/*
** Copyright (c) 2007 D. Richard Hipp
**
** This program is free software; you can redistribute it and/or
** modify it under the terms of the GNU General Public
** License version 2 as published by the Free Software Foundation.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
** General Public License for more details.
**
** You should have received a copy of the GNU General Public
** License along with this library; if not, write to the
** Free Software Foundation, Inc., 59 Temple Place - Suite 330,
** Boston, MA 02111-1307, USA.
**
** Author contact information:
** drh@hwaci.com
** http://www.hwaci.com/drh/
**
*******************************************************************************
**
** This file contains an implementation of the "subscript" interpreter.
**
** Subscript attempts to be an extremely light-weight scripting
** language. It contains the barest of bare essentials. It is
** stack-based and forth-like. Everything is in a single global
** namespace. There is only a single datatype of zero-terminated
** string. The stack is of fixed, limited depth. The hash table
** is of a limited and fixed size.
**
** This module attempts to be completely self-contained so that it can
** be portable to other projects.
*/
#include "config.h"
#include "subscript.h"
#include <assert.h>
/*
** Configuration constants
*/
#define SBSCONFIG_NHASH 41 /* Size of the hash table */
#define SBSCONFIG_NSTACK 10 /* Maximum stack depth */
#define SBSCONFIG_ERRSIZE 100 /* Maximum size of an error message */
/*
** Available token types:
*/
#define SBSTT_WHITESPACE 1 /* ex: \040 */
#define SBSTT_NAME 2 /* ex: /abcde */
#define SBSTT_VERB 3 /* ex: abcde */
#define SBSTT_STRING 4 /* ex: {...} */
#define SBSTT_INTEGER 5 /* Integer including option sign */
#define SBSTT_INCOMPLETE 6 /* Unterminated string token */
#define SBSTT_UNKNOWN 7 /* Unknown token */
#define SBSTT_EOF 8 /* End of input */
/*
** Given an input string z of length n, identify the token that
** starts at z[0]. Write the token type into *pTokenType and
** return the length of the token.
*/
static int sbs_next_token(const char *z, int n, int *pTokenType){
int c;
if( n<=0 || z[0]==0 ){
*pTokenType = SBSTT_EOF;
return 0;
}
c = z[0];
if( isspace(c) ){
int i;
*pTokenType = SBSTT_WHITESPACE;
for(i=1; i<n && isspace(z[i]); i++){}
return i;
}
if( c=='#' ){
int i;
for(i=1; i<n && z[i] && z[i-1]!='\n'; i++){}
*pTokenType = SBSTT_WHITESPACE;
return i;
}
if( c=='{' ){
int depth = 1;
int i;
for(i=1; i<n && z[i]; i++){
if( z[i]=='{' ){
depth++;
}else if( z[i]=='}' ){
depth--;
if( depth==0 ){
i++;
break;
}
}
}
if( depth ){
*pTokenType = SBSTT_INCOMPLETE;
}else{
*pTokenType = SBSTT_STRING;
}
return i;
}
if( c=='/' && n>=2 && isalpha(z[1]) ){
int i;
for(i=2; i<n && (isalnum(z[i]) || z[i]=='_'); i++){}
*pTokenType = SBSTT_NAME;
return i;
}
if( isalpha(c) ){
int i;
for(i=1; i<n && (isalnum(z[i]) || z[i]=='_'); i++){}
*pTokenType = SBSTT_VERB;
return i;
}
if( isdigit(c) || ((c=='-' || c=='+') && n>=2 && isdigit(z[1])) ){
int i;
for(i=1; i<n && isdigit(z[i]); i++){}
*pTokenType = SBSTT_INTEGER;
return i;
}
*pTokenType = SBSTT_UNKNOWN;
return 1;
