ASCII art diagram converter
Given the RFC 1035 message diagram from Section 4.1.1 (Header section format) as a string: http://www.ietf.org/rfc/rfc1035.txt
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Where (every column of the table is 1 bit):
ID is 16 bits QR = Query (0) or Response (1) Opcode = Four bits defining kind of query: 0: a standard query (QUERY) 1: an inverse query (IQUERY) 2: a server status request (STATUS) 3-15: reserved for future use AA = Authoritative Answer bit TC = Truncation bit RD = Recursion Desired bit RA = Recursion Available bit Z = Reserved RCODE = Response code QC = Question Count ANC = Answer Count AUC = Authority Count ADC = Additional Count
Write a function, member function, class or template that accepts a similar multi-line string as input to define a data structure or something else able to decode or store a header with that specified bit structure.
If your language has macros, introspection, code generation, or powerful enough templates, then accept such string at compile-time to define the header data structure statically.
Such "Header" function or template should accept a table with 8, 16, 32 or 64 columns, and any number of rows. For simplicity the only allowed symbols to define the table are + - | (plus, minus, pipe), and whitespace. Lines of the input string composed just of whitespace should be ignored. Leading and trailing whitespace in the input string should be ignored, as well as before and after each table row. The box for each bit of the diagram takes four chars "+--+". The code should perform a little of validation of the input string, but for brevity a full validation is not required.
Bonus: perform a thoroughly validation of the input string.
D
This solution generates anonymous struct code at compile-time, that can be mixed-in inside a struct or class. <lang d>string makeStructFromDiagram(in string rawDiagram) pure @safe {
import std.conv: text; import std.format: format; import std.string: strip, splitLines, indexOf; import std.array: empty, popFront;
static void commitCurrent(ref uint anonCount,
ref uint totalBits,
ref size_t currentBits,
ref string code,
ref string currentName) pure @safe {
if (currentBits) {
code ~= "\t";
currentName = currentName.strip;
if (currentName.empty) {
anonCount++;
currentName = "anonymous_field_" ~ anonCount.text;
}
string type;
if (currentBits == 1)
type = "bool";
else if (currentBits <= ubyte.sizeof * 8)
type = "ubyte";
else if (currentBits <= ushort.sizeof * 8)
type = "ushort";
else if (currentBits <= uint.sizeof * 8)
type = "uint";
else if (currentBits <= ulong.sizeof * 8)
type = "ulong";
//else if (currentBits <= ucent.sizeof * 8)
// type = "ucent";
else assert(0, "Too many bits for the item " ~ currentName);
immutable byteOffset = totalBits / 8;
immutable bitOffset = totalBits % 8;
// Getter:
code ~= "@property " ~ type ~ " " ~ currentName ~
"() const pure nothrow @safe {\n";
code ~= "\t\t";
if (currentBits == 1) {
code ~= format("return (_payload[%d] & (1 << (7-%d))) ? true : false;",
byteOffset, bitOffset);
} else if (currentBits < 8) {
auto mask = (1 << currentBits) - 1;
mask <<= 7 - bitOffset - currentBits + 1;
code ~= format("return (_payload[%d] & 0b%08b) >> %d;",
byteOffset, mask, 7 - bitOffset - currentBits + 1);
} else {
assert(currentBits % 8 == 0);
assert(bitOffset == 0);
code ~= type ~ " v = 0;\n\t\t";
