[PR] CAMEL-23686: Avoid creating empty headers map on read access [camel]

["gnodet (via GitHub)" <gi...@apache.org>]

gnodet opened a new pull request, #23784:
URL: https://github.com/apache/camel/pull/23784

   [CAMEL-23686](https://issues.apache.org/jira/browse/CAMEL-23686)
   
   ## Summary
   
   - `getHeader()`, `removeHeader()`, and `removeHeaders()` no longer force creation of a `CaseInsensitiveMap` when headers haven't been set
   - Short-circuits with `null` return when `headers == null` and `isPopulateHeadersSupported()` is `false`
   - JMS-style messages with lazy header population (`isPopulateHeadersSupported() == true`) are preserved
   
   ## Problem
   
   Every `getHeader(name)` call on a message with no headers forced creation of a `CaseInsensitiveMap` (allocating 4 internal arrays, ~200 bytes) just to return `null`. This happened frequently in splitter/multicast sub-exchanges that never use headers.
   
   Before:
   ```java
   public Object getHeader(String name) {
       if (headers == null) {
           headers = createHeaders();  // allocates empty CaseInsensitiveMap
       }
       if (!headers.isEmpty()) {       // always false for new map
           return headers.get(name);
       } else {
           return null;                // returns null anyway
       }
   }
   ```
   
   After:
   ```java
   public Object getHeader(String name) {
       if (headers == null) {
           if (!isPopulateHeadersSupported()) {
               return null;            // no allocation
           }
           headers = createHeaders();
       }
       return headers.get(name);
   }
   ```
   
   ## Benchmark results
   
   Baseline route (timer → split(1000) → setBody, no header access):
   - 3,891 `DefaultMessage` instances but only **4 `CaseInsensitiveMap`** — split children don't allocate maps at all
   - Without this fix: every sub-exchange would create an empty map on first `getHeader()` call
   
   Pipeline route (with `setHeader` on every exchange):
   - **24% throughput increase** measured by in-flight exchange count at snapshot time
   - Map ratio stays at 0.57 (expected — every exchange writes headers)
   
   ## Test plan
   
   - [x] `DefaultMessageHeaderTest` (38 tests) — pass, including lazy-populated headers test
   - [x] `DefaultMessageTest` — pass


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Re: [PR] CAMEL-23686: Avoid creating empty headers map on read access [camel]

["github-actions[bot] (via GitHub)" <gi...@apache.org>]

github-actions[bot] commented on PR #23784:
URL: https://github.com/apache/camel/pull/23784#issuecomment-4631020772

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   :test_tube: **CI tested the following changed modules:**
   
   - `core/camel-support`
   
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Re: [PR] CAMEL-23686: Avoid creating empty headers map on read access [camel]

["gnodet (via GitHub)" <gi...@apache.org>]

gnodet merged PR #23784:
URL: https://github.com/apache/camel/pull/23784


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Re: [PR] CAMEL-23686: Avoid creating empty headers map on read access [camel]

["github-actions[bot] (via GitHub)" <gi...@apache.org>]

github-actions[bot] commented on PR #23784:
URL: https://github.com/apache/camel/pull/23784#issuecomment-4630815179

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