}
/*
** Values are stored in the hash table as instances of the following
** structure.
*/
typedef struct SbSValue SbSValue;
struct SbSValue {
int flags; /* Bitmask of SBSVAL_* values */
union {
struct {
int size; /* Number of bytes in string, not counting final zero */
char *z; /* Pointer to string content */
} str; /* Value if SBSVAL_STR */
struct {
int (*xVerb)(Subscript*), void*); /* Function to do the work */
void *pArg; /* 2nd parameter to xVerb */
} verb; /* Value if SBSVAL_VERB */
} u;
};
#define SBSVAL_VERB 0x0001 /* Value stored in u.verb */
#define SBSVAL_STR 0x0002 /* Value stored in u.str */
#define SBSVAL_DYN 0x0004 /* u.str.z is dynamically allocated */
#define SBSVAL_EXEC 0x0008 /* u.str.z is a script */
/*
** Release any memory allocated by a value.
*/
static void sbs_value_reset(SbSValue *p){
if( p->flags & SBSVAL_DYN ){
free(p->u.str.z);
p->flags = SBSVAL_STR;
p->u.str.z = "";
p->u.str.size = 0;
}
}
/*
** An entry in the hash table is an instance of this structure.
*/
typedef struct UsHashEntry UsHashEntry;
struct UsHashEntry {
UsHashEntry *pNext; /* Next entry with the same hash on zKey */
SbSValue val; /* The payload */
int nKey; /* Length of the key */
char zKey[0]; /* The key */
};
/*
** A hash table is an instance of the following structure.
*/
typedef struct UsHashTab UsHashTab;
struct UsHashTab {
UsHashEntry *aHash[SBSCONFIG_NHASH]; /* The hash table */
};
/*
** Compute a hash on a string.
*/
static int sbs_hash(const char *z, int n){
int h = 0;
int i;
for(i=0; i<n; i++){
h ^= (h<<1) | z[i];
}
h &= 0x7ffffff;
return h % SBSCONFIG_NHASH;
}
/*
** Look up a value in the hash table. Return a pointer to the value.
** Return NULL if not found.
*/
static const SbSValue *sbs_fetch(
sbs_hash *pHash,
const char *zKey,
int nKey
){
int h;
UsHashEntry *p;
if( nKey<0 ) nKey = strlen(zKey);
h = sbs_hash(zKey, nKey);
for(p = pHash->aHash[h]; p; p=p->pNext){
if( p->nKey==nKey && memcmp(p->zKey,zKey,nKey)==0 ){
return &p->val;
}
}
return 0;
}
/*
** Store a value in the hash table. Overwrite any prior value stored
** under the same name.
**
** If the value in the 4th argument needs to be reset or freed,
** the hash table will take over responsibiliity for doing so.
*/
static int sbs_store(
sbs_hash *pHash, /* Insert into this hash table */
const char *zKey, /* The key */
int nKey, /* Size of the key */
const SbSValue *pValue /* The value to be stored */
){
int h;
UsHashEntry *p;
if( nKey<0 ) nKey = strlen(zKey);
h = sbs_hash(zKey, nKey);
for(p = pHash->aHash[h]; p; p=p->pNext){
if( p->nKey==nKey && memcmp(p->zKey,zKey,nKey)==0 ){
sbs_value_reset(&p->val);
memcpy(&p->val, pValue, sizeof(p->val));
return SBS_OK;
}
}
pNew = malloc( sizeof(*pNew) + nKey );
if( pNew ){
pNew->nKey = nKey;
memcpy(pNew->zKey, zKey, nKey+1);
memcpy(&pNew->val, pValue, sizeof(pNew->val));
pNew->pNext = pHash->aHash[h];
pHash->aHash[h] = pNew;
return SBS_OK;
}
return SBS_ERROR;
}
/*
** Reset a hash table.
*/
static void sbs_hash_reset(sbs_hash *pHash){
int i;
UsHashEntry *p, *pNext;
for(i=0; i<SBSCONFIG_NHASH; i++){
for(p=pHash->aHash[i]; p; p=pNext){
pNext = p->pNext;
sbs_value_reset(&p->val);
free(p);
}
}
memset(pHash, 0, sizeof(*pHash));
}
/*
** An instance of the Subscript interpreter
*/
struct Subscript {
int nStack; /* Number of entries on stack */
UsHashTab symTab; /* The symbol table */
char zErrMsg[SBSCONFIG_ERRSIZE]; /* Space to write an error message */
SbSValue aStack[SBSCONFIG_NSTACK]; /* The stack */
};
/*
** Push a value onto the stack of an interpreter
*/
static int sbs_push(Subscript *p, SbSValue *pVal){
SbSValue *pStk;
if( p->nStack>=SBSCONFIG_NSTACK ){
sqlite3_snprintf(SBSCONFIG_ERRSIZE, p->zErrMsg, "stack overflow");
return SBS_ERROR;
}
p->aStack[p->nStack++] = *pVal;
return SBS_OK;
}
/*
** Destroy an underscore interpreter
*/
void SbS_Destroy(struct Subscript *p){
int i;
sbs_hash_reset(&p->symTab);
for(i=0; i<p->nStack; i++){
sbs_value_reset(&p->aStack[i]);
}
free(p);
