712 lines
22 KiB
Go
712 lines
22 KiB
Go
// Copyright 2016 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package tls implements functionality for dealing with TLS-encoded data,
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// as defined in RFC 5246. This includes parsing and generation of TLS-encoded
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// data, together with utility functions for dealing with the DigitallySigned
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// TLS type.
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package tls
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"reflect"
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"strconv"
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"strings"
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)
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// This file holds utility functions for TLS encoding/decoding data
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// as per RFC 5246 section 4.
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// A structuralError suggests that the TLS data is valid, but the Go type
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// which is receiving it doesn't match.
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type structuralError struct {
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field string
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msg string
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}
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func (e structuralError) Error() string {
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var prefix string
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if e.field != "" {
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prefix = e.field + ": "
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}
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return "tls: structure error: " + prefix + e.msg
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}
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// A syntaxError suggests that the TLS data is invalid.
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type syntaxError struct {
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field string
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msg string
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}
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func (e syntaxError) Error() string {
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var prefix string
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if e.field != "" {
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prefix = e.field + ": "
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}
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return "tls: syntax error: " + prefix + e.msg
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}
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// Uint24 is an unsigned 3-byte integer.
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type Uint24 uint32
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// Enum is an unsigned integer.
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type Enum uint64
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var (
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uint8Type = reflect.TypeOf(uint8(0))
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uint16Type = reflect.TypeOf(uint16(0))
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uint24Type = reflect.TypeOf(Uint24(0))
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uint32Type = reflect.TypeOf(uint32(0))
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uint64Type = reflect.TypeOf(uint64(0))
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enumType = reflect.TypeOf(Enum(0))
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)
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// Unmarshal parses the TLS-encoded data in b and uses the reflect package to
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// fill in an arbitrary value pointed at by val. Because Unmarshal uses the
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// reflect package, the structs being written to must use exported fields
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// (upper case names).
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//
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// The mappings between TLS types and Go types is as follows; some fields
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// must have tags (to indicate their encoded size).
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//
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// TLS Go Required Tags
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// opaque byte / uint8
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// uint8 byte / uint8
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// uint16 uint16
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// uint24 tls.Uint24
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// uint32 uint32
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// uint64 uint64
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// enum tls.Enum size:S or maxval:N
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// Type<N,M> []Type minlen:N,maxlen:M
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// opaque[N] [N]byte / [N]uint8
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// uint8[N] [N]byte / [N]uint8
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// struct { } struct { }
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// select(T) {
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// case e1: Type *T selector:Field,val:e1
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// }
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//
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// TLS variants (RFC 5246 s4.6.1) are only supported when the value of the
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// associated enumeration type is available earlier in the same enclosing
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// struct, and each possible variant is marked with a selector tag (to
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// indicate which field selects the variants) and a val tag (to indicate
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// what value of the selector picks this particular field).
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//
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// For example, a TLS structure:
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//
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// enum { e1(1), e2(2) } EnumType;
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// struct {
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// EnumType sel;
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// select(sel) {
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// case e1: uint16
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// case e2: uint32
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// } data;
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// } VariantItem;
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//
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// would have a corresponding Go type:
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//
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// type VariantItem struct {
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// Sel tls.Enum `tls:"maxval:2"`
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// Data16 *uint16 `tls:"selector:Sel,val:1"`
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// Data32 *uint32 `tls:"selector:Sel,val:2"`
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// }
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//
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// TLS fixed-length vectors of types other than opaque or uint8 are not supported.
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//
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// For TLS variable-length vectors that are themselves used in other vectors,
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// create a single-field structure to represent the inner type. For example, for:
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//
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// opaque InnerType<1..65535>;
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// struct {
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// InnerType inners<1,65535>;
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// } Something;
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//
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// convert to:
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//
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// type InnerType struct {
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// Val []byte `tls:"minlen:1,maxlen:65535"`
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// }
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// type Something struct {
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// Inners []InnerType `tls:"minlen:1,maxlen:65535"`
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// }
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//
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// If the encoded value does not fit in the Go type, Unmarshal returns a parse error.
