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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package cryptobyte_test
import (
"errors"
"fmt"
"golang.org/x/crypto/cryptobyte"
"golang.org/x/crypto/cryptobyte/asn1"
)
func ExampleString_lengthPrefixed() {
// This is an example of parsing length-prefixed data (as found in, for
// example, TLS). Imagine a 16-bit prefixed series of 8-bit prefixed
// strings.
input := cryptobyte.String([]byte{0, 12, 5, 'h', 'e', 'l', 'l', 'o', 5, 'w', 'o', 'r', 'l', 'd'})
var result []string
var values cryptobyte.String
if !input.ReadUint16LengthPrefixed(&values) ||
!input.Empty() {
panic("bad format")
}
for !values.Empty() {
var value cryptobyte.String
if !values.ReadUint8LengthPrefixed(&value) {
panic("bad format")
}
result = append(result, string(value))
}
// Output: []string{"hello", "world"}
fmt.Printf("%#v\n", result)
}
func ExampleString_aSN1() {
// This is an example of parsing ASN.1 data that looks like:
// Foo ::= SEQUENCE {
// version [6] INTEGER DEFAULT 0
// data OCTET STRING
// }
input := cryptobyte.String([]byte{0x30, 12, 0xa6, 3, 2, 1, 2, 4, 5, 'h', 'e', 'l', 'l', 'o'})
var (
version int64
data, inner, versionBytes cryptobyte.String
haveVersion bool
)
if !input.ReadASN1(&inner, asn1.SEQUENCE) ||
!input.Empty() ||
!inner.ReadOptionalASN1(&versionBytes, &haveVersion, asn1.Tag(6).Constructed().ContextSpecific()) ||
(haveVersion && !versionBytes.ReadASN1Integer(&version)) ||
(haveVersion && !versionBytes.Empty()) ||
!inner.ReadASN1(&data, asn1.OCTET_STRING) ||
!inner.Empty() {
panic("bad format")
}
// Output: haveVersion: true, version: 2, data: hello
fmt.Printf("haveVersion: %t, version: %d, data: %s\n", haveVersion, version, string(data))
}
func ExampleBuilder_aSN1() {
// This is an example of building ASN.1 data that looks like:
// Foo ::= SEQUENCE {
// version [6] INTEGER DEFAULT 0
// data OCTET STRING
// }
version := int64(2)
data := []byte("hello")
const defaultVersion = 0
var b cryptobyte.Builder
b.AddASN1(asn1.SEQUENCE, func(b *cryptobyte.Builder) {
if version != defaultVersion {
b.AddASN1(asn1.Tag(6).Constructed().ContextSpecific(), func(b *cryptobyte.Builder) {
b.AddASN1Int64(version)
})
}
b.AddASN1OctetString(data)
})
result, err := b.Bytes()
if err != nil {
panic(err)
}
// Output: 300ca603020102040568656c6c6f
fmt.Printf("%x\n", result)
}
func ExampleBuilder_lengthPrefixed() {
// This is an example of building length-prefixed data (as found in,
// for example, TLS). Imagine a 16-bit prefixed series of 8-bit
// prefixed strings.
input := []string{"hello", "world"}
var b cryptobyte.Builder
b.AddUint16LengthPrefixed(func(b *cryptobyte.Builder) {
for _, value := range input {
b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes([]byte(value))
})
}
})
result, err := b.Bytes()
if err != nil {
panic(err)
}
// Output: 000c0568656c6c6f05776f726c64
fmt.Printf("%x\n", result)
}
func ExampleBuilder_lengthPrefixOverflow() {
// Writing more data that can be expressed by the length prefix results
// in an error from Bytes().
tooLarge := make([]byte, 256)
var b cryptobyte.Builder
b.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddBytes(tooLarge)
})
result, err := b.Bytes()
fmt.Printf("len=%d err=%s\n", len(result), err)
// Output: len=0 err=cryptobyte: pending child length 256 exceeds 1-byte length prefix
}
func ExampleBuilderContinuation_errorHandling() {
var b cryptobyte.Builder
// Continuations that panic with a BuildError will cause Bytes to
// return the inner error.
b.AddUint16LengthPrefixed(func(b *cryptobyte.Builder) {
b.AddUint32(0)
panic(cryptobyte.BuildError{Err: errors.New("example error")})
})
result, err := b.Bytes()
fmt.Printf("len=%d err=%s\n", len(result), err)
// Output: len=0 err=example error
}