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WinHTTP overview

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This topic explains how to use Windows HTTP Services (WinHTTP) functionality for a Microsoft Game Development Kit (GDK) title. It is a lower-level HTTP client API that is available for PC and Xbox console Microsoft Game Development Kit (GDK) titles. You can use it to create regular HTTP and WebSocket service endpoints.

Since it is lower-level, there are additional considerations and steps to implement so that you can achieve secure and robust communication for your title. We recommend that your title implementation adheres to all communication security best practices (NDA topic).

WinHTTP version differences

In general, Microsoft Game Development Kit (GDK) titles interact with WinHTTP in the same way that they interact with WinHTTP in Win32 applications.

When developing for Microsoft Game Development Kit (GDK) titles, only the flat C/C++ API for WinHTTP is available. This means that HTTP functionalities must be built on this HTTP client API.

Add WinHTTP to your Xbox console project

On console, you should #include <winhttp.h> in your source files. You must link against XGamePlatform.lib, rather than directly against Winhttp.lib. Only the APIs under the WINAPI_PARTITION_GAMES API family work in Microsoft Game Development Kit (GDK) titles. On Windows PC, you should continue to link against Winhttp.lib.

For an example of how to integrate WinHTTP into your Microsoft Game Development Kit (GDK) title, see the SimpleWinHttp sample. It provides a solid, fully compliant starting point for your own WinHTTP implementation and includes the WinHttpManager class. It exposes a simple asynchronous API surface.

Network initialization and WinHTTP

Before making the first call to WinHttpOpen, Microsoft Game Development Kit (GDK) titles must ensure that the networking stack is initialized. If WinHttpOpen is called too early during the title's launch process, WinHttpOpen or subsequent WinHTTP calls might fail or crash in a non-deterministic way. Requests can appear to succeed but actually fail or vice-versa before the network is declared as initialized. For details about how to determine when the networking stack is initialized, see Network initialization and connectivity.

Title suspend/resume and WinHTTP

Titles should initiate the process to close all WinHTTP handles when a title suspension notification is received. WinHTTP handle cleanup is asynchronous. As a result, you should close your handles in the following order: all request handles followed by all connection handles followed by all session handles. The asynchronous nature of WinHTTP handle cleanup is to ensure notification threading safety. Even though it's asynchronous, WinHTTP handle cleanup doesn't delay for any period of time. This makes it easily fit within the one-second suspend-deferral timeout.

On resume, titles should follow the same procedure as described in Network initialization and WinHTTP and wait for the network to move back to the ready state before continuing with WinHTTP usage. A long period of time might have elapsed between suspend and resume events, requiring the network to once again stabilize before WinHTTP APIs become deterministic again.

Memory and concurrency considerations

The number of concurrent WinHTTP requests should always be kept below eight to ensure that the asynchronous state within WinHTTP operates correctly and within its memory budget. This limit applies to all concurrent operations within the title runtime, including calls from Xbox services APIs and XCurl.

As an extension to WinSock Memory Considerations, you should ensure that when receiving data you always have a pended buffer with WinHttpReadData (or are waiting for a callback from a WinHttpQueryDataAvailable call) in order to transfer data into your user mode process from the kernel mode memory pools as quickly as possible and minimize the amount of kernel memory consumed by your HTTP operation.

The WinHttpQueryHeaders getter function requires transient memory allocations. It allocates a scratch buffer of size equal to the lpdwBufferLength parameter for internal use (and frees it before the function returns). For this reason, you should use the WINHTTP_NO_OUTPUT_BUFFER double calling pattern to minimize the size of the scratch buffers and limit how many concurrent calls to WinHttpQueryHeaders you are making at once to avoid excessive system memory usage that could lead to system instability. Note that the default maximum size for headers is 64KB as specified by the WINHTTP_OPTION_MAX_RESPONSE_HEADER_SIZE WinHTTP option.

WinHttpOpen considerations

Flags

You must pass the flags in the following table to WinHttpOpen.

Parameter Value
dwAccessType WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY
pszProxyW WINHTTP_NO_PROXY_NAME
pszProxyBypassW WINHTTP_NO_PROXY_BYPASS
dwFlags WINHTTP_FLAG_SECURE_DEFAULTS

The combination of WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY, WINHTTP_NO_PROXY_NAME, and WINHTTP_NO_PROXY_BYPASS allows the Microsoft Game Development Kit (GDK) platform to automatically handle proxies such as Fiddler and other edge-case networking environments.

The WINHTTP_FLAG_SECURE_DEFAULTS flag is a new flag that's specifically designed to help Microsoft Game Development Kit (GDK) titles to adhere to the security best practices by setting the recommended secure connection behavior. It's available on Xbox One consoles and will be available on Windows PC in a future Windows OS update. Trying to pass WINHTTP_FLAG_SECURE_DEFAULTS on existing Windows OS versions results in an invalid parameter failure. This flag has a significant side effect—it forces WinHTTP into the asynchronous mode because this flag implicitly includes the WINHTTP_FLAG_ASYNC flag. On Windows PC OS versions that don't support this flag, you should pass WINHTTP_FLAG_ASYNC instead to minimize differences in the remainder of your WinHTTP implementation.