}
/*
** Set the error message for an interpreter. Verb implementations
** use this routine when they encounter an error.
*/
void SbS_SetErrorMessage(struct Subscript *p, const char *zErr){
int nErr = strlen(zErr);
if( nErr>sizeof(p->zErrMsg)-1 ){
nErr = sizeof(p->zErrMsg)-1;
}
memcpy(p->zErrMsg, zErr, nErr);
p->zErrMsg[nErr] = 0;
}
/*
** Return a pointer to the current error message for the
** interpreter.
*/
const char *SbS_GetErrorMessage(struct Subscript *p){
return p->zErrMsg;
}
/*
** Add a new verb the given interpreter
*/
int SbS_AddVerb(
struct Subscript *p,
const char *zVerb,
int (*xVerb)(struct Subscript*,void*),
void *pArg
){
SbSValue v;
v.flags = SBSVAL_VERB;
v.u.verb.xVerb = xVerb;
v.u.verb.pArg = pArg;
return sbs_store(&p->symTab, zVerb, -1, &v);
}
/*
** Push a string value onto the stack.
**
** If the 4th parameter is 0, then the string is static.
** If the 4th parameter is non-zero then the string was obtained
** from malloc and Subscript will take responsibility for freeing
** it.
**
** Return 0 on success and non-zero if there is an error.
*/
int SbS_Push(
struct Subscript *p, /* Push onto this interpreter */
const char *z, /* String value to push */
int n, /* Length of the string, or -1 */
int dyn /* If true, z was obtained from malloc */
){
SbSValue v;
v.flags = SBSVAL_STR;
if( needToFree ){
v.flags |= SBSVAL_DYN;
}
if( n<0 ) n = strlen(z);
v.u.str.size = n;
v.u.str.z = z;
return sbs_push(p, &v);
}
/*
** Push an integer value onto the stack.
**
** This routine really just converts the integer into a string
** then calls SbS_Push.
*/
int SbS_PushInt(struct Subscript *p, int iVal){
if( iVal==0 ){
return SbS_Push(p, "0", 1, 0);
}else if( iVal==1 ){
return SbS_Push(p, "1", 1, 0);
}else{
char *z;
int n;
char zVal[50];
sprintf(zVal, "%d", iVal);
n = strlen(zVal);
z = malloc( n+1 );
if( z ){
strcpy(z, zVal);
return SbS_Push(p, z, n, 1);
}else{
return SBS_ERROR;
}
}
}
/*
** Pop and destroy zero or more values from the stack.
** Return the number of values remaining on the stack after
** the pops occur.
*/
int SbS_Pop(struct Subscript *p, int N){
while( N>0 && p->nStack>0 ){
p->nStack--;
sbs_value_reset(&p->aStack[p->nStack]);
N--;
}
return p->nStack;
}
/*
** Return the N-th element of the stack. 0 is the top of the stack.
** 1 is the first element down. 2 is the second element. And so forth.
** Return NULL if there is no N-th element.
**
** The pointer returned is only valid until the value is popped
** from the stack.
*/
const char *SbS_StackValue(struct Subscript *p, int N, int *pSize){
SbSValue *pVal;
if( N<0 || N>=p->nStack ){
return 0;
}
pVal = &p->aStack[p->nStack-N-1];
if( (pVal->flags & SBSVAL_STR)==0 ){
return 0;
}
*pSize = pVal->u.str.size;
return pVal->u.str.z;
