Documentation ¶
Overview ¶
Package cryptobyte contains types that help with parsing and constructing length-prefixed, binary messages, including ASN.1 DER. (The asn1 subpackage contains useful ASN.1 constants.)
The String type is for parsing. It wraps a []byte slice and provides helper functions for consuming structures, value by value.
The Builder type is for constructing messages. It providers helper functions for appending values and also for appending length-prefixed submessages – without having to worry about calculating the length prefix ahead of time.
See the documentation and examples for the Builder and String types to get started.
Index ¶
- type BuildError
- type Builder
- func (b *Builder) AddASN1(tag asn1.Tag, f BuilderContinuation)
- func (b *Builder) AddASN1BigInt(n *big.Int)
- func (b *Builder) AddASN1BitString(data []byte)
- func (b *Builder) AddASN1Boolean(v bool)
- func (b *Builder) AddASN1Enum(v int64)
- func (b *Builder) AddASN1GeneralizedTime(t time.Time)
- func (b *Builder) AddASN1Int64(v int64)
- func (b *Builder) AddASN1Int64WithTag(v int64, tag asn1.Tag)
- func (b *Builder) AddASN1NULL()
- func (b *Builder) AddASN1ObjectIdentifier(oid encoding_asn1.ObjectIdentifier)
- func (b *Builder) AddASN1OctetString(bytes []byte)
- func (b *Builder) AddASN1Uint64(v uint64)
- func (b *Builder) AddBytes(v []byte)
- func (b *Builder) AddUint16(v uint16)
- func (b *Builder) AddUint16LengthPrefixed(f BuilderContinuation)
- func (b *Builder) AddUint24(v uint32)
- func (b *Builder) AddUint24LengthPrefixed(f BuilderContinuation)
- func (b *Builder) AddUint32(v uint32)
- func (b *Builder) AddUint32LengthPrefixed(f BuilderContinuation)
- func (b *Builder) AddUint8(v uint8)
- func (b *Builder) AddUint8LengthPrefixed(f BuilderContinuation)
- func (b *Builder) AddValue(v MarshalingValue)
- func (b *Builder) Bytes() ([]byte, error)
- func (b *Builder) BytesOrPanic() []byte
- func (b *Builder) MarshalASN1(v interface{})
- type BuilderContinuation
- type MarshalingValue
- type String
- func (s *String) CopyBytes(out []byte) bool
- func (s String) Empty() bool
- func (s String) PeekASN1Tag(tag asn1.Tag) bool
- func (s *String) ReadASN1(out *String, tag asn1.Tag) bool
- func (s *String) ReadASN1BitString(out *encoding_asn1.BitString) bool
- func (s *String) ReadASN1BitStringAsBytes(out *[]byte) bool
- func (s *String) ReadASN1Boolean(out *bool) bool
- func (s *String) ReadASN1Bytes(out *[]byte, tag asn1.Tag) bool
- func (s *String) ReadASN1Element(out *String, tag asn1.Tag) bool
- func (s *String) ReadASN1Enum(out *int) bool
- func (s *String) ReadASN1GeneralizedTime(out *time.Time) bool
- func (s *String) ReadASN1Int64WithTag(out *int64, tag asn1.Tag) bool
- func (s *String) ReadASN1Integer(out interface{}) bool
- func (s *String) ReadASN1ObjectIdentifier(out *encoding_asn1.ObjectIdentifier) bool
- func (s *String) ReadAnyASN1(out *String, outTag *asn1.Tag) bool
- func (s *String) ReadAnyASN1Element(out *String, outTag *asn1.Tag) bool
- func (s *String) ReadBytes(out *[]byte, n int) bool
- func (s *String) ReadOptionalASN1(out *String, outPresent *bool, tag asn1.Tag) bool
- func (s *String) ReadOptionalASN1Boolean(out *bool, defaultValue bool) bool
- func (s *String) ReadOptionalASN1Integer(out interface{}, tag asn1.Tag, defaultValue interface{}) bool
- func (s *String) ReadOptionalASN1OctetString(out *[]byte, outPresent *bool, tag asn1.Tag) bool
- func (s *String) ReadUint16(out *uint16) bool
- func (s *String) ReadUint16LengthPrefixed(out *String) bool
- func (s *String) ReadUint24(out *uint32) bool
- func (s *String) ReadUint24LengthPrefixed(out *String) bool
- func (s *String) ReadUint32(out *uint32) bool
- func (s *String) ReadUint8(out *uint8) bool
- func (s *String) ReadUint8LengthPrefixed(out *String) bool
- func (s *String) Skip(n int) bool
- func (s *String) SkipASN1(tag asn1.Tag) bool
- func (s *String) SkipOptionalASN1(tag asn1.Tag) bool
Examples ¶
Constants ¶
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Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type BuildError ¶ added in v1.0.9
type BuildError struct {
Err error
}
BuildError wraps an error. If a BuilderContinuation panics with this value, the panic will be recovered and the inner error will be returned from Builder.Bytes.
