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XPath query implementation for protocol-buffers

Overview

Protobufquery is an XPath query package for ProtocolBuffer documents. It lets you extract data from parsed ProtocolBuffer message through an XPath expression. Built-in XPath expression cache avoid re-compilation of XPath expression for each query.

Getting Started

Install Package

go get github.com/doclambda/protobufquery

Load ProtocolBuffer message.

msg := addressbookSample.ProtoReflect()
doc, err := Parse(msg)

ProtocolBuffer messages can also be instantiated dynamically using the dynamicpb package. Check out the referenced documentation for examples on loading bytes into those instances.

Example data

Using the ProtocolBuffer definition in testcases/addressbook we can define an example addressbook as

addressbook.AddressBook{
	People: []*addressbook.Person {
		{
			Name:  "John Doe",
			Id:    101,
			Email: "[email protected]",
			Age:   42,
		},
		{
			Name: "Jane Doe",
			Id:   102,
			Age:  40,
		},
		{
			Name:  "Jack Doe",
			Id:    201,
			Email: "[email protected]",
			Age:   12,
			Phones: []*addressbook.Person_PhoneNumber{
				{Number: "555-555-5555", Type: addressbook.Person_WORK},
			},
		},
		{
			Name:  "Jack Buck",
			Id:    301,
			Email: "[email protected]",
			Age:   19,
			Phones: []*addressbook.Person_PhoneNumber{
				{Number: "555-555-0000", Type: addressbook.Person_HOME},
				{Number: "555-555-0001", Type: addressbook.Person_MOBILE},
				{Number: "555-555-0002", Type: addressbook.Person_WORK},
			},
		},
		{
			Name:  "Janet Doe",
			Id:    1001,
			Email: "[email protected]",
			Age:   16,
			Phones: []*addressbook.Person_PhoneNumber{
				{Number: "555-777-0000"},
				{Number: "555-777-0001", Type: addressbook.Person_HOME},
			},
		},
	},
	Tags: []string {"home", "private", "friends"},
}

Using this definition we can perform the example queries below.

Get the XML equivalent of the addressbook.

xml := doc.OutputXML()

Find all names in the addressbook.

list := protobufquery.Find(doc, "/descendant::*[name() = 'people']/name")
// or equal to
list := protobufquery.Find(doc, "//name")
// or by QueryAll()
nodes, err := protobufquery.QueryAll(doc, "//name")

Find the third entry in the addressbook.

list := protobufquery.Find(doc, "/people[3]")

Find the first phone number.

book := protobufquery.Find(doc, "//phones[1]/number")

Find the last phone number.

book := protobufquery.Find(doc, "//phones[last()]/number")

Find all people without email address.

list := protobufquery.Find(doc, "/people[not(email)]")

Find all persons older than 18.

list := protobufquery.Find(doc, "/people[age > 18]")

Examples

func main() {
	addressbookSample := &addressbook.AddressBook{
		People: []*addressbook.Person {
			{
				Name:  "John Doe",
				Id:    101,
				Email: "[email protected]",
				Age:   42,
			},
			{
				Name: "Jane Doe",
				Id:   102,
				Age:  40,
			},
			{
				Name:  "Jack Doe",
				Id:    201,
				Email: "[email protected]",
				Age:   12,
				Phones: []*addressbook.Person_PhoneNumber{
					{Number: "555-555-5555", Type: addressbook.Person_WORK},
				},
			},
			{
				Name:  "Jack Buck",
				Id:    301,
				Email: "[email protected]",
				Age:   19,
				Phones: []*addressbook.Person_PhoneNumber{
					{Number: "555-555-0000", Type: addressbook.Person_HOME},
					{Number: "555-555-0001", Type: addressbook.Person_MOBILE},
					{Number: "555-555-0002", Type: addressbook.Person_WORK},
				},
			},
			{
				Name:  "Janet Doe",
				Id:    1001,
				Email: "[email protected]",
				Age:   16,
				Phones: []*addressbook.Person_PhoneNumber{
					{Number: "555-777-0000"},
					{Number: "555-777-0001", Type: addressbook.Person_HOME},
				},
			},
		},
		Tags: []string {"home", "private", "friends"},
	}
	doc, err := protobufquery.Parse(addressbookSample.ProtoReflect())
	if err != nil {
		panic(err)
	}

