path: root/generic/tclEnv.c

/*
 * tclEnv.c --
 *
 *	Tcl support for environment variables, including a setenv function.
 *	This file contains the generic portion of the environment module. It
 *	is primarily responsible for keeping the "env" arrays in sync with the
 *	system environment variables.
 *
 * Copyright (c) 1991-1994 The Regents of the University of California.
 * Copyright (c) 1994-1998 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"

TCL_DECLARE_MUTEX(envMutex)	/* To serialize access to environ. */

static struct {
    int cacheSize;		/* Number of env strings in cache. */
    char **cache;		/* Array containing all of the environment
				 * strings that Tcl has allocated. */
#ifndef USE_PUTENV
    char **ourEnviron;		/* Cache of the array that we allocate. We
				 * need to track this in case another
				 * subsystem swaps around the environ array
				 * like we do. */
    int ourEnvironSize;		/* Non-zero means that the environ array was
				 * malloced and has this many total entries
				 * allocated to it (not all may be in use at
				 * once). Zero means that the environment
				 * array is in its original static state. */
#endif
} env;

/*
 * Declarations for local functions defined in this file:
 */

static char *		EnvTraceProc(ClientData clientData, Tcl_Interp *interp,
			    const char *name1, const char *name2, int flags);
static void		ReplaceString(const char *oldStr, char *newStr);
MODULE_SCOPE void	TclSetEnv(const char *name, const char *value);
MODULE_SCOPE void	TclUnsetEnv(const char *name);

/*
 *----------------------------------------------------------------------
 *
 * TclSetupEnv --
 *
 *	This function is invoked for an interpreter to make environment
 *	variables accessible from that interpreter via the "env" associative
 *	array.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The interpreter is added to a list of interpreters managed by us, so
 *	that its view of envariables can be kept consistent with the view in
 *	other interpreters. If this is the first call to TclSetupEnv, then
 *	additional initialization happens, such as copying the environment to
 *	dynamically-allocated space for ease of management.
 *
 *----------------------------------------------------------------------
 */

void
TclSetupEnv(
    Tcl_Interp *interp)		/* Interpreter whose "env" array is to be
				 * managed. */
{
    Var *varPtr, *arrayPtr;
    Tcl_Obj *varNamePtr;
    Tcl_DString envString;
    Tcl_HashTable namesHash;
    Tcl_HashEntry *hPtr;
    Tcl_HashSearch search;

    /*
     * Synchronize the values in the environ array with the contents of the
     * Tcl "env" variable. To do this:
     *    1) Remove the trace that fires when the "env" var is updated.
     *    2) Find the existing contents of the "env", storing in a hash table.
     *    3) Create/update elements for each environ variable, removing
     *	     elements from the hash table as we go.
     *    4) Remove the elements for each remaining entry in the hash table,
     *	     which must have existed before yet have no analog in the environ
     *	     variable.
     *    5) Add a trace that synchronizes the "env" array.
     */

    Tcl_UntraceVar2(interp, "env", NULL,
	    TCL_GLOBAL_ONLY | TCL_TRACE_WRITES | TCL_TRACE_UNSETS |
	    TCL_TRACE_READS | TCL_TRACE_ARRAY, EnvTraceProc, NULL);

    /*
     * Find out what elements are currently in the global env array.
     */

    TclNewLiteralStringObj(varNamePtr, "env");
    Tcl_IncrRefCount(varNamePtr);
    Tcl_InitObjHashTable(&namesHash);
    varPtr = TclObjLookupVarEx(interp, varNamePtr, NULL, TCL_GLOBAL_ONLY,
	    /*msg*/ 0, /*createPart1*/ 0, /*createPart2*/ 0, &arrayPtr);
    TclFindArrayPtrElements(varPtr, &namesHash);

    /*
     * Go through the environment array and transfer its values into Tcl. At
     * the same time, remove those elements we add/update from the hash table
     * of existing elements, so that after this part processes, that table
     * will hold just the parts to remove.
     */

    if (environ[0] != NULL) {
	int i;