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func Unmarshal(b []byte, val interface{}) ([]byte, error) {
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return UnmarshalWithParams(b, val, "")
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}
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// UnmarshalWithParams allows field parameters to be specified for the
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// top-level element. The form of the params is the same as the field tags.
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func UnmarshalWithParams(b []byte, val interface{}, params string) ([]byte, error) {
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info, err := fieldTagToFieldInfo(params, "")
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if err != nil {
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return nil, err
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}
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// The passed in interface{} is a pointer (to allow the value to be written
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// to); extract the pointed-to object as a reflect.Value, so parseField
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// can do various introspection things.
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v := reflect.ValueOf(val).Elem()
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offset, err := parseField(v, b, 0, info)
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if err != nil {
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return nil, err
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}
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return b[offset:], nil
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}
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// Return the number of bytes needed to encode values up to (and including) x.
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func byteCount(x uint64) uint {
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switch {
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case x < 0x100:
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return 1
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case x < 0x10000:
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return 2
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case x < 0x1000000:
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return 3
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case x < 0x100000000:
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return 4
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case x < 0x10000000000:
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return 5
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case x < 0x1000000000000:
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return 6
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case x < 0x100000000000000:
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return 7
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default:
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return 8
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}
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}
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type fieldInfo struct {
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count uint // Number of bytes
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countSet bool
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minlen uint64 // Only relevant for slices
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maxlen uint64 // Only relevant for slices
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selector string // Only relevant for select sub-values
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val uint64 // Only relevant for select sub-values
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name string // Used for better error messages
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}
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func (i *fieldInfo) fieldName() string {
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if i == nil {
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return ""
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}
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return i.name
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}
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// Given a tag string, return a fieldInfo describing the field.
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func fieldTagToFieldInfo(str string, name string) (*fieldInfo, error) {
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var info *fieldInfo
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// Iterate over clauses in the tag, ignoring any that don't parse properly.
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for _, part := range strings.Split(str, ",") {
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switch {
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case strings.HasPrefix(part, "maxval:"):
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if v, err := strconv.ParseUint(part[7:], 10, 64); err == nil {
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info = &fieldInfo{count: byteCount(v), countSet: true}
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}
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case strings.HasPrefix(part, "size:"):
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if sz, err := strconv.ParseUint(part[5:], 10, 32); err == nil {
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info = &fieldInfo{count: uint(sz), countSet: true}
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}
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case strings.HasPrefix(part, "maxlen:"):
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v, err := strconv.ParseUint(part[7:], 10, 64)
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if err != nil {
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continue
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}
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if info == nil {
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info = &fieldInfo{}
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}
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info.count = byteCount(v)
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info.countSet = true
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info.maxlen = v
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case strings.HasPrefix(part, "minlen:"):
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v, err := strconv.ParseUint(part[7:], 10, 64)
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if err != nil {
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continue
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}
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if info == nil {
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info = &fieldInfo{}
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}
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info.minlen = v
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case strings.HasPrefix(part, "selector:"):
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if info == nil {
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info = &fieldInfo{}
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}
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info.selector = part[9:]
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case strings.HasPrefix(part, "val:"):
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v, err := strconv.ParseUint(part[4:], 10, 64)
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if err != nil {
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continue
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}
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if info == nil {
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info = &fieldInfo{}
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}
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info.val = v
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}
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}
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if info != nil {
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info.name = name
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if info.selector == "" {
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if info.count < 1 {
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return nil, structuralError{name, "field of unknown size in " + str}
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} else if info.count > 8 {
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return nil, structuralError{name, "specified size too large in " + str}
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} else if info.minlen > info.maxlen {
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return nil, structuralError{name, "specified length range inverted in " + str}
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} else if info.val > 0 {
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return nil, structuralError{name, "specified selector value but not field in " + str}
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}
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}
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} else if name != "" {
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info = &fieldInfo{name: name}
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}
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return info, nil
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}
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// Check that a value fits into a field described by a fieldInfo structure.
