How to read/modify form data that goes through Spring Cloud Gateway? - spring

Question

I am trying to validate and log form data that goes through Spring Cloud Gateway. I have tried a few methods and encounter a few problems and I could not read it properly. I have tried:
#Component
public class GatewayRequestFilter {
#Bean
public GlobalFilter apply() {
return (exchange, chain) -> {
MediaType contentType = exchange.getRequest().getHeaders().getContentType();
ModifyRequestBodyGatewayFilterFactory.Config modifyRequestConfig = new ModifyRequestBodyGatewayFilterFactory.Config();
/// Method 1
if (contentType.includes(MediaType.MULTIPART_FORM_DATA)) {
modifyRequestConfig.setRewriteFunction(String.class, String.class, (exchange1, originalRequestBody) -> {
validateAndAuditLog(exchange1, originalRequestBody);
return Mono.just(originalRequestBody);
});
}
/// Method 2
if (contentType.includes(MediaType.MULTIPART_FORM_DATA)) {
return exchange.getMultipartData().flatMap(originalRequestBody -> {
validateAndAuditLog(exchange1, originalRequestBody);
return chain.filter(exchange);
});
}
/// Method 3:
/// https://github.com/spring-cloud/spring-cloud-gateway/issues/1307#issuecomment-553910834
return new ModifyRequestBodyGatewayFilterFactory().apply(modifyRequestConfig).filter(exchange, chain);
};
}
}
For the 1st and 3rd method, if I set inClass as String.class then I can see data in some kind of http format. The problem is that I don't know how to parse it into hashMap or LinkedMultiValueMap to access each of value using key. Here is the output I get:
----------------------------162653831591335516327921
Content-Disposition: form-data; name="simple-text"
text
----------------------------162653831591335516327921
Content-Disposition: form-data; name="simple-file"; filename="simple-file"
Content-Type: application/octet-stream
Simple file
----------------------------162653831591335516327921--
If I change inClass as Object.class then there is another error:
{
"timestamp": "2020-04-03T02:37:57.096+0000",
"path": "/tc/test/test",
"status": 500,
"error": "Internal Server Error",
"message": "Content type 'multipart/form-data;boundary=--------------------------537619313111072161580699' not supported for bodyType=java.lang.Object",
"requestId": "0592497a-1"
}
For the 2nd method I can get data in LinkedMultiValueMap which is good because I can read each data using key value and I can also get uploaded files name, but the problem is that, it hang for 10s before pass the request to down stream.
Anyone has any idea what should I do to read or modify form data that goes through Spring Cloud Gateway?

Answer 1

Rewriting the answer with example.
Basic approach is defined here, though it needs lot of refinement to work for multi-part.
https://developpaper.com/question/how-to-modify-the-request-parameters-of-multipart-form-data-format-in-spring-cloud-gateway/
For any approach to work once you read the data, you need to set a modified request object to exchange downstream to be processed again. Setting the new multi-part object downstream is bit tricky because there is not a straightforward way to convert string->multi-part->string.
Here is a sample code based on the approach. Note that this for now works only if multi-part contains form fields and not file type fields, because in later case we are dealing with a stream, which can be embedded anywhere within the entire multi-part request, and it is not possible to modify such request without blocking calls, which the netty does not allow.
private final List<HttpMessageReader<?>> messageReaders = HandlerStrategies.withDefaults().messageReaders();
public GatewayFilter apply(Config config) {
return new OrderedGatewayFilter((exchange, chain) -> {
ServerRequest serverRequest = ServerRequest.create(exchange, messageReaders);
// get modified body from original body o
Mono<MultiValueMap<String, String>> modifiedBody = serverRequest.bodyToMono(String.class).flatMap(o -> {
// create mock request to read body
SynchronossPartHttpMessageReader synchronossReader = new SynchronossPartHttpMessageReader();
MultipartHttpMessageReader reader = new MultipartHttpMessageReader(synchronossReader);
MockServerHttpRequest request = MockServerHttpRequest.post("").contentType(exchange.getRequest().getHeaders().getContentType()).body(o);
Mono<MultiValueMap<String, Part>> monoRequestParts = reader.readMono(MULTIPART_DATA_TYPE, request, Collections.emptyMap());
// modify parts
return monoRequestParts.flatMap(requestParts -> {
Map<String, List<String>> modifedBodyArray = requestParts.entrySet().stream().map(entry -> {
String key = entry.getKey();
LOGGER.info(key);
List<String> entries = entry.getValue().stream().map(part -> {
LOGGER.info("{}", part);
// read the input part
String input = ((FormFieldPart) part).value();
// return the modified input part
return new String(modifyRequest(config, exchange, key, input));
}).collect(Collectors.toList());
return new Map.Entry<String, List<String>>() {
#Override
public String getKey() {
return key;
}
#Override
public List<String> getValue() {
return entries;
}
#Override
public List<String> setValue(List<String> param1) {
return param1;
}
};
}).collect(Collectors.toMap(k -> k.getKey(), k -> k.getValue()));
return Mono.just(new LinkedMultiValueMap<String, String>(modifedBodyArray));
});
});
// insert the new modified body
BodyInserter bodyInserter = BodyInserters.fromPublisher(modifiedBody, new ParameterizedTypeReference<MultiValueMap<String, String>>() {});
HttpHeaders headers = new HttpHeaders();
headers.putAll(exchange.getRequest().getHeaders());
// the new content type will be computed by bodyInserter
// and then set in the request decorator
headers.remove(HttpHeaders.CONTENT_LENGTH);
CachedBodyOutputMessage outputMessage = new CachedBodyOutputMessage(exchange, headers);
return bodyInserter.insert(outputMessage, new BodyInserterContext())
.then(Mono.defer(() -> {
ServerHttpRequest decorator = decorate(exchange, headers, outputMessage);
return chain.filter(exchange.mutate().request(decorator).build());
}));
}, RouteToRequestUrlFilter.ROUTE_TO_URL_FILTER_ORDER + 1);
}
// some of the helper methods
private String modifyRequest(Config config, ServerWebExchange exchange, String key, String input) {
// do your thing in here !!!
return input;
}
private ServerHttpRequestDecorator decorate(ServerWebExchange exchange, HttpHeaders headers, CachedBodyOutputMessage outputMessage) {
return new ServerHttpRequestDecorator(exchange.getRequest()) {
#Override
public HttpHeaders getHeaders() {
long contentLength = headers.getContentLength();
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.putAll(headers);
if (contentLength > 0) {
httpHeaders.setContentLength(contentLength);
} else {
// TODO: this causes a 'HTTP/1.1 411 Length Required' // on httpbin.org
httpHeaders.set(HttpHeaders.TRANSFER_ENCODING, "chunked");
}
return httpHeaders;
}
#Override
public Flux<DataBuffer> getBody() {
return outputMessage.getBody();
}
};
}