Fix WirespecWebClient ClassCastException on Spring Framework 7 / Spring Boot 4

[nsmnds]

Summary

WirespecWebClient (both the Kotlin and Java reactive clients) threw a ClassCastException on every response when running on Spring Framework 7 / Spring Boot 4:

java.lang.ClassCastException: class org.springframework.http.ReadOnlyHttpHeaders
cannot be cast to class java.util.Map

Root cause

The clients converted downstream response headers into the Map<String, List<String>> expected by Wirespec.RawResponse by passing Spring's HttpHeaders straight into CollectionUtils.toMultiValueMap(...), which relies on HttpHeaders being a Map.

• In Spring 6.x, HttpHeaders implements MultiValueMap<String, String> (and therefore Map), so the upcast is valid and the artifact compiles cleanly.
• In Spring 7.0 (Spring Boot 4), HttpHeaders was redesigned and no longer implements Map/MultiValueMap. The published jar — compiled against Spring 6 — therefore fails the cast at runtime on Spring 7.

Fix

Stop assuming HttpHeaders is a Map. Convert headers by iterating via HttpHeaders.forEach(BiConsumer) into a LinkedMultiValueMap, replacing the three toMultiValueMap(...) call sites in each client.

Backwards compatibility ✅

The change is binary compatible with both Spring 6 and Spring 7. forEach(BiConsumer<? super String, ? super List<String>>) exists with an identical binary descriptor (Ljava/util/function/BiConsumer;)V in both versions:

• Spring 6 — inherited as the default method from Map
• Spring 7 — declared directly on HttpHeaders

So a single jar compiled against Spring 6 (as this repo is, on spring-webflux 6.1.13) resolves the call correctly at runtime on Spring 7 as well. No keySet()/headerNames() (which differ between versions) is used.

Changes

• WirespecWebClient.kt (Kotlin) — added a private HttpHeaders.toRawHeaders() helper and replaced all three toMultiValueMap(...) call sites.
• WirespecWebClient.java (Java) — added a private static toRawHeaders(HttpHeaders) helper and replaced all three CollectionUtils.toMultiValueMap(...) call sites.

Verification

• :src:integration:spring:compileKotlinJvm and compileJvmMainJava compile cleanly against Spring 6.1.13.
• The existing client integration tests (*it.client.*), including ResponseHeaderCaseInsensitivityTest, which exercise the exact response-header mapping path, pass.

🤖 Generated with Claude Code

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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