Add maxRemainingBodyLength() getter to HttpResponse (#1913)

* Initial plan

* Add remainingBodyLength() getter to HttpParser and HttpResponse

Co-authored-by: uNetworkingAB <110806833+uNetworkingAB@users.noreply.github.com>

* Improve comments for remainingBodyLength() to cover all states

Co-authored-by: uNetworkingAB <110806833+uNetworkingAB@users.noreply.github.com>

* Rename remainingBodyLength to maxRemainingBodyLength

* Rename remainingBodyLength to maxRemainingBodyLength

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: uNetworkingAB <110806833+uNetworkingAB@users.noreply.github.com>

Author: Copilot

src/HttpParser.h

@@ -615,6 +615,14 @@ struct HttpParser {
     }
 
 public:
+    /* Returns the remaining body length if set via content-length, UINT64_MAX if transfer-encoding is chunked, or 0 if no body */
+    uint64_t maxRemainingBodyLength() {
+        if (isParsingChunkedEncoding(remainingStreamingBytes)) {
+            return UINT64_MAX;
+        }
+        return remainingStreamingBytes;
+    }
+
     std::pair<unsigned int, void *> consumePostPadded(char *data, unsigned int length, void *user, void *reserved, MoveOnlyFunction<void *(void *, HttpRequest *)> &&requestHandler, MoveOnlyFunction<void *(void *, std::string_view, bool)> &&dataHandler) {
 
         /* This resets BloomFilter by construction, but later we also reset it again.

src/HttpResponse.h

@@ -488,6 +488,13 @@ struct HttpResponse : public AsyncSocket<SSL> {
         return httpResponseData->offset;
     }
 
+    /* Get the remaining body length if set via content-length, UINT64_MAX if transfer-encoding is chunked, or 0 if no body */
+    uint64_t maxRemainingBodyLength() {
+        HttpResponseData<SSL> *httpResponseData = getHttpResponseData();
+
+        return httpResponseData->maxRemainingBodyLength();
+    }
+
     /* If you are messing around with sendfile you might want to override the offset. */
     void overrideWriteOffset(uintmax_t offset) {
         HttpResponseData<SSL> *httpResponseData = getHttpResponseData();