std::net::lookup_host repeats output #24250
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This is happening because the underlying call to getaddrinfo doesn't provide an addrinfo as a hint, and so the linked list of returned addrinfo structs contains addrinfo for both TCP and UDP protocols. A simple fix would be to simply pass in a hint specifying only one protocol (e.g. TCP) However I'm not sure how often you'll find a hostname that has UDP available but not TCP and vice versa, and whether or not it's worth capturing that with something like LookupHostUdp and LookupHostTcp. |
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Requiring a hint argument specifying tcp vs udp makes sense to me. |
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Use hints with getaddrinfo() in std::net::lookup_host() As noted in rust-lang#24250, `std::net::lookup_host()` repeats each IPv[46] address in the result set. The number of repetitions is OS-dependent; e.g., Linux and FreeBSD give three copies, OpenBSD gives two. Filtering the duplicates can be done by the user if `lookup_host()` is used explicitly, but not with functions like `TcpStream::connect()`. What happens with the latter is that any unsuccessful connection attempt will be repeated as many times as there are duplicates of the address. The program: ```rust use std::net::TcpStream; fn main() { let _stream = TcpStream::connect("localhost:4444").unwrap(); } ``` results in the following capture: [capture-before.txt](https://github.com/rust-lang/rust/files/352004/capture-before.txt) assuming that "localhost" resolves both to ::1 and 127.0.0.1, and that the listening program opens just an IPv4 socket (e.g., `nc -l 127.0.0.1 4444`.) The reason for this behavior is explained in [this comment](rust-lang#24250 (comment)): `getaddrinfo()` is not constrained. Various OSS projects (I checked out Postfix, OpenLDAP, Apache HTTPD and BIND) which use `getaddrinfo()` generally constrain the result set by using a non-NULL `hints` parameter and setting at least `ai_socktype` to `SOCK_STREAM`. `SOCK_DGRAM` would also work. Other parameters are unnecessary for pure name resolution. The patch in this PR initializes a `hints` struct and passes it to `getaddrinfo()`, which eliminates the duplicates. The same test program as above with this change produces: [capture-after.txt](https://github.com/rust-lang/rust/files/352042/capture-after.txt) All `libstd` tests pass with this patch.
Manishearth
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Use hints with getaddrinfo() in std::net::lookup_host() As noted in rust-lang#24250, `std::net::lookup_host()` repeats each IPv[46] address in the result set. The number of repetitions is OS-dependent; e.g., Linux and FreeBSD give three copies, OpenBSD gives two. Filtering the duplicates can be done by the user if `lookup_host()` is used explicitly, but not with functions like `TcpStream::connect()`. What happens with the latter is that any unsuccessful connection attempt will be repeated as many times as there are duplicates of the address. The program: ```rust use std::net::TcpStream; fn main() { let _stream = TcpStream::connect("localhost:4444").unwrap(); } ``` results in the following capture: [capture-before.txt](https://github.com/rust-lang/rust/files/352004/capture-before.txt) assuming that "localhost" resolves both to ::1 and 127.0.0.1, and that the listening program opens just an IPv4 socket (e.g., `nc -l 127.0.0.1 4444`.) The reason for this behavior is explained in [this comment](rust-lang#24250 (comment)): `getaddrinfo()` is not constrained. Various OSS projects (I checked out Postfix, OpenLDAP, Apache HTTPD and BIND) which use `getaddrinfo()` generally constrain the result set by using a non-NULL `hints` parameter and setting at least `ai_socktype` to `SOCK_STREAM`. `SOCK_DGRAM` would also work. Other parameters are unnecessary for pure name resolution. The patch in this PR initializes a `hints` struct and passes it to `getaddrinfo()`, which eliminates the duplicates. The same test program as above with this change produces: [capture-after.txt](https://github.com/rust-lang/rust/files/352042/capture-after.txt) All `libstd` tests pass with this patch.
bors
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Use hints with getaddrinfo() in std::net::lookup_host() As noted in #24250, `std::net::lookup_host()` repeats each IPv[46] address in the result set. The number of repetitions is OS-dependent; e.g., Linux and FreeBSD give three copies, OpenBSD gives two. Filtering the duplicates can be done by the user if `lookup_host()` is used explicitly, but not with functions like `TcpStream::connect()`. What happens with the latter is that any unsuccessful connection attempt will be repeated as many times as there are duplicates of the address. The program: ```rust use std::net::TcpStream; fn main() { let _stream = TcpStream::connect("localhost:4444").unwrap(); } ``` results in the following capture: [capture-before.txt](https://github.com/rust-lang/rust/files/352004/capture-before.txt) assuming that "localhost" resolves both to ::1 and 127.0.0.1, and that the listening program opens just an IPv4 socket (e.g., `nc -l 127.0.0.1 4444`.) The reason for this behavior is explained in [this comment](#24250 (comment)): `getaddrinfo()` is not constrained. Various OSS projects (I checked out Postfix, OpenLDAP, Apache HTTPD and BIND) which use `getaddrinfo()` generally constrain the result set by using a non-NULL `hints` parameter and setting at least `ai_socktype` to `SOCK_STREAM`. `SOCK_DGRAM` would also work. Other parameters are unnecessary for pure name resolution. The patch in this PR initializes a `hints` struct and passes it to `getaddrinfo()`, which eliminates the duplicates. The same test program as above with this change produces: [capture-after.txt](https://github.com/rust-lang/rust/files/352042/capture-after.txt) All `libstd` tests pass with this patch.
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Fixed by #34700 |
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Using std::net::lookup_host seems to duplicate each IP in the result set.
The documentation snippet (https://doc.rust-lang.org/std/net/fn.lookup_host.html) is enough to reproduce.
I also have a simple gist here: https://gist.github.com/nieksand/9c42100be6dc52df3305
I'm using the latest Rust from master branch on MacOS X 10.9.5. I have not checked on other platforms. I see this for any hostname that I try, so I don't think it's a problem on the nameserver side.
Expected behavior is seeing each IP address listed only once.
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