code ~= "version(LittleEndian) {\n\t\t";
foreach (immutable i; 0 .. currentBits / 8)
code ~= "\tv |= (cast(" ~ type ~ ") _payload[" ~
text(byteOffset + i) ~ "]) << (" ~
text((currentBits / 8) - i - 1) ~
" * 8);\n\t\t";
code ~= "} else static assert(0);\n\t\t";
code ~= "return v;";
}
code ~= "\n";
code ~= "\t}\n\t";
// Setter:
code ~= "@property void " ~ currentName ~ "(in " ~ type ~
" value) pure nothrow @safe {\n";
code ~= "\t\t";
if (currentBits < 8) {
auto mask = (1 << currentBits) - 1;
mask <<= 7 - bitOffset - currentBits + 1;
code ~= format("_payload[%d] &= ~0b%08b;\n\t\t",
byteOffset, mask);
code ~= "assert(value < " ~ text(1 << currentBits) ~
");\n\t\t";
code~=format("_payload[%d] |= cast(ubyte) value << %d;",
byteOffset, 7 - bitOffset - currentBits + 1);
} else {
assert(currentBits % 8 == 0);
assert(bitOffset == 0);
code ~= "version(LittleEndian) {\n\t\t";
foreach (immutable i; 0 .. currentBits / 8)
code ~= "\t_payload[" ~ text(byteOffset + i) ~
"] = (value >> (" ~
text((currentBits / 8) - i - 1) ~
" * 8) & 0xff);\n\t\t";
code ~= "} else static assert(0);";
}
code ~= "\n";
code ~= "\t}\n";
totalBits += currentBits;
}
currentBits = 0;
currentName = null;
}
enum C : char { pipe='|', cross='+' }
enum cWidth = 3; // Width of a bit cell in the table.
immutable diagram = rawDiagram.strip;
size_t bitCountPerRow = 0, currentBits;
uint anonCount = 0, totalBits;
string currentName;
string code = "struct {\n"; // Anonymous.
foreach (line; diagram.splitLines) {
assert(!line.empty);
line = line.strip;
if (line[0] == C.cross) {
commitCurrent(anonCount, totalBits, currentBits, code, currentName);
if (bitCountPerRow == 0)
bitCountPerRow = (line.length - 1) / cWidth;
else
assert(bitCountPerRow == (line.length - 1) / cWidth);
} else {
// A field of some sort.
while (line.length > 2) {
assert(line[0] != '/',
"Variable length data not supported");
assert(line[0] == C.pipe, "Malformed table");
line.popFront;
const idx = line[0 .. $ - 1].indexOf(C.pipe);
if (idx != -1) {
const field = line[0 .. idx];
line = line[idx .. $];
commitCurrent(anonCount, totalBits, currentBits, code, currentName);
currentName = field;
currentBits = (field.length + 1) / cWidth;
commitCurrent(anonCount, totalBits, currentBits, code, currentName);
} else {
// The full row or a continuation of the last.
currentName ~= line[0 .. $ - 1];
// At this point, line does not include the first
// C.pipe, but the length will include the last.
currentBits += line.length / cWidth;
line = line[$ .. $];
}
}
}
}
// Using bytes to avoid endianness issues. // hopefully the compiler will optimize it, otherwise // maybe we could specialize the properties more. code ~= "\n\tprivate ubyte[" ~ text((totalBits + 7) / 8) ~ "] _payload;\n";
return code ~ "}";
}
void main() { // Testing.
import std.stdio;
enum diagram = " +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+";
// To debug the code generation: //pragma(msg, diagram.makeStructFromDiagram);
// Usage.
static struct Header {
mixin(diagram.makeStructFromDiagram);
}
Header h; h.ID = 10; h.RA = true; h.ARCOUNT = 255; h.Opcode = 7;
// See the byte representation to test the setter's details. h._payload.writeln;
// Test the getters: assert(h.ID == 10); assert(h.RA == true); assert(h.ARCOUNT == 255); assert(h.Opcode == 7);
}</lang>
- Output:
[0, 10, 56, 128, 0, 0, 0, 0, 0, 0, 0, 255]
Static support for BigEndian is easy to add.
