#include <u.h>#include <libc.h>#include <ctype.h>#include "pdf.h" static inttrailerread(Pdf *pdf){	Object *o;	int prev; 	if((o = pdfobj(pdf, pdf->s)) == nil)		goto err;	if(o->type != Odict){		werrstr("isn't a dictionary");		goto err;	}	if((prev = dictint(o, "Prev")) > 0 && (Sseek(pdf->s, prev, 0) < 0 || xrefreadold(pdf) != 0))		goto err; 	pdf->root = pdfref(dictget(o, "Root"));	pdf->info = pdfref(dictget(o, "Info"));	pdf->top = o; 	return 0;err:	pdfobjfree(o);	return -1;} Pdf *pdfopen(void *bio){	Pdf *pdf;	Object *o;	Stream *stream;	char tmp[64], *s, *x;	int xreftb; /* 7.5.4 xref table offset from the beginning of the file */	int i, n, off; 	fmtinstall('H', encodefmt);	fmtinstall('O', Ofmt);	fmtinstall('T', Tfmt);	fmtinstall(L'⊗', ⊗fmt); 	o = nil;	pdf = nil;	if((stream = Sbio(bio)) == nil || (pdf = calloc(1, sizeof(*pdf))) == nil)		goto err;	pdf->s = stream; 	/* check header */	if(Sread(stream, tmp, 8) != 8 ||	   strncmp(tmp, "%PDF-", 5) != 0 || !isdigit(tmp[5]) || tmp[6] != '.' || !isdigit(tmp[7])){		werrstr("not a pdf");		goto err;	} 	/* 7.5.4, 7.5.8 xref table */ 	/* read a block of data */	n = sizeof(tmp)-1;	Sseek(stream, -n, 2);	if(Sread(stream, tmp, n) != n){badtrailer:		werrstr("invalid trailer");		goto err;	}	tmp[n] = 0; 	/* search for a valid string that the block ends with */	for(i = n-1, s = &tmp[i]; i > 0 && *s != 0; i--, s--);	s++; 	/* find "startxref" */	if((x = strrchr(s, 'f')) == nil || !isws(x[1]) || x-8 < s+1 || memcmp(x-8, "startxref", 9) != 0)		goto badtrailer;	x++;	if((xreftb = strtol(x, nil, 10)) < 1)		goto badtrailer; 	/* read xref */	if(Sseek(stream, xreftb, 0) != xreftb){		werrstr("xref position out of range");		goto err;	}	for(;;){		while(isspace(Sgetc(stream)));		Sungetc(stream);		off = Soffset(stream);		if(Sread(stream, tmp, sizeof(tmp)) < 8){badxref:			werrstr("invalid xref: %r");			goto err;		}		if(memcmp(tmp, "xref", 4) == 0){			if(Sseek(stream, -sizeof(tmp), 1) < 0 || xrefreadold(pdf) != 0)				goto err;			/* there could be more updates, try it */		}else if(memcmp(tmp, "trailer", 7) == 0){ /* 7.5.5 file trailer */			/* move to the trailer dictionary */			n = off + 8;			if(Sseek(stream, n, 0) != n || trailerread(pdf) != 0){				werrstr("invalid trailer: %r");				goto err;			}			/* trailer is supposed to be the last thing */			break;		}else if(isdigit(tmp[0])){ /* could be 7.5.8 xref stream (since PDF 1.5) */			if(Sseek(stream, xreftb, 0) != xreftb)				goto badxref;			if(xrefreadstream(pdf) != 0)				goto err;			break;		}	} 	/* root is required, info is optional */	if(pdf->root == &null){		werrstr("no root: %r");		goto err;	} 	return pdf;err:	werrstr("pdfopen: %r [at %p]", (void*)Soffset(stream));	pdfclose(pdf);	pdfobjfree(o);	return nil;} voidpdfclose(Pdf *pdf){	if(pdf == nil)		return;	if(pdf->s != nil)		Sclose(pdf->s);	free(pdf->xref);	free(pdf);}