commit 70053d655f13f7ecbea5789cf4ea505bfce21f75 from: Pompolic date: Wed May 20 15:18:43 2020 UTC Merge branch 'master' of gitlab.special-circumstanc.es:pesco/pdf commit - 162e65e85fe6ac42d796fa3ce4fc19c237777069 commit + 70053d655f13f7ecbea5789cf4ea505bfce21f75 blob - eae25e8a2040dec85d1ccbea20d0597990b0970a blob + 70321e71d3a5794d35fdb53f91189589073b3d02 --- TODO +++ TODO @@ -1,8 +1,91 @@ - - move main routine(s) into separate source file. - - move filter implementation(s) into separate source file. + - fix the object stream parser to split input at logical boundaries, as + provided by the object index ("N pairs of integers") at the beginning of the + stream data. - - investigate memory use on big documents (millions of objects). + this follows discussion with peter wyatt where he initially said that the + objects should be delimited by normal PDF token rules, but PDFA then came + to the conclusion that, in fact, this was a mistake and the logical + begin/end info should delimit things. i.e. if your index says that an object + begins at offset 0 and ends at offset 3, followed by one that ends at 6, and + the input is "123456", this parses as two numbers, 123 and 456. + currently the code follows the incorrect former approach, (re-) using the + "elemr" parser that is otherwise used with arrays. the above example would + parse as one element, the number 123456, in contradiction to the index + (which we parse but ignore). + + we have to explicitly walk the index, run our "obj" parser on each + respective snippet of input, and wrap the results up in a parse result. we + should also validate conditions on the index beforehand. these are + thankfully sane (monotonic offsets etc.) and mentioned in the spec. + + - move main routine(s) and filter implementation(s) into separate source + files. e.g.: + - main.c: main function and helpers; starting from its include block + - pdf.c: parser proper; grammar and basic semantic actions + - filter.c: filters + - maybe another file just for xref or stream stuff? + + - refactor / clean up the (ascii) filter implementations. + + - rework VIOL to produce a "violation" token in the AST (via h_action). then, + a validation (h_attr_bool) should let the parse fail if applicable (severity + vs. strictness). non-fatal violations should be extracted and printed to + stderr after the parse. + - somehow rid VIOL() of the internal parser for getting at the severity + parameter. this is, i guess, an artefact of h_action() taking a single void + pointer of context, so it was not trivial to pass two arguments (message and + severity) to the action. + + - (maybe?) change stream parsing to just stop at "endstream endobj" when + /Length is indirect and the filter or postordinate parser doesn't delimit + itself. this is not strictly to-spec, but probably an OK restriction to make + in practice. a consistency checks can be made against the length after all + objects have been parsed. + + note: the current design aims to follow the spec to the letter in that the + /Length entry of a stream determines its length, and nothing else. from this + it follows that we must find and parse these lengths in "island style". + thus, the current code is a hybrid of linear and island parsing. if the + reliance on /Length can be broken, the island-based resolver can go and we + can have a proper split between two separate parsers - one pure linear and + one pure island. + + - parse and print content streams. + - parse/validate additional stream types/filters (images...). + + - consider reviving the effort to get "obj" to parse with LALR. the messy + grammar for arrays with "elemd", "elemr", etc. still stems from project, as + does the explicit handling of whitespace -- note that TOK() is only used in + KW() and that no instances of KW() remain under "obj". + + alternatively, consider fully reverting the grammar to its clearer PEG form. + i would probably keep the explicit whitespace, though. + + what stopped me before was the difficulty to resolve some things without + precedence rules; specifically line endings in string literals. + is a "crlf" or a "cr" followed by an "lf"? LALR cannot decide + unless you encode that anything following a "cr" doesn't start with . + string literals are currently defined differently. the best way to do it, + AFAICS, would be to match (in string literals) all subsequent line endings + in one nonterminal and to encode there that a plain "cr" is never followed + by "lf". + + FWIW, the motivation for LALR parsing of "obj" was the prospect of parsing + an object stream incrementally, as chunks come in from the decompressor + (or an arbitrary filter chain). + + NB: the reason why we must distinguish "crlf" from "cr" "lf" at all is of + course that in a string literal, the former means "\n" and the latter means + "\n\n". + + - implement random-access ("island") parser (walking objects from /Root). + i'm not sure how much we need to know about the "DOM" for this. maybe + nothing? since everything is built out of basic objects and we can just + blindly follow references? + - check linear and random-access parses for consistency. + + - replace disparate parsing routines (applied to different pieces of input) with one big HParser that uses h_seek() to move around. this will enable packrat to cache, for instance, the xref tables instead of us parsing them @@ -11,19 +94,10 @@ - parse stream objects without reference to their /Length entry by simply trying all possible ways and consistency-checking them against the xref table in the end, via h_attr_bool(). + XXX is this actually possible (without unreasonable complications)? - - include position information, at least for objects, in the (JSON) output. - - format warnings/errors (stderr) as JSON, too. + - investigate memory use on big documents (millions of objects). - - make custom token types for all appropriate parts of the parse result. - - - parse content streams. - - - implement random-access parser (walking objects from /Root). - - check linear and random-access parses for consistency. - - - handle garbage before %PDF- and after %%EOF - - handle garbage at other points in the input? - - - add ASCII filter types. - - add LZW filter. + - make custom token types for all appropriate parts of the parse result so + that they can be properly distinguished in the output. + - include position information, at least for objects, in the (JSON) output.