It also supports larger values like this, that is 32 bits long:
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ThirtyTwo | | | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
J
<lang J>require'strings'
soul=: -. {. normalize=: [:soul' ',dltb;._2
mask=: 0: _1} '+' = {. partition=: '|' = mask #"1 soul labels=: ;@(([: <@}: <@dltb;._1)"1~ '|'&=)@soul names=: ;:^:(0 = L.)
unpacker=:1 :0
p=. , partition normalize m p #.;.1 (8#2) ,@:#: ]
)
packer=:1 :0
w=. -#;.1 ,partition normalize m
_8 (#.\ ;) w ({. #:)&.> ]
)
getter=:1 :0
nm=. labels normalize m
(nm i. names@[) { ]
)
setter=:1 :0
q=. '
n=. q,~q,;:inv labels normalize m
1 :('(',n,' i.&names m)}')
)
starter=:1 :0
0"0 labels normalize m
)</lang>
Sample definition (note the deliberate introduction of extraneous whitespace in locations the task requires us to ignore it.
<lang j>sample=: 0 :0
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
)
unpack=: sample unpacker pack=: sample packer get=: sample getter set=: sample setter start=: sample starter</lang>
Example data for sample definition:
<lang J>
4095 13 5 6144 4096 'ID Opcode RCODE ARCOUNT QDCOUNT' set start
4095 0 13 0 0 0 0 0 5 4096 0 0 6144
pack 4095 13 5 6144 4096 'ID Opcode RCODE ARCOUNT QDCOUNT' set start
15 255 104 5 16 0 0 0 0 0 24 0
unpack 0 10 56 128 0 0 0 0 0 0 0 255
10 0 7 0 0 0 1 0 0 0 0 0 255
'Opcode' get unpack 0 10 56 128 0 0 0 0 0 0 0 255
7</lang>
In other words:
- unpack converts an octet sequence to the corresponding numeric sequence
- pack converts a numeric sequence to the corresponding octet sequence
- get extracts named elements from the numeric sequence
- set updates named elements in the numeric sequence
- start represents the default "all zeros" sequence which may be used to derive other sequences
Note that this implementation assumes that the ascii diagram represents the native word width on a single line, and assumes well formed data.
Racket
Three files:
ascii-art-parser.rkt: provides the functionascii-art->struct, which converts ASCII art from a string (or input port) to a list of word-number, bit range and idascii-art-reader.rkt: uses this to provide a sytntaxdefine-ascii-art-structurewhich defines a structure using the art worktest-ascci-art-reader.rkt: gives it all a rigourousish going over
Note that if you want to extend the word width too 32-bits (or more) add multiples of eight bit blocks horizontally (i.e. --+--+--+--+--+--+--+--+). IMO Having the diagrams 16-bits wide reflects the choice of a 16-bit word as the natural word size of the interface. If it were 32 or 64, the blocks would have to be wider.
ascii-art-parser.rkt
Note that this is in the racket/base language so it doesn't overburden the modules that import it, especially since they're at the suntax phase.
<lang racket>#lang racket/base
(require (only-in racket/list drop-right)
(only-in racket/string string-trim))
(provide ascii-art->struct)
- reads ascii art from a string or input-port
- returns
- list of (word-number highest-bit lowest-bit name-symbol)
- bits per word
(define (ascii-art->struct art)
(define art-inport
(cond
[(string? art) (open-input-string art)]
[(input-port? art) art]
[else (raise-argument-error 'ascii-art->struct
"(or/c string? input-port?)"