	Tcl_MutexLock(&envMutex);
	for (i = 0; environ[i] != NULL; i++) {
	    Tcl_Obj *obj1, *obj2;
	    char *p1, *p2;

	    p1 = Tcl_ExternalToUtfDString(NULL, environ[i], -1, &envString);
	    p2 = strchr(p1, '=');
	    if (p2 == NULL) {
		/*
		 * This condition seem to happen occasionally under some
		 * versions of Solaris, or when encoding accidents swallow the
		 * '='; ignore the entry.
		 */

		continue;
	    }
	    p2++;
	    p2[-1] = '\0';
	    obj1 = Tcl_NewStringObj(p1, -1);
	    obj2 = Tcl_NewStringObj(p2, -1);
	    Tcl_DStringFree(&envString);

	    Tcl_IncrRefCount(obj1);
	    Tcl_IncrRefCount(obj2);
	    Tcl_ObjSetVar2(interp, varNamePtr, obj1, obj2, TCL_GLOBAL_ONLY);
	    hPtr = Tcl_FindHashEntry(&namesHash, obj1);
	    if (hPtr != NULL) {
		Tcl_DeleteHashEntry(hPtr);
	    }
	    Tcl_DecrRefCount(obj1);
	    Tcl_DecrRefCount(obj2);
	}
	Tcl_MutexUnlock(&envMutex);
    }

    /*
     * Delete those elements that existed in the array but which had no
     * counterparts in the environment array.
     */

    for (hPtr=Tcl_FirstHashEntry(&namesHash, &search); hPtr!=NULL;
	    hPtr=Tcl_NextHashEntry(&search)) {
	Tcl_Obj *elemName = Tcl_GetHashValue(hPtr);

	TclObjUnsetVar2(interp, varNamePtr, elemName, TCL_GLOBAL_ONLY);
    }
    Tcl_DeleteHashTable(&namesHash);
    Tcl_DecrRefCount(varNamePtr);

    /*
     * Re-establish the trace.
     */

    Tcl_TraceVar2(interp, "env", NULL,
	    TCL_GLOBAL_ONLY | TCL_TRACE_WRITES | TCL_TRACE_UNSETS |
	    TCL_TRACE_READS | TCL_TRACE_ARRAY, EnvTraceProc, NULL);
}

/*
 *----------------------------------------------------------------------
 *
 * TclSetEnv --
 *
 *	Set an environment variable, replacing an existing value or creating a
 *	new variable if there doesn't exist a variable by the given name. This
 *	function is intended to be a stand-in for the UNIX "setenv" function
 *	so that applications using that function will interface properly to
 *	Tcl. To make it a stand-in, the Makefile must define "TclSetEnv" to
 *	"setenv".
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The environ array gets updated.
 *
 *----------------------------------------------------------------------
 */

void
TclSetEnv(
    const char *name,		/* Name of variable whose value is to be set
				 * (UTF-8). */
    const char *value)		/* New value for variable (UTF-8). */
{
    Tcl_DString envString;
    unsigned nameLength, valueLength;
    int index, length;
    char *p, *oldValue;
    const char *p2;

    /*
     * Figure out where the entry is going to go. If the name doesn't already
     * exist, enlarge the array if necessary to make room. If the name exists,
     * free its old entry.
     */

    Tcl_MutexLock(&envMutex);
    index = TclpFindVariable(name, &length);

    if (index == -1) {
#ifndef USE_PUTENV
	/*
	 * We need to handle the case where the environment may be changed
	 * outside our control. ourEnvironSize is only valid if the current
	 * environment is the one we allocated. [Bug 979640]
	 */

	if ((env.ourEnviron != environ) || (length+2 > env.ourEnvironSize)) {
	    char **newEnviron = ckalloc((length + 5) * sizeof(char *));

	    memcpy(newEnviron, environ, length * sizeof(char *));
	    if ((env.ourEnvironSize != 0) && (env.ourEnviron != NULL)) {
		ckfree(env.ourEnviron);
	    }
	    environ = env.ourEnviron = newEnviron;
	    env.ourEnvironSize = length + 5;
	}
	index = length;
	environ[index + 1] = NULL;
#endif /* USE_PUTENV */
	oldValue = NULL;
	nameLength = strlen(name);
    } else {
	const char *env;

