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7980722f55
Even though I wrote them, I keep forgetting their semantics. In particular I can never quite remember off the top of my head whether they modify their input command line, or allocate it fresh. To make that clearer, I've made it a const parameter. (That means the output argstart pointers have the same awkward const -> mutable conversion as strchr - but then, strchr is itself precedent for that being the usual way to not-quite-handle that annoyance in C!)
322 lines
12 KiB
C
322 lines
12 KiB
C
/*
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* Split a complete command line into argc/argv, attempting to do it
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* exactly the same way the Visual Studio C library would do it (so
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* that our console utilities, which receive argc and argv already
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* broken apart by the C library, will have their command lines
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* processed in the same way as the GUI utilities which get a whole
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* command line and must call this function).
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*
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* Does not modify the input command line.
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*
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* The final parameter (argstart) is used to return a second array
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* of char * pointers, the same length as argv, each one pointing
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* at the start of the corresponding element of argv in the
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* original command line. So if you get half way through processing
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* your command line in argc/argv form and then decide you want to
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* treat the rest as a raw string, you can. If you don't want to,
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* `argstart' can be safely left NULL.
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*/
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#include "putty.h"
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/*
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* The precise argument-breaking rules vary with compiler version, or
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* rather, with the crt0-type startup code that comes with each
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* compiler's C library. We do our best to match the compiler version,
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* so that we faithfully imitate in our GUI utilities what the
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* corresponding set of CLI utilities can't be prevented from doing.
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*
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* The basic rules are:
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*
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* - Single quotes are not special characters.
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*
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* - Double quotes are removed, but within them spaces cease to be
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* special.
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*
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* - Backslashes are _only_ special when a sequence of them appear
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* just before a double quote. In this situation, they are treated
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* like C backslashes: so \" just gives a literal quote, \\" gives
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* a literal backslash and then opens or closes a double-quoted
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* segment, \\\" gives a literal backslash and then a literal
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* quote, \\\\" gives two literal backslashes and then opens/closes
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* a double-quoted segment, and so forth. Note that this behaviour
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* is identical inside and outside double quotes.
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*
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* - Two successive double quotes become one literal double quote,
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* but only _inside_ a double-quoted segment. Outside, they just
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* form an empty double-quoted segment (which may cause an empty
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* argument word).
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*
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* That only leaves the interesting question of what happens when one
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* or more backslashes precedes two or more double quotes, starting
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* inside a double-quoted string.
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*
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* Modern Visual Studio (as of 2021)
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* ---------------------------------
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*
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* I investigated this in an ordinary CLI program, using the
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* toolchain's crt0 to split a command line of the form
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*
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* "a\\\"""b c" d
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*
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* Here I tabulate number of backslashes (across the top) against
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* number of quotes (down the left), and indicate how many backslashes
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* are output, how many quotes are output, and whether a quoted
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* segment is open at the end of the sequence:
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*
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* backslashes
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*
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* 0 1 2 3 4
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*
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* 0 0,0,y | 1,0,y 2,0,y 3,0,y 4,0,y
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* --------+-----------------------------
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* 1 0,0,n | 0,1,y 1,0,n 1,1,y 2,0,n
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* q 2 0,1,y | 0,1,n 1,1,y 1,1,n 2,1,y
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* u 3 0,1,n | 0,2,y 1,1,n 1,2,y 2,1,n
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* o 4 0,2,y | 0,2,n 1,2,y 1,2,n 2,2,y
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* t 5 0,2,n | 0,3,y 1,2,n 1,3,y 2,2,n
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* e 6 0,3,y | 0,3,n 1,3,y 1,3,n 2,3,y
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* s 7 0,3,n | 0,4,y 1,3,n 1,4,y 2,3,n
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* 8 0,4,y | 0,4,n 1,4,y 1,4,n 2,4,y
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*
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* The row at the top of this table, with quotes=0, demonstrates what
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* I claimed above, that when a sequence of backslashes are not
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* followed by a double quote, they don't act specially at all. The
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* rest of the table shows that the backslashes escape each other in
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* pairs (so that with 2n or 2n+1 input backslashes you get n output
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* ones); if there's an odd number of input backslashes then the last
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* one escapes the first double quote (so you get a literal quote and
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* enter a quoted string); thereafter, each input quote character
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* either opens or closes a quoted string, and if it closes one, it
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* generates a literal " as a side effect.
