# EM HTTP Request

EM HTTP Request allows multiple simultaneous asynchronous requests. (The other HTTP libraries are synchronous). The scenarios below demonstrate how VCR can be used with asynchronous em-http requests.

## Background ()

*Given* a file named "vcr\_setup.rb" with:

```
require 'em-http-request'

$server = start_sinatra_app do
  %w[ foo bar bazz ].each_with_index do |path, index|
    get "/#{path}" do
      sleep index * 0.1 # ensure the async callbacks are invoked in order
      ARGV[0] + ' ' + path
    end
  end
end

require 'vcr'

VCR.configure do |c|
  c.hook_into :webmock
  c.cassette_library_dir = 'cassettes'
  c.before_record do |i|
    i.request.uri.sub!(/:\d+/, ':7777')
  end
end
```

## multiple simultaneous HttpRequest objects

*Given* a file named "make\_requests.rb" with:

```
require 'vcr_setup'

VCR.use_cassette('em_http') do
  EventMachine.run do
    http_array = %w[ foo bar bazz ].map do |p|
      EventMachine::HttpRequest.new("http://localhost:#{$server.port}/#{p}").get
    end

    http_array.each do |http|
      http.callback do
        puts http.response

        if http_array.all? { |h| h.response.to_s != '' }
          EventMachine.stop
        end
      end
    end
  end
end
```

*When* I run `ruby make_requests.rb Hello`

*Then* the output should contain:

```
Hello foo
Hello bar
Hello bazz
```

*And* the file "cassettes/em\_http.yml" should contain YAML like:

```
--- 
http_interactions: 
- request: 
    method: get
    uri: http://localhost:7777/foo
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Type: 
      - text/html;charset=utf-8
      Content-Length: 
      - "9"
    body: 
      encoding: UTF-8
      string: Hello foo
    http_version: 
  recorded_at: Tue, 01 Nov 2011 04:58:44 GMT
- request: 
    method: get
    uri: http://localhost:7777/bar
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Type: 
      - text/html;charset=utf-8
      Content-Length: 
      - "9"
    body: 
      encoding: UTF-8
      string: Hello bar
    http_version: 
  recorded_at: Tue, 01 Nov 2011 04:58:44 GMT
- request: 
    method: get
    uri: http://localhost:7777/bazz
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Type: 
      - text/html;charset=utf-8
      Content-Length: 
      - "10"
    body: 
      encoding: UTF-8
      string: Hello bazz
    http_version: 
  recorded_at: Tue, 01 Nov 2011 04:58:44 GMT
recorded_with: VCR 2.0.0
```

*When* I run `ruby make_requests.rb Goodbye`

*Then* the output should contain:

```
Hello foo
Hello bar
Hello bazz
```

## MultiRequest

*Given* a file named "make\_requests.rb" with:

```
require 'vcr_setup'

VCR.use_cassette('em_http') do
  EventMachine.run do
    multi = EventMachine::MultiRequest.new

    %w[ foo bar bazz ].each do |path|
      multi.add(path, EventMachine::HttpRequest.new("http://localhost:#{$server.port}/#{path}").get)
    end

    multi.callback do
      responses = Hash[multi.responses[:callback]]

      %w[ foo bar bazz ].each do |path|
        puts responses[path].response
      end

      EventMachine.stop
    end
  end
end
```

*When* I run `ruby make_requests.rb Hello`

*Then* the output should contain:

```
Hello foo
Hello bar
Hello bazz
```

*And* the file "cassettes/em\_http.yml" should contain YAML like:

```
--- 
http_interactions: 
- request: 
    method: get
    uri: http://localhost:7777/foo
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Type: 
      - text/html;charset=utf-8
      Content-Length: 
      - "9"
    body: 
      encoding: UTF-8
      string: Hello foo
    http_version: 
  recorded_at: Tue, 01 Nov 2011 04:58:44 GMT
- request: 
    method: get
    uri: http://localhost:7777/bar
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Type: 
      - text/html;charset=utf-8
      Content-Length: 
      - "9"
    body: 
      encoding: UTF-8
      string: Hello bar
    http_version: 
  recorded_at: Tue, 01 Nov 2011 04:58:44 GMT
- request: 
    method: get
    uri: http://localhost:7777/bazz
    body: 
      encoding: UTF-8
      string: ""
    headers: {}
  response: 
    status: 
      code: 200
      message: OK
    headers: 
      Content-Type: 
      - text/html;charset=utf-8
      Content-Length: 
      - "10"
    body: 
      encoding: UTF-8
      string: Hello bazz
    http_version: 
  recorded_at: Tue, 01 Nov 2011 04:58:44 GMT
recorded_with: VCR 2.0.0
```

*When* I run `ruby make_requests.rb Goodbye`

*Then* the output should contain:

```
Hello foo
Hello bar
Hello bazz
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://andrewmcodes.gitbook.io/vcr/v5.0.0/http_libraries/em_http_request.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.