Reader
reader = PDF::Reader.new(StringIO.new(pdf_content))
expect(reader.pages.first.text).to include("наприклад")
# Approach 2: Check raw content
expect(pdf_content.force_encoding('UTF-8')).to include("наприклад")
# Approach 3: Use simpler text patterns
expect(reader.pages.first.text).to include("от") # Instead of "наприклад"
end
end
3. Fallback Mechanisms
Implement fallback strategies for different character sets:
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def safe_text_rendering(text, pdf)
begin
pdf.text text
rescue Prawn::Errors::IncompatibleStringEncoding
fallback_text = text.encode('UTF-8', invalid: :replace,
undef: :replace, replace: '?')
pdf.text fallback_text
end
end
Conclusion
Font support issues in PDF generation and testing require a multi-faceted approach. Key takeaways:
- Always verify PDF output manually before automated testing
- Use appropriate fonts with complete character support
- Consider alternative testing strategies when PDF::Inspector falls short
- Implement proper error handling and fallback mechanisms
- Choose simpler text patterns for testing when possible