2 // Fraunhofer Institut fuer offene Kommunikationssysteme (FOKUS)
3 // Kompetenzzentrum fuer Satelitenkommunikation (SatCom)
4 // Stefan Bund <g0dil@berlios.be>
6 // This program is free software; you can redistribute it and/or modify
7 // it under the terms of the GNU General Public License as published by
8 // the Free Software Foundation; either version 2 of the License, or
9 // (at your option) any later version.
11 // This program is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
16 // You should have received a copy of the GNU General Public License
17 // along with this program; if not, write to the
18 // Free Software Foundation, Inc.,
19 // 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
22 \brief PacketParser public header */
24 /** \defgroup packetparser The PacketParser facility
26 The PacketParser facility provides a framework to implement very lightweight classes which parse
27 the raw content of a packet into meaningful values. PacketParsers are always passed around
28 <em>by value</em>, they can be understood as pointers into the packet data with added type
29 information providing parsing functions.
31 Packet parsers are \e only used within the packet framework. You should never allocate a new
32 parser instance directly, you should the Packet library let that do for you (either by having
33 the parser as a packet parser in a packet type or by having a member in the packet parser which
34 allocates the parser as a sub-parser).
36 Parsers are built hierarchically. A high-level parser will return other parsers when accessing
37 an element (Example: Asking an EthernetParser for the ethertype field by calling the parsers \c
38 type() member will return an \c UInt16 parser). The lowest level building blocks then return the
39 values. This hierarchical structure greatly simplifies building complex parsers.
41 Since parsers are very lightweight and are passed by value, packet fields are accessed using the
42 corresponding accessor method:
47 // Assign new value to an integer parser
50 // Write out above value
51 std::cerr << p->someField() << "\n";
53 // Use the generic parser-assignment operator '<<' to copy field values
54 p->someVector()[1].someOtherField() << q->someField();
55 p->someVector() << q->someVector()
58 Here \c someField(), \c someOtherField() and \c someVector() are accessor methods named after
59 the field name. Each returns a parser object. Simple parsers can be used like their
60 corresponding basic type (e.g. a Parse_UInt16 field can be used like an unsigned integer), more
61 complex parsers provide type specific access members. Assigning a value to a parser will change
62 the underlying representation (the packet data).
64 Parsers can be grouped into several categories. These categories are not all defined rigorously
65 but are nevertheless helpful when working with the parsers:
66 \li <em>Value parsers</em> provide the lowest level parsers (e.g. senf::Parse_UInt16 which
67 returns an integer value).
68 \li <em>Collection parsers</em> are parsers which model a collection of sub-elements like
69 senf::Parse_List or senf::Parse_Vector.
70 \li <em>Composite parsers</em> collect several fields of arbitrary type into a new
71 parser. Parsers defined using the \ref packetparsermacros fall under this category.
72 \li <em>Packet parsers</em> are used to define a packet type.
74 \warning Parsers are like iterators: They are invalidated <em>whenever the size of the packet's
75 data is changed</em>. You should not store a parser anywhere. If you want to keep a parser
76 reference, use the senf::SafePacketParser wrapper. You still will need to take extra care to
77 ensure the parser is not invalidated.
79 \section parserimpl Packet parser categories
81 Every parser is derived from senf::PacketParserBase. This class provides the necessary
82 housekeeping information and provides the parsers with access to the data. You may in principle
83 define arbitrary methods as parser members (e.g. methods to calculate a checksum, methods
84 processing fields in some way and so on). You should however be very wary to access data outside
85 the range assigned to the packet (the range starting at \c i() and with a size of senf::bytes()
88 Each parser type has specific features
90 \subsection parserimpl_value Value parsers
92 For a parser \a SomeParser to be a value parser, the following expressions must be valid:
94 // SomeParser must have a 'value_type', The 'value_type' must be default constructible, copy
95 // constructible and assignable
96 SomeParser::value_type v;
98 // An instance of 'SomeParser' must have a 'value' member which returns a value which may be
99 // assigned to a variable of type 'value_type'
100 v = p.someParserField().value()
102 // It must be possible to assign a new value using the 'value' member
103 p.someParserField().value(v)
106 If at all possible, the 'value_type' should not reference the packet data using iterators or
107 pointers, it should hold a copy of the value (it's Ok for \c value() to return such a reference
108 as long as assigning it to a \c value_type variable will copy the value).
