src/apc/scanner.c

   1 /*!@file
   2   \brief   APC Directory Scanner
   3   \details This hand-written parser/scanner traverses a directory tree and
   4            tokenizes elements of the structure which correspond to APC grammar.
   5            The parser is implemented as a 2D stack which populates a list of
   6            child directories at each depth, handling only the leaf nodes
   7            (regular files) of the directory open at the current depth to
   8            conserve memory and speed up traversal.
   9            The scanner works with the lexer to lexically analyze text, and
  10            assumes the existence of an external 'lex' function
  11   \author  Jordan Lavatai
  12   \date    Aug 2016
  13   ----------------------------------------------------------------------------*/
  14 /* Standard */
  15 #include <stdio.h>  //print
  16 #include <errno.h>  //errno
  17 /* Posix */
  18 #include <err.h>    //warnx
  19 #include <stdlib.h> //exit
  20 #include <unistd.h> //chdir
  21 #include <dirent.h> //opendir
  22 /* Public */
  23 int scanner_init(void);
  24 int scanner(void);
  25 /* Private */
  26 #ifndef DL_STACKSIZE
  27 #define DL_STACKSIZE     64
  28 #endif
  29 #ifndef DL_CD_STACKSIZE
  30 #define DL_CD_STACKSIZE  DL_STACKSIZE //square tree
  31 #endif
  32 extern //lexer.c
  33 int  lexer_lex(const char*);
  34 extern //lexer.c
  35 void lexer_pushtok(int, int);
  36 static
  37 int  dredge_current_depth(void);
  38 extern //lexer.c
  39 struct dirent* lexer_direntpa[];
  40 extern //main.c
  41 const char* cargs['Z'];
  42
  43 struct dirlist
  44 { DIR*           dirp;
  45   struct dirent* child_directory_stack[DL_CD_STACKSIZE],** cds;
  46 } directory_list_stack[DL_STACKSIZE + 1],* dls; //+1 for the root dir
  47
  48 /* Directory Listing Stack
  49    FILO Stack for keeping an open DIR* at each directory depth for treewalk.
  50    This stack is depth-safe, checking its depth during push operations, but not
  51    during pop operations, to ensure the thread doesn't open too many files at
  52    once (512 in c runtime), or traverse too far through symbolic links.
  53    A directory listing includes a DIR* and all DIR-typed entity in the directory
  54    as recognized by dirent, populated externally (and optionally).
  55    This stack behaves abnormally by incrementing its PUSH operation prior to
  56    evaluation, and the POP operations after evaluation.  This behavior allows
  57    the 'DL_CURDEPTH' operation to map to the current element in the 'dl_stack'
  58    array, and it is always treated as the "current depth". This also allows us
  59    to init the root directory to 'directory_list_stack'[0] and pop it in a safe
  60    and explicit manner.
  61 */
  62 #define DL_STACK        (directory_list_stack)
  63 #define DL_STACKP       (dls)
  64 #define DL_CD_STACK     ((*DL_STACKP).child_directory_stack)
  65 #define DL_CD_STACKP    ((*DL_STACKP).cds)
  66 #define DL_CURDIR()     ((*DL_STACKP).dirp)
  67 #define DL_LEN()        (DL_STACKP - DL_STACK)
  68 #define DL_CD_LEN()     (DL_CD_STACKP - DL_CD_STACK)
  69 #define DL_INIT()       (DL_STACKP = DL_STACK)
  70 #define DL_CD_INIT()    (DL_CD_STACKP = DL_CD_STACK)
  71 #define DL_POP()        ((*DL_STACKP--).dirp)
  72 #define DL_CD_POP()     (*--DL_CD_STACKP)
  73 #define DL_PUSH(D)      ((*++DL_STACKP).dirp = D)
  74 #define DL_CD_PUSH(E)   (*DL_CD_STACKP++ = E)
  75
  76
  77 /* Initializer
  78    Initializer expects a function pointer to its lexical analysis function.
  79    Sets up stack pointers and returns boolean true if 'opendir' encounters an
  80    error, or if dredge_current_depth returns boolean true.
  81 */
  82 int scanner_init
  83 #define CWDSTR  "./"
  84 #define ROOTDIR (cargs['r'] ? cargs['r'] : CWDSTR)
  85 ()
  86 { DL_INIT();
  87   DL_STACK[0].dirp = opendir(ROOTDIR);
  88   return DL_STACK[0].dirp == NULL || dredge_current_depth() == 0;
  89 }
  90
  91 /* Scanner
  92    The main driver of the scanner will advance the current treewalk state and
  93    tokenize tree-based push/pop operations.  It will call 'lexer_lex' to
  94    tokenize directory names prior to making a push operation. safe checking for
  95    all returns from the filesystem handler will exit on serious system errors.