art)]))
(define lines
(for/list ((l (in-port (lambda (p)
(define pk (peek-char p))
(case pk ((#\+ #\|) (read-line p))
(else eof)))
art-inport)))
l))
(when (null? lines)
(error 'ascii-art->struct "no lines"))
(define bit-re #px"[|+]([^|+]*)")
(define cell-re #px"[|]([^|]*)")
(define bit-boundaries (regexp-match-positions* bit-re (car lines)))
(define bits/word (sub1 (length bit-boundaries)))
(unless (zero? (modulo bits/word 8))
(error 'ascii-art->struct "diagram is not a multiple of 8 bits wide"))
(define-values (pos->bit-start# pos->bit-end#)
(for/fold ((s# (hash)) (e# (hash)))
((box (in-range bits/word))
(boundary (in-list bit-boundaries)))
(define bit (- bits/word box 1))
(values (hash-set s# (car boundary) bit)
(hash-set e# (cdr boundary) bit))))
(define fields
(apply append
(for/list ((line-number (in-naturals))
(line (in-list lines))
#:when (odd? line-number))
(define word (quotient line-number 2))
(define cell-positions (regexp-match-positions* cell-re line))
(define cell-contents (regexp-match* cell-re line))
(for/list ((cp (in-list (drop-right cell-positions 1)))
(cnt (in-list cell-contents)))
(define cell-start-bit (hash-ref pos->bit-start# (car cp)))
(define cell-end-bit (hash-ref pos->bit-end# (cdr cp)))
(list word cell-start-bit cell-end-bit (string->symbol (string-trim (substring cnt 1))))))))
(values fields bits/word))</lang>
ascii-art-reader.rkt
<lang racket>#lang racket
(require (for-syntax "ascii-art-parser.rkt"))
(require (for-syntax racket/syntax))
(provide (all-defined-out))
(define-syntax (define-ascii-art-structure stx)
(syntax-case stx ()
[(_ id art)
(let*-values (((all-fields bits/word) (ascii-art->struct (syntax-e #'art))))
(with-syntax
((bytes->id (format-id stx "bytes->~a" #'id))
(id->bytes (format-id stx "~a->bytes" #'id))
(word-size (add1 (car (for/last ((f all-fields)) f))))
(fld-ids (map cadddr all-fields))
(fld-setters
(cons
#'id
(for/list ((fld (in-list all-fields)))
(let* ((bytes/word (quotient bits/word 8))
(start-byte (let ((word-no (car fld))) (* word-no bytes/word))))
`(bitwise-bit-field (integer-bytes->integer bs
#f
(system-big-endian?)
,start-byte
,(+ start-byte bytes/word))
,(caddr fld)
,(add1 (cadr fld)))))))
(set-fields-bits
(list*
'begin
(for/list ((fld (in-list all-fields)))
(define val (cadddr fld))
(define start-bit (cadr fld))
(define end-bit (caddr fld))
(define start-byte (let ((word-no (car fld))) (* word-no (quotient bits/word 8))))
(define fld-bit-width (- start-bit end-bit -1))
(define aligned?/width (and (= end-bit 0)
(= (modulo start-bit 8) 7)
(quotient fld-bit-width 8)))
(case aligned?/width
[(2 4)
`(integer->integer-bytes ,val
,aligned?/width
#f
(system-big-endian?)
rv
,start-byte)]
[else
(define the-byte (+ start-byte (quotient end-bit 8)))
`(bytes-set! rv
,the-byte
(bitwise-ior (arithmetic-shift (bitwise-bit-field ,val 0 ,fld-bit-width)
,(modulo end-bit 8))
(bytes-ref rv ,the-byte)))])))))
#`(begin
(struct id fld-ids #:mutable)
(define (bytes->id bs)
fld-setters)