110 \subsection parserimpl_collection Collection parsers
112 A collection parser \a SomeParser should model STL containers. The parsers themselves will
113 probably only // provide a reduced interface, but the collection parser should have a \c
114 collection member which is a wrapper providing the full interface.
116 SomeParser::container c (p.someParserField());
119 You will probably only very seldom need to implement a completely new collection
120 parser. Instead, you can rely on senf::Parse_Vector or senf::Parse_List and implement new
123 \subsection parserimpl_composite Composite parsers
125 If possible, composite parsers should be implemented using the \ref packetparsermacros. In
126 addition to the normal parser requirements, these macros ensure, that for each field,
127 <em>fieldname</em><tt>_t</tt> is a typedef for the fields parser and
128 <em>fieldname</em><tt>_offset</tt> is the offset of the field in bytes from the beginning of the
129 parser (either a constant for fixed size parsers or a member function for dynamically sized
130 parsers). When defining composite parsers without the help of the \ref packetparsermacros, you
131 should provide those same members.
133 \subsection parserimpl_packet Packet parsers
135 Packet parsers are composite parsers with relaxed requirements. Since a packet parser will never
136 be used as a sub-parser (it will not be used within another composite parser or as value type in
137 a collection parser), the value returned by senf::bytes for this parser must not necessarily
138 cover the complete packet (e.g. if the packet has a trailer, the trailer will live outside the
139 range given by senf::bytes). You may define any member you want to have in your packets field
140 interface. These members may access the packet data in any way. You just need to ensure, that
141 the integration into the packet-type is correct (the senf::PacketTypeMixin will by default use
142 senf::bytes() to find the end of the header).
146 #ifndef HH_PacketParser_
147 #define HH_PacketParser_ 1
150 #include <boost/utility/enable_if.hpp>
151 #include <boost/type_traits.hpp>
152 #include <boost/optional.hpp>
153 #include "Utils/SafeBool.hh"
154 #include "PacketTypes.hh"
155 #include "PacketData.hh"
157 #include "PacketParser.mpp"
158 ///////////////////////////////hh.p////////////////////////////////////////
162 /** \brief Parser Base class
164 Parsers come in two flavors: fixed and dynamically sized parsers. A <em>fixed size
165 parser</em> has a constant size, it will always parse a fixed number of bytes. The low-level
166 'final' parsers (like the integer parsers) are fixed size parsers as are composite parsers
167 built up only of fixed-size fields.
169 A <em>dynamically sized</em> parser on the other hand infers it's size from the contents of
170 the data parsed. Any parser containing at least one dynamically sized sub-parser will itself
171 be dynamically sized.
173 Both kinds of parser need to derive from PacketParserBase and implement several required
174 members. Which members to implement depends on the parsers flavor. There are two ways how to
176 \li If the parser just consists of a simple sequence of consecutive fields (sub-parsers),
177 the \ref SENF_PACKET_PARSER_DEFINE_FIELDS and \ref
178 SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS macros provide a simple and convenient way to
180 \li In more complex cases, you need to implement the necessary members manually.
182 This documentation is about the manual implementation. You should nevertheless read through
183 this to understand, what above macros are doing.
185 The following example documents the interface (which must be) provided by a parser:
187 struct FooParser : public PacketParserBase
189 FooParser(data_iterator i, state_type s) : PacketParserBase(i,s) {}
191 // If this parser has a fixed size, you must define this size here This definition
192 // allows the parser to be used within the list, vector and array parsers static
193 static const size_type fixed_bytes = some_constant_size;
195 // If the parser does not have a fixed size, you must implement the bytes() member to
196 // return the size. ONLY EVER DEFINE ONE OF fixed_bytes OR bytes().
197 size_type bytes() const;
199 // If you define bytes(), you also need to define the init_bytes. This is the number
200 // of bytes to allocate when creating a new object
201 static const size_type init_bytes = some_constant_size;
203 // You also may define an init() member. This will be called to initialize a newly
204 // created data object. The default implementation just does nothing.