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*
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* Older Visual Studio
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* -------------------
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*
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* But here's the corresponding table from the older Visual Studio 7:
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*
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* backslashes
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*
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* 0 1 2 3 4
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*
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* 0 0,0,y | 1,0,y 2,0,y 3,0,y 4,0,y
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* --------+-----------------------------
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* 1 0,0,n | 0,1,y 1,0,n 1,1,y 2,0,n
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* q 2 0,1,n | 0,1,n 1,1,n 1,1,n 2,1,n
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* u 3 0,1,y | 0,2,n 1,1,y 1,2,n 2,1,y
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* o 4 0,1,n | 0,2,y 1,1,n 1,2,y 2,1,n
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* t 5 0,2,n | 0,2,n 1,2,n 1,2,n 2,2,n
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* e 6 0,2,y | 0,3,n 1,2,y 1,3,n 2,2,y
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* s 7 0,2,n | 0,3,y 1,2,n 1,3,y 2,2,n
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* 8 0,3,n | 0,3,n 1,3,n 1,3,n 2,3,n
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* 9 0,3,y | 0,4,n 1,3,y 1,4,n 2,3,y
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* 10 0,3,n | 0,4,y 1,3,n 1,4,y 2,3,n
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* 11 0,4,n | 0,4,n 1,4,n 1,4,n 2,4,n
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*
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* There is very weird mod-3 behaviour going on here in the number of
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* quotes, and it even applies when there aren't any backslashes! How
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* ghastly.
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*
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* With a bit of thought, this extremely odd diagram suddenly
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* coalesced itself into a coherent, if still ghastly, model of how
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* things work:
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*
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* - As before, backslashes are only special when one or more of them
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* appear contiguously before at least one double quote. In this
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* situation the backslashes do exactly what you'd expect: each one
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* quotes the next thing in front of it, so you end up with n/2
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* literal backslashes (if n is even) or (n-1)/2 literal
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* backslashes and a literal quote (if n is odd). In the latter
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* case the double quote character right after the backslashes is
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* used up.
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*
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* - After that, any remaining double quotes are processed. A string
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* of contiguous unescaped double quotes has a mod-3 behaviour:
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*
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* * inside a quoted segment, a quote ends the segment.
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* * _immediately_ after ending a quoted segment, a quote simply
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* produces a literal quote.
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* * otherwise, outside a quoted segment, a quote begins a quoted
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* segment.
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*
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* So, for example, if we started inside a quoted segment then two
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* contiguous quotes would close the segment and produce a literal
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* quote; three would close the segment, produce a literal quote,
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* and open a new segment. If we started outside a quoted segment,
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* then two contiguous quotes would open and then close a segment,
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* producing no output (but potentially creating a zero-length
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* argument); but three quotes would open and close a segment and
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* then produce a literal quote.
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*
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* I don't know exactly when the bug fix happened, but I know that VS7
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* had the odd mod-3 behaviour. So the #if below will ensure that
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* modern (2015 onwards) versions of VS use the new more sensible
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* behaviour, and VS7 uses the old one. Things in between may be
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* wrong; if anyone cares, patches to change the cutoff version in
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* this #if are welcome.
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*/
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#if _MSC_VER < 1400
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#define MOD3 1
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#else
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#define MOD3 0
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#endif
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#ifdef SPLIT_INTO_ARGV_W
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#define FUNCTION split_into_argv_w
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#define CHAR wchar_t
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#define STRLEN wcslen
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#else
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#define FUNCTION split_into_argv
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#define CHAR char
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#define STRLEN strlen
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#endif
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static inline bool is_word_sep(CHAR c)
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{
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return c == ' ' || c == '\t';
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}
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void FUNCTION(const CHAR *cmdline, bool includes_program_name,
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int *argc, CHAR ***argv, CHAR ***argstart)
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{
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const CHAR *p;
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CHAR *outputline, *q;
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CHAR **outputargv, **outputargstart;
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int outputargc;
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/*
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* First deal with the simplest of all special cases: if there
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* aren't any arguments, return 0,NULL,NULL.
