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.
Perl 6
<lang perl6>grammar RFC1025 {
rule TOP { <.line-separator> [<line> <.line-separator>]+ } rule line-separator { <.ws> '+--'+ '+' } token line { <.ws> '|' +%% <field> } token field { \s* <label> \s* } token label { \w+[\s+\w+]* }
}
sub bits ($item) { ($item.chars + 1) div 3 }
sub deconstruct ($bits, %struct) {
map { $bits.substr(.<from>, .<bits>) }, @(%struct<fields>);
}
sub interpret ($header) {
my $datagram = RFC1025.parse($header); my %struct; for $datagram.<line> -> $line { FIRST %struct<line-width> = $line.&bits; state $from = 0; %struct<fields>.push: %(:bits(.&bits), :ID(.<label>.Str), :from($from.clone), :to(($from+=.&bits)-1)) for $line<field>; } %struct
}
use experimental :pack;
my $diagram = q:to/END/;
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
END
my %structure = interpret($diagram);
say 'Line width: ', %structure<line-width>, ' bits'; printf("Name: %7s, bit count: %2d, bit %2d to bit %2d\n", .<ID>, .<bits>, .<from>, .<to>) for @(%structure<fields>); say "\nGenerate a random 12 byte \"header\""; say my $buf = Buf.new((^0xFF .roll) xx 12); say "\nShow it converted to a bit string"; say my $bitstr = $buf.unpack('C*')».fmt("%08b").join; say "\nAnd unpack it"; printf("%7s, %02d bits: %s\n", %structure<fields>[$_]<ID>, %structure<fields>[$_]<bits>,
deconstruct($bitstr, %structure)[$_]) for ^@(%structure<fields>);</lang>
- Output:
Line width: 16 bits Name: ID, bit count: 16, bit 0 to bit 15 Name: QR, bit count: 1, bit 16 to bit 16 Name: Opcode, bit count: 4, bit 17 to bit 20 Name: AA, bit count: 1, bit 21 to bit 21 Name: TC, bit count: 1, bit 22 to bit 22 Name: RD, bit count: 1, bit 23 to bit 23 Name: RA, bit count: 1, bit 24 to bit 24 Name: Z, bit count: 3, bit 25 to bit 27 Name: RCODE, bit count: 4, bit 28 to bit 31 Name: QDCOUNT, bit count: 16, bit 32 to bit 47 Name: ANCOUNT, bit count: 16, bit 48 to bit 63 Name: NSCOUNT, bit count: 16, bit 64 to bit 79 Name: ARCOUNT, bit count: 16, bit 80 to bit 95 Generate a random 12 byte "header" Buf:0x<78 47 7b bf 54 96 e1 2e 1b f1 69 a4> Show it converted to a bit string 011110000100011101111011101111110101010010010110111000010010111000011011111100010110100110100100 And unpack it ID, 16 bits: 0111100001000111 QR, 01 bits: 0 Opcode, 04 bits: 1111 AA, 01 bits: 0 TC, 01 bits: 1 RD, 01 bits: 1 RA, 01 bits: 1 Z, 03 bits: 011 RCODE, 04 bits: 1111 QDCOUNT, 16 bits: 0101010010010110 ANCOUNT, 16 bits: 1110000100101110 NSCOUNT, 16 bits: 0001101111110001 ARCOUNT, 16 bits: 0110100110100100
Phix
Should work on any width, but didn't actually test, or verify width is 8/16/32/64. <lang Phix>function interpret(sequence lines)
if remainder(length(lines),2)!=1 then crash("missing header/footer?") end if string l1 = lines[1] integer w = length(l1) -- sug: check this is 8/16/32/64 integer bits = (w-1)/3 if l1!=join(repeat("+",bits+1),"--") then crash("malformed header?") end if sequence res = {} integer offset = 0 for i=1 to length(lines) do string li = lines[i] if remainder(i,2) then if li!=l1 then crash("missing separator (line %d)?",{i}) end if else if li[1]!='|' or li[w]!='|' then crash("missing separator on line %d",{i}) end if integer k = 1 while true do integer l = find('|',li,k+1) string desc = trim(li[k+1..l-1]) {k,l} = {l,(l-k)/3} res = append(res,{desc,l,offset}) offset += l if k=w then exit end if end while end if end for res = append(res,{"total",0,offset}) return res
end function
procedure unpack(string data, sequence res)
if length(data)*8!=res[$][3] then crash("wrong length") end if string bin = "" for i=1 to length(data) do bin &= sprintf("%08b",data[i]) end for printf(1,"\n\nTest bit string:\n%s\n\nUnpacked:\n",{bin}) for i=1 to length(res)-1 do {string name, integer bits, integer offset} = res[i] printf(1,"%7s, %02d bits: %s\n",{name,bits,bin[offset+1..offset+bits]}) end for
end procedure
function trimskip(string diagram) -- -- split's ",no_empty:=true)" is not quite enough here. -- Note that if copy/paste slips in any tab characters, -- it will most likely trigger a length mismatch error. --
