faux/clish/variable/variable_expand.c

/*
 * shell_variable_expand.c
 */
#include "private.h"
#include "lub/string.h"

#include <stdlib.h>
#include <assert.h>
#include <string.h>

#include <sys/types.h>
#include <regex.h>
/*
 * These are the escape characters which are used by default when 
 * expanding variables. These characters will be backslash escaped
 * to prevent them from being interpreted in a script.
 *
 * This is a security feature to prevent users from arbitarily setting
 * parameters to contain special sequences.
 */
static const char *default_escape_chars = "`|$<>&()#";

/*----------------------------------------------------------- */
/*
 * search the current viewid string for a variable
 */
static char *find_viewid_var(const char *viewid, const char *name)
{
	char *result = NULL;
	regex_t regex;
	int status;
	char *pattern = NULL;
	regmatch_t pmatches[2];

	/* build up the pattern to match */
	lub_string_cat(&pattern, name);
	lub_string_cat(&pattern, "[ ]*=([^;]*)");

	/* compile the regular expression to find this variable */
	status = regcomp(&regex, pattern, REG_EXTENDED);
	assert(0 == status);
	lub_string_free(pattern);

	/* now perform the matching */
	/*lint -e64 Type mismatch (arg. no. 4) */
	/* 
	 * lint seems to equate regmatch_t[] as being of type regmatch_t !!!
	 */
	status = regexec(&regex, viewid, 2, pmatches, 0);
	/*lint +e64 */
	if (0 == status) {
		regoff_t len = pmatches[1].rm_eo - pmatches[1].rm_so;
		const char *value = &viewid[pmatches[1].rm_so];
		/* found a match */
		result = lub_string_dupn(value, (unsigned)len);
	}
	/* release the regular expression */
	regfree(&regex);

	return result;
}

/*----------------------------------------------------------- */
/*
 * expand context dependent fixed-name variables
 */
static char *find_context_var(const context_t * this, const char *name)
{
	char *result = NULL;
	regex_t regex;
	int status;
	char *pattern = NULL;
	regmatch_t pmatches[2];

	if (!lub_string_nocasecmp(name, "__cmd")) {
		if (this->cmd)
			result = lub_string_dup(clish_command__get_name(this->cmd));
	} else if (!lub_string_nocasecmp(name, "__line")) {
		if (this->cmd && this->pargv)
			result = clish_variable__get_line(this->cmd, this->pargv);
	} else if (!lub_string_nocasecmp(name, "__params")) {
		if (this->cmd && this->pargv)
			result = clish_variable__get_params(this->cmd, this->pargv);
	}

	return result;
}

/*----------------------------------------------------------- */
/*
 * This needs to escape any dangerous characters within the command line
 * to prevent gaining access to the underlying system shell.
 */
static char *escape_special_chars(const char *string, const char *escape_chars)
{
	char *result = NULL;
	const char *p;

	if (NULL == escape_chars) {
		escape_chars = default_escape_chars;
	}
	for (p = string; p && *p; p++)
	{
		/* find any special characters and prefix them with '\' */
		size_t len = strcspn(p, escape_chars);
		lub_string_catn(&result, p, len);
		p += len;
		if (*p) {
			lub_string_catn(&result, "\\", 1);
			lub_string_catn(&result, p, 1);
		} else {
			break;
		}
	}
	return result;
}

/*--------------------------------------------------------- */
static char *context_retrieve(const context_t * this, const char *name)
{
	char *result = NULL;
	const char *tmp = NULL;
	const char *escape_chars = NULL;
	char *string = NULL;
	assert(name);

	/* try and substitute a parameter value */
	if (this && this->pargv) {
		const clish_parg_t *parg =
		    clish_pargv_find_arg(this->pargv, name);
		if (NULL != parg) {
			/* substitute the command line value */
			tmp = clish_parg__get_value(parg);
		}
	}

	if (NULL == tmp) {
		/* try and substitute a viewId variable */
		if (this && this->viewid) {
			tmp = string = find_viewid_var(this->viewid, name);
		}
	}

	if (NULL == tmp) {
		/* try and substitute context fixed variable */
		tmp = string = find_context_var(this, name);
	}

