Lexer pdf

This may be a big difference for a human, but it is no different for a correctly implemented PDF lexer! Over the years, the wording of the Character set clause clause 7. When considered logically and based on a detailed reading of the full PDF specification, any adjacent pair of PDF tokens may or may not require whitespace as the token delimiter. This will depend on the specific rules for the characters bytes that comprise each token, and whether a specific delimiter character can be included or not.

A key point is that PDF does NOT always require whitespace between tokens and that various special characters are defined to be explicit token delimiters. However other characters are often not handled correctly as token delimiters, especially if they are context-dependent on the prior token. And this can lead to parser differentials, non-interoperable PDFs, or worse - parser crashes. The matrix document describes the possible token pairings.

This illustrates that in some cases multiple characters bytes can be used as the first character in a token, creating even more combinations of adjacent character pairings. Thus there are 3 test cases for when a PDF real number is the second token. This creates multiple adjacent compacted character pairings that are all valid token pairings after, for example, a PDF array end token ] :.

An analysis of the parsed token stream and confirmation of the constructed PDF objects against the test PDF file is required. By ensuring that all PDF lexers are fully and correctly implemented against the PDF standard, document interoperability, reliability and product robustness are improved.

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author s and do not necessarily reflect the views of the Defense Advanced Research Projects Agency DARPA. Approved for public release. I have read and agree to the Privacy Policy. This involves correctly processing all PDF token delimiters and whitespace characters so that the logical sequence of tokens representing keywords, literals, identifiers and PDF objects can then be processed downstream by the parser If a lexer is not correct, then a PDF parser will either see a meaningless jumble of tokens that it does not understand and PDF processing will fail, or possibly a valid but entirely different sequence of tokens than the PDF writing software intended.

This creates multiple adjacent compacted character pairings that are all valid token pairings after, for example, a PDF array end token ] : ] Peter Wyatt. News Events Resources. Communities Members About us. First name. Last Name. Email address I have read and agree to the Privacy Policy. Some chunks. The actual encoding depends on the. Therefore the bytes are 'raw encoded' into characters,. Length ;. ReadByte ;. If the token starts with a digit, the parameter.

If it is false, the lexer scans for a single integer. If it is a reference,. Again :. ScanComment ;. IsWhiteSpace nextChar. ScanNextChar true ;. BeginArray ;. EndArray ;. BeginDictionary ;. EndDictionary ;. IsDigit ch. IsLetter ch. Eof ;. HandleUnexpectedCharacter ch ;. None ;. Read bytes , 0 , length ;. Resize ref bytes , read ;. GetString bytes , 0 , bytes. Percent ;. Comment ;. Slash ;. Name ;. Parse new string hex , NumberStyles.

AllowHexSpecifier ;. It is neither an integer nor a real. Append ch ;. ThrowParserException " More than one period in number. Real ;. ToString , CultureInfo. InvariantCulture ;. Integer ;. UInteger ;. Obj ;. EndObj ;. Null ;. Boolean ;. BeginStream ;. EndStream ;. XRef ;. Trailer ;. StartXRef ;. Samples are f or n in iref. Keyword ;. ParenLeft ;.