Go template for converting gRPC service proto files into a Postman Collection using `protoc-gen-doc`.

postman.tmpl

{{- $messages := (index .Files 0).Messages -}}
{{- if gt (len .Files) 1 -}}
{{- range $file := (slice .Files 1) -}}
{{- $messages = concat $messages $file.Messages -}}
{{- end -}}
{{- end -}}
{
  "info": {
    "name": "{{coalesce (env "POSTMAN_COLLECTION_NAME") "Imported gRPC JSON API"}}",
    "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json",
    "description": "## Messages\n\n
{{- range $msg := $messages }}
{{- $msgDesc := (toJson $msg.Description) }}#### {{ $msg.FullName }}\n\n
{{- substr 1 (int (sub (len $msgDesc) 1)) $msgDesc }}\n\n
{{- if $msg.HasFields }}| Field | Type | Description |\n| ----- | ---- | ----------- |\n
{{- range $f := $msg.Fields }}
{{- $desc := (toJson $f.Description) }}{{ $descLen := len $desc}}| {{$f.Name}} | {{$f.FullType}} | {{substr 1 (int (sub (len $desc) 1)) $desc}} |\n
{{- end }}
{{- end }}\n
{{- end }}"
  },
  "item": [
{{- $fileLen := len .Files }}
{{- range $fileIndex, $file := .Files -}}
{{- if $file.HasServices }}
    {
      "name": "{{$file.Name}}",
      "description": {{$file.Description | toJson }},
      "item": [
{{- $serviceLen := len $file.Services}}
{{- range $serviceIndex, $service := .Services}}
        {
          "name": "{{$service.FullName}}",
          "description": {{$service.Description | toJson }},
          "items": [
{{- $methodLen := len $service.Methods}}
{{- range $methodIndex, $method := $service.Methods}}
            {
              "name": "{{$method.Name}}",
              "request": {
                "description": {{(printf "%s\n\n\n\nRequest Message: `%s`\n\nResponse Message: `%s`\n" $method.Description $method.RequestFullType $method.ResponseFullType) | toJson }},
                "method": "POST",
                "header": [
                  {
                    "key": "Content-Type",
                    "value": "application/grpc+json"
                  },
                  {
                    "key": "Grpc-Insecure",
                    "value": "{{"{{"}}grpcInsecure{{"}}"}}"
                  }
                ],
                "url": {
                  "raw": "{{"{{"}}baseURL{{"}}"}}/{{$service.FullName}}/{{$method.Name}}",
                  "host": [
                    "{{"{{"}}baseURL{{"}}"}}"
                  ],
                  "path": [
                    "{{$service.FullName}}",
                    "{{$method.Name}}"
                  ]
                },
                "body": {
                  "mode": "raw",
{{- range $msg := $messages -}}
{{if eq $msg.FullName $method.RequestFullType }}
                  "raw": "{\n
{{- $fieldLen := len $msg.Fields -}}
{{- range $fieldIndex, $field := $msg.Fields -}}
{{"  \\\""}}{{$field.Name}}\": {{ if eq $field.FullType "string" -}}
{{- "\\\"\\\"" -}}
{{- else if eq $field.FullType "bool" -}}
{{- "true" -}}
{{- else if (has $field.FullType (list "int" "int32" "int64" "double" "float" "uint32" "uint64" "sint32" "sint64" "fixed32" "fixed64" "sfixed32" "sfixed64")) -}}
{{- "0" -}}
{{- else -}}
{{- "{}" -}}
{{- end -}}{{if lt $fieldIndex (sub $fieldLen 1)}},\n{{end}}
{{- end }}\n}"
                }
{{- end }}
{{- end }}
              }
            }{{if lt $methodIndex (sub $methodLen 1)}},{{end}}
{{- end}}
          ]
        }{{if lt $serviceIndex (sub $serviceLen 1)}},{{end}}
      ]
{{- end}}
    }{{if (lt $fileIndex (sub $fileLen 1))}}{{if (first (slice $.Files (add $fileIndex 1) 1)).HasServices}},{{end}}{{end}}
{{- end}}
{{- end}}
  ]
}