	/* get the contents of an environment variable */
	if (NULL == tmp) {
		tmp = getenv(name);
	}
	if (this && this->cmd) {
		/* override the escape characters */
		escape_chars = clish_command__get_escape_chars(this->cmd);
	}
	result = escape_special_chars(tmp, escape_chars);
	if (NULL != string) {
		/* free the dynamic memory */
		lub_string_free(string);
	}
	return result;
}

/*--------------------------------------------------------- */
/* 
 * return the next segment of text from the provided string
 * segments are delimited by variables within the string.
 */
static char *context_nextsegment(const context_t * this, const char **string)
{
	const char *p = *string;
	char *result = NULL;
	size_t len = 0;

	if (p) {
		if (*p && (p[0] == '$') && (p[1] == '{')) {
			/* start of a variable */
			const char *tmp;
			p += 2;
			tmp = p;

			/* 
			 * find the end of the variable 
			 */
			while (*p && p++[0] != '}') {
				len++;
			}

			/* ignore non-terminated variables */
			if (p[-1] == '}') {
				bool_t valid = BOOL_FALSE;
				char *text, *q;

				/* get the variable text */
				text = lub_string_dupn(tmp, len);
				/*
				 * tokenise this INTO ':' separated words
				 * and either expand or duplicate into the result string.
				 * Only return a result if at least 
				 * of the words is an expandable variable
				 */
				for (q = strtok(text, ":");
				     q; q = strtok(NULL, ":")) {
					char *var = context_retrieve(this, q);

					/* copy the expansion or the raw word */
					lub_string_cat(&result, var ? var : q);

					/* record any expansions */
					if (NULL != var) {
						valid = BOOL_TRUE;
					}
					lub_string_free(var);
				}

				if (BOOL_FALSE == valid) {
					/* not a valid variable expansion */
					lub_string_free(result);
					result = lub_string_dup("");
				}

				/* finished with the variable text */
				lub_string_free(text);
			}
		} else {
			/* find the start of a variable */
			while (*p) {
				if ((p[0] == '$') && (p[1] == '{')) {
					break;
				}
				len++;
				p++;
			}
			if (len > 0) {
				result = lub_string_dupn(*string, len);
			}
		}
		/* move the string pointer on for next time... */
		*string = p;
	}
	return result;
}

/*--------------------------------------------------------- */
/*
 * This function builds a dynamic string based on that provided
 * subtituting each occurance of a "${FRED}" type variable sub-string
 * with the appropriate value.
 */
char *clish_variable_expand(const char *string,
			    const char *viewid,
			    const clish_command_t * cmd, clish_pargv_t * pargv)
{
	char *seg, *result = NULL;
	context_t context;

	/* setup the context */
	context.viewid = viewid;
	context.cmd = cmd;
	context.pargv = pargv;

	/* read each segment and extend the result */
	while (NULL != (seg = context_nextsegment(&context, &string))) {
		lub_string_cat(&result, seg);
		lub_string_free(seg);
	}

	return result;
}

/*--------------------------------------------------------- */
char *clish_variable__get_params(const clish_command_t * cmd, clish_pargv_t * pargv)
{
	char *line = NULL;
	unsigned i, cnt;
	const clish_param_t *param;
	const clish_parg_t *parg;

	if (!pargv)
		return NULL;

	cnt = clish_pargv__get_count(pargv);
	for (i = 0; i < cnt; i++) {
		param = clish_pargv__get_param(pargv, i);
		if (clish_param__get_hidden(param))
			continue;
		parg = clish_pargv__get_parg(pargv, i);
		if (NULL != line)
			lub_string_cat(&line, " ");
		lub_string_cat(&line, clish_parg__get_value(parg));
	}

	return line;
}

/*--------------------------------------------------------- */
char *clish_variable__get_line(const clish_command_t * cmd, clish_pargv_t * pargv)
{
	char *line = NULL;
	char *params = NULL;

	lub_string_cat(&line, clish_command__get_name(cmd));

	if (!pargv)
		return line;

	params = clish_variable__get_params(cmd, pargv);
	if (params) {
		lub_string_cat(&line, " ");
		lub_string_cat(&line, params);
	}
	lub_string_free(params);

	return line;
}

/*--------------------------------------------------------- */