path: root/Modules/getpath.c

/***********************************************************
Copyright 1991-1995 by Stichting Mathematisch Centrum, Amsterdam,
The Netherlands.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its
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While CWI is the initial source for this software, a modified version
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******************************************************************/

/* Return the initial module search path. */

#include "Python.h"
#include "osdefs.h"

#include <sys/types.h>
#include <sys/stat.h>
#include <strings.h>

#if HAVE_UNISTD_H
#include <unistd.h>
#endif /* HAVE_UNISTD_H */

/* Search in some common locations for the associated Python libraries.
 *
 * Two directories must be found, the platform independent directory
 * (prefix), containing the common .py and .pyc files, and the platform
 * dependent directory (exec_prefix), containing the shared library
 * modules.  Note that prefix and exec_prefix can be the same directory,
 * but for some installations, they are different.
 *
 * Py_GetPath() carries out separate searches for prefix and exec_prefix.
 * Each search tries a number of different locations until a ``landmark''
 * file or directory is found.  If no prefix or exec_prefix is found, a
 * warning message is issued and the preprocessor defined PREFIX and
 * EXEC_PREFIX are used (even though they will not work); python carries on
 * as best as is possible, but most imports will fail.
 *
 * Before any searches are done, the location of the executable is
 * determined.  If argv[0] has one or more slashs in it, it is used
 * unchanged.  Otherwise, it must have been invoked from the shell's path,
 * so we search $PATH for the named executable and use that.  If the
 * executable was not found on $PATH (or there was no $PATH environment
 * variable), the original argv[0] string is used.
 *
 * Next, the executable location is examined to see if it is a symbolic
 * link.  If so, the link is chased (correctly interpreting a relative
 * pathname if one is found) and the directory of the link target is used.
 *
 * Finally, argv0_path is set to the directory containing the executable
 * (i.e. the last component is stripped).
 *
 * With argv0_path in hand, we perform a number of steps.  The same steps
 * are performed for prefix and for exec_prefix, but with a different
 * landmark.
 *
 * Step 1. Are we running python out of the build directory?  This is
 * checked by looking for a different kind of landmark relative to
 * argv0_path.  For prefix, the landmark's path is derived from the VPATH
 * preprocessor variable (taking into account that its value is almost, but
 * not quite, what we need).  For exec_prefix, the landmark is
 * Modules/Setup.  If the landmark is found, we're done.
 *
 * For the remaining steps, the prefix landmark will always be
 * lib/python$VERSION/string.py and the exec_prefix will always be
 * lib/python$VERSION/sharedmodules, where $VERSION is Python's version
 * number as supplied by the Makefile.  Note that this means that no more
 * build directory checking is performed; if the first step did not find
 * the landmarks, the assumption is that python is running from an
 * installed setup.
 *
 * Step 2. See if the $PYTHONHOME environment variable points to the
 * installed location of the Python libraries.  If $PYTHONHOME is set, then
 * it points to prefix and exec_prefix.  $PYTHONHOME can be a single
 * directory, which is used for both, or the prefix and exec_prefix
 * directories separated by a colon.
 *
 * Step 3. Try to find prefix and exec_prefix relative to argv0_path,
 * backtracking up the path until it is exhausted.  This is the most common
 * step to succeed.  Note that if prefix and exec_prefix are different,
 * exec_prefix is more likely to be found; however if exec_prefix is a
 * subdirectory of prefix, both will be found.
 *
 * Step 4. Search the directories pointed to by the preprocessor variables
 * PREFIX and EXEC_PREFIX.  These are supplied by the Makefile but can be
 * passed in as options to the configure script.
 *
 * That's it!
 *
 * Well, almost.  Once we have determined prefix and exec_prefix, the
 * preprocesor variable PYTHONPATH is used to construct a path.  Each
 * relative path on PYTHONPATH is prefixed with prefix.  Then the directory
 * containing the shared library modules is appended.  The environment
 * variable $PYTHONPATH is inserted in front of it all.  Finally, the
 * prefix and exec_prefix globals are tweaked so they reflect the values
 * expected by other code, by stripping the "lib/python$VERSION/..." stuff
 * off.  If either points to the build directory, the globals are reset to
 * the corresponding preprocessor variables (so sys.prefix will reflect the
 * installation location, even though sys.path points into the build
 * directory).  This seems to make more sense given that currently the only
 * known use of sys.prefix and sys.exec_prefix is for the ILU installation
 * process to find the installed Python tree.
 */

