Refactor pipe_read_line to return the full line

Commit 5b2f4afffe6 refactored find_other_exec() and in the process
created pipe_read_line() into a static routine for reading a single
line of output, aimed at reading version numbers.  Commit a7e8ece41
later exposed it externally in order to read a postgresql.conf GUC
using "postgres -C ..".  Further, f06b1c598 also made use of it for
reading a version string much like find_other_exec().  The internal
variable remained "pgver", even when used for other purposes.

Since the function requires passing a buffer and its size, and at
most size - 1 bytes will be read via fgets(), there is a truncation
risk when using this for reading GUCs (like how pg_rewind does,
though the risk in this case is marginal).

To keep this as generic functionality for reading a line from a pipe,
this refactors pipe_read_line() into returning an allocated buffer
containing all of the line to remove the risk of silent truncation.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Discussion: https://postgr.es/m/DEDF73CE-D528-49A3-9089-B3592FD671A9@yesql.se

1 files changed, 4 insertions, 2 deletions

diff --git a/src/bin/pg_upgrade/exec.c b/src/bin/pg_upgrade/exec.c
index fec8dc4c2f7..3552cf00afb 100644
--- a/src/bin/pg_upgrade/exec.c
+++ b/src/bin/pg_upgrade/exec.c
@@ -431,7 +431,7 @@ static void
 check_exec(const char *dir, const char *program, bool check_version)
 {
 	char		path[MAXPGPATH];
-	char		line[MAXPGPATH];
+	char	   *line;
 	char		cmd[MAXPGPATH];
 	char		versionstr[128];
 
@@ -442,7 +442,7 @@ check_exec(const char *dir, const char *program, bool check_version)
 
 	snprintf(cmd, sizeof(cmd), "\"%s\" -V", path);
 
-	if (!pipe_read_line(cmd, line, sizeof(line)))
+	if ((line = pipe_read_line(cmd)) == NULL)
 		pg_fatal("check for \"%s\" failed: cannot execute",
 				 path);
 
@@ -456,4 +456,6 @@ check_exec(const char *dir, const char *program, bool check_version)
 			pg_fatal("check for \"%s\" failed: incorrect version: found \"%s\", expected \"%s\"",
 					 path, line, versionstr);
 	}
+
+	pg_free(line);
 }