Accept header with trailing comma produces HTTP "406 Not Acceptable"

[j3r0lin]

Spring version: 5.1.8.RELEASE

Send a http request with header like this, containing , at the end.

Accept: application/json, 

HeaderContentNegotiationStrategy will produce a HttpMediaTypeNotAcceptableException.

org.springframework.web.HttpMediaTypeNotAcceptableException: Could not parse 'Accept' header [application/json,]: Invalid mime type "": 'mimeType' must not be empty
	at org.springframework.web.accept.HeaderContentNegotiationStrategy.resolveMediaTypes(HeaderContentNegotiationStrategy.java:59) ~[spring-web-5.1.8.RELEASE.jar!/:5.1.8.RELEASE]
	at org.springframework.web.accept.ContentNegotiationManager.resolveMediaTypes(ContentNegotiationManager.java:124) ~[spring-web-5.1.8.RELEASE.jar!/:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.getAcceptableMediaTypes(AbstractMessageConverterMethodProcessor.java:391) ~[spring-webmvc-5.1.8.RELEASE.jar!/:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:229) ~[spring-webmvc-5.1.8.RELEASE.jar!/:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:225) ~[spring-webmvc-5.1.8.RELEASE.jar!/:5.1.8.RELEASE]
	at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82) ~[spring-web-5.1.8.RELEASE.jar!/:5.1.8.RELEASE]

That http request works before 5.1.2.RELEASE.

Maybe the cause of this is the parsing method refactoring in this commit f4b05dc.

StringUtils.tokenizeToStringArray(mimeTypes, ",") will trim tokens and ignore empty tokens by default, but now, the replacement method not support that anymore.

[sbrannen]

Send a http request with header like this, containing , at the end.

What is your use case for that?

What client is sending the Accept request header with a trailing comma?

[j3r0lin]

I'm using an HTTP client named Paw. It sends that request from its built in oauth2 client.

Although it seems to be an invalid header, it did work before.

[sbrannen]

Thanks for the feedback. I've labeled this as a regression.

[sbrannen]

The following test passes against the v5.1.2.RELEASE tag and fails on the current 5.1.x branch (beginning with the v5.1.3.RELEASE tag).

@Test
public void parseMediaTypesWithTrailingComma() {
	List<MediaType> mediaTypes = MediaType.parseMediaTypes("text/plain, text/html, ");
	assertNotNull("No media types returned", mediaTypes);
	assertEquals("Incorrect number of media types", 2, mediaTypes.size());
}

The following fails on master.

@Test
public void parseMimeTypesWithTrailingComma() {
	List<MimeType> mimeTypes = MimeTypeUtils.parseMimeTypes("text/plain, text/html,");
	assertThat(mimeTypes).as("No mime types returned").isNotNull();
	assertThat(mimeTypes.size()).as("Invalid number of mime types").isEqualTo(2);
}