Add MSG_PEEK socket flag #492
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bors
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Jan 10, 2017
Add MSG_PEEK socket flag
#### MSG_PEEK
This PR exposes a cross-platform `MSG_PEEK` flag that a user may pass into the `flags` parameter for `recv()`, `recvfrom()`, or `recvmsg()` calls.
```
MSG_PEEK
This flag causes the receive operation to return data from the
beginning of the receive queue without removing that data from the
queue. Thus, a subsequent receive call will return the same data.
```
In short, users may call `recv()` to "peek" at new data (or a message) without consuming it. Recall that in the normal case, calls to `recv()` consume the data from the socket's receive queue, making it unavailable to future calls.
#### Motivation
This change enables `libc` users, such as the rust standard library, to potentially add peeking functionality to TCP and UDP implementations, like `TcpStream` and `UdpSocket`, without being concerned about the highly platform-dependent nature of the flags.
(In this case, the flag's value `0x2` is very consistent, but that is not the case for many of the `MSG_*` flags. It makes sense to keep these differences confined to `libc`)
#### Reference
[bsd/apple: socket.h](https://opensource.apple.com/source/xnu/xnu-2050.7.9/bsd/sys/socket.h)
[bsd/freebsdlike/freebsd: socket.h](https://github.com/freebsd/freebsd/blob/master/sys/sys/socket.h#L418)
[bsd/freebsdlike/dragonfly: socket.h](https://github.com/DragonFlyBSD/DragonFlyBSD/blob/1f249c981c4e89e7cde1836a75b61cac36dc7ac5/sys/sys/socket.h#L367)
[bsd/netbsdlike: socket.h](https://github.com/IIJ-NetBSD/netbsd-src/blob/af5d253140491f2d1816c59ecb8a4d8a8d927688/sys/sys/socket.h#L517)
[unix/haiku: socket.h](https://github.com/haiku/haiku/blob/b65adbdfbc322bb7d86d74049389c688e9962f15/headers/posix/sys/socket.h#L114)
[unix/notbsd/linux: socket.h](https://github.com/torvalds/linux/blob/5924bbecd0267d87c24110cbe2041b5075173a25/include/linux/socket.h#L264)
[unix/notbsd/android: socket.h](https://android.googlesource.com/platform/development/+/73a5a3baaa5089f1ab2049e5934fa5d8a3f3e76a/ndk/platforms/android-20/include/sys/socket.h#229)
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☀️ Test successful - status-appveyor, status-travis |
Susurrus
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Mar 26, 2017
fix build for eventfd feature
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MSG_PEEK
This PR exposes a cross-platform
MSG_PEEKflag that a user may pass into theflagsparameter forrecv(),recvfrom(), orrecvmsg()calls.In short, users may call
recv()to "peek" at new data (or a message) without consuming it. Recall that in the normal case, calls torecv()consume the data from the socket's receive queue, making it unavailable to future calls.Motivation
This change enables
libcusers, such as the rust standard library, to potentially add peeking functionality to TCP and UDP implementations, likeTcpStreamandUdpSocket, without being concerned about the highly platform-dependent nature of the flags.(In this case, the flag's value
0x2is very consistent, but that is not the case for many of theMSG_*flags. It makes sense to keep these differences confined tolibc)Reference
bsd/apple: socket.h
bsd/freebsdlike/freebsd: socket.h
bsd/freebsdlike/dragonfly: socket.h
bsd/netbsdlike: socket.h
unix/haiku: socket.h
unix/notbsd/linux: socket.h
unix/notbsd/android: socket.h