207 // ////////////////////////////////////////////////////////////////////////
209 // Add here members returning (sub-)parsers for the fields. The 'parse' member is
210 // used to construct the sub-parsers. This member either takes an iterator to the
211 // data to be parsed or just an offset in bytes.
213 senf::Parse_UInt16 type() const { return parse<Parse_UInt16>( 0 ); }
214 senf::Parse_UInt16 size() const { return parse<Parse_UInt16>( 2 ); }
218 You should never call the \c bytes() member of a parser directly. Instead you should use the
219 freestanding senf::bytes() function. This function will return the correct size irrespective
220 of the parsers flavor. You may access \c fixed_bytes directly, however be aware that this
221 will restrict your code to fixed size parsers (which depending on the circumstances may be
222 exactly what you want).
224 In the same way, don't access \c init_bytes directly, always use the senf::init_bytes
225 meta-function class which correctly supports fixed size parsers.
227 \ingroup packetparser
229 class PacketParserBase
232 ///////////////////////////////////////////////////////////////////////////
235 typedef detail::packet::iterator data_iterator; ///< Raw data iterator type
236 typedef detail::packet::size_type size_type; ///< Unsigned integral type
237 typedef detail::packet::difference_type difference_type; ///< Signed integral type
238 typedef detail::packet::byte byte; ///< Unsigned 8bit value, the raw value type
239 typedef PacketData * state_type; ///< Type of the 'state' parameter
241 ///////////////////////////////////////////////////////////////////////////
242 ///\name Structors and default members
245 // no default constructor
247 // default destructor
248 // no conversion constructors
251 ///////////////////////////////////////////////////////////////////////////
253 data_iterator i() const; ///< Return beginning of data to parse
254 /**< The parser is expected to interpret the data beginning
255 here. The size of the interpreted is given by
256 <tt>senf::bytes(</tt><em>parser
257 instance</em><tt>)</tt>. */
258 state_type state() const; ///< Return state of this parser
259 /**< The value returned should be interpreted as an opaque
260 value provided just to be forwarded to other
262 PacketData & data() const; ///< Access the packets raw data container
263 /**< This member will return the raw data container holding
264 the data which is parsed by \c this parser. */
266 void init() const; ///< Default implementation
267 /**< This is just an empty default
268 implementation. Re-implement this member in your own
269 parsers if needed. */
272 PacketParserBase(data_iterator i, state_type s); ///< Standard constructor
273 /**< This is the constructor used by most parsers. The
274 parameters are just forwarded from the derived classes
275 constructor parameters. */
276 PacketParserBase(data_iterator i, state_type s, size_type size);
277 ///< Size checking constructor
278 /**< In addition to the standard constructor, this
279 constructor will validate, that there is enough data in
280 the raw data container to parse \a size bytes after \a
283 This constructor is called by all 'final' parsers
284 (e.g. the integer parsers) and \e only by those
285 parsers. Most parsers do \e not check the validity of
286 the iterator, this is delayed until the very last
287 parser. This allows to partial parse truncated
290 \throw TruncatedPacketException if the raw data
291 container does not hold at least \a size bytes
292 beginning at \a i. */
294 bool check(size_type size); ///< Check size of data container
295 /**< \returns \c true, if the data container holds at least
296 \a size beginning at i(), \c false otherwise. */
297 void validate(size_type size); ///< Validate size of data container
298 /**< \throws TruncatedPacketException if the raw data
299 container does not hold at least \a size bytes
302 template <class Parser> Parser parse(data_iterator i) const; ///< Create sub-parser
303 /**< Creates a new instance of \a Parser to parse data
304 beginning at \a i. Automatically passes \a state() to
306 template <class Parser> Parser parse(size_type n) const; ///< Create sub-parser
307 /**< Creates a new instance of \a Parser to parse data
308 * beginning at i()<tt> + </tt>\a n. Automatically passes \a
309 state() to the new parser. */
311 void defaultInit() const; ///< Default implementation
312 /**< This is just an empty default
313 implementation. Re-implement this member in your own
314 parsers if needed. */
322 template <class Parser> friend class SafePacketParser;
325 /** \brief Return raw size parsed by the given parser object
327 This function will either call <tt>p.bytes()</tt> or return <tt>Parser::fixed_bytes</tt>
328 depending on the type of parser.