(define (id->bytes art-in)
(match-define (id #,@#'fld-ids) art-in)
(define rv (make-bytes (* word-size #,(quotient bits/word 8))))
set-fields-bits
rv))))]))</lang>
test-ascii-art-reader.rkt
<lang racket>#lang racket
(require "ascii-art-reader.rkt")
(require "ascii-art-parser.rkt")
(require tests/eli-tester)
(define rfc-1035-header-art
#<<EOS
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ EOS
)
(define-values (rslt rslt-b/w) (ascii-art->struct rfc-1035-header-art))
(test
rslt-b/w => 16 rslt => '((0 15 0 ID) (1 15 15 QR) (1 14 11 Opcode) (1 10 10 AA) (1 9 9 TC) (1 8 8 RD) (1 7 7 RA) (1 6 4 Z) (1 3 0 RCODE) (2 15 0 QDCOUNT) (3 15 0 ANCOUNT) (4 15 0 NSCOUNT) (5 15 0 ARCOUNT)))
(define-ascii-art-structure rfc-1035-header #<<EOS +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ EOS
)
(define h-bytes
(bytes-append (integer->integer-bytes #x1234 2 #f) (integer->integer-bytes #x5678 2 #f) (integer->integer-bytes #x9abc 2 #f) (integer->integer-bytes #xdef0 2 #f) (integer->integer-bytes #xfedc 2 #f) (integer->integer-bytes #xba98 2 #f)))
(define h-bytes~
(bytes-append (integer->integer-bytes #x1234 2 #f (not (system-big-endian?))) (integer->integer-bytes #x5678 2 #f (not (system-big-endian?))) (integer->integer-bytes #x9abc 2 #f (not (system-big-endian?))) (integer->integer-bytes #xdef0 2 #f (not (system-big-endian?))) (integer->integer-bytes #xfedc 2 #f (not (system-big-endian?))) (integer->integer-bytes #xba98 2 #f (not (system-big-endian?)))))
(define h (bytes->rfc-1035-header h-bytes)) (define bytes-h (rfc-1035-header->bytes h))
(define h~ (bytes->rfc-1035-header h-bytes~)) (define bytes-h~ (rfc-1035-header->bytes h~))
(test
(rfc-1035-header-ID h) => #x1234 (rfc-1035-header-ARCOUNT h) => #xBA98 (rfc-1035-header-RCODE h) => 8 (rfc-1035-header-ID h~) => #x3412 (rfc-1035-header-ARCOUNT h~) => #x98BA (rfc-1035-header-RCODE h~) => 6 h-bytes => bytes-h h-bytes~ => bytes-h~)
(set-rfc-1035-header-RA! h 0)
(set-rfc-1035-header-Z! h 7) (test
(rfc-1035-header-Z (bytes->rfc-1035-header (rfc-1035-header->bytes h))) => 7 (rfc-1035-header-RA (bytes->rfc-1035-header (rfc-1035-header->bytes h))) => 0)
(set-rfc-1035-header-Z! h 15) ;; naughty -- might splat RA (test
(rfc-1035-header-Z (bytes->rfc-1035-header (rfc-1035-header->bytes h))) => 7 (rfc-1035-header-RA (bytes->rfc-1035-header (rfc-1035-header->bytes h))) => 0)</lang>
- Output:
Nothing much to see... all tests pass
REXX
<lang rexx>/*REXX pgm intreprets an ASCII art diagram for names & their bit length.*/ numeric digits 100 /*be able to handle large numbers*/ parse arg iFID test . /*optional input─FID & test─data.*/ if iFID== | iFID==',' then iFID= 'ASCIIART.TXT' /*use default iFID*/ if test== | test==',' then test= 'cafe8050800000808080000a' /*data.*/ e = '***error*** illegal input txt' /*literal used for error messages*/ w=0; wb=0; !.=0; $= /*W (max width name), bits, names*/ p.=0; p.0=1 /*P.α is structure bit position.*/
