ref: 60fd4c1038c15de25849494c7fd3df6e12b5bb67
dir: /pdfext.c/
/* Parse and extract PDF objects */
#include <u.h>
#include <libc.h>
#include <ctype.h>
#include <stdio.h>
#include "post.h"
/* the number white space characters */
int pdf_ws(char *pdf, int len, int pos)
{
int i = pos;
while (i < len && isspace((unsigned char) pdf[i]))
i++;
return i - pos;
}
/* s: string, d: dictionary, l: list, n: number, /: name, r: reference */
int pdf_type(char *pdf, int len, int pos)
{
pos += pdf_ws(pdf, len, pos);
if (pdf[pos] == '/')
return '/';
if (pdf[pos] == '(')
return 's';
if (pdf[pos] == '<' && pdf[pos + 1] != '<')
return 's';
if (pdf[pos] == '<' && pdf[pos + 1] == '<')
return 'd';
if (pdf[pos] == '[')
return 'l';
if (strchr("0123456789+-.", (unsigned char) pdf[pos])) {
if (!isdigit((unsigned char) pdf[pos]))
return 'n';
while (pos < len && isdigit((unsigned char) pdf[pos]))
pos++;
pos += pdf_ws(pdf, len, pos);
if (!isdigit((unsigned char) pdf[pos]))
return 'n';
while (pos < len && isdigit((unsigned char) pdf[pos]))
pos++;
pos += pdf_ws(pdf, len, pos);
return pos < len && pdf[pos] == 'R' ? 'r' : 'n';
}
return -1;
}
/* the length of a pdf object */
int pdf_len(char *pdf, int len, int pos)
{
int c;
int old = pos;
if (pos >= len)
return 0;
pos += pdf_ws(pdf, len, pos);
c = (unsigned char) pdf[pos];
if (strchr("0123456789+-.", c)) {
if (pdf_type(pdf, len, pos) == 'r') {
char *r = memchr(pdf + pos, 'R', len - pos);
return r - (pdf + old) + 1;
}
pos++;
while (pos < len && strchr("0123456789.", (unsigned char) pdf[pos]))
pos++;
}
if (c == '(') {
int depth = 1;
pos++;
while (pos < len && depth > 0) {
if (pdf[pos] == '(')
depth++;
if (pdf[pos] == ')')
depth--;
if (pdf[pos] == '\\')
pos++;
pos++;
}
}
if (c == '<' && pos + 1 < len && pdf[pos + 1] == '<') {
pos += 2;
while (pos + 2 < len && (pdf[pos] != '>' || pdf[pos + 1] != '>')) {
pos += pdf_len(pdf, len, pos);
pos += pdf_len(pdf, len, pos);
pos += pdf_ws(pdf, len, pos);
}
if (pos + 2 < len)
pos += 2;
} else if (c == '<') {
while (pos < len && pdf[pos] != '>')
pos++;
if (pos < len)
pos++;
}
if (c == '/') {
pos++;
while (pos < len && !strchr(" \t\r\n\f()<>[]{}/%",
(unsigned char) pdf[pos]))
pos++;
}
if (c == '[') {
pos++;
while (pos < len && pdf[pos] != ']') {
pos += pdf_len(pdf, len, pos);
pos += pdf_ws(pdf, len, pos);
}
pos++;
}
return pos - old;
}
static int startswith(char *s, char *t)
{
while (*s && *t)
if (*s++ != *t++)
return 0;
return 1;
}
/* read an indirect reference */
int pdf_obj(char *pdf, int len, int pos, int *obj, int *rev)
{
if (pdf_type(pdf, len, pos) != 'r')
return -1;
*obj = atoi(pdf + pos);
pos += pdf_len(pdf, len, pos);
*rev = atoi(pdf + pos);
return 0;
}
/* the value of a pdf dictionary key */
int pdf_dval(char *pdf, int len, int pos, char *key)
{
pos += 2;
while (pos + 2 < len && (pdf[pos] != '>' || pdf[pos + 1] != '>')) {
pos += pdf_ws(pdf, len, pos);
if (pdf_len(pdf, len, pos) == strlen(key) && startswith(key, pdf + pos)) {
pos += pdf_len(pdf, len, pos);
pos += pdf_ws(pdf, len, pos);
return pos;
}
pos += pdf_len(pdf, len, pos);
pos += pdf_len(pdf, len, pos);
pos += pdf_ws(pdf, len, pos);
}
return -1;
}
