IHttpCachePolicy::GetUserCachePolicy Method
Returns the cache policy for the user.
Syntax
virtual HTTP_CACHE_POLICY* GetUserCachePolicy(
VOID
) = 0;
Parameters
This method takes no parameters.
Return Value
A pointer to an HTTP_CACHE_POLICY.
Remarks
CHttpModule derived classes that register for request or response events receive an IHttpContext pointer as a parameter on the corresponding virtual method. Call the IHttpContext::GetResponse method, then the IHttpResponse::GetCachePolicy method, and finally the GetUserCachePolicy method to retrieve an HTTP_CACHE_POLICY pointer.
The GetUserCachePolicy return value depends on implementation. You should use the following information as a guideline, but it may not be correct in all scenarios:
The current default implementer of the IHttpCachePolicy interface declares a private``HTTP_CACHE_POLICY structure. During the construction of this implementer, the Policy member of this structure is set to HttpCachePolicyNocache, and the SecondsToLive member of this structure is set to 0. The GetUserCachePolicy method returns the address of this same HTTP_CACHE_POLICY structure.
Notes for Implementers
IHttpCachePolicy implementers are responsible for memory management with this data; therefore, IHttpCachePolicy implementers that use dynamic memory allocation must release or call delete on the HTTP_CACHE_POLICY pointer when it is no longer needed.
Notes for Callers
IHttpCachePolicy implementers are responsible for memory management with this data; therefore, IHttpCachePolicy clients must not release or call delete on the returned HTTP_CACHE_POLICY pointer when this data is no longer needed.
Example
The following code example demonstrates how to create a global module that listens for RQ_BEGIN_REQUEST and RQ_SEND_RESPONSE events. The module then retrieves an IHttpCachePolicy pointer and writes cache policy information for the user to the response stream.
#pragma warning( disable : 4290 )
#pragma warning( disable : 4530 )
#define _WINSOCKAPI_
#include <windows.h>
#include <sal.h>
#include <tchar.h>
#include <httptrace.h>
#include <httpserv.h>
#include <httpcach.h>
#include <string>
using namespace std;
// The CConvert class mirrors the Convert class that is
// defined in the .NET Framework. It converts primitives
// and other data types to wstring types.
class CConvert
{
public:
// The ToString method converts a long to a wstring.
// l: the long value to convert to a wstring.
// return: the long as a wstring.
static wstring ToString(long l)
{
WCHAR str[256];
str[0] = '\0';
_ltow_s(l, str, 256, 10);
return str;
}
// The ToByteString converts a double-byte
// character string to a single-byte string.
// str: the double-byte string to convert.
// return: a single-byte string copied from str.
static string ToByteString(const wstring& str)
{
// Get the length of the
// double-byte string.
size_t length = str.length();
// Create a temporary char pointer.
char* byteChar = new char[length+1];
byteChar[0] = '\0';
// Copy the double-byte character string
// into the single-byte string.
size_t charsReturned = 0;
wcstombs_s(&charsReturned, byteChar,
length+1, str.c_str(), length+1);
// Create a string to return.
string retString = byteChar;
// Delete the temporary string and
// set that string to NULL.
delete[] byteChar;
byteChar = NULL;
// Return the single-byte string.
return retString;
}
// The ToString method converts a ULONG to a wstring.
// u: the ULONG value to convert to a wstring.
// return: the value of u as a wstring.
static wstring ToString(ULONG u)
{
return (ToString((long)u));
}
};
// The CResponseWriter class writes
// text to the response stream.
class CResponseWriter
{
public:
// Creates the CResponseWriter class.
// response: the IHttpResponse
// pointer to write to.
// throws: a _com_error exception if
// the IHttpResponse pointer is NULL.
CResponseWriter(IHttpResponse* response)
throw (_com_error)
{
// If the response is NULL,
// throw an exception.
if (NULL == response)
{
ThrowOnFail(E_INVALIDARG);
}
// Set the internal response.
m_response = response;
}
// The destructor for the CResponseWriter
// class. The CResponseWriter method
// sets the IHttpResponse pointer to NULL.
virtual ~CResponseWriter()
{
m_response = NULL;
}
// The Write method writes the
// PCSTR to the response stream.
// pszValue: the PCSTR to write.
// throws: a _com_error if the
// Write method fails.
void Write
(
PCSTR pszValue
) throw (_com_error)
{
// The string must not be
// NULL, and its length must
// be greater than 0.
if ((NULL == pszValue) ||
(strlen(pszValue) < 1))
{
// Throw an invalid argument
// exception.
