HTTP header parsing fails for header lines > 4096 bytes (fixed buffer limitation)

When using the POCO C++ HTTP server, header parsing fails if a single HTTP header line exceeds the internal buffer size (HTTPBufferAllocator::BUFFER_SIZE, default 4096 bytes).

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Problem Details

The HTTP parser reads headers line-by-line using a fixed-size buffer.

If a single header line (header name + value) exceeds this size:

• The line may be truncated or rejected
• Parsing can stop prematurely
• Subsequent headers may not be parsed
• No clear or explicit error is consistently reported

This is especially problematic for modern authentication scenarios, such as large JWT bearer tokens in the Authorization header.

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Reproduction Scenario

1. Send an HTTP request containing a very large header value, for example:

Authorization: Bearer <~4000+ character JWT> X-Test: value

1. Observe the behavior in the POCO HTTP server:

• Authorization may fail or the header may be only partially read
• X-Test and subsequent headers may be missing from the parsed request

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Expected Behavior

The HTTP parser should do one of the following:

• Handle header lines larger than 4096 bytes, within a reasonable configurable limit
• Provide a configurable buffer size for header parsing
• Cleanly reject oversized headers with an explicit and documented error

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Actual Behavior

• Parsing stops silently or only partially completes
• Following headers are ignored
• There is no obvious supported configuration to increase the limit without modifying POCO source code

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Environment

• OS: Linux
• POCO Version: 1.12.1

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Suggested Improvements

Option 1 (recommended) Make the buffer size configurable, for example via an API such as:

HTTPBufferAllocator::setBufferSize(size_t size);

Option 2 Increase the default buffer size.

Option 3 Replace the fixed-size buffer with a dynamically growing buffer (for example using std::string or equivalent).