/* return a dictionary key */
int pdf_dkey(char *pdf, int len, int pos, int key)
{
int i = 0;
pos += 2;
while (pos + 2 < len && (pdf[pos] != '>' || pdf[pos + 1] != '>')) {
pos += pdf_ws(pdf, len, pos);
if (i++ == key)
return pos;
pos += pdf_len(pdf, len, pos);
pos += pdf_len(pdf, len, pos);
pos += pdf_ws(pdf, len, pos);
}
return -1;
}
/* return a list entry */
int pdf_lval(char *pdf, int len, int pos, int idx)
{
int i = 0;
pos++;
while (pos < len && pdf[pos] != ']') {
if (i++ == idx)
return pos;
pos += pdf_len(pdf, len, pos);
pos += pdf_ws(pdf, len, pos);
}
return -1;
}
static void *my_memrchr(void *m, int c, long n)
{
int i;
for (i = 0; i < n; i++)
if (*(unsigned char *) ((uchar*)m + n - 1 - i) == c)
return (uchar*)m + n - 1 - i;
return NULL;
}
static int prevline(char *pdf, int len, int off)
{
char *nl = my_memrchr(pdf, '\n', off);
if (nl && nl > pdf) {
char *nl2 = my_memrchr(pdf, '\n', nl - pdf - 1);
if (nl2)
return nl2 - pdf + 1;
}
return -1;
}
static int nextline(char *pdf, int len, int off)
{
char *nl = memchr(pdf + off, '\n', len - off);
if (nl)
return nl - pdf + 1;
return -1;
}
/* the position of the trailer */
int pdf_trailer(char *pdf, int len)
{
int pos = prevline(pdf, len, len); /* %%EOF */
while (!startswith(pdf + pos, "trailer"))
if ((pos = prevline(pdf, len, pos)) < 0)
return -1;
return nextline(pdf, len, pos); /* skip trailer\n */
}
/* the position of the last xref table */
static int pdf_xref(char *pdf, int len)
{
int pos = prevline(pdf, len, len); /* %%EOF */
if ((pos = prevline(pdf, len, pos)) < 0)
return -1;
/* read startxref offset */
if (sscanf(pdf + pos, "%d", &pos) != 1 || pos >= len || pos < 0)
return -1;
return nextline(pdf, len, pos); /* skip xref\n */
}
/* find a pdf object */
int pdf_find(char *pdf, int len, int obj, int rev)
{
int obj_beg, obj_cnt;
int cur_rev, cur_pos;
char *beg;
int i;
int pos = pdf_xref(pdf, len);
if (pos < 0)
return -1;
/* the numbers after xref */
while (pos < len && sscanf(pdf + pos, "%d %d", &obj_beg, &obj_cnt) == 2) {
for (i = 0; i < obj_cnt; i++) {
if ((pos = nextline(pdf, len, pos)) < 0)
return -1;
if (sscanf(pdf + pos, "%d %d", &cur_pos, &cur_rev) != 2)
return -1;
if (obj_beg + i == obj && cur_rev == rev) {
if (cur_pos < 0 || cur_pos >= len)
return -1;
if (!(beg = strstr(pdf + cur_pos, "obj")))
return -1;
pos = beg - pdf + 3;
pos += pdf_ws(pdf, len, pos);
return pos;
}
}
}
return -1;
}
/* read and dereference an indirect reference */
int pdf_ref(char *pdf, int len, int pos)
{
int obj, rev;
if (pdf_obj(pdf, len, pos, &obj, &rev))
return -1;
return pdf_find(pdf, len, obj, rev);
}
/* retrieve and dereference a dictionary entry */
int pdf_dval_val(char *pdf, int len, int pos, char *key)
{
int val = pdf_dval(pdf, len, pos, key);
int val_obj, val_rev;
if (val < 0)
return -1;
if (pdf_type(pdf, len, val) == 'r') {
pdf_obj(pdf, len, val, &val_obj, &val_rev);
return pdf_find(pdf, len, val_obj, val_rev);
}
return val;
}
/* retrieve a dictionary entry, which is an indirect reference */
int pdf_dval_obj(char *pdf, int len, int pos, char *key)
{
int val = pdf_dval(pdf, len, pos, key);
if (val < 0)
return -1;
return pdf_ref(pdf, len, val);
}