ThrowOnFail(E_INVALIDARG);
}
// Create a data chunk structure.
HTTP_DATA_CHUNK dataChunk;
// Set the chunk to a chunk in memory.
dataChunk.DataChunkType =
HttpDataChunkFromMemory;
// Set the chunk to
// the pszValue parameter.
dataChunk.FromMemory.pBuffer =
(PVOID)pszValue;
// Set the chunk size
// to the pszValue length.
dataChunk.FromMemory.BufferLength =
(USHORT)strlen(pszValue);
// Declare and initialize OUT
// parameters for the WriteEntityChunks
// method.
DWORD pcbSent = 0;
BOOL pfCompletionExpected = FALSE;
// Write the entity chunks to
// the response stream.
HRESULT hr =
m_response->WriteEntityChunks
(&dataChunk,
1,
FALSE,
FALSE,
&pcbSent,
&pfCompletionExpected);
// Throw an exception if the call
// to WriteEntityChunks is not a
// success.
ThrowOnFail(hr);
}
// The WriteLine method writes a string
// and newline characters to the response steam.
// pszValue: the PCSTR string to write.
// throws: a _com_error if the PCSTR
// or the newline characters are not
// written to the response stream.
void WriteLine
(
PCSTR pszValue
) throw (_com_error)
{
// Try to write the pszValue parameter.
Write(pszValue);
// Try to write the newline characters.
Write("\r\n");
}
// Convenience method that writes a name
// and value pair to the response stream.
// name: the name of the parameter.
// value: the value of the parameter.
// throws: a _com_error exception if
// the response stream is not written.
void WriteLine
(
const wstring& name,
const wstring& value
) throw (_com_error)
{
// Convert the UNICODE strings
// to mutlibyte strings.
string nameMulti =
CConvert::ToByteString(name);
string valueMulti =
CConvert::ToByteString(value);
// Create the string to write.
string writeString =
nameMulti +
string(": ") +
valueMulti;
// Write the line to
// the response stream.
WriteLine(writeString.c_str());
}
// Tests an HRESULT for success.
// hr: the HRESULT value to inspect.
// throws: a _com_error if the HRESULT
// parameter is not S_OK.
static void ThrowOnFail(HRESULT hr)
{
if (FAILED(hr))
{
_com_error ce(hr);
throw ce;
}
}
private:
// Specify the IHttpResponse
// pointer to write to.
IHttpResponse* m_response;
};
// The CCachePolicyModule is a CHttpModule
// class that handles response processing
// by updating the IHttpCachePolicy pointer
// and writing that IHttpCachePolicy data
// to the response stream.
class CCachePolicyModule : public CHttpModule
{
public:
// The CHttpResponseModule method is
// the public virtual destructor for
// the CHttpResponseModule class.
virtual ~CCachePolicyModule()
{
}
// The OnSendResponse method is the method
// supporting the RQ_SEND_RESPONSE event type.
// pHttpContext: the current IHttpContext pointer.
// pProvider: the current IHttpEventProvider pointer.
// return: RQ_NOTIFICATION_FINISH_REQUEST if the
// IHttpCachePolicy data is written. Otherwise,
// RQ_NOTIFICATION_CONTINUE.
virtual
REQUEST_NOTIFICATION_STATUS
OnSendResponse
(
IN IHttpContext* pHttpContext,
IN ISendResponseProvider* pProvider
)
{
// Return if the IHttpContext
// pointer is NULL.
if (NULL == pHttpContext)
{
return RQ_NOTIFICATION_CONTINUE;
}
// Get the IHttpResponse pointer
// from the IHttpContext pointer.
IHttpResponse* response =
pHttpContext->GetResponse();
// Return if the IHttpResponse
// pointer is NULL.
if (NULL == response)
{
return RQ_NOTIFICATION_CONTINUE;
}
// Get the IHttpCachePolicy pointer
// from the IHttpResponse pointer.
IHttpCachePolicy* policy =
response->GetCachePolicy();
// Return if the IHttpCachePolicy
// pointer is NULL.
if (NULL == policy)
{
return RQ_NOTIFICATION_CONTINUE;
}
// Wrap calls in one try-catch statement
// because a CResponseWriter might throw
// a _com_error exception.
try
{
// Create a CResponseWriter using
// the IHttpResponse pointer.
CResponseWriter writer(response);
// Clear the existing response stream.
response->Clear();
// Set the response header to plain text.
