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152 lines
4.2 KiB
C
152 lines
4.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* psprintf.c
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* sprintf into an allocated-on-demand buffer
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*
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/common/psprintf.c
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef FRONTEND
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#include "postgres.h"
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#include "utils/memutils.h"
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#else
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#include "postgres_fe.h"
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/* It's possible we could use a different value for this in frontend code */
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#define MaxAllocSize ((Size) 0x3fffffff) /* 1 gigabyte - 1 */
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#endif
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/*
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* psprintf
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*
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* Format text data under the control of fmt (an sprintf-style format string)
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* and return it in an allocated-on-demand buffer. The buffer is allocated
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* with palloc in the backend, or malloc in frontend builds. Caller is
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* responsible to free the buffer when no longer needed, if appropriate.
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*
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* Errors are not returned to the caller, but are reported via elog(ERROR)
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* in the backend, or printf-to-stderr-and-exit() in frontend builds.
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* One should therefore think twice about using this in libpq.
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*/
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char *
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psprintf(const char *fmt,...)
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{
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int save_errno = errno;
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size_t len = 128; /* initial assumption about buffer size */
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for (;;)
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{
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char *result;
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va_list args;
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size_t newlen;
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/*
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* Allocate result buffer. Note that in frontend this maps to malloc
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* with exit-on-error.
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*/
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result = (char *) palloc(len);
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/* Try to format the data. */
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errno = save_errno;
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va_start(args, fmt);
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newlen = pvsnprintf(result, len, fmt, args);
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va_end(args);
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if (newlen < len)
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return result; /* success */
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/* Release buffer and loop around to try again with larger len. */
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pfree(result);
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len = newlen;
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}
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}
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/*
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* pvsnprintf
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*
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* Attempt to format text data under the control of fmt (an sprintf-style
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* format string) and insert it into buf (which has length len).
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*
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* If successful, return the number of bytes emitted, not counting the
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* trailing zero byte. This will always be strictly less than len.
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*
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* If there's not enough space in buf, return an estimate of the buffer size
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* needed to succeed (this *must* be more than the given len, else callers
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* might loop infinitely).
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*
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* Other error cases do not return, but exit via elog(ERROR) or exit().
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* Hence, this shouldn't be used inside libpq.
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*
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* Caution: callers must be sure to preserve their entry-time errno
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* when looping, in case the fmt contains "%m".
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*
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* Note that the semantics of the return value are not exactly C99's.
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* First, we don't promise that the estimated buffer size is exactly right;
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* callers must be prepared to loop multiple times to get the right size.
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* (Given a C99-compliant vsnprintf, that won't happen, but it is rumored
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* that some implementations don't always return the same value ...)
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* Second, we return the recommended buffer size, not one less than that;
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* this lets overflow concerns be handled here rather than in the callers.
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*/
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size_t
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pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
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{
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int nprinted;
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nprinted = vsnprintf(buf, len, fmt, args);
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/* We assume failure means the fmt is bogus, hence hard failure is OK */
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if (unlikely(nprinted < 0))
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{
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#ifndef FRONTEND
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elog(ERROR, "vsnprintf failed: %m with format string \"%s\"", fmt);
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#else
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fprintf(stderr, "vsnprintf failed: %s with format string \"%s\"\n",
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strerror(errno), fmt);
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exit(EXIT_FAILURE);
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#endif
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}
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if ((size_t) nprinted < len)
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{
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/* Success. Note nprinted does not include trailing null. */
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return (size_t) nprinted;
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}
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/*
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* We assume a C99-compliant vsnprintf, so believe its estimate of the
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* required space, and add one for the trailing null. (If it's wrong, the
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* logic will still work, but we may loop multiple times.)
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*
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* Choke if the required space would exceed MaxAllocSize. Note we use
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* this palloc-oriented overflow limit even when in frontend.
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*/
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if (unlikely((size_t) nprinted > MaxAllocSize - 1))
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{
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#ifndef FRONTEND
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ereport(ERROR,
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(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
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errmsg("out of memory")));
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#else
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fprintf(stderr, _("out of memory\n"));
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exit(EXIT_FAILURE);
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#endif
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}
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return nprinted + 1;
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}
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