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   36: .\" Author: Archie Cobbs <archie@freebsd.org>
   37: .\"
   38: .\" $Id: tmpl.3,v 1.1.1.1 2012/02/21 23:25:53 misho Exp $
   39: .\"
   40: .Dd April 22, 2002
   41: .Dt TMPL 3
   42: .Os
   43: .Sh NAME
   44: .Nm tmpl
   45: .Nd templates
   46: .Sh LIBRARY
   47: PDEL Library (libpdel, \-lpdel)
   48: .Sh SYNOPSIS
   49: .Ft "struct tmpl *"
   50: .Fn tmpl_create "FILE *input" "int *num_errors" "const char *mtype"
   51: .Ft "struct tmpl *"
   52: .Fn tmpl_create_mmap "const char *path" "int *num_errors" "const char *mtype"
   53: .Ft void
   54: .Fn tmpl_destroy "struct tmpl **tmplp"
   55: .Ft "struct tmpl_ctx *"
   56: .Fn tmpl_ctx_create "void *arg" "const char *mtype" "tmpl_handler_t *handler" "tmpl_errfmtr_t *errfmtr"
   57: .Ft "void *"
   58: .Fn tmpl_ctx_get_arg "struct tmpl_ctx *ctx"
   59: .Ft "const char *"
   60: .Fn tmpl_ctx_get_mtype "struct tmpl_ctx *ctx"
   61: .Ft "const char *"
   62: .Fn tmpl_ctx_get_var "struct tmpl_ctx *ctx" "const char *name"
   63: .Ft "int"
   64: .Fn tmpl_ctx_set_var "struct tmpl_ctx *ctx" "const char *name" "const char *value"
   65: .Ft "char *"
   66: .Fn tmpl_list_handler "struct tmpl_ctx *ctx" "const struct tmpl_func *userfuncs" "u_int uflen" "char **errmsgp" "int argc" "char **argv"
   67: .Ft void
   68: .Fn tmpl_ctx_destroy "struct tmpl_ctx **ctxp"
   69: .Ft int
   70: .Fn tmpl_execute "struct tmpl *tmpl" "struct tmpl_ctx *ctx" "FILE *output" "int flags"
   71: .Ft int
   72: .Fn tmpl_execute_func "struct tmpl_ctx *ctx" "FILE *output" "char **errmsgp" "int argc" "char **argv" "int flags"
   73: .Ft void
   74: .Fn tmpl_ctx_reset "struct tmpl_ctx *ctx"
   75: .Sh DESCRIPTION
   76: .\"
   77: .Ss Overview
   78: .\"
   79: The
   80: .Nm tmpl
   81: library supports programmatic generation of output
   82: based on input from
   83: .Nm tmpl
   84: template files.
   85: Output is generated by parsing and then executing a tmpl file.
   86: .Pp
   87: The tmpl file simply contains the desired output, with invocations
   88: of various tmpl functions, denoted by the
   89: .Dq @
   90: character, interspersed.
   91: Tmpl functions take zero or more arguments, where each argument can
   92: be either a doubly-quoted string or another, nested tmpl function.
   93: .Pp
   94: When executed, the output of a tmpl file is simply the contents of the
   95: file, with each tmpl function replaced by the value returned by that function.
   96: Several functions, including control flow constructs, are built-in,
   97: and compile-time and run-time user defined functions are supported.
   98: .Pp
   99: Here is a simple example tmpl input file:
  100: .Pp
  101: .Bd -literal -compact -offset 3n
  102: I'm going to count to three:
  103: 
  104: @set("i", "1")
  105: @while(@le(@get("i"), "3"))
  106:       @get("i")
  107:       @set("i", @add(@get("i"), "1"))
  108: @endwhile
  109: 
  110: Done.
  111: .Ed
  112: .Pp
  113: If this template were executed, the output would be: 
  114: .Bd -literal -offset 3n
  115: I'm going to count to three:
  116: 
  117: 
  118: 
  119:       1
  120: 
  121:       2
  122: 
  123:       3
  124: 
  125: 
  126: 
  127: Done.
  128: .Ed
  129: .Pp
  130: While the example above uses only built-in functions, user-defined functions
  131: written in C may be invoked in the same way.
  132: .\"
  133: .Sh Parsing
  134: .\"
  135: This section describes the precise rules that govern how
  136: .Nm tmpl
  137: files are parsed.
  138: .Pp
  139: A tmpl file is parsed by scanning for special function calls.
  140: A function call is an at sign ('@') followed by a contiguous sequence
  141: of letters, digits, and underscores, followed by matching parentheses
  142: containing zero or more function arguments.