	nodes, err := protobufquery.QueryAll(doc, "//people")
	if err != nil {
		panic(err)
	}

	for _, person := range nodes {
		name := protobufquery.FindOne(person, "name").InnerText()
		numbers := make([]string, 0)
		for _, node := range protobufquery.Find(person, "phones/number") {
			numbers = append(numbers, node.InnerText())
		}
		fmt.Printf("%s: %s", name, strings.Join(numbers, ","))
	}
}

Implement Principle

If you are familiar with XPath and XML, you can easily figure out how to write your XPath expression.

addressbook.AddressBook{
	People: []*addressbook.Person {
		{
			Name:  "John Doe",
			Id:    101,
			Email: "[email protected]",
			Age:   42,
		},
		{
			Name: "Jane Doe",
			Id:   102,
			Age:  40,
		},
		{
			Name:  "Jack Doe",
			Id:    201,
			Email: "[email protected]",
			Age:   12,
			Phones: []*addressbook.Person_PhoneNumber{
				{Number: "555-555-5555", Type: addressbook.Person_WORK},
			},
		},
		{
			Name:  "Jack Buck",
			Id:    301,
			Email: "[email protected]",
			Age:   19,
			Phones: []*addressbook.Person_PhoneNumber{
				{Number: "555-555-0000", Type: addressbook.Person_HOME},
				{Number: "555-555-0001", Type: addressbook.Person_MOBILE},
				{Number: "555-555-0002", Type: addressbook.Person_WORK},
			},
		},
		{
			Name:  "Janet Doe",
			Id:    1001,
			Email: "[email protected]",
			Age:   16,
			Phones: []*addressbook.Person_PhoneNumber{
				{Number: "555-777-0000"},
				{Number: "555-777-0001", Type: addressbook.Person_HOME},
			},
		},
	},
	Tags: []string {"home", "private", "friends"},
}

The above ProtocolBuffer representation above will be convert by protobufquery to a structure similar to the XML document below:

<?xml version="1.0" encoding="UTF-8"?>
<people>
  <name>John Doe</name>
  <id>101</id>
  <email>[email protected]</email>
  <age>42</age>
</people>
<people>
  <name>Jane Doe</name>
  <id>102</id>
  <age>40</age>
</people>
<people>
  <name>Jack Doe</name>
  <id>201</id>
  <email>[email protected]</email>
  <age>12</age>
  <phones>
    <number>555-555-5555</number>
    <type>2</type>
  </phones>
</people>
<people>
  <name>Jack Buck</name>
  <id>301</id>
  <email>[email protected]</email>
  <age>19</age>
  <phones>
    <number>555-555-0000</number>
    <type>1</type>
  </phones>
  <phones>
    <number>555-555-0001</number>
  </phones>
  <phones>
    <number>555-555-0002</number>
    <type>2</type>
  </phones>
</people>
<people>
  <name>Janet Doe</name>
  <id>1001</id>
  <email>[email protected]</email>
  <age>16</age>
  <phones>
    <number>555-777-0000</number>
  </phones>
  <phones>
    <number>555-777-0001</number>
    <type>1</type>
  </phones>
</people>
<tags>
  <element>home</element>
  <element>private</element>
  <element>friends</element>
</tags>

Note: element is an anonymous element without name.

List of XPath query packages

Name Description
htmlquery XPath query package for the HTML document
xmlquery XPath query package for the XML document
jsonquery XPath query package for the JSON document
protobufquery XPath query package for ProtocolBuffer messages