[XrdHttp] A GET with 'Want-Digest' header request issued on a non-exi…

…sting file will return a 404 error instead of 500

src/XrdHttp/XrdHttpReq.cc

@@ -1805,7 +1805,16 @@ XrdHttpReq::PostProcessChecksum(std::string &digest_header) {
     if (convert_to_base64) {free(digest_value);}
     return 0;
   } else {
-    prot->SendSimpleResp(500, NULL, NULL, "Underlying filesystem failed to calculate checksum.", 0, false);
+    // This is a result of the "Ugly" hack put in place to prevent a failing stat() on a
+    // non-manager server to fail a transfer.
+    // In the case a user issues a GET with a 'Want-Digest' header on a non-existing file, the non-failing
+    // stat() will result in a failed checksum query giving a 500 error back to the user.
+    // Here we just return a 404 instead. httpStatusCode and httpStatusText contain the right reason why the request failed.
+    if(xrderrcode != kXR_NotFound) {
+      httpStatusCode = 500;
+      httpStatusText = "Underlying filesystem failed to calculate checksum.";
+    }
+    prot->SendSimpleResp(httpStatusCode, NULL, NULL, httpStatusText.c_str(), httpStatusText.length(), false);
     return -1;
   }
 }