  143: The text between functions calls is ignored (it doesn't even have to
  144: be text).
  145: .Pp
  146: Function arguments may be either other nested function calls (the argument
  147: to the outer function is the result of the inner function invocation),
  148: or constant literal strings in double quotes (the argument is the
  149: value of the string).
  150: Therefore, all function arguments begin with either an at sign or
  151: a double quote character.
  152: Function arguments are separated by commas and may have surrounding
  153: whitespace, which is ignored.
  154: .Pp
  155: Constant literal strings are enclosed in double quotes and respect the
  156: usual C backslash escapes.
  157: .Pp
  158: Built-in functions (see below) that take zero arguments do not require
  159: parentheses, but parentheses may be included for separation purposes.
  160: .Pp
  161: A parsed tmpl file is represented by a
  162: .Li "struct tmpl" .
  163: .\"
  164: .Sh Execution
  165: .\"
  166: .Pp
  167: The parsing of a tmpl file and its execution are separate steps.
  168: Once a tmpl file has been parsed, it may be executed several times.
  169: Execution requires a
  170: .Em context ,
  171: represented by a
  172: .Li "struct tmpl_ctx" ,
  173: and generates output which is written to an output stream.
  174: .Pp
  175: When the template is executed, the text between function calls is
  176: copied to the output stream without modification, while the function
  177: calls are replaced with their values, which are strings.
  178: Functions are evaluated as they are encountered during execution.
  179: .Pp
  180: The
  181: .Nm tmpl
  182: library includes several built-in functions, including
  183: special control flow functions that control input processing.
  184: The user code may also implement custom functions.
  185: .Pp
  186: User functions may return
  187: .Dv NULL
  188: and set
  189: .Va errno
  190: to indicate an error; they may also set an error string (if
  191: no error string is set,
  192: .Xr strerror 3
  193: is used to generate one).
  194: When such an error occurs, the function does not return at all.
  195: Instead, an error message is propagated up to the outer-most function call.
  196: The error message is reformatted by an optional user-supplied error
  197: formatter function, and then the formatted message is written
  198: to the output stream.
  199: .\"
  200: .Sh Built-in Functions
  201: .\"
  202: The built-in functions are listed below.
  203: In these definitions, the numeric value of a string is the result
  204: of parsing it with
  205: .Xr strtol 3 ,
  206: and a string is considered "true" if it has a numeric value other than zero.
  207: .Pp
  208: .Bl -hang -compact -width "xx"
  209: .It Em "Control flow"
  210: .Bl -hang -width "xx"
  211: .It Li "@while(x) ... @endwhile"
  212: .Pp
  213: The text in between is repeated as long as the argument supplied to
  214: .Li "@while()"
  215: is true. 
  216: .It Li "@loop(x) ... @endloop"
  217: .Pp
  218: The text in between is repeated N times, where N is the numerical value
  219: of the argument passed to
  220: .Li "@loop()" .
  221: .It Li "@loopindex(x)"
  222: .Pp
  223: Takes zero or one argument; returns the loop index (counting from zero)
  224: of the loop that is N loops out from the innermost containing loop, where
  225: N is the numerical value of the argument, or -1 if no such loop exists.
  226: If the argument is omitted it is assumed to be zero.
  227: .It Li "@if(x) ... [ @elif(y) ... ] [ @else ... ] @endif"
  228: .Pp
  229: Conditional execution depending on the truth value of the argument to
  230: .Li "@if()" .
  231: Zero or more
  232: .Li "@elif()"
  233: blocks may be followed by zero or one
  234: .Li "@else"
  235: block.
  236: An
  237: .Li "@endif"
  238: is always required. 
  239: .It Li "@break()"
  240: .Pp
  241: Break out of the innermost enclosing
  242: .Li "@loop"
  243: or
  244: .Li "@while" .
  245: .It Li "@continue()"
  246: .Pp
  247: Continue with the next iteration of the nearest enclosing
  248: .Li "@loop"
  249: or
  250: .Li "@while" .
  251: .It Li "@return()"
  252: .Pp
  253: Return from within a run-time function.
  254: .It Li "@eval(x)
  255: .Pp
  256: Parses the argument as a template, executes it, and returns the resulting
  257: output.
  258: .El
  259: .Pp
  260: .It Em "Run-time variables and functions"
  261: .Bl -hang -width "xx"
  262: .It Li "@set(name, value)"
  263: .Pp
  264: Sets the run-time variable named by the first argument to have the
  265: value equal to the second argument.
  266: All run-time variables are global and exist as long as the associated
  267: execution context exists.