  96
  97    after pushing a new directory to the directory list, the scanner will dredge
  98    the directory and alphabetically sort all file entries into the lexer's file
  99    array, while placing all subdirectory entries in the current depth's child
 100    directory stack to the scanned later.
 101
 102    Returns the number of elements added to the lexer's file array.
 103 */
 104 int scanner
 105 #define S(S)#S //stringifier
 106 #define ERR_CHILD  "Fatal: Maximum of " S(DL_CD_STACKSIZE)      \
 107   " child directories exceeded for directory at depth %i\n"     \
 108   ,DL_LEN()
 109 #define ERR_DEPTH  "Fatal: Maximum directory depth of " S(DL_STACKSIZE) \
 110   " exceeded during directory scan\n"
 111 #define ERR_DL     "Fatal: Directory List Stack Corruption %x\n", DL_LEN()
 112 #define TOK_CLOPEN  0x55, 0 //TODO
 113 #define TOK_CLCLOSE 0x56, 0 //TODO
 114 ()
 115 { struct dirent* direntp;
 116  parse:
 117   if (DL_CD_LEN() >= DL_CD_STACKSIZE)//fail if maxchildren exceeded
 118     { fprintf(stderr, ERR_CHILD);
 119       goto fail;
 120     }
 121   if (DL_CD_LEN() > 0)             //There are entities to process at this depth
 122     { if (direntp = DL_CD_POP())      //If the dirent is null, the library
 123         goto libfail;                 //function in dirent has failed
 124       lexer_lex(direntp->d_name);     //lex the directory name
 125       if (DL_LEN() >= DL_STACKSIZE)   //fail if maxdepth exceeded
 126         { fprintf(stderr, ERR_DEPTH);
 127           goto fail;
 128         }
 129       if (chdir(direntp->d_name))     //move into the new directory
 130         goto libfail;
 131       if (DL_PUSH(opendir(CWDSTR)))   //open the cwd
 132         goto libfail;
 133       lexer_pushtok(TOK_CLOPEN);      //Push "Open Directory" token
 134       return dredge_current_depth();  //Filter and sort the current depth
 135     }
 136   else if (DL_LEN() >= 0)       //Any dirs left? (Including root)
 137     { if (closedir(DL_POP()))         //close the directory we just left
 138         goto libfail;
 139       lexer_pushtok(TOK_CLCLOSE);     //Push "Close Directory" token
 140       if (DL_LEN() == -1)             //If we just popped root, we're done
 141         return 0;
 142       if (!chdir(".."))               //Move up a directory and start over
 143         goto parse;
 144     }
 145   fprintf(stderr, ERR_DL);
 146  libfail:
 147   perror("parsedir");
 148  fail:
 149   exit(EXIT_FAILURE);
 150 }
 151
 152 /* Directory Entity Sort and Filter (Dredge)
 153    This filter removes all unhandled file types, and places any 'DT_DIR' type
 154    files in the current Directory List's directory stack.  Upon finishing,
 155    the 'CE_STACK' is sorted alphabetically, and the current 'DL_CD_STACK' is
 156    populated.  Prints warnings for unhandled files.
 157
 158    Returns -1 if 'readdir' encounters an error, otherwise returns the number of
 159    directory entries sent to the external 'lexer_direntpa' array.
 160 */
 161 typedef
 162 int (*qcomp)(const void*, const void*);
 163 static inline
 164 int dredge_current_depth
 165 #define READDIR_ERROR (-1)
 166 #define READDIR_DONE  (0)
 167 #define DPS_LEN()     (direntpp - lexer_direntpa)
 168 #define DPS_PUSH(E)   (*direntpp++ = E)
 169 ()
 170 { struct dirent**  direntpp = lexer_direntpa;
 171   DIR*             cwd      = DL_CURDIR();
 172   struct dirent*   direntp;
 173   DL_CD_INIT();
 174  scan_next:
 175   if ((direntp = readdir(cwd)) != NULL)
 176     { switch (direntp->d_type)
 177         { case DT_REG:
 178             DPS_PUSH(direntp);
 179             goto scan_next;
 180           case DT_DIR:
 181             DL_CD_PUSH(direntp);
 182             goto scan_next;
 183           case DT_UNKNOWN:
 184             warnx("unknown file %s: ignoring", direntp->d_name);
 185           default:
 186             goto scan_next;
 187         }
 188     }
 189   if (errno)
 190     return -1;
 191   qsort(lexer_direntpa, DPS_LEN(), sizeof direntp, (qcomp)alphasort);
 192   return DPS_LEN();
 193 }
 194