Guide [Dump] Halo MCC — Launcher Libcurl Error Codes & Result Strings

[byte_corvus]

Anyone digging into the connection logic of the Master Chief Collection launcher has likely seen it choke on various network errors. I managed to pull the internal error mapping from the binary — it's essentially a wrapper for libcurl return codes, but having the specific strings the launcher expects is useful for debugging your own bypasses or connection tools.

Technical Breakdown
The launcher uses these cases to handle everything from protocol mismatches to SSL handshake failures. If you're seeing a specific result code in your logs or during a deep-dive with a debugger, these strings will tell you exactly where the pipe is leaking.

{
case 0:
result = "No error";
break;
case 1:
result = "Unsupported protocol";
break;
case 2:
result = "Failed initialization";
break;
case 3:
result = "URL using bad/illegal format or missing URL";
break;
case 4:
result = "A requested feature, protocol or option was not found built-in in this libcurl due to a build-time decision.";
break;
case 5:
result = "Couldn't resolve proxy name";
break;
case 6:
result = "Couldn't resolve host name";
break;
case 7:
result = "Couldn't connect to server";
break;
case 8:
result = "Weird server reply";
break;
case 9:
result = "Access denied to remote resource";
break;
case 10:
result = "FTP: The server failed to connect to data port";
break;
case 11:
result = "FTP: unknown PASS reply";
break;
case 12:
result = "FTP: Accepting server connect has timed out";
break;
case 13:
result = "FTP: unknown PASV reply";
break;
case 14:
result = "FTP: unknown 227 response format";
break;
case 15:
result = "FTP: can't figure out the host in the PASV response";
break;
case 16:
result = "Error in the HTTP2 framing layer";
break;
case 17:
result = "FTP: couldn't set file type";
break;
case 18:
result = "Transferred a partial file";
break;
case 19:
result = "FTP: couldn't retrieve (RETR failed) the specified file";
break;
case 21:
result = "Quote command returned error";
break;
case 22:
result = "HTTP response code said error";
break;
case 23:
result = "Failed writing received data to disk/application";
break;
case 25:
result = "Upload failed (at start/before it took off)";
break;
case 26:
result = "Failed to open/read local data from file/application";
break;
case 27:
result = "Out of memory";
break;
case 28:
result = "Timeout was reached";
break;
case 30:
result = "FTP: command PORT failed";
break;
case 31:
result = "FTP: command REST failed";
break;
case 33:
result = "Requested range was not delivered by the server";
break;
case 34:
result = "Internal problem setting up the POST";
break;
case 35:
result = "SSL connect error";
break;
case 36:
result = "Couldn't resume download";
break;
case 37:
result = "Couldn't read a file:// file";
break;
case 38:
result = "LDAP: cannot bind";
break;
case 39:
result = "LDAP: search failed";
break;
case 41:
result = "A required function in the library was not found";
break;
case 42:
result = "Operation was aborted by an application callback";
break;
case 43:
result = "A libcurl function was given a bad argument";
break;
case 45:
result = "Failed binding local connection end";
break;
case 47:
result = "Number of redirects hit maximum amount";
break;
case 48:
result = "An unknown option was passed in to libcurl";
break;
case 49:
result = "Malformed telnet option";
break;
case 52:
result = "Server returned nothing (no headers, no data)";
break;
case 53:
result = "SSL crypto engine not found";
break;
case 54:
result = "Can not set SSL crypto engine as default";
break;
case 55:
result = "Failed sending data to the peer";
break;
case 56:
result = "Failure when receiving data from the peer";
break;
case 58:
result = "Problem with the local SSL certificate";
break;
case 59:
result = "Couldn't use specified SSL cipher";
break;
case 60:
result = "SSL peer certificate or SSH remote key was not OK";
break;
case 61:
result = "Unrecognized or bad HTTP Content or Transfer-Encoding";
break;
case 62:
result = "Invalid LDAP URL";
break;
case 63:
result = "Maximum file size exceeded";
break;
case 64:
result = "Requested SSL level failed";
break;
case 65:
result = "Send failed since rewinding of the data stream failed";
break;
case 66:
result = "Failed to initialise SSL crypto engine";
break;
case 67:
result = "Login denied";
break;
case 68:
result = "TFTP: File Not Found";
break;
case 69:
result = "TFTP: Access Violation";
break;
case 70:
result = "Disk full or allocation exceeded";
break;
case 71:
result = "TFTP: Illegal operation";
break;
case 72:
result = "TFTP: Unknown transfer ID";
break;
case 73:
result = "Remote file already exists";
break;
case 74:
result = "TFTP: No such user";
break;
case 75:
result = "Conversion failed";
break;
case 76:
result = "Caller must register CURLOPT_CONV_ callback options";
break;
case 77:
result = "Problem with the SSL CA cert (path? access rights?)";
break;
case 78:
result = "Remote file not found";
break;
case 79:
result = "Error in the SSH layer";
break;
case 80:
result = "Failed to shut down the SSL connection";
break;
case 81:
result = "Socket not ready for send/recv";
break;
case 82:
result = "Failed to load CRL file (path? access rights?, format?)";
break;
case 83:
result = "Issuer check against peer certificate failed";
break;
case 84:
result = "FTP: The server did not accept the PRET command.";
break;
case 85:
result = "RTSP CSeq mismatch or invalid CSeq";
break;
case 86:
result = "RTSP session error";
break;
case 87:
result = "Unable to parse FTP file list";
break;
case 88:
result = "Chunk callback failed";
break;
case 89:
result = "The max connection limit is reached";
break;
case 90:
result = "SSL public key does not match pinned public key";
break;
case 91:
result = "SSL server certificate status verification FAILED";
break;
case 92:
result = "Stream error in the HTTP/2 framing layer";
break;
case 93:
result = "API function called from within callback";
break;
case 94:
result = "An authentication function returned an error";
break;
case 95:
result = "HTTP/3 error";
break;
case 96:
result = "QUIC connection error";
break;
default:
result = "Unknown error";
break;
}
return result;
}

Spoiler: Full Protocol and Extension List

The launcher includes handles for various protocols including FTP, TFTP, and LDAP, though most of the actual telemetry and update traffic goes through standard HTTP/2 or HTTP/3 layers. Seeing error 95 or 96 (QUIC/HTTP3) usually points to local firewall or ISP interference.

1. Check cases 35, 53, 54, 58 for SSL/TLS issues.
2. Check cases 5, 6, 7 for DNS/Proxy resolution failures.
3. Check case 91 if you're messing with certificate pinning.

Usage Notes
If you are writing a custom launcher or a simple proxy-based tool to redirect MCC traffic, match your return headers to these IDs to avoid the launcher hanging or crashing with an \"Unknown error\". It's helpful for keeping the game in a state where it thinks it's still connected when you're actually running locally.

Anyone found any hidden endpoints while tracing these? Drop your logs below.