330 The value returned does \e not take into account the amount of data actually available. So
331 you always need to validate this value against the packet size if you directly access the
332 data. The standard low-level parses all do this check automatically to guard against
335 \param[in] p Parser object to check
336 \returns number of bytes this parser expects to parser
337 \ingroup packetparser
339 template <class Parser>
340 PacketParserBase::size_type bytes(Parser p);
342 namespace detail { template <class Parser> class ParserInitBytes; }
344 /** \brief Return number of bytes to allocate to new object of given type
346 This meta-function is called like
348 senf::init_bytes<SomeParser>::value
351 This expression evaluates to a compile-time constant integral expression of type
352 senf::PacketParserBase::size_type. This meta-function will return \c Parser::fixed_bytes or
353 \c Parser::init_bytes depending on the type of parser.
355 \param[in] Parser The Parser to return init_bytes for
356 \returns Number of bytes to allocate to the new object
357 \ingroup packetparser
359 template <class Parser>
360 struct init_bytes : public detail::ParserInitBytes<Parser>
364 template <class Parser>
365 typename boost::enable_if<
366 boost::is_base_of<PacketParserBase, Parser>,
368 operator<<(Parser target, Parser source);
370 /** \brief Generic parser copying
372 This operator allows to copy the values of identical parsers. This operation does \e not
373 depend on the parsers detailed implementation, it will just replace the data bytes of the
374 target parser with those from the source parser. This allows to easily copy around complex
375 packet substructures.
377 This operation is different from the ordinary assignment operator: It does not change the \a
378 target parser, it changes the data referenced by the \a target parser.
380 \ingroup packetparser
382 template <class Parser>
383 Parser operator<<(Parser target, Parser source);
387 template <class Parser, class Value>
388 typename boost::enable_if_c <
389 boost::is_base_of<PacketParserBase, Parser>::value
390 && ! boost::is_base_of<PacketParserBase, Value>::value,
392 operator<<(Parser target, Value const & value);
394 /** \brief Generic parser value assignment
396 This operator allows to assign a value to parsers which implement a <tt>value(</tt>\a
397 value<tt>)</tt> member. This operator allows to use a common syntax for assigning values or
400 \ingroup packetparser
402 template <class Parser, class Value>
403 Parser operator<<(Parser target, Value const & value);
406 /** \defgroup packetparsermacros Helper macros for defining new packet parsers
408 To simplify the definition of simple packet parsers, several macros are provided. Before
409 using these macros you should familiarize yourself with the packet parser interface as
410 described in senf::PacketParserBase.
412 These macros simplify providing the above defined interface. A typical packet declaration
413 using these macros has the following form (This is a concrete example from the definition of
414 the ethernet packet in <tt>DefaultBundle/EthernetPacket.hh</tt>)
417 struct Parse_EthVLan : public PacketParserBase
419 typedef Parse_UIntField < 0, 3 > Parse_Priority;
420 typedef Parse_Flag < 3 > Parse_CFI;
421 typedef Parse_UIntField < 4, 16 > Parse_VLanId;
422 typedef Parse_UInt16 Parse_Type;
424 SENF_PACKET_PARSER_INIT(Parse_EthVLan);
426 SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS(
427 ((OverlayField)( priority, Parse_Priority ))
428 ((OverlayField)( cfi, Parse_CFI ))
429 ((Field )( vlanId, Parse_VLanId ))
430 ((Field )( type, Parse_Type )) );
434 The macros take care of the following:
435 \li They define the accessor functions returning parsers of the given type.
436 \li They automatically calculate the offset of the fields from the preceding fields.
437 \li The macros provide a definition for \c init()
438 \li The macros define the \c bytes(), \c fixed_bytes and \c init_bytes members as needed.
440 You may define either a fixed or a dynamically sized parser. Fixed size parsers are defined
441 using \ref SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS, dynamically sized parsers are defined
442 using \ref SENF_PACKET_PARSER_DEFINE_FIELDS. The different members are implemented such
445 \li The needed parser constructor is defined
446 \li \c init() calls \c defaultInit(). \c defaultInit() is defined to call \c init() on each
448 \li \c bytes() (on dynamically sized parser) respectively \c fixed_bytes (on fixed size
449 parsers) is defined to return the sum of the sizes of all fields.
