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118 lines
4.7 KiB
Racket
118 lines
4.7 KiB
Racket
#lang debug racket
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(require rackunit)
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(provide (all-defined-out))
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(define (xref-offset bs)
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(match (regexp-match #px"(?<=startxref\n)\\d+" bs)
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[(list val) (read (open-input-bytes val))]
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[_ (error 'no-xref)]))
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(define-syntax (pat-lex stx)
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(syntax-case stx (else)
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[(_ PORT [PAT . REST] ... [else ELSE-CLAUSE])
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(with-syntax ([(REST ...)
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(map (λ (stx) (syntax-case stx ()
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[() #'(=> car)]
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[_ stx])) (syntax->list #'(REST ...)))])
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#'(cond
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[(regexp-try-match (pregexp (string-append "^" PAT)) PORT) . REST] ... [else ELSE-CLAUSE]))]))
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(define (between-delimiters bs left right)
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(parameterize ([current-input-port (if (input-port? bs) bs (open-input-bytes bs))])
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(let loop ([acc null][depth 0])
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(cond
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[(regexp-try-match (pregexp (string-append "^" (regexp-quote (~a left)))) (current-input-port))
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=> (λ (m)
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(loop (if (empty? acc)
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acc ; impliedly throw away first left delimiter
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(cons (car m) acc)) (add1 depth)))]
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[(regexp-try-match (pregexp (string-append "^" (regexp-quote (~a right)))) (current-input-port))
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=> (λ (m)
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(case depth
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[(1) (bytes-append* (reverse acc))]
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[else (loop (cons (car m) acc) (sub1 depth))]))]
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[else
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(define bstr (read-byte))
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(and (not (eof-object? bstr))
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(loop (if (zero? depth)
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acc ; impliedly throw away leading non-delimiter bytes
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(cons (bytes bstr) acc)) depth))]))))
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(module+ test
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(require rackunit)
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(define bs #"a<<b<<c>>x<<z>>d>>e<<f>>g")
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(check-equal? (between-delimiters bs #"<<" #">>") #"b<<c>>x<<z>>d")
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(check-equal? (between-delimiters (between-delimiters bs #"<<" #">>") #"<<" #">>") #"c")
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(check-false (between-delimiters #"abc" #"<<" #">>"))
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(check-equal? (between-delimiters #"[a[b]c]" #"[" #"]") #"a[b]c")
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(check-equal? (let ([ip (open-input-bytes #"<</foo 42>>z")])
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(parse-1 ip)
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(port->bytes ip)) #"z"))
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(define (parse-1 ip)
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(cond
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;; the complication is that arrays & dicts can contain other arrays & dicts
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;; so we have to scan ahead in an intelligent way.
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[(equal? (peek-bytes 1 0 ip) #"[") ;; array
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(parse-pdf-bytes (between-delimiters ip #"[" #"]"))]
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[(equal? (peek-bytes 2 0 ip) #"<<") ;; dict, maybe with stream
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(define items (parse-pdf-bytes (between-delimiters ip #"<<" #">>")))
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(unless (even? (length items)) (raise items))
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(define dic
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(sort ; put hash into order so it's comparable
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(for/list ([kv (in-slice 2 items)]
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;; suppress these keys so we can compare pdfkit & pitfall output
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#:unless (member (car kv) (list #"/Producer" #"/Creator" #"/CreationDate")))
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(apply cons kv))
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bytes<?
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#:key car))
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(cond
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[(regexp-try-match #px"^\\s*stream\n" ip)
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(define stream-length
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(read (open-input-bytes (cdr (assoc #"/Length" dic)))))
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(define stream (read-bytes stream-length ip))
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(append dic (list (cons 'stream stream)))]
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[else dic])]
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[else
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(pat-lex ip
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["\\s+" (parse-1 ip)] ; whitespace
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["\\d+ 0 obj" (parse-1 ip)] ;; obj name
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["\\d+ 0 R"] ; xref
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["[-]?\\d+"] ; number
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["\\(.*?\\)"] ; parenstring
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["/\\S+"] ; keystring
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[else eof])]))
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(define (parse-pdf-bytes bs)
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(for/list ([tok (in-port parse-1 (open-input-bytes bs))])
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tok))
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(define (pdf->dict pdf)
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(define pdf-bs (file->bytes pdf))
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(define xoff (xref-offset pdf-bs))
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(define xref-ip (open-input-bytes (subbytes pdf-bs (+ xoff (bytes-length #"xref\n0")))))
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(define ref-count (read xref-ip))
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(define obj-locations
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(append
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(sort ; sort by byte offset
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(cdr ; drop zeroth record: there is no zeroth object
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(for/list ([i (in-range ref-count)])
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(cons i (read (open-input-bytes (car (regexp-match #px"\\d{10}" xref-ip)))))))
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< #:key cdr)
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(list (cons #f xoff))))
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(sort ; sort by index
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(parameterize ([current-input-port (open-input-bytes pdf-bs)])
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(for/list ([(idx start) (in-dict obj-locations)]
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[(_ end) (in-dict (cdr obj-locations))])
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(cons idx (parse-pdf-bytes (peek-bytes (- end start) start)))))
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< #:key car))
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(define-simple-check (check-pdfs-equal? ps1 ps2)
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(equal? (pdf->dict ps1) (pdf->dict ps2)))
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#;(module+ main
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(for ([p (in-directory)]
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#:when (path-has-extension? p #"pdf"))
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(with-handlers ([exn:fail? (λ (exn) (println (format "~a failed" p)))])
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(pdf->dict p))))
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