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123 lines
3.6 KiB
Go
123 lines
3.6 KiB
Go
// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package protopath provides functionality for
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// representing a sequence of protobuf reflection operations on a message.
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package protopath
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import (
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"fmt"
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"google.golang.org/protobuf/internal/msgfmt"
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"google.golang.org/protobuf/reflect/protoreflect"
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)
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// NOTE: The Path and Values are separate types here since there are use cases
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// where you would like to "address" some value in a message with just the path
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// and don't have the value information available.
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//
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// This is different from how "github.com/google/go-cmp/cmp".Path operates,
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// which combines both path and value information together.
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// Since the cmp package itself is the only one ever constructing a cmp.Path,
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// it will always have the value available.
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// Path is a sequence of protobuf reflection steps applied to some root
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// protobuf message value to arrive at the current value.
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// The first step must be a Root step.
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type Path []Step
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// TODO: Provide a Parse function that parses something similar to or
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// perhaps identical to the output of Path.String.
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// Index returns the ith step in the path and supports negative indexing.
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// A negative index starts counting from the tail of the Path such that -1
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// refers to the last step, -2 refers to the second-to-last step, and so on.
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// It returns a zero Step value if the index is out-of-bounds.
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func (p Path) Index(i int) Step {
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if i < 0 {
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i = len(p) + i
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}
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if i < 0 || i >= len(p) {
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return Step{}
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}
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return p[i]
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}
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// String returns a structured representation of the path
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// by concatenating the string representation of every path step.
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func (p Path) String() string {
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var b []byte
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for _, s := range p {
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b = s.appendString(b)
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}
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return string(b)
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}
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// Values is a Path paired with a sequence of values at each step.
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// The lengths of Path and Values must be identical.
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// The first step must be a Root step and
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// the first value must be a concrete message value.
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type Values struct {
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Path Path
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Values []protoreflect.Value
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}
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// Len reports the length of the path and values.
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// If the path and values have differing length, it returns the minimum length.
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func (p Values) Len() int {
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n := len(p.Path)
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if n > len(p.Values) {
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n = len(p.Values)
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}
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return n
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}
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// Index returns the ith step and value and supports negative indexing.
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// A negative index starts counting from the tail of the Values such that -1
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// refers to the last pair, -2 refers to the second-to-last pair, and so on.
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func (p Values) Index(i int) (out struct {
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Step Step
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Value protoreflect.Value
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}) {
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// NOTE: This returns a single struct instead of two return values so that
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// callers can make use of the the value in an expression:
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// vs.Index(i).Value.Interface()
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n := p.Len()
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if i < 0 {
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i = n + i
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}
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if i < 0 || i >= n {
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return out
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}
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out.Step = p.Path[i]
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out.Value = p.Values[i]
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return out
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}
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// String returns a humanly readable representation of the path and last value.
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// Do not depend on the output being stable.
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//
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// For example:
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//
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// (path.to.MyMessage).list_field[5].map_field["hello"] = {hello: "world"}
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func (p Values) String() string {
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n := p.Len()
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if n == 0 {
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return ""
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}
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// Determine the field descriptor associated with the last step.
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var fd protoreflect.FieldDescriptor
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last := p.Index(-1)
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switch last.Step.kind {
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case FieldAccessStep:
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fd = last.Step.FieldDescriptor()
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case MapIndexStep, ListIndexStep:
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fd = p.Index(-2).Step.FieldDescriptor()
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}
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// Format the full path with the last value.
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return fmt.Sprintf("%v = %v", p.Path[:n], msgfmt.FormatValue(last.Value, fd))
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}
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