450 \li On dynamically sized parsers, \c init_bytes is defined to return the sum of the
451 \c init_size's of all fields
453 The central definition macros are \ref SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS and \ref
454 SENF_PACKET_PARSER_DEFINE_FIELDS. The argument to both has the same structure. It is a
455 (boost preprocessor style) sequence of field definitions where each field definition
456 provides the builder macro to use and the name and type of the field to define:
458 SENF_PACKET_PARSER_DEFINE[_FIXED]_FIELDS(
459 (( <builder> )( <name>, <type> ))
464 For each field, this command will define
465 \li A method \a name() returning an instance of the \a type parser
466 \li \a name<tt>_t</tt> as a typedef for \a type, the fields value
467 \li \a name<tt>_offset</tt> to give the offset of the field from the beginning of the
468 parser. If the parser is a fixed size parser, this will be a static constant, otherwise
471 The \a builder argument selects, how the field is defined
472 \li <tt>Field</tt> defines a field and increments the current position by the size of the
474 \li <tt>OverlayField</tt> defines a field like <tt>Field</tt> but does \e not increment the
475 position. In the above example, this is used to overlay the different bitfield parsers:
476 All overlaying bitfield parser except the last one (the one with the highest bit
477 numbers) is marked as OverlayField.
479 The \a name argument defines the name of the accessor method.
481 The \a type argument is the parser to return for that field. Since none of the arguments may
482 contain a comma, <em>This argument cannot be a multi-parameter template</em>. Always use
483 typedefs to access templated parsers as shown above.
485 The \ref SENF_PACKET_PARSER_INIT macro defines the constructor and the \c init() member. If
486 you want to provide your own \c init() implementation, use \ref
487 SENF_PACKET_PARSER_NO_INIT. The first statement in your init method should probably to call
488 \c defaultInit(). This will call the \c init() member of all the fields. Afterwards you can
489 set up the field values as needed:
491 struct SomePacket : public senf::PacketParserBase
493 SENF_PACKET_PARSER_NO_INIT(SomePacket);
495 typedef senf::Parse_UInt8 Parse_Type;
496 typedef senf::Parse_Vector< senf::Parse_UInt32,
497 senf::SimpleVectorSizer<senf::Parse_UInt16>
500 SENF_PACKET_PARSER_DEFINE_FIELDS(
501 ((Field)( type, Parse_Type ))
502 ((Field)( elements, Parse_Elements ))
508 elements().push_back(0x01020304u);
513 \ingroup packetparser
516 /** \brief Define initialization members of a parser
518 This macro defines the packet parser constructor and the \c init() member. \c init() is
519 defined to just call \c defaultInit() which is defined by the other macros to call \c init()
520 on each of the parsers fields.
522 \ingroup packetparsermacros
525 # define SENF_PACKET_PARSER_INIT(name) \
526 name(data_iterator i, state_type s) : senf::PacketParserBase(i,s) {} \
527 void init() const { defaultInit(); }
529 /** \brief Define initialization members of a parser except init()
531 This macro is like SENF_PACKET_PARSER_INIT but does \e not define \c init(). This allows you
532 to provide your own implementation. You should call \c defaultInit() first before
533 initializing your data fields.
535 \ingroup packetparsermacros
538 # define SENF_PACKET_PARSER_NO_INIT(name) \
539 name(data_iterator i, state_type s) : senf::PacketParserBase(i,s) {}
541 /** \brief Define fields for a dynamically sized parser
543 Define the fields as specified in \a fields. This macro supports dynamically sized
544 subfields, the resulting parser will be dynamically sized.
546 \ingroup packetparsermacros
549 # define SENF_PACKET_PARSER_DEFINE_FIELDS(fields) \
550 SENF_PACKET_PARSER_I_DEFINE_FIELDS(0,fields)
552 /** \brief Define fields for a dynamically sized parser (with offset)
554 Define the fields as specified in \a fields. This macro supports dynamically sized
555 subfields, the resulting parser will be dynamically sized.