HRESULT hr =
response->SetHeader(HttpHeaderContentType,
"text/plain",
(USHORT)strlen("text/plain"),
TRUE);
// Throw an excepion if the
// SetHeader method failed.
CResponseWriter::ThrowOnFail(hr);
// Write the IHttpCachePolicy pointer
// data to the response stream.
Write(policy, writer);
}
catch(_com_error& ce)
{
// Set the error status
// using the COM exception.
response->SetStatus(500,
"OnSendResponse",
0, ce.Error());
// Continue processing.
return RQ_NOTIFICATION_CONTINUE;
}
// Finish the request because
// the response is written.
return RQ_NOTIFICATION_FINISH_REQUEST;
}
protected:
// The Write method writes HTTP_CACHE_POLICY_TYPE
// data to the response stream.
// policyType: the HTTP_CACHE_POLICY_TYPE.
// writer: the CResponseWriter to use
// for writing to the response stream.
// throws: a _com_error exception.
static void Write
(
HTTP_CACHE_POLICY_TYPE policyType,
CResponseWriter& writer
) throw (_com_error)
{
// Create an empty string to write the
// value of the HTTP_CACHE_POLICY_TYPE to.
wstring value;
// Write to the value string dependent
// upon the value of the HTTP_CACHE_POLICY_TYPE.
switch (policyType)
{
case HttpCachePolicyNocache:
{
value = L"HttpCachePolicyNocache";
break;
}
case HttpCachePolicyUserInvalidates:
{
value = L"HttpCachePolicyUserInvalidates";
break;
}
case HttpCachePolicyTimeToLive:
{
value = L"HttpCachePolicyTimeToLive";
break;
}
case HttpCachePolicyMaximum:
{
value = L"HttpCachePolicyMaximum";
break;
}
default:
{
value = L"Error";
break;
}
}
// Write the policy type as a
// string to the response stream.
writer.WriteLine(L"Policy Type", value);
}
// The Write method writes HTTP_CACHE_POLICY
// pointer data to the response stream.
// cachePolicy: the HTTP_CACHE_POLICY
// pointer to write.
// writer: the CResponseWriter to use
// for writing to the response stream.
// throws: a _com_error exception.
static void Write
(
HTTP_CACHE_POLICY* cachePolicy,
CResponseWriter& writer
) throw (_com_error)
{
// If the HTTP_CACHE_POLICY pointer
// is NULL then return.
if (NULL == cachePolicy)
{
return;
}
// Get the HTTP_CACHE_POLICY_TYPE from
// the HTTP_CACHE_POLICY pointer.
HTTP_CACHE_POLICY_TYPE policyType =
cachePolicy->Policy;
// Write the HTTP_CACHE_POLICY_TYPE
// to the response stream.
Write(policyType, writer);
// Get the seconds to live from
// the HTTP_CACHE_POLICY pointer.
ULONG secondsToLiveULONG =
cachePolicy->SecondsToLive;
// Convert the ULONG to a wstring.
wstring secondsToLive =
CConvert::ToString(secondsToLiveULONG);
// Write the Seconds-to-Live
// to the response stream.
writer.WriteLine(L"Seconds-to-Live", secondsToLive);
}
// The Write method writes IHttpCachePolicy
// pointer data to the response stream.
// httpCachePolicy: the IHttpCachePolicy
// pointer to write to the stream.
// writer: the CResponseWriter writer
// for writing to the response stream.
// throws: a _com_error exception.
static void Write
(
IHttpCachePolicy* httpCachePolicy,
CResponseWriter& writer
) throw (_com_error)
{
// If the IHttpCachePolicy
// pointer is NULL, return.
if (NULL == httpCachePolicy)
{
return;
}
// Get the HTTP_CACHE_POLICY
// pointer from the IHttpCachePolicy
// pointer for the user.
HTTP_CACHE_POLICY* userCachePolicy =
httpCachePolicy->GetUserCachePolicy();
// Write the HTTP_CACHE_POLICY
// pointer data for the user to
// the response stream.
Write(userCachePolicy, writer);
}
};
// The CCachePolicyFactory class implements the
// IHttpModuleFactory interface and creates a new
// CCachePolicyModule pointer and registers that
// pointer for request and response events.
class CCachePolicyFactory : public IHttpModuleFactory
{
public:
// The RegisterCHttpModule method creates a new
// CCachePolicyFactory pointer and sets this new
// CCachePolicyFactory pointer as the IHttpModuleFactory
// pointer on the IHttpModuleRegistrationInfo pointer.
// dwServerVersion: the current server version.