Note

The WINHTTP_FLAG_SECURE_DEFAULTS flag requires a matching WINHTTP_FLAG_SECURE flag passed to WinHttpOpenRequest and blocks unencrypted HTTP requests. On development kits for internal debugging and testing, you may create an additional WinHTTP session handle and specify the WINHTTP_FLAG_ASYNC flag to WinHttpOpen. This will allow you to then make an unencrypted HTTP request during development by not specifying the WINHTTP_FLAG_SECURE flag to WinHttpOpenRequest. You should still use session handles opened with the WINHTTP_FLAG_SECURE_DEFAULTS for non-debug traffic to match the request behavior your title will see in RETAIL.

WINHTTP_OPTION_SECURE_PROTOCOLS

After you have a new session handle that was created by WinHttpOpen, you must call WinHttpSetOption with option WINHTTP_OPTION_SECURE_PROTOCOLS and pass the corresponding XNetworkingSecurityInformation::enabledHttpSecurityProtocolFlags that was retrieved by a call to XNetworkingQuerySecurityInformationForUrlUtf16Async for a matching URL that this session handle will be used for. You should also store the XNetworkingSecurityInformation structure on your context object for use in the validating the TLS/SSL handshake step.

Caching session handles

HTTP session handles that were created through WinHttpOpen are expensive from a memory perspective and incur a large start-up cost that delays the first HTTP request. We recommend that you cache HTTP session handles as much as possible within your title to avoid these costs.

However, it's not possible to change the WINHTTP_OPTION_SECURE_PROTOCOLS option on a session handle. You should keep a cache of XNetworkingSecurityInformation::enabledHttpSecurityProtocolFlags values mapped to WinHTTP session handles to ensure that you have a different session handle for each different secure protocol flag.

The cache that your title maintains must be cleared on suspend notifications and should be rebuilt from scratch on resume (after waiting for the network to become initialized).

WinHttpConnect considerations

Unlike session handles, connection handles that are created through WinHttpConnect should never be cached. New handles should be created for every new request and/or retry attempt. WinHTTP connection handles, despite their name, have no relationship to the underlying server Transmission Control Protocol (TCP) connections. WinHTTP manages the lifetimes of the underlying server connections with the session handle and automatically reuses open server connections where possible for new connection handles.

URL Canonicalization

WinHTTP expects all URLs to be canonicalized into the a-z, A-Z, and 0-9 US-ASCII characters. For more information about canonicalization, see Uniform Resource Locators (URLs) in WinHTTP. Whenever possible, we recommend that you hard-code the URLs that your title uses in canonicalized form. This avoids the memory allocations and performance issues that are incurred by using the WinHttpCrackUrl and WinHttpCreateUrl functions to dynamically canonicalize your URLs.

URL splitting

WinHTTP requires a null-terminated host name string to be passed to WinHttpConnect while the path and object are passed to WinHttpOpenRequest. This means that your title must pass both the full URL, including the concatenated host name and path in some places and only the host name or path in others. We recommend that you hard-code both in your title to avoid the need to use WinHttpCrackUrl and WinHttpCreateUrl to dynamically concatenate or split the URLs.

WinHttpOpenRequest considerations

Similar to WinHTTP connection handles, WinHTTP request handles that were created through the WinHttpOpenRequest function should never be cached. New handles should be created for every new request and/or retry attempt.

As a security best practice, titles should always pass the WINHTTP_FLAG_SECURE flag for the dwFlags parameter when calling the WinHttpOpenRequest function.

Retrieving and applying Xbox services tokens

Tokens aren't automatically inserted for Microsoft Game Development Kit (GDK) titles. Instead, the title should retrieve Xbox services authentication tokens and signatures with the Microsoft Game Development Kit (GDK) XUser APIs. After the title has a user, the title should call XUserGetTokenAndSignatureUtf16Async to retrieve the token and signature strings for each individual request. These two strings should then be passed as headers in the call to WinHttpAddRequestHeadersEx, WinHttpSendRequest, or WinHttpAddRequestHeaders.

To generate a proper signature, XUserGetTokenAndSignatureUtf16Async expects the title to pass all headers and the entire body. For a POST or PUT with a large body, the title can pass a subset of the body that was configured in Partner Center. For more information, see Web services (NDA topic). At this time, Xbox network doesn't provide a mechanism for retrieving this configuration. Clients are expected to either hard-code the values or retrieve them through a custom, title-specific endpoint.

XUserGetTokenAndSignatureUtf16Async performs all necessary caching internally and should be called for each HTTP attempt, including a retry. If the title receives a 401 Unauthorized HTTP response status code for any HTTP request, the title should retry the request and force a refresh of the Xbox services authentication token. This is achieved by retrieving a new token with XUserGetTokenAndSignatureUtf16Async and passing the XUserGetTokenAndSignatureOptions::ForceRefresh enum value.