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*/
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while (*cmdline && is_word_sep(*cmdline)) cmdline++;
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if (!*cmdline) {
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if (argc) *argc = 0;
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if (argv) *argv = NULL;
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if (argstart) *argstart = NULL;
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return;
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}
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/*
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* This will guaranteeably be big enough; we can realloc it
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* down later.
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*/
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{
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size_t len = STRLEN(cmdline);
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outputline = snewn(1+len, CHAR);
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outputargv = snewn((len+1) / 2, CHAR *);
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outputargstart = snewn((len+1) / 2, CHAR *);
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}
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p = cmdline; q = outputline; outputargc = 0;
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while (*p) {
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bool quote;
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/* Skip whitespace searching for start of argument. */
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while (*p && is_word_sep(*p)) p++;
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if (!*p) break;
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/*
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* Check if this argument is the program name. If so,
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* different rules apply.
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*
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* In most arguments, the special characters are the double
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* quote and the backslash. An exception is the program name
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* at the start of the command line, in which backslashes are
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* _not_ special - if one appears before a quote, it does not
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* make the quote literal.
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*
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* The C library must implement this special rule, and we must
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* follow suit here, in order to match the way CreateProcess
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* scans the command line to determine the program name. It
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* will consider that all these commands refer to the same
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* file equally validly:
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*
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* "C:\Program Files\Foo"\bar.exe
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* "C:\Program Files\Foo\"bar.exe
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* "C:\Program Files\Foo\bar.exe"
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*
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* Each one contains a quoted section that protects the space
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* in "Program Files", and the closing quote takes effect the
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* same in all cases - even though, in the middle case, it's
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* immediately preceded by one of the path separators in the
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* name. For CreateProcess, backslashes aren't special.
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*
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* So, if our caller told us that the input command line
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* includes the program name (which it does if it came from
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* GetCommandLine, but not if it was passed in to WinMain),
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* then we must treat the 0th output argument specially, by
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* not considering backslashes to affect the quoting.
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*/
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bool backslash_special = !(outputargc == 0 && includes_program_name);
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/* We have an argument; start it. */
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outputargv[outputargc] = q;
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outputargstart[outputargc] = (CHAR *)p;
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outputargc++;
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quote = false;
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/* Copy data into the argument until it's finished. */
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while (*p) {
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if (!quote && is_word_sep(*p))
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break; /* argument is finished */
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if (*p == '"' || (*p == '\\' && backslash_special)) {
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/*
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* We have a sequence of zero or more backslashes
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* followed by a sequence of zero or more quotes.
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* Count up how many of each, and then deal with
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* them as appropriate.
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*/
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int i, slashes = 0, quotes = 0;
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while (*p == '\\') slashes++, p++;
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while (*p == '"') quotes++, p++;
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if (!quotes) {
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/*
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* Special case: if there are no quotes,
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* slashes are not special at all, so just copy
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* n slashes to the output string.
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*/
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while (slashes--) *q++ = '\\';
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} else {
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/* Slashes annihilate in pairs. */
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while (slashes >= 2) slashes -= 2, *q++ = '\\';
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/* One remaining slash takes out the first quote. */
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if (slashes) quotes--, *q++ = '"';
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if (quotes > 0) {
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/* Outside a quote segment, a quote starts one. */
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if (!quote) quotes--;
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#if !MOD3
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/* New behaviour: produce n/2 literal quotes... */
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for (i = 2; i <= quotes; i += 2) *q++ = '"';
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/* ... and end in a quote segment iff 2 divides n. */
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quote = (quotes % 2 == 0);
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#else
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/* Old behaviour: produce (n+1)/3 literal quotes... */
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for (i = 3; i <= quotes+1; i += 3) *q++ = '"';
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/* ... and end in a quote segment iff 3 divides n. */
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quote = (quotes % 3 == 0);
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#endif
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}
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}
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} else {
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*q++ = *p++;
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}
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}
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/* At the end of an argument, just append a trailing NUL. */
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*q++ = '\0';
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}
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outputargv = sresize(outputargv, outputargc, CHAR *);
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outputargstart = sresize(outputargstart, outputargc, CHAR *);
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if (argc) *argc = outputargc;
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if (argv) *argv = outputargv; else sfree(outputargv);
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if (argstart) *argstart = outputargstart; else sfree(outputargstart);
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}
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