zz_helloworld.proto

// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

option java_multiple_files = true;
option java_package = "io.grpc.examples.helloworld";
option java_outer_classname = "HelloWorldProto";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a "greeting"
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

zz_helloworld_collection.json

{
  "info": {
    "name": "Hello World gRPC JSON API",
    "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json",
    "description": "## Messages\n\n#### helloworld.HelloReply\n\nThe response message containing the greetings\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| message | string |  |\n\n#### helloworld.HelloRequest\n\nThe request message containing the user's name.\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| name | string |  |\n\n"
  },
  "item": [
    {
      "name": "helloworld.proto",
      "description": "",
      "item": [
        {
          "name": "helloworld.Greeter",
          "description": "The greeting service definition.",
          "items": [
            {
              "name": "SayHello",
              "request": {
                "description": "Sends a \"greeting\"\n\n\n\nRequest Message: `helloworld.HelloRequest`\n\nResponse Message: `helloworld.HelloReply`\n",
                "method": "POST",
                "header": [
                  {
                    "key": "Content-Type",
                    "value": "application/grpc+json"
                  },
                  {
                    "key": "Grpc-Insecure",
                    "value": "{{grpcInsecure}}"
                  }
                ],
                "url": {
                  "raw": "{{baseURL}}/helloworld.Greeter/SayHello",
                  "host": [
                    "{{baseURL}}"
                  ],
                  "path": [
                    "helloworld.Greeter",
                    "SayHello"
                  ]
                },
                "body": {
                  "mode": "raw",
                  "raw": "{\n  \"name\": \"\"\n}"
                }
              }
            }
          ]
        }
      ]
    }
  ]
}

zz_route_guide.proto

// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

option java_multiple_files = true;
option java_package = "io.grpc.examples.routeguide";
option java_outer_classname = "RouteGuideProto";
option objc_class_prefix = "RTG";

package routeguide;

// Interface exported by the server.
service RouteGuide {
  // A simple RPC.
  //
  // Obtains the feature at a given position.
  //
  // A feature with an empty name is returned if there's no feature at the given
  // position.
  rpc GetFeature(Point) returns (Feature) {}

  // A server-to-client streaming RPC.
  //
  // Obtains the Features available within the given Rectangle.  Results are
  // streamed rather than returned at once (e.g. in a response message with a
  // repeated field), as the rectangle may cover a large area and contain a
  // huge number of features.
  rpc ListFeatures(Rectangle) returns (stream Feature) {}

  // A client-to-server streaming RPC.
  //
  // Accepts a stream of Points on a route being traversed, returning a
  // RouteSummary when traversal is completed.
  rpc RecordRoute(stream Point) returns (RouteSummary) {}

  // A Bidirectional streaming RPC.
  //
  // Accepts a stream of RouteNotes sent while a route is being traversed,
  // while receiving other RouteNotes (e.g. from other users).
  rpc RouteChat(stream RouteNote) returns (stream RouteNote) {}
}

// Points are represented as latitude-longitude pairs in the E7 representation
// (degrees multiplied by 10**7 and rounded to the nearest integer).
// Latitudes should be in the range +/- 90 degrees and longitude should be in
// the range +/- 180 degrees (inclusive).
message Point {
  int32 latitude = 1;
  int32 longitude = 2;
}

// A latitude-longitude rectangle, represented as two diagonally opposite
// points "lo" and "hi".
message Rectangle {
  // One corner of the rectangle.
  Point lo = 1;

  // The other corner of the rectangle.
  Point hi = 2;
}

// A feature names something at a given point.
//
// If a feature could not be named, the name is empty.
message Feature {
  // The name of the feature.
  string name = 1;

  // The point where the feature is detected.
  Point location = 2;
}

// A RouteNote is a message sent while at a given point.
message RouteNote {
  // The location from which the message is sent.
  Point location = 1;

