1unvis(3bsd) LOCAL unvis(3bsd)
2
4 unvis, strunvis, strnunvis, strunvisx, strnunvisx — decode a visual rep‐
5 resentation of characters
6
8 Utility functions from BSD systems (libbsd, -lbsd)
9
11 #include <vis.h>
12 (See libbsd(7) for include usage.)
13 int
15 unvis(char *cp, int c, int *astate, int flag);
16 int
18 strunvis(char *dst, const char *src);
19 int
21 strnunvis(char *dst, size_t dlen, const char *src);
22 int
24 strunvisx(char *dst, const char *src, int flag);
25 int
27 strnunvisx(char *dst, size_t dlen, const char *src, int flag);
28
30 The unvis(), strunvis() and strunvisx() functions are used to decode a
31 visual representation of characters, as produced by the vis(3bsd) func‐
32 tion, back into the original form.
33 The unvis() function is called with successive characters in c until a
35 valid sequence is recognized, at which time the decoded character is
36 available at the character pointed to by cp.
37 The strunvis() function decodes the characters pointed to by src into the
39 buffer pointed to by dst. The strunvis() function simply copies src to
40 dst, decoding any escape sequences along the way, and returns the number
41 of characters placed into dst, or -1 if an invalid escape sequence was
42 detected. The size of dst should be equal to the size of src (that is,
43 no expansion takes place during decoding).
44 The strunvisx() function does the same as the strunvis() function, but it
46 allows you to add a flag that specifies the style the string src is en‐
47 coded with. Currently, the supported flags are: VIS_HTTPSTYLE and
48 VIS_MIMESTYLE.
49 The unvis() function implements a state machine that can be used to de‐
51 code an arbitrary stream of bytes. All state associated with the bytes
52 being decoded is stored outside the unvis() function (that is, a pointer
53 to the state is passed in), so calls decoding different streams can be
54 freely intermixed. To start decoding a stream of bytes, first initialize
55 an integer to zero. Call unvis() with each successive byte, along with a
56 pointer to this integer, and a pointer to a destination character. The
57 unvis() function has several return codes that must be handled properly.
58 They are:
59 0 (zero) Another character is necessary; nothing has been recog‐
61 nized yet.
62 UNVIS_VALID A valid character has been recognized and is available
64 at the location pointed to by cp.
65 UNVIS_VALIDPUSH A valid character has been recognized and is available
67 at the location pointed to by cp; however, the character
68 currently passed in should be passed in again.
69 UNVIS_NOCHAR A valid sequence was detected, but no character was pro‐
71 duced. This return code is necessary to indicate a log‐
72 ical break between characters.
73 UNVIS_SYNBAD An invalid escape sequence was detected, or the decoder
75 is in an unknown state. The decoder is placed into the
76 starting state.
77 When all bytes in the stream have been processed, call unvis() one more
79 time with flag set to UNVIS_END to extract any remaining character (the
80 character passed in is ignored).
81 The flag argument is also used to specify the encoding style of the
83 source. If set to VIS_HTTPSTYLE or VIS_HTTP1808, unvis() will decode URI
84 strings as specified in RFC 1808. If set to VIS_HTTP1866, unvis() will
85 decode entity references and numeric character references as specified in
86 RFC 1866. If set to VIS_MIMESTYLE, unvis() will decode MIME Quoted-
87 Printable strings as specified in RFC 2045. If set to VIS_NOESCAPE,
88 unvis() will not decode ‘\’ quoted characters.
89 The following code fragment illustrates a proper use of unvis().
91 int state = 0;
93 char out;
94 while ((ch = getchar()) != EOF) {
96 again:
97 switch(unvis(&out, ch, &state, 0)) {
98 case 0:
99 case UNVIS_NOCHAR:
100 break;
101 case UNVIS_VALID:
102 (void)putchar(out);
103 break;
104 case UNVIS_VALIDPUSH:
105 (void)putchar(out);
106 goto again;
107 case UNVIS_SYNBAD:
108 errx(EXIT_FAILURE, "Bad character sequence!");
109 }
110 }
111 if (unvis(&out, '\0', &state, UNVIS_END) == UNVIS_VALID)
112 (void)putchar(out);
113
115 The functions strunvis(), strnunvis(), strunvisx(), and strnunvisx() will
116 return -1 on error and set errno to:
117 [EINVAL] An invalid escape sequence was detected, or the de‐
119 coder is in an unknown state.
120 In addition the functions strnunvis() and strnunvisx() will can also set
122 errno on error to:
123 [ENOSPC] Not enough space to perform the conversion.
125
127 unvis(1), vis(1), vis(3bsd)
128 R. Fielding, Relative Uniform Resource Locators, RFC1808.
130
132 The unvis() function first appeared in 4.4BSD. The strnunvis() and
133 strnunvisx() functions appeared in NetBSD 6.0.
134
136 The names VIS_HTTP1808 and VIS_HTTP1866 are wrong. Percent-encoding was
137 defined in RFC 1738, the original RFC for URL. RFC 1866 defines HTML
138 2.0, an application of SGML, from which it inherits concepts of numeric
139 character references and entity references.
140BSD March 12, 2011 BSD