mirror of
https://github.com/tailscale/tailscale.git
synced 2024-11-26 03:25:35 +00:00
da8def8e13
The //go:build syntax was introduced in Go 1.17: https://go.dev/doc/go1.17#build-lines gofmt has kept the +build and go:build lines in sync since then, but enough time has passed. Time to remove them. Done with: perl -i -npe 's,^// \+build.*\n,,' $(git grep -l -F '+build') Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
75 lines
2.1 KiB
Go
75 lines
2.1 KiB
Go
// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
|
||
// Use of this source code is governed by a BSD-style
|
||
// license that can be found in the LICENSE file.
|
||
|
||
// Only built on 64-bit platforms to avoid complexity
|
||
|
||
//go:build amd64 || arm64 || mips64le || ppc64le || riscv64
|
||
|
||
package cstruct
|
||
|
||
import "fmt"
|
||
|
||
// This test provides a semi-realistic example of how you can
|
||
// use this package to decode a C structure.
|
||
func ExampleDecoder() {
|
||
// Our example C structure:
|
||
// struct mystruct {
|
||
// char *p;
|
||
// char c;
|
||
// /* implicit: char _pad[3]; */
|
||
// int x;
|
||
// };
|
||
//
|
||
// The Go structure definition:
|
||
type myStruct struct {
|
||
Ptr uintptr
|
||
Ch byte
|
||
Intval uint32
|
||
}
|
||
|
||
// Our "in-memory" version of the above structure
|
||
buf := []byte{
|
||
1, 2, 3, 4, 0, 0, 0, 0, // ptr
|
||
5, // ch
|
||
99, 99, 99, // padding
|
||
78, 6, 0, 0, // x
|
||
}
|
||
d := NewDecoder(buf)
|
||
|
||
// Decode the structure; if one of these function returns an error,
|
||
// then subsequent decoder functions will return the zero value.
|
||
var x myStruct
|
||
x.Ptr = d.Uintptr()
|
||
x.Ch = d.Byte()
|
||
x.Intval = d.Uint32()
|
||
|
||
// Note that per the Go language spec:
|
||
// [...] when evaluating the operands of an expression, assignment,
|
||
// or return statement, all function calls, method calls, and
|
||
// (channel) communication operations are evaluated in lexical
|
||
// left-to-right order
|
||
//
|
||
// Since each field is assigned via a function call, one could use the
|
||
// following snippet to decode the struct.
|
||
// x := myStruct{
|
||
// Ptr: d.Uintptr(),
|
||
// Ch: d.Byte(),
|
||
// Intval: d.Uint32(),
|
||
// }
|
||
//
|
||
// However, this means that reordering the fields in the initialization
|
||
// statement–normally a semantically identical operation–would change
|
||
// the way the structure is parsed. Thus we do it as above with
|
||
// explicit ordering.
|
||
|
||
// After finishing with the decoder, check errors
|
||
if err := d.Err(); err != nil {
|
||
panic(err)
|
||
}
|
||
|
||
// Print the decoder offset and structure
|
||
fmt.Printf("off=%d struct=%#v\n", d.Offset(), x)
|
||
// Output: off=16 struct=cstruct.myStruct{Ptr:0x4030201, Ch:0x5, Intval:0x64e}
|
||
}
|