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func (i fieldInfo) check(val uint64, fldName string) error {
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if val >= (1 << (8 * i.count)) {
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return structuralError{fldName, fmt.Sprintf("value %d too large for size", val)}
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}
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if i.maxlen != 0 {
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if val < i.minlen {
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return structuralError{fldName, fmt.Sprintf("value %d too small for minimum %d", val, i.minlen)}
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}
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if val > i.maxlen {
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return structuralError{fldName, fmt.Sprintf("value %d too large for maximum %d", val, i.maxlen)}
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}
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}
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return nil
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}
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// readVarUint reads an big-endian unsigned integer of the given size in
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// bytes.
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func readVarUint(data []byte, info *fieldInfo) (uint64, error) {
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if info == nil || !info.countSet {
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return 0, structuralError{info.fieldName(), "no field size information available"}
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}
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if len(data) < int(info.count) {
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return 0, syntaxError{info.fieldName(), "truncated variable-length integer"}
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}
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var result uint64
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for i := uint(0); i < info.count; i++ {
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result = (result << 8) | uint64(data[i])
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}
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if err := info.check(result, info.name); err != nil {
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return 0, err
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}
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return result, nil
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}
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// parseField is the main parsing function. Given a byte slice and an offset
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// (in bytes) into the data, it will try to parse a suitable ASN.1 value out
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// and store it in the given Value.
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func parseField(v reflect.Value, data []byte, initOffset int, info *fieldInfo) (int, error) {
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offset := initOffset
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rest := data[offset:]
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fieldType := v.Type()
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// First look for known fixed types.
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switch fieldType {
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case uint8Type:
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if len(rest) < 1 {
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return offset, syntaxError{info.fieldName(), "truncated uint8"}
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}
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v.SetUint(uint64(rest[0]))
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offset++
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return offset, nil
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case uint16Type:
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if len(rest) < 2 {
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return offset, syntaxError{info.fieldName(), "truncated uint16"}
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}
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v.SetUint(uint64(binary.BigEndian.Uint16(rest)))
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offset += 2
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return offset, nil
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case uint24Type:
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if len(rest) < 3 {
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return offset, syntaxError{info.fieldName(), "truncated uint24"}
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}
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v.SetUint(uint64(data[0])<<16 | uint64(data[1])<<8 | uint64(data[2]))
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offset += 3
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return offset, nil
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case uint32Type:
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if len(rest) < 4 {
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return offset, syntaxError{info.fieldName(), "truncated uint32"}
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}
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v.SetUint(uint64(binary.BigEndian.Uint32(rest)))
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offset += 4
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return offset, nil
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case uint64Type:
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if len(rest) < 8 {
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return offset, syntaxError{info.fieldName(), "truncated uint64"}
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}
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v.SetUint(uint64(binary.BigEndian.Uint64(rest)))
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offset += 8
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return offset, nil
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}
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// Now deal with user-defined types.
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switch v.Kind() {
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case enumType.Kind():
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// Assume that anything of the same kind as Enum is an Enum, so that
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// users can alias types of their own to Enum.
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val, err := readVarUint(rest, info)
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if err != nil {
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return offset, err
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}
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v.SetUint(val)
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offset += int(info.count)
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return offset, nil
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case reflect.Struct:
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structType := fieldType
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// TLS includes a select(Enum) {..} construct, where the value of an enum
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// indicates which variant field is present (like a C union). We require
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// that the enum value be an earlier field in the same structure (the selector),
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// and that each of the possible variant destination fields be pointers.
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// So the Go mapping looks like:
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// type variantType struct {
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// Which tls.Enum `tls:"size:1"` // this is the selector
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// Val1 *type1 `tls:"selector:Which,val:1"` // this is a destination
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// Val2 *type2 `tls:"selector:Which,val:1"` // this is a destination
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// }
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// To deal with this, we track any enum-like fields and their values...
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enums := make(map[string]uint64)
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// .. and we track which selector names we've seen (in the destination field tags),
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// and whether a destination for that selector has been chosen.
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selectorSeen := make(map[string]bool)
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for i := 0; i < structType.NumField(); i++ {
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// Find information about this field.
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tag := structType.Field(i).Tag.Get("tls")
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fieldInfo, err := fieldTagToFieldInfo(tag, structType.Field(i).Name)
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if err != nil {
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return offset, err
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}
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destination := v.Field(i)
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if fieldInfo.selector != "" {
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// This is a possible select(Enum) destination, so first check that the referenced
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// selector field has already been seen earlier in the struct.