	/*
	 * Compare the new value to the existing value. If they're the same
	 * then quit immediately (e.g. don't rewrite the value or propagate it
	 * to other interpreters). Otherwise, when there are N interpreters
	 * there will be N! propagations of the same value among the
	 * interpreters.
	 */

	env = Tcl_ExternalToUtfDString(NULL, environ[index], -1, &envString);
	if (strcmp(value, env + (length + 1)) == 0) {
	    Tcl_DStringFree(&envString);
	    Tcl_MutexUnlock(&envMutex);
	    return;
	}
	Tcl_DStringFree(&envString);

	oldValue = environ[index];
	nameLength = (unsigned) length;
    }

    /*
     * Create a new entry. Build a complete UTF string that contains a
     * "name=value" pattern. Then convert the string to the native encoding,
     * and set the environ array value.
     */

    valueLength = strlen(value);
    p = ckalloc(nameLength + valueLength + 2);
    memcpy(p, name, nameLength);
    p[nameLength] = '=';
    memcpy(p+nameLength+1, value, valueLength+1);
    p2 = Tcl_UtfToExternalDString(NULL, p, -1, &envString);

    /*
     * Copy the native string to heap memory.
     */

    p = ckrealloc(p, Tcl_DStringLength(&envString) + 1);
    memcpy(p, p2, (unsigned) Tcl_DStringLength(&envString) + 1);
    Tcl_DStringFree(&envString);

#ifdef USE_PUTENV
    /*
     * Update the system environment.
     */

    putenv(p);
    index = TclpFindVariable(name, &length);
#else
    environ[index] = p;
#endif /* USE_PUTENV */

    /*
     * Watch out for versions of putenv that copy the string (e.g. VC++). In
     * this case we need to free the string immediately. Otherwise update the
     * string in the cache.
     */

    if ((index != -1) && (environ[index] == p)) {
	ReplaceString(oldValue, p);
#ifdef HAVE_PUTENV_THAT_COPIES
    } else {
	/*
	 * This putenv() copies instead of taking ownership.
	 */

	ckfree(p);
#endif /* HAVE_PUTENV_THAT_COPIES */
    }

    Tcl_MutexUnlock(&envMutex);

    if (!strcmp(name, "HOME")) {
	/*
	 * If the user's home directory has changed, we must invalidate the
	 * filesystem cache, because '~' expansions will now be incorrect.
	 */

	Tcl_FSMountsChanged(NULL);
    }
}

/*
 *----------------------------------------------------------------------
 *
 * Tcl_PutEnv --
 *
 *	Set an environment variable. Similar to setenv except that the
 *	information is passed in a single string of the form NAME=value,
 *	rather than as separate name strings. This function is intended to be
 *	a stand-in for the UNIX "putenv" function so that applications using
 *	that function will interface properly to Tcl. To make it a stand-in,
 *	the Makefile will define "Tcl_PutEnv" to "putenv".
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	The environ array gets updated, as do all of the interpreters that we
 *	manage.
 *
 *----------------------------------------------------------------------
 */

int
Tcl_PutEnv(
    const char *assignment)	/* Info about environment variable in the form
				 * NAME=value. (native) */
{
    Tcl_DString nameString;
    const char *name;
    char *value;

    if (assignment == NULL) {
	return 0;
    }

    /*
     * First convert the native string to UTF. Then separate the string into
     * name and value parts, and call TclSetEnv to do all of the real work.
     */

    name = Tcl_ExternalToUtfDString(NULL, assignment, -1, &nameString);
    value = strchr(name, '=');

    if ((value != NULL) && (value != name)) {
	value[0] = '\0';
	TclSetEnv(name, value+1);
    }

    Tcl_DStringFree(&nameString);
    return 0;
}

/*
 *----------------------------------------------------------------------
 *
 * TclUnsetEnv --
 *
 *	Remove an environment variable, updating the "env" arrays in all
 *	interpreters managed by us. This function is intended to replace the
 *	UNIX "unsetenv" function (but to do this the Makefile must be modified
 *	to redefine "TclUnsetEnv" to "unsetenv".
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Interpreters are updated, as is environ.
 *
 *----------------------------------------------------------------------
 */

void
TclUnsetEnv(
    const char *name)		/* Name of variable to remove (UTF-8). */
{
    char *oldValue;
    int length;
    int index;
#ifdef USE_PUTENV_FOR_UNSET
    Tcl_DString envString;
    char *string;
#else
    char **envPtr;
#endif /* USE_PUTENV_FOR_UNSET */