/* [↓] read the input text file.*/ do j=1 while lines(iFID)\==0; q=linein(iFID); say '═════text='q q=strip(q) /*strip leading & trailing blanks*/ _L=left(q,1); _R=right(q,1) /*get extreme left & right chars.*/ if q== then iterate /*skip if this is a blank record.*/
if _L=='+' then do /*is this record an "in-between"?*/
if verify(q,'+-')\==0 then say e '(invalid grid):' q
iterate /*skip this record, it's a "+". */
end
if _L\=='|' | _R\=='|' then do; say e '(boundry): ' q; iterate; end
do until q=='|' /* [↓] parse record for names. */
parse var q '|' n '|' -1 q; x=n; n=strip(n); w=max(w,length(n))
if n== then leave /*N is null? We're done scanning*/
if words(n)\==1 then do; say e'(invalid name): ' n; iterate j; end
/* [↑] add more name validations*/
$$=$; nn=n; upper $$ nn /*N can be a mixed─case name. */
if wordpos(nn,$$)\==0 then do; say e '(dup name):' n; iterate j; end
$=$ n /*add the N (name) to the $ list.*/
#=words($); !.#=(length(x)+1)%3 /*assign the number of bits for N*/
wb=max(wb, !.#) /*find the maximum number of bits*/
prev=#-1 /*# names previous to this name. */
p.#= p.prev + !.prev /*calculate the structure bit pos*/
end /*until q==···*/
end /*j*/
if j==1 then do; say e '(file not found): ' iFID; exit 12; end say
do k=1 for words($)
say right(word($,k),w)right(!.k,4) "bits, bit position:"right(p.k,5)
end /*k*/
say /* [↓] Any (hex) data to test? */ if test== then exit /*stick a fork in it, we're done.*/ bits=x2b(test); L=length(test) /*convert test data to a bit str.*/ wm=length(x2d(b2x(copies(1,wb)))) + 1 /*used for displaying maximum #s.*/ say 'test (hex)=' test " length="L 'hexadecimal digits.' say
do r=1 by 8+8 to L*4 _1=substr(bits,r,8,0); _2=substr(bits,r+8,8,0) say 'test (bit)=' _1 _2 ' hex=' b2x(_1) b2x(_2) end /*r*/
say
do m=1 for words($) /* [↓] show hex str in lowercase*/
_=translate( b2x(substr(bits,p.m,!.m)), 'abcdef', "ABCDEF" )
say right(word($,m),w+2) ' decimal='right(x2d(_),wm) ' hex=' _
end /*m*/
/*stick a fork in it, we're done.*/</lang>
output when using the default input file:
═════text=
═════text=
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text= | ID |
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text= |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text= | QDCOUNT |
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text= | ANCOUNT |
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text= | NSCOUNT |
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text= | ARCOUNT |
═════text= +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
═════text=
═════text=
ID 16 bits, bit position: 1
QR 1 bits, bit position: 17
Opcode 4 bits, bit position: 18
AA 1 bits, bit position: 22
TC 1 bits, bit position: 23
RD 1 bits, bit position: 24
RA 1 bits, bit position: 25
Z 3 bits, bit position: 26
RCODE 4 bits, bit position: 29
QDCOUNT 16 bits, bit position: 33
ANCOUNT 16 bits, bit position: 49
NSCOUNT 16 bits, bit position: 65
ARCOUNT 16 bits, bit position: 81
test (hex)= cafe8050800000808080000a length=24 hexadecimal digits.
