So when trying to do a POST (I don¹t think it matters POST or GET) with the
multi interface with libcurl from cvs and c-ares (also from cvs) I noticed
the following behavior. Cares will do the blocking I/O to check /etc/hosts
(maybe we can expose the struct ares_options.lookups = "b" as a curl multi
option) then if it doesn¹t find the host do the DNS lookup. Libcurl will
provide back via the socket_change_callback that the app should listen for
the DNS lookup¹s response. However, once the DNS lookup succeeds it won¹t
tell the client app to stop looking for the DNS lookup¹s response like the
way libcurl does for other types of connections. I feel this is a bug and
will dig into the code a little to provide a fix. Thoughts?

Chris

strace: Took out the syscalls that didn¹t matter

#check /etc/hosts
     0.000089 open("/etc/hosts", O_RDONLY) = 6
     0.000104 fstat(6, {st_mode=S_IFREG|0644, st_size=238, ...}) = 0
     0.000080 mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x2aaaaaf51000
     0.000116 read(6, "# Do not remove the following li"..., 4096) = 238
     0.000087 read(6, "", 4096) = 0
     0.000044 close(6) = 0
     0.000044 munmap(0x2aaaaaf51000, 4096) = 0
#didn¹t find it do a DNS lookup
     0.000048 socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 6
     0.000049 fcntl(6, F_GETFL) = 0x2 (flags O_RDWR)
     0.000044 fcntl(6, F_SETFL, O_RDWR|O_NONBLOCK) = 0
     0.000046 fcntl(6, F_SETFD, FD_CLOEXEC) = 0
     0.000080 connect(6, {sa_family=AF_INET, sin_port=htons(53),
sin_addr=inet_addr("10.18.255.53")}, 16) = 0
     0.000056 sendto(6,
"\30\336\1\0\0\1\0\0\0\0\0\0\10megaload\3vip\10facebo"..., 43, MSG_NOSIGNAL,
NULL, 0) = 43
     0.000075 poll([{fd=6, events=POLLIN}], 1, 0) = 0
     0.000058 epoll_ctl(3, EPOLL_CTL_ADD, 6,
{EPOLLIN|EPOLLPRI|EPOLLERR|EPOLLHUP, {u32=6327216, u64=6327216}}) = 0
     0.000059 epoll_wait(3, {{EPOLLIN, {u32=6327216, u64=6327216}}}, 200,
93) = 1
     0.000048 poll([{fd=6, events=POLLIN, revents=POLLIN}], 1, 0) = 1
     0.000050 recvfrom(6,
"\30\336\205\200\0\1\0\2\0\1\0\1\10megaload\3vip\10facebo"..., 513, 0, NULL,
NULL) = 124
     0.000073 close(6) = 0
#DNS lookup succeeded. No idea what the next line is
     0.000100 recvfrom(-1, 0x7fffdac51e70, 513, 0, 0, 0) = -1 EBADF (Bad
file descriptor)
#create the socket for the http post
     0.000048 socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 6
     0.000049 fcntl(6, F_GETFL) = 0x2 (flags O_RDWR)
     0.000073 fcntl(6, F_SETFL, O_RDWR|O_NONBLOCK) = 0
     0.000045 connect(6, {sa_family=AF_INET, sin_port=htons(8082),
sin_addr=inet_addr("10.8.253.108")}, 16) = -1 EINPROGRESS (Operation now in
progress)
     0.000089 poll([{fd=6, events=POLLOUT}], 1, 0) = 0
#my epoll_ctl tries to modify fd=6 because it was never told to delete fd=6
     0.000070 epoll_ctl(3, EPOLL_CTL_MOD, 6, {EPOLLOUT|EPOLLERR|EPOLLHUP,
{u32=6327216, u64=6327216}}) = -1 ENOENT (No such file or directory)
Received on 2008-06-11