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openflow/usr/include/nspr/prenv.h

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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef prenv_h___
+#define prenv_h___
+
+#include "prtypes.h"
+
+/*******************************************************************************/
+/*******************************************************************************/
+/****************** THESE FUNCTIONS MAY NOT BE THREAD SAFE *********************/
+/*******************************************************************************/
+/*******************************************************************************/
+
+PR_BEGIN_EXTERN_C
+
+/*
+** PR_GetEnv() -- Retrieve value of environment variable
+** 
+** Description:
+** PR_GetEnv() is modeled on Unix getenv().
+** 
+** 
+** Inputs: 
+**   var -- The name of the environment variable
+** 
+** Returns:
+**   The value of the environment variable 'var' or NULL if
+** the variable is undefined.
+** 
+** Restrictions:
+**   You'd think that a POSIX getenv(), putenv() would be
+**   consistently implemented everywhere. Surprise! It is not. On
+**   some platforms, a putenv() where the argument is of
+**   the form "name"  causes the named environment variable to
+**   be un-set; that is: a subsequent getenv() returns NULL. On
+**   other platforms, the putenv() fails, on others, it is a
+**   no-op. Similarly, a putenv() where the argument is of the
+**   form "name=" causes the named environment variable to be
+**   un-set; a subsequent call to getenv() returns NULL. On
+**   other platforms, a subsequent call to getenv() returns a
+**   pointer to a null-string (a byte of zero).
+** 
+**   PR_GetEnv(), PR_SetEnv() provide a consistent behavior 
+**   across all supported platforms. There are, however, some
+**   restrictions and some practices you must use to achieve
+**   consistent results everywhere.
+** 
+**   When manipulating the environment there is no way to un-set
+**   an environment variable across all platforms. We suggest
+**   you interpret the return of a pointer to null-string to
+**   mean the same as a return of NULL from PR_GetEnv().
+** 
+**   A call to PR_SetEnv() where the parameter is of the form
+**   "name" will return PR_FAILURE; the environment remains
+**   unchanged. A call to PR_SetEnv() where the parameter is
+**   of the form "name=" may un-set the envrionment variable on
+**   some platforms; on others it may set the value of the
+**   environment variable to the null-string.
+** 
+**   For example, to test for NULL return or return of the
+**   null-string from PR_GetEnv(), use the following code
+**   fragment:
+** 
+**      char *val = PR_GetEnv("foo");
+**      if ((NULL == val) || ('\0' == *val)) { 
+**          ... interpret this as un-set ... 
+**      }
+** 
+**   The caller must ensure that the string passed
+**   to PR_SetEnv() is persistent. That is: The string should
+**   not be on the stack, where it can be overwritten
+**   on return from the function calling PR_SetEnv().
+**   Similarly, the string passed to PR_SetEnv() must not be
+**   overwritten by other actions of the process. ... Some
+**   platforms use the string by reference rather than copying
+**   it into the environment space. ... You have been warned!
+** 
+**   Use of platform-native functions that manipulate the
+**   environment (getenv(), putenv(), 
+**   SetEnvironmentVariable(), etc.) must not be used with
+**   NSPR's similar functions. The platform-native functions
+**   may not be thread safe and/or may operate on different
+**   conceptual environment space than that operated upon by
+**   NSPR's functions or other environment manipulating
+**   functions on the same platform. (!)
+** 
+*/
+NSPR_API(char*) PR_GetEnv(const char *var);
+
+/*
+** PR_GetEnvSecure() -- get a security-sensitive environment variable
+**
+** Description:
+**
+** PR_GetEnvSecure() is similar to PR_GetEnv(), but it returns NULL if
+** the program was run with elevated privilege (e.g., setuid or setgid
+** on Unix).  This can be used for cases like log file paths which
+** could otherwise be used for privilege escalation.  Note that some
+** platforms may have platform-specific privilege elevation mechanisms
+** not recognized by this function; see the implementation for details.
+*/
+NSPR_API(char*) PR_GetEnvSecure(const char *var);
+
+/*
+** PR_SetEnv() -- set, unset or change an environment variable
+** 
+** Description:
+** PR_SetEnv() is modeled on the Unix putenv() function.
+** 
+** Inputs: 
+**   string -- pointer to a caller supplied
+**   constant, persistent string of the form name=value. Where
+**   name is the name of the environment variable to be set or
+**   changed; value is the value assigned to the variable.
+**
+** Returns: 
+**   PRStatus.
+** 
+** Restrictions: 
+**   See the Restrictions documented in the description of
+**   PR_GetEnv() in this header file.
+** 
+** 
+*/
+NSPR_API(PRStatus) PR_SetEnv(const char *string);
+
+/*
+** PR_DuplicateEnvironment() -- Obtain a copy of the environment.
+**
+** Description:
+** PR_DuplicateEnvironment() copies the environment so that it can be
+** modified without changing the current process's environment, and
+** then passed to interfaces such as POSIX execve().  In particular,
+** this avoids needing to allocate memory or take locks in the child
+** after a fork(); neither of these is allowed by POSIX after a
+** multithreaded process calls fork(), and PR_SetEnv does both.
+**
+** Inputs:
+**   none
+**
+** Returns:
+**   A pointer to a null-terminated array of null-terminated strings,
+**   like the traditional global variable "environ".  The array and
+**   the strings are allocated with PR_Malloc(), and it is the
+**   caller's responsibility to free them.
+**
+**   In case of memory allocation failure, or if the operating system
+**   doesn't support reading the entire environment through the global
+**   variable "environ" or similar, returns NULL instead.
+**
+** Restrictions:
+**   Similarly to PR_GetEnv(), this function may not interoperate as
+**   expected with the operating system's native environment accessors.
+*/
+NSPR_API(char **) PR_DuplicateEnvironment(void);
+
+PR_END_EXTERN_C
+
+#endif /* prenv_h___ */