  268: .It Li "@get(name)"
  269: .Pp
  270: Returns the value of the run-time variable named by the first argument,
  271: or the empty string if the variable is not set.
  272: .It Li "@define(name) ... @enddef"
  273: .Pp
  274: Defines a run-time function.
  275: The text in between is executed whenever @name(...) is invoked.
  276: During this execution, the variables
  277: .Fa argc
  278: and
  279: .Fa arg0 ,
  280: .Fa arg1 ,
  281: \&... are set to the function argument count and arguments, respectively;
  282: .Fa arg0
  283: is always equal to the name of the function.
  284: All run-time functions are global and exist as long as the associated
  285: execution context exists.
  286: .It Li "@invoke()
  287: .Pp
  288: Invokes a function.
  289: The function to be invoked and its arguments are described by the
  290: run-time variables
  291: .Fa argc
  292: and
  293: .Fa arg0 ,
  294: .Fa arg1 ,
  295: \&...
  296: as above.
  297: So
  298: .Fa arg0
  299: is the function name and
  300: .Fa arg0 ,
  301: .Fa arg1 ,
  302: \&...
  303: are the function arguments.
  304: @invoke() itself does not take any arguments.
  305: .El
  306: .Pp
  307: .It Em "Evaluators"
  308: .Bl -hang -width "xx"
  309: .It Li "@equal(x, y)"
  310: .Pp
  311: Returns "1" if x and y are identical, otherwise "0".
  312: .It Li "@not(x)"
  313: .Pp
  314: Returns "1" if x is false, otherwise "0".
  315: .It Li "@and(...)"
  316: .Pp
  317: Returns "1" if all of the arguments are true, otherwise "0".
  318: .It Li "@or(...)"
  319: .Pp
  320: Returns "1" if any of the arguments is true, otherwise "0".
  321: .It Li "@add(...)"
  322: .Pp
  323: Returns the sum of the arguments.
  324: .It Li "@sub(x, ...)"
  325: .Pp
  326: Returns the second and subsequent arguments subtracted from the first.
  327: .It Li "@mul(...)"
  328: .Pp
  329: Returns the product of the arguments.
  330: .It Li "@div(x, y)"
  331: .Pp
  332: Returns the first argument divided by the second.
  333: .It Li "@mod(x, y)"
  334: .Pp
  335: Returns the first argument modulo the second.
  336: .It Li "@lt(x, y)"
  337: .Pp
  338: Returns "1" if the first argument is less than the second, otherwise "0".
  339: .It Li "@le(x, y)"
  340: .Pp
  341: Returns "1" if the first argument is less than or equal to the second,
  342: otherwise "0".
  343: .It Li "@gt(x, y)"
  344: .Pp
  345: Returns "1" if the first argument is greater than the second, otherwise "0".
  346: .It Li "@ge(x, y)"
  347: .Pp
  348: Returns "1" if the first argument is greater than or equal to the second,
  349: otherwise "0".
  350: .El
  351: .Pp
  352: .It Em "String functions"
  353: .Bl -hang -width "xx"
  354: .It Li "@cat(...)"
  355: .Pp
  356: Returns the concatenation of all of the arguments.
  357: .It Li "@@()"
  358: .Pp
  359: Returns "@".
  360: .It Li "@error(arg)
  361: .Pp
  362: Returns the argument formatted using the caller-supplied error formatter.
  363: .It Li "@htmlencode(arg)
  364: .Pp
  365: Encodes the argument with HTML escapes and returns the result.
  366: .It Li "@urlencode(arg)
  367: .Pp
  368: Encodes the argument with URL escapes and returns the result.
  369: .El
  370: .Pp
  371: .It Em "I/O functions"
  372: .Bl -hang -width "xx"
  373: .It Li "@flush()
  374: .Pp
  375: Flushes the output stream.
  376: .It Li "@output(arg)
  377: .Pp
  378: Outputs the argument directly to the output stream. That is,
  379: if this function is invoked from within a user-defined function,
  380: the argument goes directly to the template output rather than
  381: being concatenated to the return value of the function.
  382: .El
  383: .Pp
  384: .El
  385: .\"
  386: .Sh API
  387: .\"
  388: .Fn tmpl_create
  389: parses input from
  390: .Fa input
  391: and creates and returns a new template object,
  392: which uses
  393: .Xr typed_mem 3
  394: type
  395: .Fa mtype .
  396: If
  397: .Fa num_errors
  398: is not
  399: .Dv NULL ,
  400: then the number of parse errors detected is stored in
  401: .Fa "*num_errors" .
  402: A parse error is an occurrence of the
  403: .Dq @
  404: character that is not the beginning of a well-formed
  405: .Nm
  406: function invocation.