  // The message to be sent.
  string message = 2;
}

// A RouteSummary is received in response to a RecordRoute rpc.
//
// It contains the number of individual points received, the number of
// detected features, and the total distance covered as the cumulative sum of
// the distance between each point.
message RouteSummary {
  // The number of points received.
  int32 point_count = 1;

  // The number of known features passed while traversing the route.
  int32 feature_count = 2;

  // The distance covered in metres.
  int32 distance = 3;

  // The duration of the traversal in seconds.
  int32 elapsed_time = 4;
}

zz_route_guide_collection.json

{
  "info": {
    "name": "Route Guide gRPC JSON API",
    "schema": "https://schema.getpostman.com/json/collection/v2.1.0/collection.json",
    "description": "## Messages\n\n#### routeguide.Feature\n\nA feature names something at a given point.\n\nIf a feature could not be named, the name is empty.\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| name | string | The name of the feature. |\n| location | routeguide.Point | The point where the feature is detected. |\n\n#### routeguide.Point\n\nPoints are represented as latitude-longitude pairs in the E7 representation\n(degrees multiplied by 10**7 and rounded to the nearest integer).\nLatitudes should be in the range +/- 90 degrees and longitude should be in\nthe range +/- 180 degrees (inclusive).\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| latitude | int32 |  |\n| longitude | int32 |  |\n\n#### routeguide.Rectangle\n\nA latitude-longitude rectangle, represented as two diagonally opposite\npoints \"lo\" and \"hi\".\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| lo | routeguide.Point | One corner of the rectangle. |\n| hi | routeguide.Point | The other corner of the rectangle. |\n\n#### routeguide.RouteNote\n\nA RouteNote is a message sent while at a given point.\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| location | routeguide.Point | The location from which the message is sent. |\n| message | string | The message to be sent. |\n\n#### routeguide.RouteSummary\n\nA RouteSummary is received in response to a RecordRoute rpc.\n\nIt contains the number of individual points received, the number of\ndetected features, and the total distance covered as the cumulative sum of\nthe distance between each point.\n\n| Field | Type | Description |\n| ----- | ---- | ----------- |\n| point_count | int32 | The number of points received. |\n| feature_count | int32 | The number of known features passed while traversing the route. |\n| distance | int32 | The distance covered in metres. |\n| elapsed_time | int32 | The duration of the traversal in seconds. |\n\n"
  },
  "item": [
    {
      "name": "route_guide.proto",
      "description": "",
      "item": [
        {
          "name": "routeguide.RouteGuide",
          "description": "Interface exported by the server.",
          "items": [
            {
              "name": "GetFeature",
              "request": {
                "description": "A simple RPC.\n\nObtains the feature at a given position.\n\nA feature with an empty name is returned if there's no feature at the given\nposition.\n\n\n\nRequest Message: `routeguide.Point`\n\nResponse Message: `routeguide.Feature`\n",
                "method": "POST",
                "header": [
                  {
                    "key": "Content-Type",
                    "value": "application/grpc+json"
                  },
                  {
                    "key": "Grpc-Insecure",
                    "value": "{{grpcInsecure}}"
                  }
                ],
                "url": {
                  "raw": "{{baseURL}}/routeguide.RouteGuide/GetFeature",
                  "host": [
                    "{{baseURL}}"
                  ],
                  "path": [
                    "routeguide.RouteGuide",
                    "GetFeature"
                  ]
                },
                "body": {
                  "mode": "raw",
                  "raw": "{\n  \"latitude\": 0,\n  \"longitude\": 0\n}"
                }
              }
            },
            {
              "name": "ListFeatures",
              "request": {