#ifndef VERSION
#define VERSION "1.5"
#endif

#ifndef VPATH
#define VPATH "."
#endif

#ifndef PREFIX
#define PREFIX "/usr/local"
#endif

#ifndef EXEC_PREFIX
#define EXEC_PREFIX PREFIX
#endif

#ifndef PYTHONPATH
/* I know this isn't K&R C, but the Makefile specifies it anyway */
#define PYTHONPATH PREFIX "/lib/python" VERSION ":" \
	           PREFIX "/lib/python" VERSION "/test" ":" \
	      EXEC_PREFIX "/lib/python" VERSION "/sharedmodules"
#endif

#ifndef LANDMARK
#define LANDMARK "string.py"
#endif

static char prefix[MAXPATHLEN+1];
static char exec_prefix[MAXPATHLEN+1];
static char *module_search_path = NULL;
static char lib_python[20]; /* Dynamically set to "lib/python" VERSION */

static void
reduce(dir)
	char *dir;
{
	int i = strlen(dir);
	while (i > 0 && dir[i] != SEP)
		--i;
	dir[i] = '\0';
}
	

static int
exists(filename)
	char *filename;
{
	struct stat buf;
	return stat(filename, &buf) == 0;
}


static void
join(buffer, stuff)
	char *buffer;
	char *stuff;
{
	int n, k;
	if (stuff[0] == SEP)
		n = 0;
	else {
		n = strlen(buffer);
		if (n > 0 && buffer[n-1] != SEP && n < MAXPATHLEN)
			buffer[n++] = SEP;
	}
	k = strlen(stuff);
	if (n + k > MAXPATHLEN)
		k = MAXPATHLEN - n;
	strncpy(buffer+n, stuff, k);
	buffer[n+k] = '\0';
}


static int
search_for_prefix(argv0_path, home)
	char *argv0_path;
	char *home;
{
	int i, n;
	char *vpath;

	/* Check to see if argv[0] is in the build directory */
	strcpy(prefix, argv0_path);
	join(prefix, "Modules/Setup");
	if (exists(prefix)) {
		/* Check VPATH to see if argv0_path is in the build directory.
		 * Complication: the VPATH passed in is relative to the
		 * Modules build directory and points to the Modules source
		 * directory; we need it relative to the build tree and
		 * pointing to the source tree.  Solution: chop off a leading
		 * ".." (but only if it's there -- it could be an absolute
		 * path) and chop off the final component (assuming it's
		 * "Modules").
		 */
		vpath = VPATH;
		if (vpath[0] == '.' && vpath[1] == '.' && vpath[2] == '/')
			vpath += 3;
		strcpy(prefix, argv0_path);
		join(prefix, vpath);
		reduce(prefix);
		join(prefix, "Lib");
		join(prefix, LANDMARK);
		if (exists(prefix))
			return -1;
	}

	if (home) {
		/* Check $PYTHONHOME */
		char *delim;
		strcpy(prefix, home);
		delim = strchr(prefix, DELIM);
		if (delim)
			*delim = '\0';
		join(prefix, lib_python);
		join(prefix, LANDMARK);
		if (exists(prefix))
			return 1;
	}

	/* Search from argv0_path, until root is found */
	strcpy(prefix, argv0_path);
	do {
		n = strlen(prefix);
		join(prefix, lib_python);
		join(prefix, LANDMARK);
		if (exists(prefix))
			return 1;
		prefix[n] = '\0';
		reduce(prefix);
	} while (prefix[0]);

	/* Look at configure's PREFIX */
	strcpy(prefix, PREFIX);
	join(prefix, lib_python);
	join(prefix, LANDMARK);
	if (exists(prefix))
		return 1;

	/* Fail */
	return 0;
}


static int
search_for_exec_prefix(argv0_path, home)
	char *argv0_path;
	char *home;
{
	int i, n;

	/* Check to see if argv[0] is in the build directory */
	strcpy(exec_prefix, argv0_path);
	join(exec_prefix, "Modules/Setup");
	if (exists(exec_prefix)) {
		reduce(exec_prefix);
		return -1;
	}

	if (home) {
		/* Check $PYTHONHOME */
		char *delim;
		delim = strchr(home, DELIM);
		if (delim)
			strcpy(exec_prefix, delim+1);
		else
			strcpy(exec_prefix, home);
		join(exec_prefix, lib_python);
		join(exec_prefix, "sharedmodules");
		if (exists(exec_prefix))
			return 1;
	}

	/* Search from argv0_path, until root is found */
	strcpy(exec_prefix, argv0_path);
	do {
		n = strlen(exec_prefix);
		join(exec_prefix, lib_python);
		join(exec_prefix, "sharedmodules");
		if (exists(exec_prefix))
			return 1;
		exec_prefix[n] = '\0';
		reduce(exec_prefix);
	} while (exec_prefix[0]);

	/* Look at configure's EXEC_PREFIX */
	strcpy(exec_prefix, EXEC_PREFIX);
	join(exec_prefix, lib_python);
	join(exec_prefix, "sharedmodules");
	if (exists(exec_prefix))
		return 1;

	/* Fail */
	return 0;
}


static void
calculate_path()
{
	extern char *Py_GetProgramName();

	char delimiter[2] = {DELIM, '\0'};
	char separator[2] = {SEP, '\0'};
	char *pythonpath = PYTHONPATH;
	char *rtpypath = getenv("PYTHONPATH");
	char *home = getenv("PYTHONHOME");
	char *path = getenv("PATH");
	char *prog = Py_GetProgramName();
	char argv0_path[MAXPATHLEN+1];
	char progpath[MAXPATHLEN+1];
	int pfound, efound; /* 1 if found; -1 if found build directory */
	char *buf;
	int bufsz;
	int prefixsz;
	char *defpath = pythonpath;

	/* Initialize this dynamically for K&R C */
	sprintf(lib_python, "lib/python%s", VERSION);

	/* If there is no slash in the argv0 path, then we have to
	 * assume python is on the user's $PATH, since there's no
	 * other way to find a directory to start the search from.  If
	 * $PATH isn't exported, you lose.
	 */
	if (strchr(prog, SEP))
		strcpy(progpath, prog);
	else if (path) {
		while (1) {
			char *delim = strchr(path, DELIM);

			if (delim) {
				int len = delim - path;
				strncpy(progpath, path, len);
				*(progpath + len) = '\0';
			}
			else
				strcpy(progpath, path);

			join(progpath, prog);
			if (exists(progpath))
				break;

			if (!delim) {
				progpath[0] = '\0';
				break;
			}
			path = delim + 1;
		}
	}
	else
		progpath[0] = '\0';

	strcpy(argv0_path, progpath);
	
#if HAVE_READLINK
	{
		char tmpbuffer[MAXPATHLEN+1];
		int linklen = readlink(progpath, tmpbuffer, MAXPATHLEN);
		if (linklen != -1) {
			/* It's not null terminated! */
			tmpbuffer[linklen] = '\0';
			if (tmpbuffer[0] == SEP)
				strcpy(argv0_path, tmpbuffer);
			else {
				/* Interpret relative to progpath */
				reduce(argv0_path);
				join(argv0_path, tmpbuffer);
			}
		}
	}
#endif /* HAVE_READLINK */

	reduce(argv0_path);

	if (!(pfound = search_for_prefix(argv0_path, home))) {
		fprintf(stderr,
		   "Could not find platform independent libraries <prefix>\n");
		strcpy(prefix, PREFIX);
		join(prefix, lib_python);
	}
	else
		reduce(prefix);
	
	if (!(efound = search_for_exec_prefix(argv0_path, home))) {
		fprintf(stderr,
		"Could not find platform dependent libraries <exec_prefix>\n");
		strcpy(exec_prefix, EXEC_PREFIX);
		join(exec_prefix, "lib/sharedmodules");
	}
	/* If we found EXEC_PREFIX do *not* reduce it!  (Yet.) */

	if (!pfound || !efound)
		fprintf(stderr,
		 "Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]\n");

	/* Calculate size of return buffer.
	 */
	bufsz = 0;

	if (rtpypath)
		bufsz += strlen(rtpypath) + 1;

	prefixsz = strlen(prefix) + 1;

	while (1) {
		char *delim = strchr(defpath, DELIM);

		if (defpath[0] != SEP)
			/* Paths are relative to prefix */
			bufsz += prefixsz;

		if (delim)
			bufsz += delim - defpath + 1;
		else {
			bufsz += strlen(defpath) + 1;
			break;
		}
		defpath = delim + 1;
	}

	bufsz += strlen(exec_prefix) + 1;

	/* This is the only malloc call in this file */
	buf = malloc(bufsz);

	if (buf == NULL) {
		/* We can't exit, so print a warning and limp along */
		fprintf(stderr, "Not enough memory for dynamic PYTHONPATH.\n");
		fprintf(stderr, "Using default static PYTHONPATH.\n");
		module_search_path = PYTHONPATH;
	}
	else {
		/* Run-time value of $PYTHONPATH goes first */
		if (rtpypath) {
			strcpy(buf, rtpypath);
			strcat(buf, delimiter);
		}
		else
			buf[0] = '\0';

		/* Next goes merge of compile-time $PYTHONPATH with
		 * dynamically located prefix.
		 */
		defpath = pythonpath;
		while (1) {
			char *delim = strchr(defpath, DELIM);

			if (defpath[0] != SEP) {
				strcat(buf, prefix);
				strcat(buf, separator);
			}

			if (delim) {
				int len = delim - defpath + 1;
				int end = strlen(buf) + len;
				strncat(buf, defpath, len);
				*(buf + end) = '\0';
			}
			else {
				strcat(buf, defpath);
				break;
			}
			defpath = delim + 1;
		}
		strcat(buf, delimiter);

		/* Finally, on goes the directory for dynamic-load modules */
		strcat(buf, exec_prefix);

		/* And publish the results */
		module_search_path = buf;
	}

	/* Reduce prefix and exec_prefix to their essence,
	 * e.g. /usr/local/lib/python1.5 is reduced to /usr/local.
	 * If we're loading relative to the build directory,
	 * return the compiled-in defaults instead.
	 */
	if (pfound > 0) {
		reduce(prefix);
		reduce(prefix);
	}
	else
		strcpy(prefix, PREFIX);

	if (efound > 0) {
		reduce(exec_prefix);
		reduce(exec_prefix);
		reduce(exec_prefix);
	}
	else
		strcpy(exec_prefix, EXEC_PREFIX);
}


/* External interface */

char *
Py_GetPath()
{
	if (!module_search_path)
		calculate_path();
	return module_search_path;
}

char *
Py_GetPrefix()
{
	if (!module_search_path)
		calculate_path();
	return prefix;
}

char *
Py_GetExecPrefix()
{
	if (!module_search_path)
		calculate_path();
	return exec_prefix;
}