  407: .Pp
  408: .Fn tmpl_create_mmap
  409: parses the contents of the file named
  410: .Fa path ,
  411: using
  412: .Xr mmap 2
  413: internally to avoid having to store the entire file in memory.
  414: This results in less memory being used; however, if the file's contents
  415: are changed then subsequent invocations of
  416: .Fn tmpl_execute
  417: may give garbled output.
  418: .Pp
  419: .Fn tmpl_destroy
  420: destroys a template object.
  421: Upon return,
  422: .Fa "*tmplp"
  423: will be set to
  424: .Dv NULL .
  425: If
  426: .Fa "*tmplp"
  427: is already
  428: .Dv NULL
  429: when
  430: .Fn tmpl_destroy
  431: is invoked, nothing happens.
  432: .Pp
  433: .Fn tmpl_ctx_create
  434: creates a new template execution context.
  435: .Fa mtype
  436: is the
  437: .Xr typed_mem 3
  438: type used not only for the execution context object itself, but also
  439: for all strings generated during execution.
  440: In particular, all strings returned by user functions must be stored
  441: in buffers allocated with this type.
  442: The
  443: .Fa arg
  444: is a user cookie ignored by the
  445: .Nm tmpl
  446: functions.
  447: The parameters
  448: .Fa arg
  449: and
  450: .Fa mtype
  451: may be retrieved with
  452: .Fn tmpl_ctx_get_arg
  453: and
  454: .Fn tmpl_ctx_get_mtype ,
  455: respectively.
  456: .Pp
  457: .Fa handler
  458: and
  459: .Fa errfmtr
  460: point to functions having these types:
  461: .Pp
  462: .Bd -literal -compact -offset 3n
  463: typedef char *tmpl_handler_t(struct tmpl_ctx *ctx, char **errmsgp,
  464:                   int argc, char **argv);
  465: typedef char *tmpl_errfmtr_t(struct tmpl_ctx *ctx, const char *errmsg);
  466: .Ed
  467: .Pp
  468: .Fn handler
  469: returns the result of invoking the function described by
  470: .Fa argc
  471: and
  472: .Fa argv
  473: as a '\\0'-terminated string allocated with the
  474: .Xr typed_mem 3
  475: type
  476: .Fa mtype .
  477: The first argument is always the function name, and subsequent arguments
  478: are the (evaluated) arguments passed to the function.
  479: Therefore,
  480: .Fa argc
  481: is always at least one.
  482: .Pp
  483: .Fn handler
  484: may indicate an error by returning
  485: .Dv NULL ,
  486: in which case it should either set
  487: .Va errno
  488: appropriately or else set
  489: .Fa "*errmsgp"
  490: to point to an error message (which should also be allocated with
  491: .Xr typed_mem 3
  492: type
  493: .Fa mtype) ;
  494: .Fa "*errmsgp"
  495: will be
  496: .Dv NULL
  497: when
  498: .Fn handler
  499: is invoked.
  500: .Pp
  501: The error formatter function
  502: .Fn errfmtr
  503: is optional.
  504: It should return an error string allocated with
  505: .Xr typed_mem 3
  506: type
  507: .Fa mtype
  508: and formatted appropriately for the template output
  509: (e.g., in HTML).
  510: The
  511: .Fa errmsg
  512: is the original, unformatted error string returned by the function handler;
  513: if the handler did not return an explicit error message,
  514: .Li "strerror(errno)"
  515: is used for
  516: .Fa errmsg .
  517: .Pp
  518: .Fn tmpl_list_handler
  519: may be useful for implementing
  520: .Fn handler
  521: when there is a fixed list of user functions.
  522: The
  523: .Fa userfuncs
  524: parameter points to a length
  525: .Fa uflen
  526: array of
  527: .Li "struct tmpl_func" :
  528: .Pp
  529: .Bd -literal -compact -offset 3n
  530: struct tmpl_func {
  531:     const char      *name;      /* function name, null to end list */
  532:     u_int           min_args;   /* min # args (not counting name) */
  533:     u_int           max_args;   /* max # args (not counting name) */
  534:     tmpl_handler_t  *handler;   /* handler for function */
  535: };
  536: .Ed
  537: .Pp
  538: Each entry in the array describes a user function.
  539: The function called
  540: .Fa name
  541: accepts at least
  542: .Fa min_args
  543: and at most
  544: .Fa max_args
  545: parameters, and is implemented by the
  546: .Fa handler .
  547: The array must be sorted lexicographically by name.