After the title has XUserGetTokenAndSignatureUtf16Data that was retrieved by a call to XUserGetTokenAndSignatureUtf16Async, the title must transform XUserGetTokenAndSignatureUtf16Data::Token and XUserGetTokenAndSignatureUtf16Data::Signature into HTTP headers to be passed into WinHTTP. A new WinHTTP API, WinHttpAddRequestHeadersEx, has been added specifically to reduce complexity for Microsoft Game Development Kit (GDK) titles. An example of how to use this new API is shown as follows. This new API is available on Xbox One consoles and will be available on Windows PC in a future Windows OS update. On console, we recommend that you use WinHttpAddRequestHeadersEx to avoid the extra allocations and string format changes.

HRESULT
AddTokenAndSignatureDataToHttpRequest(
   XUserGetTokenAndSignatureUtf16Data* userTokenAndSignatureData,
   HINTERNET requestHandle
   )
{
   WINHTTP_EXTENDED_HEADER winhttpHeader[2];
   winhttpHeader[0].pwszName = L"Authorization";
   winhttpHeader[0].pwszValue = userTokenAndSignatureData->token;
   winhttpHeader[1].pwszName = L"Signature";
   winhttpHeader[1].pwszValue = userTokenAndSignatureData->signature;
   return HRESULT_FROM_WIN32(WinHttpAddRequestHeadersEx(
       m_handshakeRequest,
       WINHTTP_ADDREQ_FLAG_ADD,
       WINHTTP_EXTENDED_HEADER_FLAG_UNICODE,
       0,
       tokenAndSignature->signatureCount ? 2 : 1,
       winhttpHeader));
}

Note

The device or a signed-in account needs to have access to the sandbox that it's set to. Otherwise, XUserGetTokenAndSignatureUtf16Data fails.

Using the Xbox Network Security Authorization List (NSAL)

Xbox network uses the NSAL to ensure that clients establish secure and authenticated connections to your web services. Titles manage the contents of the NSAL as part of their configuration in Partner Center. For more information, see Setting up web services at Partner Center (NDA topic). The NSAL configuration is then downloaded automatically for each title and is used both to generate appropriate Xbox services tokens and to perform certificate pinning for your title's specific endpoints.}

WinHTTP asynchronous state machine considerations

The WinHTTP asynchronous state machine is the same on console as it is on Windows PC. To register a callback function with one or more notifications, use the WinHttpSetStatusCallback function. We recommend using the WINHTTP_CALLBACK_FLAG_ALL_NOTIFICATIONS flag for the dwNotificationFlags parameter for debugging purposes because WinHTTP is relatively verbose and transparent about what it's doing. While most notifications don't require any action from you, logging the data can be useful for discovering the root cause of issues.

WinHTTP uses a single thread for notifications. Titles should avoid blocking any notification function whenever possible because this prevents all HTTP requests within your process from progressing. Unserviced notifications can also increase kernel mode memory, which can lead to crashes.

WinHTTP doesn't copy your send or receive buffers and requires you to keep these buffers allocated until the corresponding completion callback. Ensure that you keep your send buffers allocated and valid from when you call WinHttpSendRequest until the corresponding WINHTTP_CALLBACK_STATUS_SENDREQUEST_COMPLETE notification is received. Similarly, every time you call WinHttpReadData, ensure that you keep your receive buffer allocated and valid until the corresponding WINHTTP_CALLBACK_STATUS_READ_COMPLETE notification is received. We also recommend using a receive buffer of at least 8 KB in size to avoid recursion problems that can lead to stack exhaustion.

Titles should also ensure that WinHTTP buffers are emptied correctly by continuing the asynchronous WinHttpQueryDataAvailable/WinHttpReadData cycle and by not blocking WinHTTP callbacks for any period of time.

Validating the Transport Layer Security (TLS)/Secure Sockets Layer (SSL) handshake

As a security best practice, titles should perform additional validation of the TLS/SSL handshake and use only TLS 1.2.

Additional validation is performed within the WINHTTP_CALLBACK_STATUS_SENDING_REQUEST notification. Within this notification, you must call the XNetworkingVerifyServerCertificate function and pass in the XNetworkingSecurityInformation structure that was retrieved from a previous corresponding call to XNetworkingQuerySecurityInformationForUrlUtf16Async. This function fails if the certificate chain is invalid. You should immediately close the WinHTTP handle before the callback completes to ensure that no data is transferred to/from the compromised server.

In addition to validating certificate chains, the XNetworkingVerifyServerCertificate function is required for Fiddler functionality on console.

Debugging WinHTTP

Fiddler is a useful tool for viewing and debugging your WinHTTP traffic. For Fiddler to capture your title traffic, you must pass the WINHTTP_ACCESS_TYPE_AUTOMATIC_PROXY, WINHTTP_NO_PROXY_NAME, and WINHTTP_NO_PROXY_BYPASS flags to WinHttpOpen. You must also call XNetworkingVerifyServerCertificate within the WINHTTP_CALLBACK_STATUS_SENDING_REQUEST notification callback.

Note

HTTP Monitor doesn't work with Microsoft Game Development Kit (GDK) titles.

See also

Windows HTTP Services (WinHTTP)

XSAPI C overview (secure link)

XUser

Setting up web services at Partner Center (NDA topic)

Fiddler on Xbox One consoles

Communication Security Best Practice Overview (NDA topic)