Improve behavior of tsearch_readline(), and remove t_readline().

Commit fbeb9da22, which added the tsearch_readline APIs, left
t_readline() in place as a compatibility measure.  But that function
has been unused and deprecated for twelve years now, so that seems
like enough time to remove it.  Doing so, and merging t_readline's
code into tsearch_readline, aids in making several useful
improvements:

* The hard-wired 4K limit on line length in tsearch data files is
removed, by using a StringInfo buffer instead of a fixed-size buffer.

* We can buy back the per-line palloc/pfree added by 3ea7e9550
in the common case where encoding conversion is not required.

* We no longer need a separate pg_verify_mbstr call, as that
functionality was folded into encoding conversion some time ago.

(We could have done some of this stuff while keeping t_readline as a
separate API, but there seems little point, since there's no reason
for anyone to still be using t_readline directly.)

Discussion: https://postgr.es/m/48A4FA71-524E-41B9-953A-FD04EF36E2E7@yesql.se

src/backend/tsearch/dict_thesaurus.c

@@ -286,11 +286,6 @@ thesaurusRead(const char *filename, DictThesaurus *d)
 					(errcode(ERRCODE_CONFIG_FILE_ERROR),
 					 errmsg("unexpected end of line")));
 
-		/*
-		 * Note: currently, tsearch_readline can't return lines exceeding 4KB,
-		 * so overflow of the word counts is impossible.  But that may not
-		 * always be true, so let's check.
-		 */
 		if (nwrd != (uint16) nwrd || posinsubst != (uint16) posinsubst)
 			ereport(ERROR,
 					(errcode(ERRCODE_CONFIG_FILE_ERROR),

src/backend/tsearch/ts_locale.c

@@ -14,6 +14,7 @@
 #include "postgres.h"
 
 #include "catalog/pg_collation.h"
+#include "common/string.h"
 #include "storage/fd.h"
 #include "tsearch/ts_locale.h"
 #include "tsearch/ts_public.h"
@@ -128,6 +129,7 @@ tsearch_readline_begin(tsearch_readline_state *stp,
 		return false;
 	stp->filename = filename;
 	stp->lineno = 0;
+	initStringInfo(&stp->buf);
 	stp->curline = NULL;
 	/* Setup error traceback support for ereport() */
 	stp->cb.callback = tsearch_readline_callback;
@@ -145,7 +147,7 @@ tsearch_readline_begin(tsearch_readline_state *stp,
 char *
 tsearch_readline(tsearch_readline_state *stp)
 {
-	char	   *result;
+	char	   *recoded;
 
 	/* Advance line number to use in error reports */
 	stp->lineno++;
@@ -153,23 +155,35 @@ tsearch_readline(tsearch_readline_state *stp)
 	/* Clear curline, it's no longer relevant */
 	if (stp->curline)
 	{
-		pfree(stp->curline);
+		if (stp->curline != stp->buf.data)
+			pfree(stp->curline);
 		stp->curline = NULL;
 	}
 
 	/* Collect next line, if there is one */
-	result = t_readline(stp->fp);
-	if (!result)
+	if (!pg_get_line_buf(stp->fp, &stp->buf))
 		return NULL;
 
-	/*
-	 * Save a copy of the line for possible use in error reports.  (We cannot
-	 * just save "result", since it's likely to get pfree'd at some point by
-	 * the caller; an error after that would try to access freed data.)
-	 */
-	stp->curline = pstrdup(result);
+	/* Validate the input as UTF-8, then convert to DB encoding if needed */
+	recoded = pg_any_to_server(stp->buf.data, stp->buf.len, PG_UTF8);
 
