Hi Tomcat developers,
I would like to propose adding configurable gzip compression parameters to
Tomcat's HTTP compression implementation. This enhancement would give users
fine-grained control over compression behavior to optimize for their specific
use cases.
---
Problem Statement
Currently, Tomcat's `GzipOutputFilter` uses hardcoded values for gzip
compression:
- Compression level: Always uses `Deflater.DEFAULT_COMPRESSION` (-1)
- Buffer size: Fixed at 512 bytes
- Sync flush: Hardcoded to `true`
This limitation prevents users from:
1. Tuning compression level for speed vs. compression ratio trade-offs
2. Adjusting buffer sizes for different response patterns (streaming vs. bulk)
3. Controlling sync flush behavior for different latency requirements
Users have raised this issue before (e.g., [Spring Boot issue #25748]),
where the Spring Boot team noted that Tomcat doesn't expose these
configuration options.
---
Proposed Solution
Add three new configurable properties to `AbstractHttp11Protocol`
and HTTP/2’s compression logic:
1. gzipLevel (int, default: -1)
- Valid range: -1 (default), 0 (no compression), 1–9
- Maps directly to `java.util.zip.Deflater` compression levels
2. gzipBufferSize (int, default: 512)
- Internal buffer size for `GZIPOutputStream`
- Must be positive
3. gzipSyncFlush (boolean, default: true)
- Controls whether flush() calls invoke the deflater’s SYNC_FLUSH
- Important for streaming scenarios
---
Implementation Details
The implementation requires small changes in the following files:
1. GzipOutputFilter.java
- Add three private fields with getters/setters
- Use configurable values instead of hardcoded ones
2. CompressionConfig.java
- Add new fields and validation logic
- Validate compression level (-1 to 9) and buffer size (>0)
3. AbstractHttp11Protocol.java
- Expose new properties delegating to CompressionConfig
- Enables configuration via `server.xml` or programmatic API
4. Http11Processor.java and StreamProcessor.java - Pass configured
values to `GzipOutputFilter` instances
---
Configuration Examples
server.xml
```xml
<Connector port="8080" protocol="HTTP/1.1"
compression="on"
gzipLevel="6"
gzipBufferSize="8192"
gzipSyncFlush="true" />
```
Benefits
Performance tuning: Balance CPU vs. bandwidth by adjusting compression level
Streaming optimization: Control buffer size and sync flush for
real-time responses
Framework integration: Enables frameworks (Spring Boot, Quarkus, etc.)
to expose these settings
Consistency: Aligns with configuration practices in Jetty and Undertow
Target Versions
This enhancement can be safely applied to:
Tomcat 11.0.x (main)
Tomcat 10.1.x
Tomcat 9.0.x
It is non-breaking and low-risk, as it only adds configuration hooks.
Patch Availability
A working implementation is available locally.
If the community is interested, I can open a Bugzilla enhancement ticket
and submit patches for Tomcat 9 → 11 along with test cases
and documentation updates.
Would the Tomcat community be interested in reviewing this enhancement?
Best regards,
--
장성호
Server Platform Developer, Server Platform Team
010-3868-8634 | [email protected]
서울특별시 강남구 테헤란로 142, 4층, 10층, 11층, 12층, 13층, 22층, 23층(역삼동, 아크플레이스) (06236)
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