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choice, ok := enums[fieldInfo.selector]
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if !ok {
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return offset, structuralError{fieldInfo.name, "selector not seen: " + fieldInfo.selector}
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}
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if structType.Field(i).Type.Kind() != reflect.Ptr {
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return offset, structuralError{fieldInfo.name, "choice field not a pointer type"}
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}
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// Is this the first mention of the selector field name? If so, remember it.
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seen, ok := selectorSeen[fieldInfo.selector]
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if !ok {
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selectorSeen[fieldInfo.selector] = false
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}
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if choice != fieldInfo.val {
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// This destination field was not the chosen one, so make it nil (we checked
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// it was a pointer above).
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v.Field(i).Set(reflect.Zero(structType.Field(i).Type))
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continue
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}
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if seen {
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// We already saw a different destination field receive the value for this
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// selector value, which indicates a badly annotated structure.
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return offset, structuralError{fieldInfo.name, "duplicate selector value for " + fieldInfo.selector}
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}
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selectorSeen[fieldInfo.selector] = true
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// Make an object of the pointed-to type and parse into that.
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v.Field(i).Set(reflect.New(structType.Field(i).Type.Elem()))
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destination = v.Field(i).Elem()
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}
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offset, err = parseField(destination, data, offset, fieldInfo)
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if err != nil {
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return offset, err
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}
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// Remember any possible tls.Enum values encountered in case they are selectors.
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if structType.Field(i).Type.Kind() == enumType.Kind() {
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enums[structType.Field(i).Name] = v.Field(i).Uint()
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}
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}
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// Now we have seen all fields in the structure, check that all select(Enum) {..} selector
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// fields found a destination to put their data in.
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for selector, seen := range selectorSeen {
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if !seen {
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return offset, syntaxError{info.fieldName(), selector + ": unhandled value for selector"}
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}
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}
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return offset, nil
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case reflect.Array:
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datalen := v.Len()
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if datalen > len(rest) {
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return offset, syntaxError{info.fieldName(), "truncated array"}
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}
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inner := rest[:datalen]
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offset += datalen
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if fieldType.Elem().Kind() != reflect.Uint8 {
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// Only byte/uint8 arrays are supported
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return offset, structuralError{info.fieldName(), "unsupported array type: " + v.Type().String()}
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}
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reflect.Copy(v, reflect.ValueOf(inner))
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return offset, nil
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case reflect.Slice:
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sliceType := fieldType
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// Slices represent variable-length vectors, which are prefixed by a length field.
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// The fieldInfo indicates the size of that length field.
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varlen, err := readVarUint(rest, info)
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if err != nil {
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return offset, err
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}
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datalen := int(varlen)
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offset += int(info.count)
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rest = rest[info.count:]
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if datalen > len(rest) {
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return offset, syntaxError{info.fieldName(), "truncated slice"}
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}
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inner := rest[:datalen]
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offset += datalen
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if fieldType.Elem().Kind() == reflect.Uint8 {
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// Fast version for []byte
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v.Set(reflect.MakeSlice(sliceType, datalen, datalen))
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reflect.Copy(v, reflect.ValueOf(inner))
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return offset, nil
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}
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v.Set(reflect.MakeSlice(sliceType, 0, datalen))
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single := reflect.New(sliceType.Elem())
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for innerOffset := 0; innerOffset < len(inner); {
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var err error
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innerOffset, err = parseField(single.Elem(), inner, innerOffset, nil)
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if err != nil {
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return offset, err
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}
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v.Set(reflect.Append(v, single.Elem()))
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}
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return offset, nil
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default:
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return offset, structuralError{info.fieldName(), fmt.Sprintf("unsupported type: %s of kind %s", fieldType, v.Kind())}
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}
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}
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// Marshal returns the TLS encoding of val.
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func Marshal(val interface{}) ([]byte, error) {
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return MarshalWithParams(val, "")
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}
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|
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// MarshalWithParams returns the TLS encoding of val, and allows field
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|
// parameters to be specified for the top-level element. The form
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// of the params is the same as the field tags.