557 The \a offset argument gives the byte offset at which to start parsing the fields. This
558 helps defining extended parser deriving from a base parser:
560 struct ExtendedParser : public BaseParser
562 ExtendedParser(data_iterator i, state_type s) : BaseParser(i,s) {}
564 SENF_PACKET_PARSER_DEFINE_FIELDS_OFFSET(senf::bytes(BaseParser(*this)),
565 ( ... fields ... ) );
575 \ingroup packetparsermacros
578 # define SENF_PACKET_PARSER_DEFINE_FIELDS_OFFSET(offset,fields) \
579 SENF_PACKET_PARSER_I_DEFINE_FIELDS(offset,fields)
581 /** \brief Define fields for a fixed size parser
583 Define the fields as specified in \a fields. This macro only supports fixed size
584 subfields, the resulting parser will also be a fixed size parser.
586 \ingroup packetparsermacros
589 # define SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS(fields) \
590 SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(0,fields)
592 /** \brief Define fields for a fixed size parser
594 Define the fields as specified in \a fields. This macro only supports fixed size
595 subfields, the resulting parser will also be a fixed size parser.
597 The \a offset argument gives the byte offset at which to start parsing the fields. This
598 helps defining extended parser deriving from a base parser:
600 struct ExtendedParser : public BaseParser
602 ExtendedParser(data_iterator i, state_type s) : BaseParser(i,s) {}
604 SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS_OFFSET(BaseParser::fixed_bytes,
605 ( ... fields ... ) );
615 \ingroup packetparsermacros
618 # define SENF_PACKET_PARSER_DEFINE_FIXED_FIELDS_OFFSET(offset,fields) \
619 SENF_PACKET_PARSER_I_DEFINE_FIXED_FIELDS(offset,fields)
621 /** \brief Default parser parsing nothing
623 struct VoidPacketParser
624 : public PacketParserBase
626 SENF_PACKET_PARSER_INIT(VoidPacketParser);
629 /** \brief Iterator re-validating Parser wrapper
631 An ordinary parser will be invalidated whenever the raw data container's size is
632 changed. This can complicate some algorithms considerably.
634 This wrapper will update the parsers iterator (the value returned by the i() member) on
635 every access. This ensures that the iterator will stay valid.
637 \attention Beware however, if you insert or remove data before the safe wrapper, the
638 location will \e not be updated accordingly and therefore the parser will be
641 Additionally a SafePacketParser has an uninitialized state. The only allowed operations in
642 this state are the boolean test for validity and assigning another parser.
644 \ingroup packetparser
646 template <class Parser>
647 class SafePacketParser
648 : public SafeBool< SafePacketParser<Parser> >
651 ///////////////////////////////////////////////////////////////////////////
654 ///////////////////////////////////////////////////////////////////////////
655 ///\name Structors and default members
658 // default copy constructor
659 // default copy assignment
660 // default destructor
661 SafePacketParser(); ///< Create an empty uninitialized SafePacketParser
663 // conversion constructors
664 SafePacketParser(Parser parser); ///< Initialize SafePacketParser from \a parser
666 SafePacketParser & operator=(Parser parser); ///< Assign \a parser to \c this
669 ///////////////////////////////////////////////////////////////////////////
671 Parser operator*() const; ///< Access the stored parser
672 /**< On every access, the stored parsers iterator will be
673 updated / re-validated. */
674 Parser const * operator->() const; ///< Access the stored parser
675 /**< On every access, the stored parsers iterator will be
676 updated / re-validated. */
677 bool boolean_test() const; ///< Check validity
682 mutable boost::optional<Parser> parser_;
683 senf::safe_data_iterator i_;
688 ///////////////////////////////hh.e////////////////////////////////////////
690 #if !defined(SENF_PACKETS_DECL_ONLY) && !defined(HH_PacketParser_i_)
691 #define HH_PacketParser_i_
692 #include "PacketParser.cci"
693 #include "PacketParser.ct"
694 #include "PacketParser.cti"
701 // c-file-style: "senf"
702 // indent-tabs-mode: nil
703 // ispell-local-dictionary: "american"
704 // compile-command: "scons -u test"
705 // comment-column: 40