    Tcl_MutexLock(&envMutex);
    index = TclpFindVariable(name, &length);

    /*
     * First make sure that the environment variable exists to avoid doing
     * needless work and to avoid recursion on the unset.
     */

    if (index == -1) {
	Tcl_MutexUnlock(&envMutex);
	return;
    }

    /*
     * Remember the old value so we can free it if Tcl created the string.
     */

    oldValue = environ[index];

    /*
     * Update the system environment. This must be done before we update the
     * interpreters or we will recurse.
     */

#ifdef USE_PUTENV_FOR_UNSET
    /*
     * For those platforms that support putenv to unset, Linux indicates
     * that no = should be included, and Windows requires it.
     */

#if defined(_WIN32)
    string = ckalloc(length + 2);
    memcpy(string, name, (size_t) length);
    string[length] = '=';
    string[length+1] = '\0';
#else
    string = ckalloc(length + 1);
    memcpy(string, name, (size_t) length);
    string[length] = '\0';
#endif /* _WIN32 */

    Tcl_UtfToExternalDString(NULL, string, -1, &envString);
    string = ckrealloc(string, Tcl_DStringLength(&envString) + 1);
    memcpy(string, Tcl_DStringValue(&envString),
	    (unsigned) Tcl_DStringLength(&envString)+1);
    Tcl_DStringFree(&envString);

    putenv(string);

    /*
     * Watch out for versions of putenv that copy the string (e.g. VC++). In
     * this case we need to free the string immediately. Otherwise update the
     * string in the cache.
     */

    if (environ[index] == string) {
	ReplaceString(oldValue, string);
#ifdef HAVE_PUTENV_THAT_COPIES
    } else {
	/*
	 * This putenv() copies instead of taking ownership.
	 */

	ckfree(string);
#endif /* HAVE_PUTENV_THAT_COPIES */
    }
#else /* !USE_PUTENV_FOR_UNSET */
    for (envPtr = environ+index+1; ; envPtr++) {
	envPtr[-1] = *envPtr;
	if (*envPtr == NULL) {
	    break;
	}
    }
    ReplaceString(oldValue, NULL);
#endif /* USE_PUTENV_FOR_UNSET */

    Tcl_MutexUnlock(&envMutex);
}

/*
 *---------------------------------------------------------------------------
 *
 * TclGetEnv --
 *
 *	Retrieve the value of an environment variable.
 *
 * Results:
 *	The result is a pointer to a string specifying the value of the
 *	environment variable, or NULL if that environment variable does not
 *	exist. Storage for the result string is allocated in valuePtr; the
 *	caller must call Tcl_DStringFree() when the result is no longer
 *	needed.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

const char *
TclGetEnv(
    const char *name,		/* Name of environment variable to find
				 * (UTF-8). */
    Tcl_DString *valuePtr)	/* Uninitialized or free DString in which the
				 * value of the environment variable is
				 * stored. */
{
    int length, index;
    const char *result;

    Tcl_MutexLock(&envMutex);
    index = TclpFindVariable(name, &length);
    result = NULL;
    if (index != -1) {
	Tcl_DString envStr;

	result = Tcl_ExternalToUtfDString(NULL, environ[index], -1, &envStr);
	result += length;
	if (*result == '=') {
	    result++;
	    Tcl_DStringInit(valuePtr);
	    Tcl_DStringAppend(valuePtr, result, -1);
	    result = Tcl_DStringValue(valuePtr);
	} else {
	    result = NULL;
	}
	Tcl_DStringFree(&envStr);
    }
    Tcl_MutexUnlock(&envMutex);
    return result;
}

/*
 *----------------------------------------------------------------------
 *
 * EnvTraceProc --
 *
 *	This function is invoked whenever an environment variable is read,
 *	modified or deleted. It propagates the change to the global "environ"
 *	array.
 *
 * Results:
 *	Returns NULL to indicate success, or an error-message if the array
 *	element being handled doesn't exist.
 *
 * Side effects:
 *	Environment variable changes get propagated. If the whole "env" array
 *	is deleted, then we stop managing things for this interpreter (usually
 *	this happens because the whole interpreter is being deleted).
 *
 *----------------------------------------------------------------------
 */

