summaryrefslogtreecommitdiffstats
path: root/src/common/pg_get_line.c
blob: 3cdf0908d2a1b81433a001daf09e83b282df32ae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
/*-------------------------------------------------------------------------
 *
 * pg_get_line.c
 *	  fgets() with an expansible result buffer
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/common/pg_get_line.c
 *
 *-------------------------------------------------------------------------
 */
#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

#include <setjmp.h>

#include "common/string.h"
#include "lib/stringinfo.h"


/*
 * pg_get_line()
 *
 * This is meant to be equivalent to fgets(), except that instead of
 * reading into a caller-supplied, fixed-size buffer, it reads into
 * a palloc'd (in frontend, really malloc'd) string, which is resized
 * as needed to handle indefinitely long input lines.  The caller is
 * responsible for pfree'ing the result string when appropriate.
 *
 * As with fgets(), returns NULL if there is a read error or if no
 * characters are available before EOF.  The caller can distinguish
 * these cases by checking ferror(stream).
 *
 * Since this is meant to be equivalent to fgets(), the trailing newline
 * (if any) is not stripped.  Callers may wish to apply pg_strip_crlf().
 *
 * Note that while I/O errors are reflected back to the caller to be
 * dealt with, an OOM condition for the palloc'd buffer will not be;
 * there'll be an ereport(ERROR) or exit(1) inside stringinfo.c.
 *
 * Also note that the palloc'd buffer is usually a lot longer than
 * strictly necessary, so it may be inadvisable to use this function
 * to collect lots of long-lived data.  A less memory-hungry option
 * is to use pg_get_line_buf() or pg_get_line_append() in a loop,
 * then pstrdup() each line.
 *
 * prompt_ctx can optionally be provided to allow this function to be
 * canceled via an existing SIGINT signal handler that will longjmp to the
 * specified place only when *(prompt_ctx->enabled) is true.  If canceled,
 * this function returns NULL, and prompt_ctx->canceled is set to true.
 */
char *
pg_get_line(FILE *stream, PromptInterruptContext *prompt_ctx)
{
	StringInfoData buf;

	initStringInfo(&buf);

	if (!pg_get_line_append(stream, &buf, prompt_ctx))
	{
		/* ensure that free() doesn't mess up errno */
		int			save_errno = errno;

		pfree(buf.data);
		errno = save_errno;
		return NULL;
	}

	return buf.data;
}

/*
 * pg_get_line_buf()
 *
 * This has similar behavior to pg_get_line(), and thence to fgets(),
 * except that the collected data is returned in a caller-supplied
 * StringInfo buffer.  This is a convenient API for code that just
 * wants to read and process one line at a time, without any artificial
 * limit on line length.
 *
 * Returns true if a line was successfully collected (including the
 * case of a non-newline-terminated line at EOF).  Returns false if
 * there was an I/O error or no data was available before EOF.
 * (Check ferror(stream) to distinguish these cases.)
 *
 * In the false-result case, buf is reset to empty.
 */
bool
pg_get_line_buf(FILE *stream, StringInfo buf)
{
	/* We just need to drop any data from the previous call */
	resetStringInfo(buf);
	return pg_get_line_append(stream, buf, NULL);
}

/*
 * pg_get_line_append()
 *
 * This has similar behavior to pg_get_line(), and thence to fgets(),
 * except that the collected data is appended to whatever is in *buf.
 * This is useful in preference to pg_get_line_buf() if the caller wants
 * to merge some lines together, e.g. to implement backslash continuation.
 *
 * Returns true if a line was successfully collected (including the
 * case of a non-newline-terminated line at EOF).  Returns false if
 * there was an I/O error or no data was available before EOF.
 * (Check ferror(stream) to distinguish these cases.)
 *
 * In the false-result case, the contents of *buf are logically unmodified,
 * though it's possible that the buffer has been resized.
 *
 * prompt_ctx can optionally be provided to allow this function to be
 * canceled via an existing SIGINT signal handler that will longjmp to the
 * specified place only when *(prompt_ctx->enabled) is true.  If canceled,
 * this function returns false, and prompt_ctx->canceled is set to true.
 */
bool
pg_get_line_append(FILE *stream, StringInfo buf,
				   PromptInterruptContext *prompt_ctx)
{
	int			orig_len = buf->len;

	if (prompt_ctx && sigsetjmp(*((sigjmp_buf *) prompt_ctx->jmpbuf), 1) != 0)
	{
		/* Got here with longjmp */
		prompt_ctx->canceled = true;
		/* Discard any data we collected before detecting error */
		buf->len = orig_len;
		buf->data[orig_len] = '\0';
		return false;
	}

	/* Loop until newline or EOF/error */
	for (;;)
	{
		char	   *res;

		/* Enable longjmp while waiting for input */
		if (prompt_ctx)
			*(prompt_ctx->enabled) = true;

		/* Read some data, appending it to whatever we already have */
		res = fgets(buf->data + buf->len, buf->maxlen - buf->len, stream);

		/* Disable longjmp again, then break if fgets failed */
		if (prompt_ctx)
			*(prompt_ctx->enabled) = false;

		if (res == NULL)
			break;

		/* Got data, so update buf->len */
		buf->len += strlen(buf->data + buf->len);

		/* Done if we have collected a newline */
		if (buf->len > orig_len && buf->data[buf->len - 1] == '\n')
			return true;

		/* Make some more room in the buffer, and loop to read more data */
		enlargeStringInfo(buf, 128);
	}

	/* Check for I/O errors and EOF */
	if (ferror(stream) || buf->len == orig_len)
	{
		/* Discard any data we collected before detecting error */
		buf->len = orig_len;
		buf->data[orig_len] = '\0';
		return false;
	}

	/* No newline at EOF, but we did collect some data */
	return true;
}