sequence lines = split(diagram,'\n') integer prevlli = 0 for i=length(lines) to 1 by -1 do string li = trim(lines[i]) integer lli = length(li) if lli then if prevlli=0 then prevlli = lli elsif lli!=prevlli then crash("mismatching lengths") end if lines[i] = li else lines[i..i] = {} end if end for return lines
end function
constant diagram = """
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ID | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ |QR| Opcode |AA|TC|RD|RA| Z | RCODE | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | QDCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ANCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | NSCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ | ARCOUNT | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
"""
sequence lines = trimskip(diagram) sequence res = interpret(lines) printf(1,"--Name-- Size Offset\n") for i=1 to length(res) do
printf(1," %-7s %2d %5d\n",res[i])
end for
unpack(x"78477bbf5496e12e1bf169a4",res)</lang>
- Output:
--Name-- Size Offset ID 16 0 QR 1 16 Opcode 4 17 AA 1 21 TC 1 22 RD 1 23 RA 1 24 Z 3 25 RCODE 4 28 QDCOUNT 16 32 ANCOUNT 16 48 NSCOUNT 16 64 ARCOUNT 16 80 total 0 96 Test bit string: 011110000100011101111011101111110101010010010110111000010010111000011011111100010110100110100100 Unpacked: ID, 16 bits: 0111100001000111 QR, 01 bits: 0 Opcode, 04 bits: 1111 AA, 01 bits: 0 TC, 01 bits: 1 RD, 01 bits: 1 RA, 01 bits: 1 Z, 03 bits: 011 RCODE, 04 bits: 1111 QDCOUNT, 16 bits: 0101010010010110 ANCOUNT, 16 bits: 1110000100101110 NSCOUNT, 16 bits: 0001101111110001 ARCOUNT, 16 bits: 0110100110100100
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-structure
which 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
Some code was added to validate the input file. <lang rexx>/*REXX program intreprets an ASCII art diagram for names and their bit length(s). */ numeric digits 100 /*be able to handle large numbers. */ parse arg iFID test . /*obtain optional input─FID & test─data*/ if iFID== | iFID=="," then iFID= 'ASCIIART.TXT' /*use the default iFID.*/ if test== | test=="," then test= 'cafe8050800000808080000a' /* " " " data.*/ e = '***error*** illegal input txt' /*a 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 and trailing blanks. */ _L=left(q, 1); _R=right(q, 1) /*get extreme left and right characters*/ 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 single "+". */ end
if _L\=='|' | _R\=="|" then do; say e '(boundry): ' q; iterate; end
do until q=='|' /* [↓] parse a record for names. */ parse var q '|' n "|" -1 q; x=n; n=strip(n); w=max(w, length(n)) if n== then leave /*Is N null? We're done scanning. */ if words(n)\==1 then do; say e'(invalid name): ' n; iterate j; end /* [↑] add more name validations. */ $$=$; nn=n; upper $$ n /*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($); !.#= (length(x) + 1) % 3 /*assign the number of bits for N. */ wb=max(wb, !.#) /*find the maximum number of bits. */ prev= # - 1 /*number of names previous to this name*/ p.#= p.prev + !.prev /*calculate the structure bit position.*/ end /*until*/ end /*j*/
if j==1 then do; say e '(file not found): ' iFID; exit 12; end say
do k=1 for words($) say right( word($, k), w)right(!.k, 4) "bits, bit position:"right(p.k, 5) end /*k*/
say /* [↓] Any (hex) data to test? */ if test== then exit /*stick a fork in it, we're all done. */ bits=x2b(test); L=length(test) /*convert test data to a bit string. */ wm=length( x2d( b2x( copies(1, wb) ) ) ) + 1 /*used for displaying maximum numbers. */ say 'test (hex)=' test " length="L 'hexadecimal digits.' say
do r=1 by 8+8 to L*4 _1=substr(bits, r, 8, 0); _2=substr(bits, r+8, 8, 0) say 'test (bit)=' _1 _2 " hex=" b2x(_1) b2x(_2) end /*r*/
say
do m=1 for words($) /* [↓] display hex string 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 all done. */</lang>
- output when using the default input:
■■■■■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
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