	/* ARGSUSED */
static char *
EnvTraceProc(
    ClientData clientData,	/* Not used. */
    Tcl_Interp *interp,		/* Interpreter whose "env" variable is being
				 * modified. */
    const char *name1,		/* Better be "env". */
    const char *name2,		/* Name of variable being modified, or NULL if
				 * whole array is being deleted (UTF-8). */
    int flags)			/* Indicates what's happening. */
{
    /*
     * For array traces, let TclSetupEnv do all the work.
     */

    if (flags & TCL_TRACE_ARRAY) {
	TclSetupEnv(interp);
	return NULL;
    }

    /*
     * If name2 is NULL, then return and do nothing.
     */

    if (name2 == NULL) {
	return NULL;
    }

    /*
     * If a value is being set, call TclSetEnv to do all of the work.
     */

    if (flags & TCL_TRACE_WRITES) {
	const char *value;

	value = Tcl_GetVar2(interp, "env", name2, TCL_GLOBAL_ONLY);
	TclSetEnv(name2, value);
    }

    /*
     * If a value is being read, call TclGetEnv to do all of the work.
     */

    if (flags & TCL_TRACE_READS) {
	Tcl_DString valueString;
	const char *value = TclGetEnv(name2, &valueString);

	if (value == NULL) {
	    return (char *) "no such variable";
	}
	Tcl_SetVar2(interp, name1, name2, value, 0);
	Tcl_DStringFree(&valueString);
    }

    /*
     * For unset traces, let TclUnsetEnv do all the work.
     */

    if (flags & TCL_TRACE_UNSETS) {
	TclUnsetEnv(name2);
    }
    return NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * ReplaceString --
 *
 *	Replace one string with another in the environment variable cache. The
 *	cache keeps track of all of the environment variables that Tcl has
 *	modified so they can be freed later.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May free the old string.
 *
 *----------------------------------------------------------------------
 */

static void
ReplaceString(
    const char *oldStr,		/* Old environment string. */
    char *newStr)		/* New environment string. */
{
    int i;

    /*
     * Check to see if the old value was allocated by Tcl. If so, it needs to
     * be deallocated to avoid memory leaks. Note that this algorithm is O(n),
     * not O(1). This will result in n-squared behavior if lots of environment
     * changes are being made.
     */

    for (i = 0; i < env.cacheSize; i++) {
	if (env.cache[i]==oldStr || env.cache[i]==NULL) {
	    break;
	}
    }
    if (i < env.cacheSize) {
	/*
	 * Replace or delete the old value.
	 */

	if (env.cache[i]) {
	    ckfree(env.cache[i]);
	}

	if (newStr) {
	    env.cache[i] = newStr;
	} else {
	    for (; i < env.cacheSize-1; i++) {
		env.cache[i] = env.cache[i+1];
	    }
	    env.cache[env.cacheSize-1] = NULL;
	}
    } else {
	/*
	 * We need to grow the cache in order to hold the new string.
	 */

	const int growth = 5;

	env.cache = ckrealloc(env.cache,
		(env.cacheSize + growth) * sizeof(char *));
	env.cache[env.cacheSize] = newStr;
	(void) memset(env.cache+env.cacheSize+1, 0,
		(size_t) (growth-1) * sizeof(char *));
	env.cacheSize += growth;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * TclFinalizeEnvironment --
 *
 *	This function releases any storage allocated by this module that isn't
 *	still in use by the global environment. Any strings that are still in
 *	the environment will be leaked.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	May deallocate storage.
 *
 *----------------------------------------------------------------------
 */

void
TclFinalizeEnvironment(void)
{
    /*
     * For now we just deallocate the cache array and none of the environment
     * strings. This may leak more memory that strictly necessary, since some
     * of the strings may no longer be in the environment. However,
     * determining which ones are ok to delete is n-squared, and is pretty
     * unlikely, so we don't bother.
     */

    if (env.cache) {
	ckfree(env.cache);
	env.cache = NULL;
	env.cacheSize = 0;
#ifndef USE_PUTENV
	env.ourEnvironSize = 0;
#endif
    }
}

/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */