WHY are these changes introduced?

guzzlehttp/psr7 2.11 deprecates passing a non-string value to MessageInterface::withHeader(), and 3.0 will require string|string[]:

Since guzzlehttp/psr7 2.11: Passing int to MessageInterface::withHeader() is deprecated; guzzlehttp/psr7 3.0 requires string|string[].

In Http::request(), the Content-Length header is set to the return value of mb_strlen($bodyString), which is an int. As a result, every request that includes a body (POST/PUT) emits this deprecation. On production this fills logs/APM with deprecation warnings, and it will become a hard incompatibility once guzzlehttp/psr7 3.0 is adopted.

WHAT is this pull request doing?

Casts the Content-Length header value to string so it satisfies the PSR-7 MessageInterface::withHeader() contract.

-                ->withHeader(HttpHeaders::CONTENT_LENGTH, mb_strlen($bodyString));
+                ->withHeader(HttpHeaders::CONTENT_LENGTH, (string) mb_strlen($bodyString));

This is behavior-preserving: psr7 already coerces the value to a string internally, so the serialized header (Content-Length: <n>) is unchanged. The existing Http/Rest/Graphql client tests that assert Content-Length: <length> continue to pass.

Type of change

• Patch: Bug (non-breaking change which fixes an issue)
• Minor: New feature (non-breaking change which adds functionality)
• Major: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added a changelog entry, prefixed by the type of change noted above
• I have added/updated tests for this change
• I have updated the documentation for public APIs from the library (if applicable)