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/*-------------------------------------------------------------------------
*
* pg_get_line.c
* fgets() with an expansible result buffer
*
* Portions Copyright (c) 1996-2021, 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 "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.
*/
char *
pg_get_line(FILE *stream)
{
StringInfoData buf;
initStringInfo(&buf);
if (!pg_get_line_append(stream, &buf))
{
/* 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);
}
/*
* 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.
*/
bool
pg_get_line_append(FILE *stream, StringInfo buf)
{
int orig_len = buf->len;
/* Read some data, appending it to whatever we already have */
while (fgets(buf->data + buf->len, buf->maxlen - buf->len, stream) != NULL)
{
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;
}
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