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|
func MarshalWithParams(val interface{}, params string) ([]byte, error) {
|
|
info, err := fieldTagToFieldInfo(params, "")
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
var out bytes.Buffer
|
|
v := reflect.ValueOf(val)
|
|
if err := marshalField(&out, v, info); err != nil {
|
|
return nil, err
|
|
}
|
|
return out.Bytes(), err
|
|
}
|
|
|
|
func marshalField(out *bytes.Buffer, v reflect.Value, info *fieldInfo) error {
|
|
var prefix string
|
|
if info != nil && len(info.name) > 0 {
|
|
prefix = info.name + ": "
|
|
}
|
|
fieldType := v.Type()
|
|
// First look for known fixed types.
|
|
switch fieldType {
|
|
case uint8Type:
|
|
out.WriteByte(byte(v.Uint()))
|
|
return nil
|
|
case uint16Type:
|
|
scratch := make([]byte, 2)
|
|
binary.BigEndian.PutUint16(scratch, uint16(v.Uint()))
|
|
out.Write(scratch)
|
|
return nil
|
|
case uint24Type:
|
|
i := v.Uint()
|
|
if i > 0xffffff {
|
|
return structuralError{info.fieldName(), fmt.Sprintf("uint24 overflow %d", i)}
|
|
}
|
|
scratch := make([]byte, 4)
|
|
binary.BigEndian.PutUint32(scratch, uint32(i))
|
|
out.Write(scratch[1:])
|
|
return nil
|
|
case uint32Type:
|
|
scratch := make([]byte, 4)
|
|
binary.BigEndian.PutUint32(scratch, uint32(v.Uint()))
|
|
out.Write(scratch)
|
|
return nil
|
|
case uint64Type:
|
|
scratch := make([]byte, 8)
|
|
binary.BigEndian.PutUint64(scratch, uint64(v.Uint()))
|
|
out.Write(scratch)
|
|
return nil
|
|
}
|
|
|
|
// Now deal with user-defined types.
|
|
switch v.Kind() {
|
|
case enumType.Kind():
|
|
i := v.Uint()
|
|
if info == nil {
|
|
return structuralError{info.fieldName(), "enum field tag missing"}
|
|
}
|
|
if err := info.check(i, prefix); err != nil {
|
|
return err
|
|
}
|
|
scratch := make([]byte, 8)
|
|
binary.BigEndian.PutUint64(scratch, uint64(i))
|
|
out.Write(scratch[(8 - info.count):])
|
|
return nil
|
|
case reflect.Struct:
|
|
structType := fieldType
|
|
enums := make(map[string]uint64) // Values of any Enum fields
|
|
// The comment parseField() describes the mapping of the TLS select(Enum) {..} construct;
|
|
// here we have selector and source (rather than destination) fields.
|
|
|
|
// Track which selector names we've seen (in the source field tags), and whether a source
|
|
// value for that selector has been processed.
|
|
selectorSeen := make(map[string]bool)
|
|
for i := 0; i < structType.NumField(); i++ {
|
|
// Find information about this field.
|
|
tag := structType.Field(i).Tag.Get("tls")
|
|
fieldInfo, err := fieldTagToFieldInfo(tag, structType.Field(i).Name)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
source := v.Field(i)
|
|
if fieldInfo.selector != "" {
|
|
// This field is a possible source for a select(Enum) {..}. First check
|
|
// the selector field name has been seen.
|
|
choice, ok := enums[fieldInfo.selector]
|
|
if !ok {
|
|
return structuralError{fieldInfo.name, "selector not seen: " + fieldInfo.selector}
|
|
}
|
|
if structType.Field(i).Type.Kind() != reflect.Ptr {
|
|
return structuralError{fieldInfo.name, "choice field not a pointer type"}
|
|
}
|
|
// Is this the first mention of the selector field name? If so, remember it.
|
|
seen, ok := selectorSeen[fieldInfo.selector]
|
|
if !ok {
|
|
selectorSeen[fieldInfo.selector] = false
|
|
}
|
|
if choice != fieldInfo.val {
|
|
// This source was not chosen; police that it should be nil.