// pModuleInfo: the current
// IHttpModuleRegistrationInfo pointer.
// pGlobalInfo: the current IHttpServer pointer.
// return: the value returned from the the call
// to the SetRequestNotifications on the
// IHttpModuleRegistrationInfo pointer.
static HRESULT RegisterCHttpModule
(
DWORD dwServerVersion,
IHttpModuleRegistrationInfo* pModuleInfo,
IHttpServer* pGlobalInfo
)
{
// Create a new CCachePolicyFactory pointer.
CCachePolicyFactory* policyFactory =
new CCachePolicyFactory;
// Test for NULL on the new
// CCachePolicyFactory pointer.
if (NULL == policyFactory)
{
// Return an out-of-memory error
// code if moduleFactory is NULL.
return HRESULT_FROM_WIN32(ERROR_NOT_ENOUGH_MEMORY);
}
// Set the request notifications for RQ_SEND_RESPONSE
// messages on the new CCachePolicyFactory pointer.
return pModuleInfo->SetRequestNotifications
(policyFactory,
RQ_SEND_RESPONSE,
0);
}
// The GetHttpModule method creates a new
// CCachePolicyModule pointer and sets the
// new CCachePolicyModule on the ppModule parameter.
// ppModule: the new CHttpResponseModule pointer to return.
// pAllocator: currently unused.
// return: ERROR_NOT_ENOUGH_MEMORY if the
// heap is exhausted; otherwise, S_OK.
virtual
HRESULT
GetHttpModule
(
OUT CHttpModule** ppModule,
IN IModuleAllocator* pAllocator
)
{
// Call the UNREFERENCED_PARAMETER macro
// with the IModuleAllocator pointer, because
// this parameter is currently unused.
UNREFERENCED_PARAMETER(pAllocator);
// Set the dereferenced ppModule
// to a new CHttpResponseModule pointer.
(*ppModule) = new CCachePolicyModule;
// If the new CHttpResponseModule is
// NULL, return an error indicating
// that heap memory is exhausted.
if (NULL == (*ppModule))
{
return HRESULT_FROM_WIN32(ERROR_NOT_ENOUGH_MEMORY);
}
// Return S_OK.
return S_OK;
}
// The Terminate method
// calls delete on this.
virtual
void
Terminate()
{
delete this;
}
protected:
// The CCachePolicyFactory method is
// the protected constructor for the
// CCachePolicyFactory class.
CCachePolicyFactory()
{
}
// The CCachePolicyFactory method is
// the protected virtual destructor for
// the CCachePolicyFactory class.
virtual ~CCachePolicyFactory()
{
}
private:
};
// The RegisterModule method is the
// main entry point for the DLL.
// dwServerVersion: the current server version.
// pModuleInfo: the current
// IHttpModuleRegistrationInfo pointer.
// pGlobalInfo: the current IHttpServer pointer.
// return: the value returned by calling the
// CCachPolicyFactory::RegisterCHttpModule method.
HRESULT
__stdcall
RegisterModule(
DWORD dwServerVersion,
IHttpModuleRegistrationInfo* pModuleInfo,
IHttpServer* pGlobalInfo
)
{
return CCachePolicyFactory::RegisterCHttpModule
(dwServerVersion,
pModuleInfo,
pGlobalInfo);
}
For more information on how to create and deploy a native DLL module, see Walkthrough: Creating a Request-Level HTTP Module By Using Native Code.
The above code writes data that is similar to the following to the response stream:
Policy Type: HttpCachePolicyNocache
Seconds-to-Live: 0
You can optionally compile the code by using the __stdcall (/Gz) calling convention instead of explicitly declaring the calling convention for each function.
Thread Safety
The GetUserCachePolicy method is thread safe. However, modifying the HTTP_CACHE_POLICY members independently is not thread safe because these members are public fields on a shared structure.
Requirements
| Type | Description |
|---|---|
| Client | - IIS 7.0 on Windows Vista - IIS 7.5 on Windows 7 - IIS 8.0 on Windows 8 - IIS 10.0 on Windows 10 |
| Server | - IIS 7.0 on Windows Server 2008 - IIS 7.5 on Windows Server 2008 R2 - IIS 8.0 on Windows Server 2012 - IIS 8.5 on Windows Server 2012 R2 - IIS 10.0 on Windows Server 2016 Technical Preview |
| Product | - IIS 7.0, IIS 7.5, IIS 8.0, IIS 8.5, IIS 10.0 - IIS Express 7.5, IIS Express 8.0, IIS Express 10.0 |
| Header | Httpserv.h |