Pivot PDF
A PDF creation library written in Rust, designed for SaaS and web applications. Low memory and CPU consumption — even for documents with hundreds of pages.
Stream Compression
Purpose
PDF files produced by this library can contain large stream objects — page content, embedded TrueType font files, and ToUnicode CMaps. Without compression, documents with many pages or embedded fonts can become unnecessarily large. FlateDecode compression (zlib/deflate) typically reduces stream sizes by 50-80%.
How It Works
Compression is controlled by a single boolean toggle on PdfDocument:
let mut doc = PdfDocument::create("output.pdf")?;
doc.set_compression(true);
When enabled, all stream objects are compressed with FlateDecode before being written. The /Filter /FlateDecode entry is added to each stream’s dictionary so PDF readers know to decompress when reading.
Compression is disabled by default to maintain backward compatibility and to make debugging easier (uncompressed streams are human-readable).
What Gets Compressed
Only stream objects can be compressed in PDF. The library produces three types:
| Stream Type | Source | Typical Savings |
|---|---|---|
| Page content | Text operators, graphics commands | Moderate (repetitive text commands) |
| FontFile2 | Embedded .ttf font data | High (binary font data) |
| ToUnicode CMap | Unicode mapping for TrueType fonts | Moderate (structured text) |
Non-stream objects (dictionaries, arrays, references) are not affected.
Design Decisions
FlateDecode Only
PDF supports multiple compression filters (LZWDecode, ASCIIHexDecode, ASCII85Decode, etc.). We use only FlateDecode because:
- It’s the universal standard — supported by every PDF reader
- Best compression ratio among PDF filters
flate2crate is well-maintained and efficient- No practical reason to support alternative filters
Default Compression Level
The flate2 crate’s default compression level (level 6) is used. This provides a good balance of compression ratio vs. CPU time. We don’t expose a compression level setting because the difference between levels is marginal for typical PDF content.
Single Toggle, Not Per-Stream
A single set_compression(bool) controls all streams rather than per-stream settings. This keeps the API simple. There’s no practical use case for compressing some streams but not others.
API
Rust
pub fn set_compression(&mut self, enabled: bool) -> &mut Self
Builder-style method matching the existing pattern (set_info, etc.).
PHP
$doc->setCompression(true);
Limitations
- Compressed streams are not human-readable (use a PDF inspection tool to debug)
- Compression adds minimal CPU overhead during PDF generation
- No font subsetting yet — full font files are embedded and compressed