}
/*
** A convenience routine for extracting an integer value from the
** stack.
*/
int SbS_StackValueInt(struct Subscript *p, int N){
int n, v;
int isNeg = 0;
char *z = SbS_StackValue(p, N, &n);
v = 0;
if( n==0 ) return 0;
if( z[0]=='-' ){
isNeg = 1;
z++;
n--;
}else if( z[0]=='+' ){
z++;
n--;
}
while( n>0 && isdigit(z[0]) ){
v = v*10 + z[0] - '0';
z++;
n--;
}
if( isNeg ){
v = -v;
}
return v;
}
/*
** Retrieve the value of a variable from the interpreter. Return
** NULL if no such variable is defined.
**
** The returned string is not necessarily (probably not) zero-terminated.
** The string may be deallocated the next time anything is done to
** the interpreter. Make a copy if you need it to persist.
*/
const char *SbS_Fetch(
struct Subscript *p, /* The interpreter we are interrogating */
const char *zKey, /* Name of the variable. Case sensitive */
int *pLength /* Write the length here */
){
SbSValue *pVal;
pVal = sbs_fetch(&p->symTab, zKey, -1);
if( pVal==0 || (pVal->flags & SBSVAL_STR)==0 ){
*pLength = 0;
return 0;
}else{
*pLength = pVal->u.str.size;
return pVal->u.str.z;
}
}
/*
** Generate an error and return non-zero if the stack has
** fewer than N elements. This is utility routine used in
** the implementation of verbs.
*/
int SbS_RequireStack(struct Subscript *p, int N, const char *zCmd){
if( p->nStack>N ) return 0;
sqlite3_snprintf(sizeof(p->zErrMsg), p->zErrMsg,
"\"%s\" requires at least %d stack elements - only found %d",
zCmd, N, p->nStack);
return 1;
}
/*
** The built-in "set" command:
**
** STRING NAME set
**
** Write the value of STRING into variable called NAME.
*/
static int setCmd(Subscript *p, void *pNotUsed){
SbSValue *pTos;
SbSValue *pNos;
if( SbS_RequireStack(p, 2, "set") ) return SBS_ERROR;
pTos = p->aStack[--p->nStack];
pNos = p->aStack[--p->nStack];
sbs_store(&p->symTab, pTos->u.str.z, pTos->u.str.size, pNos);
sbs_value_reset(pTos);
return 0;
}
/*
** Create a new underscore interpreter
*/
struct Subscript *SbS_Create(void){
Subscript *p;
p = malloc( sizeof(*p) );
if( p ){
memset(p, 0, sizeof(*p));
SbS_AddVerb(p, "set", setCmd, 0);
}
return p;
}
/*
** Evaluate the script given by the first nScript bytes of zScript[].
** Return 0 on success and non-zero for an error.
*/
int SbS_Eval(struct Subscript *p, const char *zScript, int nScript){
int rc = SBS_OK;
if( nScript<0 ) nScript = strlen(zScript);
while( nScript>0 && rc==SBS_OK ){
int n;
int ttype;
n = sbs_token_type(zScript, nScript, &ttype);
switch( ttype ){
case SBSTT_WHITESPACE: {
break;
}
case SBSTT_EOF: {
nScript = 0;
break;
}
case SBSTT_INCOMPLETE:
case SBSTT_UNKNOWN: {
rc = SBS_ERROR;
nScript = n;
break;
}
case SBSTT_INTEGER: {
rc = sbs_push(p, zScript, n);
break;
}
case SBSTT_NAME: {
rc = sbs_push(p, &zScript[1], n-1);
break;
}
case SBSTT_STRING: {
rc = sbs_push(p, &zScript[1], n-2);
break;
}
case SBSTT_VERB: {
SbSValue *pVal = sbs_fetch(p->pHash, zScript, nScript);
if( pVal==0 ){
rc = SBS_ERROR;
}else if( pVal->flags & SBSVAL_VERB ){
rc = pVal->u.verb.xVerb(p, pVal->u.verb.pArg);
}else if( pVal->flags & SBSVAL_EXEC ){
rc = SbS_Eval(p, pVal->u.str.z, pVal->u.str.size);
}else{
rc = sbs_push(p, pVal->u.str.z, pVal->u.str.size);
}
break;
}
}
zScript += n;
nScript -= n;
}
return rc;
}