grbseek.c

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/* File:  grbseek.c 		based on Decoder's trqgetmsg() func;
   Revised by:
   28oct96 Alice T. Nakajima (ATN), SAIC, Monterey
   18jun97 ATN check Edition before reading in entire msg;
   27aug97 ATN *SEEK_SET to 0 (gcc complains)
   20Oct97 ATN print #bytes read when fread fails;
   03nov97 ATN -Realloc
   22oct98 ATN *error msg;
*/
#include <stdio.h>
#include <math.h>
#include "dprints.h"		/* for dprints */
#include "gribfuncs.h"		/* prototypes */

/*
**********************************************************************
* A.  FUNCTION: grbseek
*       search the input file starting at the given offset for a GRIB 
*       message.  If found, return it in GRIB_HDR structure.
*
*    INTERFACE:
*       int grbseek (InFile, offset, Read_Index,  gh, errmsg)
*
*    ARGUMENTS (I=input, O=output, I&O=input and output):
*      (I)  char *InFile;
*           name of input file to search for message;
*     (I&O) long  *offset;
*           number of bytes to skip from the beginning of file;
*           gets updated upon leaving to absolute #bytes from beginning of
*           file to beginning of message found;
*      (I)  int  Read_Index; 
*           if set, only proceed if 'GRIB' starts exactly at the given 
*           byte offset;
*      (O)  GRIB_HDR *gh;
*           empty upon entry;  to hold the Message found and its info;
*      (O)  char *errmsg;
*           empty array, only filled if error occurred;
*
*    RETURN CODE:  
*      0> no errors, may or may not have a valid message;
*	  If no Msg was Found: 
*          a)  errmsg will hold the Warning msg;
*	   If a valid Msg was Found: 
*	   a) long *offset: if succesful, gets updated to absolute 
*             beginning of Mesg;
*          b) struct GRIB_HDR holds its info:
*            entire_msg:  is assigned to newly MAlloced 
*                    unsigned char * array to hold entire message;
*	     msg_length:  size of entire_msg array in bytes;
*	     ids_len, pds_len, gds_len, bms_len, bds_len, eds_len:
*                    size of each defined sections in bytes;
*            ids_ptr:  pts to message's Ident Data Sect;
*            pds_ptr:  pts to message's Prod Defn Sect;
*            gds_ptr:  pts to message's Grid Defn Sect;
*            bms_ptr:  pts to message's Bitmap Defn Sect;
*            bds_ptr:  pts to message's Binary Data Sect;
*            eds_ptr:  pts to message's End Data Sect;
*         c) errmsg remains empty;
*      1> fseek/fread error, all ptrs in grib_hdr set to null; errmsg filled;
*      2> got end of file, all ptrs in grib_hdr set to null; errmsg filled;
*      3> Null entire_msg pointer; errmsg filled;
*      4> unable to open input file; errmsg filled;
*
**********************************************************************
*/
#if PROTOTYPE_NEEDED
int 	grbseek (	char *InFile,FILE **fp, long *offset, int Read_Index, 
			GRIB_HDR *gh, char *errmsg)
#else
int	grbseek (InFile,fp, offset, Read_Index,gh,errmsg)
			char *InFile; 
			FILE **fp;
			long *offset; 
			int Read_Index; 
			GRIB_HDR *gh;
			char *errmsg;
#endif

{
   char *func="grbseek";
   char  *GG, sm_blk[5004], *fwa_msg=NULL;
   unsigned long lMessageSize;
   unsigned long Edition;
   long pos;            /* current byte offs fr. beg. of file */
   int bytenum;         /* Index w/in sm_blk */
   int bytestoread=5004; /* #bytes to read into sm_blk at a time */
   int check_limit;     /* #bytes in sm_blk to check */ 
   int gotone = 0;	/* set if found good msg */
   int nread;           /* #bytes got back from Read */
   int status;
   unsigned long iskip;           /* for getbyte */
   int gdsbmsflag, bit_set, sect_len; /* working vars */
   char *ptr, *end_ptr;