type Builder ¶
type Builder struct {
// contains filtered or unexported fields
}
A Builder builds byte strings from fixed-length and length-prefixed values. Builders either allocate space as needed, or are ‘fixed’, which means that they write into a given buffer and produce an error if it's exhausted.
The zero value is a usable Builder that allocates space as needed.
Simple values are marshaled and appended to a Builder using methods on the Builder. Length-prefixed values are marshaled by providing a BuilderContinuation, which is a function that writes the inner contents of the value to a given Builder. See the documentation for BuilderContinuation for details.
Example (ASN1) ¶
package main import ( "fmt" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte/asn1" ) func main() { // 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) } fmt.Printf("%x\n", result) }
Output: 300ca603020102040568656c6c6f
Example (LengthPrefixOverflow) ¶
package main import ( "fmt" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte" ) func main() { // 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
Example (LengthPrefixed) ¶
package main import ( "fmt" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte" ) func main() { // 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) } fmt.Printf("%x\n", result) }
Output: 000c0568656c6c6f05776f726c64
func NewBuilder ¶
NewBuilder creates a Builder that appends its output to the given buffer. Like append(), the slice will be reallocated if its capacity is exceeded. Use Bytes to get the final buffer.
func NewFixedBuilder ¶
NewFixedBuilder creates a Builder that appends its output into the given buffer. This builder does not reallocate the output buffer. Writes that would exceed the buffer's capacity are treated as an error.
func (*Builder) AddASN1 ¶
func (b *Builder) AddASN1(tag asn1.Tag, f BuilderContinuation)
AddASN1 appends an ASN.1 object. The object is prefixed with the given tag. Tags greater than 30 are not supported and result in an error (i.e. low-tag-number form only). The child builder passed to the BuilderContinuation can be used to build the content of the ASN.1 object.
func (*Builder) AddASN1BigInt ¶
AddASN1BigInt appends a DER-encoded ASN.1 INTEGER.
func (*Builder) AddASN1BitString ¶
AddASN1BitString appends a DER-encoded ASN.1 BIT STRING. This does not support BIT STRINGs that are not a whole number of bytes.
func (*Builder) AddASN1Boolean ¶ added in v1.0.9
func (*Builder) AddASN1Enum ¶
AddASN1Enum appends a DER-encoded ASN.1 ENUMERATION.
func (*Builder) AddASN1GeneralizedTime ¶
AddASN1GeneralizedTime appends a DER-encoded ASN.1 GENERALIZEDTIME.
func (*Builder) AddASN1Int64 ¶
AddASN1Int64 appends a DER-encoded ASN.1 INTEGER.
func (*Builder) AddASN1Int64WithTag ¶ added in v1.0.9
AddASN1Int64WithTag appends a DER-encoded ASN.1 INTEGER with the given tag.
func (*Builder) AddASN1NULL ¶ added in v1.0.9
func (b *Builder) AddASN1NULL()
func (*Builder) AddASN1ObjectIdentifier ¶ added in v1.0.9
func (b *Builder) AddASN1ObjectIdentifier(oid encoding_asn1.ObjectIdentifier)
func (*Builder) AddASN1OctetString ¶
AddASN1OctetString appends a DER-encoded ASN.1 OCTET STRING.
func (*Builder) AddASN1Uint64 ¶
AddASN1Uint64 appends a DER-encoded ASN.1 INTEGER.
func (*Builder) AddUint16LengthPrefixed ¶
func (b *Builder) AddUint16LengthPrefixed(f BuilderContinuation)
AddUint16LengthPrefixed adds a big-endian, 16-bit length-prefixed byte sequence.
func (*Builder) AddUint24 ¶
AddUint24 appends a big-endian, 24-bit value to the byte string. The highest byte of the 32-bit input value is silently truncated.
func (*Builder) AddUint24LengthPrefixed ¶
func (b *Builder) AddUint24LengthPrefixed(f BuilderContinuation)
AddUint24LengthPrefixed adds a big-endian, 24-bit length-prefixed byte sequence.