test (bit)= 11001010 11111110 hex= CA FE
test (bit)= 10000000 01010000 hex= 80 50
test (bit)= 10000000 00000000 hex= 80 00
test (bit)= 00000000 10000000 hex= 00 80
test (bit)= 10000000 10000000 hex= 80 80
test (bit)= 00000000 00001010 hex= 00 0A
ID decimal= 51966 hex= cafe
QR decimal= 1 hex= 1
Opcode decimal= 0 hex= 0
AA decimal= 0 hex= 0
TC decimal= 0 hex= 0
RD decimal= 0 hex= 0
RA decimal= 0 hex= 0
Z decimal= 5 hex= 5
RCODE decimal= 0 hex= 0
QDCOUNT decimal= 32768 hex= 8000
ANCOUNT decimal= 128 hex= 0080
NSCOUNT decimal= 32896 hex= 8080
ARCOUNT decimal= 10 hex= 000a
Tcl
This is a nice task to illustrate a couple of important concepts in Tcl:
* using dictionaries, taking advantage of their ordering properties * the binary command * using (semi-)structured text as part of your source code
In this implementation, parse produces a dictionary from names to bit-lengths. encode and decode use these to produce appropriate binary format strings, and then do what they say on the tin. As implemented, this is limited to unsigned numeric values in fields. Supporting unsigned values, strings and enums would require parsing a more complex annotation than only the ASCII art packet structure, but ought not take much more code. <lang Tcl> namespace eval asciipacket {
proc assert {expr} { ;# for "static" assertions that throw nice errors
if {![uplevel 1 [list expr $expr]]} {
raise {ASSERT ERROR} "{$expr} {[subst -noc $expr]}"
}
}
proc b2h {data} { ;# format a binary string in hex digits
binary scan $data H* hex; set hex
}
proc parse {s} {
set result {} ;# we will return a dictionary
set s [string trim $s] ;# remove whitespace
set s [split $s \n] ;# split into lines
set s [lmap x $s {string trim $x}] ;# trim whitespace from each line
set s [lassign $s border0] ;# pop off top border row
;# calculate chars per row, chars per bit
set rowlen [llength [string map {+ \ } $border0]]
set bitlen [expr {([string length $border0] - 1) / $rowlen}]
assert {$bitlen * $rowlen + 1 == [string length $border0]}
foreach {row border} $s {
assert {$border eq $border0}
set row [string trim $row |]
foreach field [split $row |] {
set len [string length |$field]
assert {$len % $bitlen == 0}
set name [string trim $field]
set nbits [expr {$len / $bitlen}]
assert {![dict exists $result $name]}
dict set result $name $nbits
}
}
return $result
}
proc encode {schema values} {
set bincodes {1 B 8 c 16 S 32 W} ;# see binary(n)
set binfmt "" ;# format string
set binargs "" ;# positional args
dict for {name bitlen} $schema {
set val [dict get $values $name]
if {[dict exists $bincodes $bitlen]} {
set fmt "[dict get $bincodes $bitlen]"
} else {
set val [format %0${bitlen}b $val]
set fmt "B${bitlen}"
}
append binfmt $fmt
lappend binargs $val
}
binary format $binfmt {*}$binargs
}
proc decode {schema data} {
set result {} ;# we will return a dict
set bincodes {1 B 8 c 16 S 32 W} ;# see binary(n)
set binfmt "" ;# format string
set binargs "" ;# positional args
dict for {name bitlen} $schema {
if {[dict exists $bincodes $bitlen]} {
set fmt "[dict get $bincodes $bitlen]u" ;# note unsigned
} else {
set fmt "B${bitlen}"
}
append binfmt $fmt
lappend binargs $name
}
binary scan $data $binfmt {*}$binargs
foreach _ $binargs {
dict set result $_ [set $_]
}
return $result
}
} </lang> And here is how to use it with the original test data: <lang Tcl> proc test {} {
set header {
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| Opcode |AA|TC|RD|RA| Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
}
set schema [asciipacket::parse $header]
set values {
ID 0xcafe
QR 1
Opcode 5
AA 1
TC 0
RD 0
RA 1
Z 4
RCODE 8
QDCOUNT 0x00a5
ANCOUNT 0x0a50
NSCOUNT 0xa500
ARCOUNT 0x500a
}
set pkt [asciipacket::encode $schema $values]
puts "encoded packet (hex): [asciipacket::b2h $pkt]"
array set decoded [asciipacket::decode $schema $pkt]
parray decoded
} test </lang>
- Output:
encoded packet (hex): cafe805080000080808000a50a50a500500a decoded(AA) = 1 decoded(ANCOUNT) = 2640 decoded(ARCOUNT) = 20490 decoded(ID) = 51966 decoded(NSCOUNT) = 42240 decoded(Opcode) = 0101 decoded(QDCOUNT) = 165 decoded(QR) = 1 decoded(RA) = 1 decoded(RCODE) = 1000 decoded(RD) = 0 decoded(TC) = 0 decoded(Z) = 100