Question regarding psql or libpq

Hi,

It seems psql(or libpq) connects to PostgreSQL twice when md5 auth is
required. Here is a strace log on my Linux machine. Is there any
reason for this?  IMO frontend/backend protocol allows to send salt
after receiving AuthenticationMD5Password using the same socket. So
there's no reason to close the socket and make it again. It seems to
be just waste of resource.

:
:
socket(PF_FILE, SOCK_STREAM, 0)         = 3 <-- create a socket
fcntl(3, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
connect(3, {sa_family=AF_FILE, path="/tmp/.s.PGSQL.5432"...}, 110) = 0
getsockopt(3, SOL_SOCKET, SO_ERROR, [28580018057641984], [4]) = 0
getsockname(3, {sa_family=AF_FILE, path=@""}, [2]) = 0
poll([{fd=3, events=POLLOUT|POLLERR}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
sendto(3, "\0\0\0006\0\3\0\0user\0foo\0database\0test\0ap"..., 54, MSG_NOSIGNAL, NULL, 0) = 54
poll([{fd=3, events=POLLIN|POLLERR}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
recvfrom(3, "R\0\0\0\f\0\0\0\5\10\6N%"..., 16384, 0, NULL, NULL) = 13
close(3)  <-- close the socket
open("/dev/tty", O_RDONLY)              = 3
open("/dev/tty", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 4
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(3, SNDCTL_TMR_CONTINUE or TCSETSF, {B38400 opost isig icanon -echo ...}) = 0
fstat(4, {st_mode=S_IFCHR|0666, st_rdev=makedev(5, 0), ...}) = 0
ioctl(4, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon -echo ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7feffbd21000
write(4, "Password for user foo: "..., 23Password for user foo: ) = 23
fstat(3, {st_mode=S_IFCHR|0666, st_rdev=makedev(5, 0), ...}) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon -echo ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7feffbd20000
read(3, "bar\n"..., 4096)               = 4
ioctl(3, SNDCTL_TMR_CONTINUE or TCSETSF, {B38400 opost isig icanon echo ...}) = 0
write(4, "\n"..., 1
)                    = 1
close(3)                                = 0
munmap(0x7feffbd20000, 4096)            = 0
close(4)                                = 0
munmap(0x7feffbd21000, 4096)            = 0
socket(PF_FILE, SOCK_STREAM, 0)         = 3 <-- and create a socket again
fcntl(3, F_SETFL, O_RDONLY|O_NONBLOCK)  = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
connect(3, {sa_family=AF_FILE, path="/tmp/.s.PGSQL.5432"...}, 110) = 0
getsockopt(3, SOL_SOCKET, SO_ERROR, [28580018057641984], [4]) = 0
getsockname(3, {sa_family=AF_FILE, path=@""}, [2]) = 0
poll([{fd=3, events=POLLOUT|POLLERR}], 1, -1) = 1 ([{fd=3, revents=POLLOUT}])
sendto(3, "\0\0\0006\0\3\0\0user\0foo\0database\0test\0ap"..., 54, MSG_NOSIGNAL, NULL, 0) = 54
poll([{fd=3, events=POLLIN|POLLERR}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
recvfrom(3, "R\0\0\0\f\0\0\0\5\264 \231\352"..., 16384, 0, NULL, NULL) = 13
sendto(3, "p\0\0\0(md5764161564364fab9083f39d97"..., 41, MSG_NOSIGNAL, NULL, 0) = 41
poll([{fd=3, events=POLLIN|POLLERR}], 1, -1) = 1 ([{fd=3, revents=POLLIN}])
recvfrom(3, "R\0\0\0\10\0\0\0\0S\0\0\0\32application_name\0ps"..., 16384, 0, NULL, NULL) = 325
:
:
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp