protogofakeit

protogofakeit provides a utility for producing fake data in Protocol Buffer messages via gofakeit.

Example

protogofakeit works by annotating fields of protobuf messages with the (gofakeit.generate) custom options. Below, an example User and related messages have been annotated:

syntax="proto3";
import "gofakeit/gofakeit.proto";

message User {
  fixed64 user_id = 1;
  string first_name = 2 [(gofakeit.generate).tag = "{firstname}"];
  string last_name = 3 [(gofakeit.generate).tag = "{lastname}"];
  string email = 4 [(gofakeit.generate).tag = "{email}"];
  Location location = 5;
  repeated string hobbies = 6 [
    (gofakeit.generate).repeated.range = { min: 1, max: 3},
    (gofakeit.generate).repeated.element.tag = "{hobby}"
  ];
  map<string, PetType> pets = 7 [
    (gofakeit.generate).map.range = { min: 1, max: 3},
    (gofakeit.generate).map.key.tag = "{petname}"
  ];
}

enum PetType {
  PET_TYPE_UNSPECIFIED = 0;
  PET_TYPE_DOG = 1;
  PET_TYPE_CAT = 2;
}

message Location {
  double latitude = 1 [(gofakeit.generate).tag = "{latitude}"];
  double longitude = 2 [(gofakeit.generate).tag = "{longitude}"];
}

protogofakeit does NOT require any code generation (beyond protoc-gen-go) to populate a message:

package main

import (
	"fmt"

	"github.com/brianvoe/gofakeit/v6"
	"github.com/rodaine/protogofakeit"
	"github.com/rodaine/protogofakeit/example/gen"
	"google.golang.org/protobuf/encoding/prototext"
)

func main() {
	faker := gofakeit.New(3)
	protoFaker := protogofakeit.New(faker)
	user := &gen.User{}
	protoFaker.FakeProto(user)
	fmt.Println(prototext.Format(user))
}

Outputs:

user_id: 15864040051628833669
first_name: "Philip"
last_name: "Casper"
email: "tyreekstroman@mitchell.biz"
location: {
  latitude: 1.383491
  longitude: -62.968324
}
hobbies: [
  "Curling"
  "Slot car"
  "Fishkeeping"
]
pets: {
  "Archie": PET_TYPE_DOG
}

Annotating Messages

The protogofakeit proto files must be imported into your proto files to set the custom options on fields.

protoc CLI

If you are using protoc, the proto directory must be in the import path to compile:

protoc \
  -I "$PROTOGOFAKEIT_PATH/proto" \
  --go_out="$OUTPUT_DIR" \
  $PROTOS

buf CLI

If you are using buf, add a dependency on buf.build/rodaine/protogofakeit to your module's buf.yaml.

# buf.yaml
version: v1
deps:
  - buf.build/rodaine/protogofakeit
# ...

Remember to run buf mod update to update the lockfile. If you are using buf managed mode for code generation, ensure the correct import path is used for protogofakeit:

# buf.gen.yaml
version: v1
managed:
  enabled: true
  go_package_prefix:
    override:
      buf.build/rodaine/protogofakeit: github.com/rodaine/protogofakeit/gen
# ...

Default Generation

By default, protogofakeit populates all fields of a message with random values:

numbers: a uniform, random value in the full range of the underlying type.
bool: a random true or false
string: a random ASCII string between 4–10 characters, inclusive.
bytes: random slice of 4–10 bytes (inclusive) in the ASCII range.
enums: a random defined value of the enum (including any value assigned to 0).
messages: the field is set and its fields are populated with random data, to the max recursion depth (default of 5).
repeated: a slice of 4–10 (inclusive) elements populated with random values.
map: a map of 4–10 (inclusive) key-value pairs populated with random keys and values. Note that the total pairs may be less if there is a key collision during generation.
oneof: a random field (or no field) contained in the oneof will be set to its random value.
optional: optional fields are always set.
google.protobuf.Timestamp: a random valid timestamp value
google.protobuf.Duration: a random valid duration value

Default sizes of string, bytes, repeated, and map fields as well as the maximum recursion depth can be customized when initializing the ProtoFaker instance via Option values. See the documentation for more details.

Skip

Fake generation can be skipped on any field by annotating it with skip:

message Skipped {
  string value = 1 [(gofakeit.generate).skip = true];
}

Scalar values will default to their zero value, while message, repeated, and map fields will be empty/unset.

Tags

The primary way of customizing field generation is via tags, which are identical to the struct tags used to customize plain-old Go structs for gofakeit. Tags act as simplified templates using curly braces ({...}) to specify "function" calls to the faker.

After resolving any functions, the tag value is then parsed to match the type of the associated field. Any parse errors result in fake generation to fail:

integers: either strconv.ParseInt(tag, 0, n) or strconv.ParseUint(tag, 0, n) if unsigned, where n is the bitsize of the field.
floats: strconv.ParseFloat(tag, n), where n is the bitsize of the field.
bool: strconv.ParseBool(tag)
string: as-is
bytes: []byte(tag)
enums: strconv.ParseInt(tag, 0, 32). Undefined enum values are supported/possible.
google.protobuf.Timestamp: time.Parse(format, tag), where format is a time.Layout based format (default of time.RFC3339Nano).
google.protobuf.Duration: time.ParseDuration(tag)

Tags are ignored on message, repeated, and map fields. The timestamp parse format can be customized when initializing the ProtoFaker instance.

message Tags {
  string name = 1 [(gofakeit.generate).tag = "{firstname}"]; // random
  string foo = 2 [(gofakeit.generate).tag = "bar"]; // constant "bar"
  int32 age = 3 [(gofakeit.generate).tag = "{intrange:13,99}"]; // function parameters
  string pet = 4[(gofakeit.generate).tag = "{petname} ({animal})"]; // mixed
}

Custom tag functions can be registered on the underlying faker, though this is strongly discouraged as it makes the tags less portable.

Templates

For more complex fake generation, Go templates are supported, enabling loops, conditionals, and other logic alongside the functions available from the underlying faker. The resulting value is parsed the same as tags above. For long templates, a series of strings can be used which are automatically concatenated by the protobuf compiler.

message Templates {
  string cmd = 1 [
    (gofakeit.generate).template = 
      '{{ $lang := RandomString (SliceString "go" "python" "javascript" }}'
      '{{ if eq $lang "go" }}go get'
      '{{ else if eq $lang "python" }}pip install'
      '{{ else }}npm install'
      '{{ end }} ({{ $lang }})'
  ];
}

Templates are orders of magnitude slower than tags, so only reach for them if you need something more powerful. Custom template functions can be registered when configuring the ProtoFaker instance, though this is strongly discouraged as it makes the templates less portable.

Repeated / Map Fields

Repeated (list) and map fields can be customized beyond the defaults, including their size and items.

Size

A repeated or map field's size can be specified via either a constant len or a random range.

message Sizes {
  repeated string a = 1 [
    (gofakeit.generate).repeated.len = 3 // exactly 3 elements
  ]; 
  map<string, int32> b = 2 [
    (gofakeit.generate).map.range = { min: 0, max: 2 } // 0-2 key-value pairs, inclusive.
  ];  
}

Items

A repeated field's elements or a map field's keys and values can have options associated with them just like singular fields. Note that message items still ignore any tag or template options.

message Elements {
  repeated string a = 1 [
    (gofakeit.generate).repeated.element.tag = "{animal}"
  ];
  map<string, int32> b = 2 [
    (gofakeit.generate).map.key.tag = "{petname}",
    (gofakeit.generate).map.value.tag = "{intrange:0,100}"
  ];
}

rodaine / protogofakeit