   DPRINT3 ("Entering %s\nfile=%s, offs=%ld \n", func, InFile, *offset);
/*
* A.1       INIT variables
*           !gh structure is cleared out
*/
   if (gh->entire_msg==NULL) {
	DPRINT1 ( "%s:  expecting non-null Grib Hdr;\n",func);
	sprintf(errmsg, "%s:  expecting non-NULL Grib Hdr;\n",func);
	status= 3;  
	goto DONE;
	}

   gh->msg_length = 0;
   gh->ids_ptr=gh->pds_ptr= 0;
   gh->gds_ptr=gh->bms_ptr=gh->bds_ptr=gh->eds_ptr=0;
   memset ((void *)gh->entire_msg, '\0', gh->abs_size);
   DPRINT2 ("gh= %ld, gh->entire_msg=%ld\n", gh, gh->entire_msg);
/*
*
* A.2       OPEN Input file 
*           IF (fails) RETURN w/ error stat 4 !errmsg filled
*/
/*   if ((fp = fopen (InFile, "rb")) == NULL) {
      DPRINT2 ("%s: Cannot open input file %s\n", func,InFile );
      sprintf (errmsg,"%s: Cannot open input file '%s'\n", func,InFile );
      status = 4;
      goto DONE;
      }
*/
  if(*fp==NULL){
	 if ((*fp = fopen (InFile, "rb")) == NULL) {
      DPRINT2 ("%s: Cannot open input file %s\n", func,InFile );
      sprintf (errmsg,"%s: Cannot open input file '%s'\n", func,InFile );
      status = 4;
      goto DONE;
      }
	}

/*
*
* A.3       FOR (loop while no error)     !read a block at a time
*/
   
   for (status=0, pos= *offset, gotone= 0; status == 0; pos += check_limit)
   {
/*
* A.3.1        IF (cannot SET file position to correct place)
*              THEN
*                 SET Status to 1 !fseek err
*                 CONTINUE (Loop around to A.3)
*              ENDIF
*/
     if (fseek(*fp, pos, 0)!=0) { 
	DPRINT2 ("%s: Got fseek error to pos= %ld\n",func, pos);
	sprintf(errmsg,"%s %s: Got fseek error to pos= %ld\n",func,InFile,pos);
	status = 1; 
	goto DONE; 
	}

/*
* A.3.2        IF (read less than 40 bytes)
*              THEN
*                 FILL error buffer
*                 RETURN status 2  !eof or <40 bytes left, errmsg filled
*              ENDIF
*/
     nread= fread (sm_blk,sizeof(char), bytestoread,*fp);
     if (nread <= 40) 
	{ 
	  if (nread<=4) {
		DPRINT0 ("No bytes left to check for msg;\n"); 
		/* Errmsg left blank cuz its just EOF */
		}
	  else {
	    sprintf(errmsg,"%s %s: skip last %d bytes, too few for a Msg\n",
	    func, InFile, nread);
	    DPRINT1 ("Only read %d bytes, too few to check for msg;\n",nread); 
	    }
	  status= 2; 
	  goto DONE; 
	}
     else check_limit= nread - 4; 

/*
*              ! search block for the next the 'G'
*              ! load entire Msg if everything is ok;
*              ! if No 'G' found, then quit right away if no 'G'
*              ! if GRIB is not at absolute Offset address, quit too;
*              ! 
* A.3.3        WHILE (there is another 'G' in this block) DO
*/
     bytenum= 0;
     while ((GG= (char *) memchr (sm_blk, 'G', check_limit)))
	{
/*--- Saw 'G' ---*/
/*
* A.3.3.1          IF ('RIB' is not after 'G') THEN
*                     IF (Offset from Index file) THEN  
*                        ABORT search;   !Break out of loop
*                     ELSE
*                        CLEAR out the 'G' in temp block
*                        CONTINUE  !Loop around to A.3.3
*                     ENDIF
*                  ENDIF
*/
	   if (strncmp(GG, "GRIB",4))    /* not 'RIB' after the 'G' */
		if ( Read_Index) 
		   break;     /* Offset IS from Indexfile:  Quit here */
		else  
		{	      /* offset is NOT fr. IndexFile:  keep looping; */
		   *GG='-';   /* no RIB after G, clear it 		*/
		   continue;  /* let Memchr find next G in block      	*/
		}

