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xCurl overview

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This topic describes the xCurl library, a Microsoft Game Development Kit (GDK) compliant implementation of the libCurl APIs. We recommend xCurl as the HTTP API for Microsoft Game Development Kit (GDK) titles. xCurl simplifies title development by adhering to all security requirements and best practices without requiring any special title logic or handling. However, it does not support WebSocket communication. If you need to implement WebSocket communication, use libHttpClient instead.

XR-134: Data Transfer Using Web Protocols requires that titles developed for Xbox consoles do not use custom HTTP stack implementations. Instead, use a stack which is provided by and maintainable via the operating system. This ensures that Xbox gamers are provided stability and security improvements over time.

xCurl differs from libCurl in that xCurl is implemented on top of WinHttp and automatically follows Microsoft Game Development Kit (GDK) requirements and best practices, including Process Lifetime Management (PLM). While xCurl is API compatible with libCurl, the transport layer within xCurl uses WinHttp exclusively and does not utilize libCurl. Thus, xCurl is not required to be kept in sync with the open-source implementation of libCurl, including bug fixes, version numbers and more. We recommend that developers use xCurl to maintain your same libCurl HTTP implementation across all platforms while changing only one header include and library linkage.

Several libCurl APIs aren't implemented in xCurl because they either are not commonly used in game development scenarios, or do not have equivalent functionality within WinHttp that can be mapped to. The differences are described later in this topic.

xCurl relies on the Gaming Runtime and can't be initialized until XGameRuntimeInitialize is called.

To understand how xCurl methods work, see the libCurl API documentation.

Note

xCurl and WinHttp are the only XR compliant options for HTTP on Xbox console. xCurl and WinHttp implementations work on both Windows PC and Xbox console with no code changes required. However, on Windows PC, you can use libCurl or any other HTTP stack directly with your Microsoft Game Development Kit (GDK) title - XR-134 does not apply to Windows PC.

Developer Support

xCurl is powered by WinHttp, not libCurl, and is a part of the Microsoft Game Development Kit (GDK).

Support requests should be sent via the recommended support paths for Microsoft Game Development Kit (GDK) titles. These include contacting your Microsoft Representative or reaching out to developer support team via the Xbox Developer Forums.

Add xCurl to your project

To use xCurl in a Microsoft Game Development Kit (GDK) game on a Windows 10 PC or an Xbox console, include the xCurl extension SDK headers and libraries in your project.

  1. Ensure that you've installed the Gaming Runtime Development Kit (GRDK) on your development PC.

  2. Open the .vcxproj file for your game, and then add the following element. This links the import library and includes xCurl.dll with the build output.

    <GDKExtLibNames>Xbox.xCurl.API</GDKExtLibNames>

  3. xCurl has a different header to differentiate itself from libCurl. In the locations where curl.h would be included in your game, replace the header with xCurl.h, shown as follows.

    #include <xCurl.h>

Configuration

xCurl is equivalent to libCurl compiled with the following build flags.

  • HTTP_ONLY
  • CURL_NO_OLDIES
  • CURL_DISABLE_PROXY
  • CURL_DISABLE_COOKIES
  • CURL_DISABLE_DOH
  • CURL_DISABLE_PROGRESS_METER
  • CURL_DISABLE_MIME
  • USE_SCHANNEL

Network initialization

xCurl handles network initialization automatically. You can setup and perform requests at any point in your title's lifecycle. Any request started before the network is initialized will be delayed and queued until the network becomes initialized; in this manner xCurl ensures that your requests will be made at the earliest possible opportunity without any extra handling required by your title.

Title suspend/resume

xCurl handles suspend and resume automatically. On suspend, all outstanding requests will be canceled immediately and fail with CURLE_NO_CONNECTION_AVAILABLE. Additionally, querying curl_easy_getinfo for CURLINFO_OS_ERRNO on these requests will return HRESULT_FROM_WIN32(PROCESS_SUSPEND_RESUME) just like any other GRTS API in case you want to handle these failures differently from general network disconnect failures.

All xCurl handles remain valid throughout the title lifecycle including across suspend/resume boundaries. There is no need to cleanup or initialize any xCurl handle on suspend/resume. Any new requests started after suspend will be delayed until resume and the subsequent network initialization to ensure that they will start as soon as possible without requiring any extra handling by your title.

Note

When using the multi interface for xCurl, your title should continue to call curl_multi_perform along with optionally curl_multi_poll or curl_multi_wait on suspend while there are outstanding requests. xCurl will block suspend until all in-progress requests are completed, and failing to call curl_multi_perform may cause your title to timeout during suspend. We recommend continuing to call curl_multi_perform throughout the entire lifecycle regardless of the suspend/resume state. xCurl handles all intricacies of the suspend state internally.

Security functionality

All HTTPS requests through xCurl follow the communication security best practices (NDA topic). xCurl automatically enforces any special certificate pinning specified through your title's "Single Sign-on Portal". Using CURLOPT_SSL_VERIFYPEER to disable certificate validation is not supported.

On development kits you may specify the unencrypted HTTP scheme, http://, for debug traffic and testing purposes. For all RETAIL requests, you must specify the HTTPS scheme, https://, to provide the recommended level of protection. xCurl requests that do not explicitly specify a scheme will infer the HTTPS scheme.

Note

xCurl does not perform automatic token insertion. To retrieve Xbox Live tokens, your title should call the XUserGetTokenAndSignatureAsync or XUserGetTokenAndSignatureUtf16Async GRTS APIs to retrieve the authorization and signature headers, and then use the CURLOPT_HEADER, CURLOPT_HTTPHEADER, or CURLOPT_HEADERFUNCTION options in a call to curl_easy_setopt to set the headers before making the request.