                "description": "A server-to-client streaming RPC.\n\nObtains the Features available within the given Rectangle.  Results are\nstreamed rather than returned at once (e.g. in a response message with a\nrepeated field), as the rectangle may cover a large area and contain a\nhuge number of features.\n\n\n\nRequest Message: `routeguide.Rectangle`\n\nResponse Message: `routeguide.Feature`\n",
                "method": "POST",
                "header": [
                  {
                    "key": "Content-Type",
                    "value": "application/grpc+json"
                  },
                  {
                    "key": "Grpc-Insecure",
                    "value": "{{grpcInsecure}}"
                  }
                ],
                "url": {
                  "raw": "{{baseURL}}/routeguide.RouteGuide/ListFeatures",
                  "host": [
                    "{{baseURL}}"
                  ],
                  "path": [
                    "routeguide.RouteGuide",
                    "ListFeatures"
                  ]
                },
                "body": {
                  "mode": "raw",
                  "raw": "{\n  \"lo\": {},\n  \"hi\": {}\n}"
                }
              }
            },
            {
              "name": "RecordRoute",
              "request": {
                "description": "A client-to-server streaming RPC.\n\nAccepts a stream of Points on a route being traversed, returning a\nRouteSummary when traversal is completed.\n\n\n\nRequest Message: `routeguide.Point`\n\nResponse Message: `routeguide.RouteSummary`\n",
                "method": "POST",
                "header": [
                  {
                    "key": "Content-Type",
                    "value": "application/grpc+json"
                  },
                  {
                    "key": "Grpc-Insecure",
                    "value": "{{grpcInsecure}}"
                  }
                ],
                "url": {
                  "raw": "{{baseURL}}/routeguide.RouteGuide/RecordRoute",
                  "host": [
                    "{{baseURL}}"
                  ],
                  "path": [
                    "routeguide.RouteGuide",
                    "RecordRoute"
                  ]
                },
                "body": {
                  "mode": "raw",
                  "raw": "{\n  \"latitude\": 0,\n  \"longitude\": 0\n}"
                }
              }
            },
            {
              "name": "RouteChat",
              "request": {
                "description": "A Bidirectional streaming RPC.\n\nAccepts a stream of RouteNotes sent while a route is being traversed,\nwhile receiving other RouteNotes (e.g. from other users).\n\n\n\nRequest Message: `routeguide.RouteNote`\n\nResponse Message: `routeguide.RouteNote`\n",
                "method": "POST",
                "header": [
                  {
                    "key": "Content-Type",
                    "value": "application/grpc+json"
                  },
                  {
                    "key": "Grpc-Insecure",
                    "value": "{{grpcInsecure}}"
                  }
                ],
                "url": {
                  "raw": "{{baseURL}}/routeguide.RouteGuide/RouteChat",
                  "host": [
                    "{{baseURL}}"
                  ],
                  "path": [
                    "routeguide.RouteGuide",
                    "RouteChat"
                  ]
                },
                "body": {
                  "mode": "raw",
                  "raw": "{\n  \"location\": {},\n  \"message\": \"\"\n}"
                }
              }
            }
          ]
        }
      ]
    }
  ]
}

This method relies on the documentation generator for protoc: https://github.com/pseudomuto/protoc-gen-doc

Install with:

go get -u github.com/pseudomuto/protoc-gen-doc/cmd/protoc-gen-doc

Download the postman.tmpl file locally.

Building the collection for helloworld.proto:

POSTMAN_COLLECTION_NAME="Hello World gRPC JSON API" protoc \
--doc_out=./ \
--doc_opt=./postman.tmpl,helloworld_collection.json \
helloworld.proto

Try importing one of these example collections into Postman. View the documentation and requests to see all populated fields.

Hello World Collection: https://gist.githubusercontent.com/kevinswiber/867699e4efe57ccde83fb510c9de6075/raw/b082f5505b22112d5f989dae2765a065de2e53fd/zz_helloworld_collection.json

Route Guide Collection: https://gist.githubusercontent.com/kevinswiber/867699e4efe57ccde83fb510c9de6075/raw/b082f5505b22112d5f989dae2765a065de2e53fd/zz_route_guide.proto