/*--- Saw 'G R I B' ----*/
/*
* A.3.3.2           CALCULATE byte position within this block
*                   where this message begins
*/
	   bytenum = GG - sm_blk;  /* byte pos w/in this block */

/*
* A.3.3.3           IF (offset is from Indexfile  AND
*                       string GRIB found is not at Absolute IndexFile's offset)
*                   THEN abort search; ENDIF
*/
	  DPRINT1 ("Found string 'GRIB' at %ld\n", pos+bytenum);
	  if (Read_Index &&  *offset != (bytenum + pos))  {
	      sprintf(errmsg,
	      "%s %s:   No Grib msg found at offset= %ld;  check Index File\n",
	      func, InFile, *offset);
	      break;		/* Abort here, Ret w/ no errros & no msg too */
	    }

/*--- Read Mesg Length, Edition ---*/
/*
* A.3.3.4          FUNCTION gbyte !extract lMessageSize
*/
	  iskip=32;
          gbyte (sm_blk+bytenum ,&lMessageSize, &iskip,24);
          DPRINT0 ("lMessageSize\n");

/*--- Make sure it's Edition 1 first ---*/
/*
* A.3.3.5          FUNCTION gbyte !extract Grib Edition Number
*                  IF (not edition 1) THEN
*                      CLEAR out the 'G' in temp block
*                      CONTINUE  !Loop around to A.3.3
*                  ENDIF
*/
	  gbyte (sm_blk+bytenum, &Edition, &iskip, 8);
	  DPRINT0 ("Edition\n");
	  if (Edition != 1) {
	      DPRINT1 ("Edition (%d) is not 1, start over\n",
	      Edition);
              *GG='-';   /* blank out G of current GRIB location found */
              continue;  /* let Memchr find next G in block        */
	   }


/*
* A.3.3.6          IF (cannot MOVE ptr to start of the message) THEN
*                     RETURN status 1   !errmsg filled
*                  ENDIF
*/
          if (fseek(*fp, (long)(pos+bytenum), 0)!=0) {
		DPRINT3 (
		"%s: FSEEK %s error to pos+bytenum= %ld\n",
		func, InFile, pos+bytenum);
		sprintf(errmsg,
		"%s %s: FSEEK error to pos+bytenum= %ld\n",
		func, InFile, pos+bytenum);
		status= 1;
		goto DONE;
		}

/*
* A.3.3.7          INIT all section length to zero
*/
	  gh->ids_len= gh->pds_len= gh->gds_len= 0;
	  gh->bds_len= gh->bms_len= gh->eds_len= 0;

/*
* A.3.3.8          EXPAND Entire_Msg array if it's smaller than msglen
*                  RETURN Malloc Err (stat=2) if fails  !errmsg filled
*/
	   if (lMessageSize > gh->abs_size  ) {
	      
/* 	      if (realloc((void *)gh->entire_msg, lMessageSize) == NULL) {..}
*	      gh->abs_size = lMessageSize;
*/
	      if (Expand_gribhdr (gh, lMessageSize, errmsg)) {
	          upd_child_errmsg (func, errmsg);
		  status = 1;   /* to get out of Outer loop */
		  goto DONE;
	       }

	      DPRINT1 ("Expanded entire_msg to be %ld bytes long\n",
	      gh->abs_size);
      	    } /* size changed */