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+.. _mozilla_projects_nss_reference_nspr_functions:
+
+NSPR functions
+==============
+
+.. container::
+
+   `NSPR <https://www.mozilla.org/projects/nspr/>`__ is a platform abstraction library that provides
+   a cross-platform API to common OS services.  NSS uses NSPR internally as the porting layer. 
+   However, a small number of NSPR functions are required for using the certificate verification and
+   SSL functions in NSS.  These NSPR functions are listed in this section.
+
+.. _nspr_initialization_and_shutdown:
+
+`NSPR initialization and shutdown <#nspr_initialization_and_shutdown>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   NSPR is automatically initialized by the first NSPR function called by the application.  Call
+   ```PR_Cleanup`` </en-US/PR_Cleanup>`__ to shut down NSPR and clean up its resources.\ `
+    </en-US/PR_Init>`__
+
+   -  `PR_Cleanup </en-US/PR_Cleanup>`__
+
+.. _error_reporting:
+
+`Error reporting <#error_reporting>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   NSS uses NSPR's thread-specific error code to report errors.  Call
+   ```PR_GetError`` </en-US/PR_GetError>`__ to get the error code of the last failed NSS or NSPR
+   function.  Call ```PR_SetError`` </en-US/PR_SetError>`__ to set the error code, which can be
+   retrieved with ``PR_GetError`` later.
+
+   The NSS functions ``PORT_GetError`` and ``PORT_SetError`` are simply wrappers of ``PR_GetError``
+   and ``PR_SetError``.
+
+   -  `PR_GetError </en-US/PR_GetError>`__
+   -  `PR_SetError </en-US/PR_SetError>`__
+
+.. _calendar_time:
+
+`Calendar time <#calendar_time>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   NSS certificate verification functions take a ``PRTime`` parameter that specifies the time
+   instant at which the validity of the certificate should verified.  The NSPR function
+   ```PR_Now`` </en-US/PR_Now>`__ returns the current time in ``PRTime``.
+
+   -  `PR_Now </en-US/PR_Now>`__
+
+.. _interval_time:
+
+`Interval time <#interval_time>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   The NSPR socket I/O functions ```PR_Recv`` </en-US/PR_Recv>`__ and
+   ```PR_Send`` </en-US/PR_Send>`__ (used by the NSS SSL functions) take a ``PRIntervalTime``
+   timeout parameter.  ``PRIntervalTime`` has an abstract, platform-dependent time unit.  Call
+   ```PR_SecondsToInterval`` </en-US/PR_SecondsToInterval>`__ or ``PR_MillisecondsToInterval`` to
+   convert a time interval in seconds or milliseconds to ``PRIntervalTime``.
+
+   -  `PR_SecondsToInterval </en-US/PR_SecondsToInterval>`__
+   -  `PR_MillisecondsToInterval </en-US/PR_MillisecondsToInterval>`__
+
+.. _nspr_io_layering:
+
+`NSPR I/O layering <#nspr_io_layering>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   NSPR file descriptors can be layered, corresponding to the layers in the network stack.  The SSL
+   library in NSS implements the SSL protocol as an NSPR I/O layer, which sits on top of another
+   NSPR I/O layer that represents TCP.
+
+   You can implement an NSPR I/O layer that wraps your own TCP socket code.  The following NSPR
+   functions allow you to create your own NSPR I/O layer and manipulate it.
+
+   -  `PR_GetUniqueIdentity </en-US/PR_GetUniqueIdentity>`__
+   -  `PR_CreateIOLayerStub </en-US/PR_CreateIOLayerStub>`__
+   -  `PR_GetDefaultIOMethods </en-US/PR_GetDefaultIOMethods>`__
+   -  `PR_GetIdentitiesLayer </en-US/PR_GetIdentitiesLayer>`__
+   -  `PR_GetLayersIdentity </en-US/PR_GetLayersIdentity>`__
+   -  `PR_PushIOLayer </en-US/PR_PushIOLayer>`__
+   -  `PR_PopIOLayer </en-US/PR_PopIOLayer>`__
+
+.. _wrapping_a_native_file_descriptor:
+
+`Wrapping a native file descriptor <#wrapping_a_native_file_descriptor>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   If your current TCP socket code uses the standard BSD socket API, a lighter-weight method than
+   creating your own NSPR I/O layer is to simply import a native file descriptor into NSPR.  This
+   method is convenient and works for most applications.
+
+   -  `PR_ImportTCPSocket </en-US/PR_ImportTCPSocket>`__
+
+.. _socket_io_functions:
+
+`Socket I/O functions <#socket_io_functions>`__
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. container::
+
+   As mentioned above, the SSL library in NSS implements the SSL protocol as an NSPR I/O layer. 
+   Users call NSPR socket I/O functions to read from, write to, and shut down an SSL connection, and
+   to close an NSPR file descriptor.
+
+   -  `PR_Read </en-US/PR_Read>`__
+   -  `PR_Write </en-US/PR_Write>`__
+   -  `PR_Recv </en-US/PR_Recv>`__
+   -  `PR_Send </en-US/PR_Send>`__
+   -  `PR_GetSocketOption </en-US/PR_GetSocketOption>`__
+   -  `PR_SetSocketOption </en-US/PR_SetSocketOption>`__
+   -  `PR_Shutdown </en-US/PR_Shutdown>`__
+   -  `PR_Close </en-US/PR_Close>`__
+\ No newline at end of file