func (*Builder) AddUint32LengthPrefixed ¶ added in v1.0.9
func (b *Builder) AddUint32LengthPrefixed(f BuilderContinuation)
AddUint32LengthPrefixed adds a big-endian, 32-bit length-prefixed byte sequence.
func (*Builder) AddUint8LengthPrefixed ¶
func (b *Builder) AddUint8LengthPrefixed(f BuilderContinuation)
AddUint8LengthPrefixed adds a 8-bit length-prefixed byte sequence.
func (*Builder) AddValue ¶
func (b *Builder) AddValue(v MarshalingValue)
AddValue calls Marshal on v, passing a pointer to the builder to append to. If Marshal returns an error, it is set on the Builder so that subsequent appends don't have an effect.
func (*Builder) Bytes ¶
Bytes returns the bytes written by the builder or an error if one has occurred during during building.
func (*Builder) BytesOrPanic ¶
BytesOrPanic returns the bytes written by the builder or panics if an error has occurred during building.
func (*Builder) MarshalASN1 ¶
func (b *Builder) MarshalASN1(v interface{})
MarshalASN1 calls encoding_asn1.Marshal on its input and appends the result if successful or records an error if one occurred.
type BuilderContinuation ¶
type BuilderContinuation func(child *Builder)
BuilderContinuation is continuation-passing interface for building length-prefixed byte sequences. Builder methods for length-prefixed sequences (AddUint8LengthPrefixed etc) will invoke the BuilderContinuation supplied to them. The child builder passed to the continuation can be used to build the content of the length-prefixed sequence. For example:
parent := cryptobyte.NewBuilder() parent.AddUint8LengthPrefixed(func (child *Builder) { child.AddUint8(42) child.AddUint8LengthPrefixed(func (grandchild *Builder) { grandchild.AddUint8(5) }) })
It is an error to write more bytes to the child than allowed by the reserved length prefix. After the continuation returns, the child must be considered invalid, i.e. users must not store any copies or references of the child that outlive the continuation.
If the continuation panics with a value of type BuildError then the inner error will be returned as the error from Bytes. If the child panics otherwise then Bytes will repanic with the same value.
Example (ErrorHandling) ¶
package main import ( "errors" "fmt" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte" ) func main() { 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
type MarshalingValue ¶
type MarshalingValue interface { // Marshal is called by Builder.AddValue. It receives a pointer to a builder // to marshal itself into. It may return an error that occurred during // marshaling, such as unset or invalid values. Marshal(b *Builder) error }
A MarshalingValue marshals itself into a Builder.
type String ¶
type String []byte
String represents a string of bytes. It provides methods for parsing fixed-length and length-prefixed values from it.
Example (ASN1) ¶
package main import ( "fmt" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte/asn1" ) func main() { // 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") } fmt.Printf("haveVersion: %t, version: %d, data: %s\n", haveVersion, version, string(data)) }
Output: haveVersion: true, version: 2, data: hello
Example (LengthPrefixed) ¶
package main import ( "fmt" "github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/cryptobyte" ) func main() { // 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)) } fmt.Printf("%#v\n", result) }
Output: []string{"hello", "world"}
func (*String) CopyBytes ¶
CopyBytes copies len(out) bytes into out and advances over them. It reports whether the copy operation was successful
func (String) PeekASN1Tag ¶
PeekASN1Tag reports whether the next ASN.1 value on the string starts with the given tag.
func (*String) ReadASN1 ¶
ReadASN1 reads the contents of a DER-encoded ASN.1 element (not including tag and length bytes) into out, and advances. The element must match the given tag. It reports whether the read was successful.
Tags greater than 30 are not supported (i.e. low-tag-number format only).
func (*String) ReadASN1BitString ¶
func (s *String) ReadASN1BitString(out *encoding_asn1.BitString) bool
ReadASN1BitString decodes an ASN.1 BIT STRING into out and advances. It reports whether the read was successful.
func (*String) ReadASN1BitStringAsBytes ¶ added in v1.0.9
ReadASN1BitString decodes an ASN.1 BIT STRING into out and advances. It is an error if the BIT STRING is not a whole number of bytes. It reports whether the read was successful.
func (*String) ReadASN1Boolean ¶ added in v1.0.9
ReadASN1Boolean decodes an ASN.1 INTEGER and converts it to a boolean representation into out and advances. It reports whether the read was successful.
func (*String) ReadASN1Bytes ¶
ReadASN1Bytes reads the contents of a DER-encoded ASN.1 element (not including tag and length bytes) into out, and advances. The element must match the given tag. It reports whether the read was successful.
func (*String) ReadASN1Element ¶
ReadASN1Element reads the contents of a DER-encoded ASN.1 element (including tag and length bytes) into out, and advances. The element must match the given tag. It reports whether the read was successful.