  548: .Fn tmpl_list_handler
  549: finds the function named by
  550: .Li "argv[0]"
  551: using a binary search of the array and invokes its
  552: .Fn handler
  553: with the supplied arguments.
  554: In the case of an error,
  555: .Fn tmpl_list_handler
  556: prepends the returned error string with the offending function call
  557: and arguments.
  558: .Pp
  559: .Fn tmpl_ctx_set_var
  560: and
  561: .Fn tmpl_ctx_get_var
  562: may be used to set and retrieve variables associated with
  563: .Fa ctx .
  564: .Pp
  565: .Fn tmpl_ctx_destroy
  566: destroys a template context.
  567: Upon return,
  568: .Fa "*ctxp"
  569: will be set to
  570: .Dv NULL .
  571: If
  572: .Fa "*ctxp"
  573: is already
  574: .Dv NULL
  575: when
  576: .Fn tmpl_ctx_destroy
  577: is invoked, nothing happens.
  578: .Pp
  579: .Fn tmpl_execute
  580: executes the parsed template
  581: .Fa tmpl
  582: using the execution context
  583: .Fa ctx ,
  584: and writes the output to
  585: .Fa output .
  586: .Fa flags
  587: may contain any of the following values OR'd together:
  588: .Pp
  589: .Bd -literal -compact -offset 3n
  590: TMPL_SKIP_NL_WHITE    Skip newline plus whitespace
  591: .Ed
  592: .Pp
  593: .Dv TMPL_SKIP_NL_WHITE
  594: causes any inter-function occurrences of a newline followed by whitespace
  595: to be ignored.
  596: This often generates more intuitive output.
  597: The example template given previously would generate this output if
  598: .Dv TMPL_SKIP_NL_WHITE
  599: were specified:
  600: .Pp
  601: .Bd -literal -compact -offset 3n
  602: I'm going to count to three:
  603: 
  604: 123
  605: 
  606: Done.
  607: .Ed
  608: .Pp
  609: .Fn tmpl_execute_func
  610: can be used to execute a single function defined in a template context.
  611: This includes non-control flow built-in functions, user functions, and
  612: run-time functions.
  613: .Fa ctx ,
  614: .Fa output ,
  615: and
  616: .Fa flags
  617: are as with
  618: .Fn tmpl_execute .
  619: The function and arguments are described by
  620: .Fa argc
  621: and
  622: .Fa argv ,
  623: and
  624: .Fa errmsgp
  625: must point to a
  626: .Li "char *"
  627: error message pointer.
  628: .Pp
  629: .Fn tmpl_ctx_reset
  630: resets an execution context to its initial state.
  631: This causes any runtime variables and functions defined during a previous
  632: execution using
  633: .Fa ctx
  634: to be forgotten.
  635: .Sh RETURN VALUES
  636: .Fn tmpl_create ,
  637: .Fn tmpl_ctx_create ,
  638: and
  639: .Fn tmpl_execute
  640: return
  641: .Dv NULL
  642: or -1 to indicate an error, with
  643: .Va errno
  644: set appropriately.
  645: .Pp
  646: .Fn tmpl_execute_func
  647: returns -1 if there was an error.
  648: In the case of a system error,
  649: .Fa "*errmsgp"
  650: will be set to
  651: .Dv NULL
  652: and
  653: .Va errno
  654: will be set appropriately; otherwise,
  655: .Fa "*errmsgp"
  656: will point to an appropriate error message allocated with
  657: .Xr typed_mem 3
  658: type
  659: .Fa mtype ,
  660: which the caller must eventually free.
  661: .Sh SEE ALSO
  662: .Xr http_servlet_tmpl 3 ,
  663: .Xr libpdel 3 ,
  664: .Xr strtol 3 ,
  665: .Xr typed_mem 3
  666: .Sh IMPLEMENTATION NOTES
  667: Here are two common sources of bugs:
  668: .Pp
  669: .Bl -dash -compact -offset 3n
  670: .It
  671: User functions returning constant strings or strings allocated
  672: with the wrong
  673: .Xr typed_mem 3
  674: type.
  675: .It
  676: Not sorting the user function array given to
  677: .Fn tmpl_list_handler .
  678: .El
  679: .Sh HISTORY
  680: The PDEL library was developed at Packet Design, LLC.
  681: .Dv "http://www.packetdesign.com/"
  682: .Sh AUTHORS
  683: .An Archie Cobbs Aq archie@freebsd.org
  684: .Sh BUGS
  685: .Fn tmpl_create ,
  686: .Fn tmpl_execute ,
  687: and
  688: .Fn tmpl_execute_func
  689: may leak small amounts of memory if the thread is canceled.