-	return result;
+	/* Save the correctly-encoded string for possible error reports */
+	stp->curline = recoded;		/* might be equal to buf.data */
+
+	/*
+	 * We always return a freshly pstrdup'd string.  This is clearly necessary
+	 * if pg_any_to_server() returned buf.data, and we need a second copy even
+	 * if encoding conversion did occur.  The caller is entitled to pfree the
+	 * returned string at any time, which would leave curline pointing to
+	 * recycled storage, causing problems if an error occurs after that point.
+	 * (It's preferable to return the result of pstrdup instead of the output
+	 * of pg_any_to_server, because the conversion result tends to be
+	 * over-allocated.  Since callers might save the result string directly
+	 * into a long-lived dictionary structure, we don't want it to be a larger
+	 * palloc chunk than necessary.  We'll reclaim the conversion result on
+	 * the next call.)
+	 */
+	return pstrdup(recoded);
 }
 
 /*
@@ -181,11 +195,13 @@ tsearch_readline_end(tsearch_readline_state *stp)
 	/* Suppress use of curline in any error reported below */
 	if (stp->curline)
 	{
-		pfree(stp->curline);
+		if (stp->curline != stp->buf.data)
+			pfree(stp->curline);
 		stp->curline = NULL;
 	}
 
 	/* Release other resources */
+	pfree(stp->buf.data);
 	FreeFile(stp->fp);
 
 	/* Pop the error context stack */
@@ -203,8 +219,7 @@ tsearch_readline_callback(void *arg)
 
 	/*
 	 * We can't include the text of the config line for errors that occur
-	 * during t_readline() itself.  This is only partly a consequence of our
-	 * arms-length use of that routine: the major cause of such errors is
+	 * during tsearch_readline() itself.  The major cause of such errors is
 	 * encoding violations, and we daren't try to print error messages
 	 * containing badly-encoded data.
 	 */
@@ -220,43 +235,6 @@ tsearch_readline_callback(void *arg)
 }
 
 
-/*
- * Read the next line from a tsearch data file (expected to be in UTF-8), and
- * convert it to database encoding if needed. The returned string is palloc'd.
- * NULL return means EOF.
- *
- * Note: direct use of this function is now deprecated.  Go through
- * tsearch_readline() to provide better error reporting.
- */
-char *
-t_readline(FILE *fp)
-{
-	int			len;
-	char	   *recoded;
-	char		buf[4096];		/* lines must not be longer than this */
-
-	if (fgets(buf, sizeof(buf), fp) == NULL)
-		return NULL;
-
-	len = strlen(buf);
-
-	/* Make sure the input is valid UTF-8 */
-	(void) pg_verify_mbstr(PG_UTF8, buf, len, false);
-
-	/* And convert */
-	recoded = pg_any_to_server(buf, len, PG_UTF8);
-	if (recoded == buf)
-	{
-		/*
-		 * conversion didn't pstrdup, so we must. We can use the length of the
-		 * original string, because no conversion was done.
-		 */
-		recoded = pnstrdup(recoded, len);
-	}
-
-	return recoded;
-}
-
 /*
  * lowerstr --- fold null-terminated string to lower case
  *

src/include/tsearch/ts_locale.h

@@ -15,6 +15,7 @@
 #include <ctype.h>
 #include <limits.h>
 
+#include "lib/stringinfo.h"
 #include "mb/pg_wchar.h"
 #include "utils/pg_locale.h"
 
@@ -33,7 +34,9 @@ typedef struct
 	FILE	   *fp;
 	const char *filename;
 	int			lineno;
-	char	   *curline;
+	StringInfoData buf;			/* current input line, in UTF-8 */
+	char	   *curline;		/* current input line, in DB's encoding */
+	/* curline may be NULL, or equal to buf.data, or a palloc'd string */
 	ErrorContextCallback cb;
 } tsearch_readline_state;
 
@@ -57,6 +60,4 @@ extern bool tsearch_readline_begin(tsearch_readline_state *stp,
 extern char *tsearch_readline(tsearch_readline_state *stp);
 extern void tsearch_readline_end(tsearch_readline_state *stp);
 
-extern char *t_readline(FILE *fp);
-
 #endif							/* __TSLOCALE_H__ */