|
|
if v.Field(i).Pointer() != uintptr(0) {
|
|
return structuralError{fieldInfo.name, "unchosen field is non-nil"}
|
|
}
|
|
continue
|
|
}
|
|
if seen {
|
|
// We already saw a different source field generate the value for this
|
|
// selector value, which indicates a badly annotated structure.
|
|
return structuralError{fieldInfo.name, "duplicate selector value for " + fieldInfo.selector}
|
|
}
|
|
selectorSeen[fieldInfo.selector] = true
|
|
if v.Field(i).Pointer() == uintptr(0) {
|
|
return structuralError{fieldInfo.name, "chosen field is nil"}
|
|
}
|
|
// Marshal from the pointed-to source object.
|
|
source = v.Field(i).Elem()
|
|
}
|
|
|
|
var fieldData bytes.Buffer
|
|
if err := marshalField(&fieldData, source, fieldInfo); err != nil {
|
|
return err
|
|
}
|
|
out.Write(fieldData.Bytes())
|
|
|
|
// Remember any tls.Enum values encountered in case they are selectors.
|
|
if structType.Field(i).Type.Kind() == enumType.Kind() {
|
|
enums[structType.Field(i).Name] = v.Field(i).Uint()
|
|
}
|
|
}
|
|
// Now we have seen all fields in the structure, check that all select(Enum) {..} selector
|
|
// fields found a source field get get their data from.
|
|
for selector, seen := range selectorSeen {
|
|
if !seen {
|
|
return syntaxError{info.fieldName(), selector + ": unhandled value for selector"}
|
|
}
|
|
}
|
|
return nil
|
|
|
|
case reflect.Array:
|
|
datalen := v.Len()
|
|
arrayType := fieldType
|
|
if arrayType.Elem().Kind() != reflect.Uint8 {
|
|
// Only byte/uint8 arrays are supported
|
|
return structuralError{info.fieldName(), "unsupported array type"}
|
|
}
|
|
bytes := make([]byte, datalen)
|
|
for i := 0; i < datalen; i++ {
|
|
bytes[i] = uint8(v.Index(i).Uint())
|
|
}
|
|
_, err := out.Write(bytes)
|
|
return err
|
|
|
|
case reflect.Slice:
|
|
if info == nil {
|
|
return structuralError{info.fieldName(), "slice field tag missing"}
|
|
}
|
|
|
|
sliceType := fieldType
|
|
if sliceType.Elem().Kind() == reflect.Uint8 {
|
|
// Fast version for []byte: first write the length as info.count bytes.
|
|
datalen := v.Len()
|
|
scratch := make([]byte, 8)
|
|
binary.BigEndian.PutUint64(scratch, uint64(datalen))
|
|
out.Write(scratch[(8 - info.count):])
|
|
|
|
if err := info.check(uint64(datalen), prefix); err != nil {
|
|
return err
|
|
}
|
|
// Then just write the data.
|
|
bytes := make([]byte, datalen)
|
|
for i := 0; i < datalen; i++ {
|
|
bytes[i] = uint8(v.Index(i).Uint())
|
|
}
|
|
_, err := out.Write(bytes)
|
|
return err
|
|
}
|
|
// General version: use a separate Buffer to write the slice entries into.
|
|
var innerBuf bytes.Buffer
|
|
for i := 0; i < v.Len(); i++ {
|
|
if err := marshalField(&innerBuf, v.Index(i), nil); err != nil {
|
|
return err
|
|
}
|
|
}
|
|
|
|
// Now insert (and check) the size.
|
|
size := uint64(innerBuf.Len())
|
|
if err := info.check(size, prefix); err != nil {
|
|
return err
|
|
}
|
|
scratch := make([]byte, 8)
|
|
binary.BigEndian.PutUint64(scratch, size)
|
|
out.Write(scratch[(8 - info.count):])
|
|
|
|
// Then copy the data.
|
|
_, err := out.Write(innerBuf.Bytes())
|
|
return err
|
|
|
|
default:
|
|
return structuralError{info.fieldName(), fmt.Sprintf("unsupported type: %s of kind %s", fieldType, v.Kind())}
|
|
}
|
|
}
|