Tags greater than 30 are not supported (i.e. low-tag-number format only).
func (*String) ReadASN1Enum ¶
ReadASN1Enum decodes an ASN.1 ENUMERATION into out and advances. It reports whether the read was successful.
func (*String) ReadASN1GeneralizedTime ¶
ReadASN1GeneralizedTime decodes an ASN.1 GENERALIZEDTIME into out and advances. It reports whether the read was successful.
func (*String) ReadASN1Int64WithTag ¶ added in v1.0.9
ReadASN1Int64WithTag decodes an ASN.1 INTEGER with the given tag into out and advances. It reports whether the read was successful and resulted in a value that can be represented in an int64.
func (*String) ReadASN1Integer ¶
ReadASN1Integer decodes an ASN.1 INTEGER into out and advances. If out does not point to an integer or to a big.Int, it panics. It reports whether the read was successful.
func (*String) ReadASN1ObjectIdentifier ¶
func (s *String) ReadASN1ObjectIdentifier(out *encoding_asn1.ObjectIdentifier) bool
ReadASN1ObjectIdentifier decodes an ASN.1 OBJECT IDENTIFIER into out and advances. It reports whether the read was successful.
func (*String) ReadAnyASN1 ¶
ReadAnyASN1 reads the contents of a DER-encoded ASN.1 element (not including tag and length bytes) into out, sets outTag to its tag, and advances. It reports whether the read was successful.
Tags greater than 30 are not supported (i.e. low-tag-number format only).
func (*String) ReadAnyASN1Element ¶
ReadAnyASN1Element reads the contents of a DER-encoded ASN.1 element (including tag and length bytes) into out, sets outTag to is tag, and advances. It reports whether the read was successful.
Tags greater than 30 are not supported (i.e. low-tag-number format only).
func (*String) ReadBytes ¶
ReadBytes reads n bytes into out and advances over them. It reports whether the read was successful.
func (*String) ReadOptionalASN1 ¶
ReadOptionalASN1 attempts to read the contents of a DER-encoded ASN.1 element (not including tag and length bytes) tagged with the given tag into out. It stores whether an element with the tag was found in outPresent, unless outPresent is nil. It reports whether the read was successful.
func (*String) ReadOptionalASN1Boolean ¶ added in v1.0.9
ReadOptionalASN1Boolean sets *out to the value of the next ASN.1 BOOLEAN or, if the next bytes are not an ASN.1 BOOLEAN, to the value of defaultValue. It reports whether the operation was successful.
func (*String) ReadOptionalASN1Integer ¶
func (s *String) ReadOptionalASN1Integer(out interface{}, tag asn1.Tag, defaultValue interface{}) bool
ReadOptionalASN1Integer attempts to read an optional ASN.1 INTEGER explicitly tagged with tag into out and advances. If no element with a matching tag is present, it writes defaultValue into out instead. If out does not point to an integer or to a big.Int, it panics. It reports whether the read was successful.
func (*String) ReadOptionalASN1OctetString ¶
ReadOptionalASN1OctetString attempts to read an optional ASN.1 OCTET STRING explicitly tagged with tag into out and advances. If no element with a matching tag is present, it sets "out" to nil instead. It reports whether the read was successful.
func (*String) ReadUint16 ¶
ReadUint16 decodes a big-endian, 16-bit value into out and advances over it. It reports whether the read was successful.
func (*String) ReadUint16LengthPrefixed ¶
ReadUint16LengthPrefixed reads the content of a big-endian, 16-bit length-prefixed value into out and advances over it. It reports whether the read was successful.
func (*String) ReadUint24 ¶
ReadUint24 decodes a big-endian, 24-bit value into out and advances over it. It reports whether the read was successful.
func (*String) ReadUint24LengthPrefixed ¶
ReadUint24LengthPrefixed reads the content of a big-endian, 24-bit length-prefixed value into out and advances over it. It reports whether the read was successful.
func (*String) ReadUint32 ¶
ReadUint32 decodes a big-endian, 32-bit value into out and advances over it. It reports whether the read was successful.
func (*String) ReadUint8 ¶
ReadUint8 decodes an 8-bit value into out and advances over it. It reports whether the read was successful.
func (*String) ReadUint8LengthPrefixed ¶
ReadUint8LengthPrefixed reads the content of an 8-bit length-prefixed value into out and advances over it. It reports whether the read was successful.