Memory and concurrency considerations

xCurl shares the same concurrent request limitations that apply to WinHttp. Titles should limit concurrent requests to eight or less to ensure that all calls operate correctly. This concurrency limit applies to concurrent requests that are issued from any of xCurl, WinHttp, and Xbox Service APIs.

xCurl uses a flip buffer to receive data. This allows it to start filling a second buffer while providing the full buffer to the read callback and then switch to provide the second buffer to the read callback while the first is being filled. However, if the read callback takes too long or if curl_multi_perform is not called frequently enough in multi mode, WinSock kernel memory may build up. For more information on WinSock kernel memory, see socket memory considerations.

Controlling xCurl allocations

By default, xCurl uses the Windows heap and can have its allocations tracked through XMemSetWin32HeapTrackingHooks. Alternately, memory functions can be provided at initialization time like libCurl.

In addition to curl_global_init_mem, xCurl provides the optional xCurl_global_init_mem. The callbacks that are provided to this version of init are similar to other Microsoft Game Development Kit (GDK) memory callbacks and provide more information than the standard libCurl callbacks about the data that's being allocated.

Supported options

The following options are supported by easy handles in xCurl.

  • CURLOPT_VERBOSE
  • CURLOPT_HEADER
  • CURLOPT_NOBODY
  • CURLOPT_FAILONERROR
  • CURLOPT_UPLOAD
  • CURLOPT_PUT
  • CURLOPT_ACCEPT_ENCODING
  • CURLOPT_TRANSFER_ENCODING
  • CURLOPT_FOLLOWLOCATION
  • CURLOPT_MAXREDIRS
  • CURLOPT_POST
  • CURLOPT_COPYPOSTFIELDS
  • CURLOPT_POSTFIELDS
  • CURLOPT_POSTFIELDSIZE
  • CURLOPT_POSTFIELDSIZE_LARGE
  • CURLOPT_POSTREDIR
  • CURLOPT_REFERER
  • CURLOPT_USERAGENT
  • CURLOPT_HTTPHEADER
  • CURLOPT_HTTPGET
  • CURLOPT_HTTP_VERSION
  • CURLOPT_CUSTOMREQUEST
  • CURLOPT_HEADERDATA
  • CURLOPT_ERRORBUFFER
  • CURLOPT_WRITEDATA
  • CURLOPT_READDATA
  • CURLOPT_INFILESIZE
  • CURLOPT_INFILESIZE_LARGE
  • CURLOPT_CURLU
  • CURLOPT_URL
  • CURLOPT_PORT
  • CURLOPT_TIMEOUT
  • CURLOPT_TIMEOUT_MS
  • CURLOPT_CONNECTTIMEOUT
  • CURLOPT_CONNECTTIMEOUT_MS
  • CURLOPT_DEBUGFUNCTION
  • CURLOPT_DEBUGDATA
  • CURLOPT_HEADERFUNCTION
  • CURLOPT_WRITEFUNCTION
  • CURLOPT_READFUNCTION
  • CURLOPT_SSL_VERIFYPEER
  • CURLOPT_SSL_VERIFYHOST
  • CURLOPT_SSLCERT
  • CURLOPT_BUFFERSIZE
  • CURLOPT_UPLOAD_BUFFERSIZE
  • CURLOPT_PRIVATE
  • CURLOPT_IGNORE_CONTENT_LENGTH
  • CURLOPT_HTTP_TRANSFER_DECODING
  • CURLOPT_HTTP_CONTENT_DECODING

Unsupported functionality

Sockets and fd_set

xCurl doesn't expose the underlying socket that's used for transport. Therefore, xCurl does not implement any option and API that would be used for socket operations. This also removes the ability to use fd_sets to wait on data to arrive through select and poll. To wait for work to arrive, use curl_multi_wait andcurl_multi_poll.

The following APIs are not present in xCurl

  • curl_easy_send
  • curl_easy_recv
  • curl_multi_socket
  • curl_multi_socket_action
  • curl_multi_socket_all
  • curl_multi_assign
  • curl_multi_fdset

The following options have no effect and return the CURLE_NOT_BUILT_IN error.

  • CURLOPT_LOCALPORT
  • CURLOPT_CONNECT_ONLY
  • CURLOPT_SOCKOPTFUNCTION
  • CURLOPT_SOCKOPTDATA
  • CURLOPT_OPENSOCKETFUNCTION
  • CURLOPT_OPENSOCKETDATA
  • CURLOPT_CLOSESOCKETFUNCTION
  • CURLOPT_CLOSESOCKETDATA
  • CURLOPT_XOAUTH2_BEARER
  • CURLOPT_PROGRESSFUNCTION
  • CURLOPT_PROGRESSDATA
  • CURLOPT_XFERINFOFUNCTION
  • CURLOPT_XFERINFODATA
  • CURLOPT_NOPROGRESS
  • CURLINFO_LASTSOCKET
  • CURLINFO_ACTIVESOCKET
  • CURLMOPT_SOCKETFUNCTION
  • CURLMOPT_SOCKETDATA
  • CURLMOPT_PIPELINING
  • CURLMOPT_PUSHFUNCTION

CURL Share

The CURL Share interface is not implemented.

Pause and resume transfers

This feature is currently unsupported. Returning CURL_WRITEFUNC_PAUSE or CURL_READFUNC_PAUSE from a callback results in an aborted operation that can't be resumed.

See also

libCurl API

Setting up web services at Partner Center (NDA topic)

Fiddler on Xbox One consoles

Communication Security Best Practice Overview (NDA topic)