EchoScript for Map Mock

EchoScript is the core of Map Mock. It can work with both Map Local and Map Remote.

By default, EchoScript code is commented out, which means it does nothing.

// on_request := func(env, req) {
//   return {}
// }

// on_response := func(env, res) {
//   return {}
// }

Callback functions

EchoScript has two standard callback functions: on_request and on_response, which can be used to modify HTTP(s) request and response respectively.

on_request

The return value of on_request is a map, which tells EchoProxy how to modify HTTP(s) request. Return an empty map {} means it does nothing.

on_request := func(env, req) {
  return {}
}

Note

on_request is called when EchoProxy receives a new HTTP(s) request from client.

The structure of on_request return value. All fields are optional.

{
  // change request method, value can be GET/POST/PUT ...
  method: string,
  // change request URL
  url: string,
  // change request URL query parameters, merge with original map
  query: map,
  // change request header key/value pairs, merge with original map
  header: map,
  // change request cookie key/value pairs, merge with original map
  cookie: map,
  // change request body: a string, file, or map
  body: string|file|map
}

on_response

The return value of on_response is a map, which tells EchoProxy how to modify HTTP(s) response. Return an empty map {} means it does nothing.

on_response := func(env, res) {
  return {}
}

Note

on_response is called when EchoProxy has received the response of HTTP(s) remote request (MapRemote), or has loaded the response from local file (MapLocal).

The structure of on_response return value. All fields are optional.

{
  // change response HTTP status code, value can be 200/302/404 ...
  code: int,
  // change response header key/value pairs, merge with original map
  header: map,
  // change response cookie key/value pairs, merge with original map
  cookie: map,
  // change response body: a string, file, or map
  body: string|file|map
}

Map modify strategy

When the field type is a map, the default modify strategy is to merge the two maps. The other types (string|int|float|file|array) use assign strategy, which means the new value overwrite old value.

field type	modify strategy
map	merge
string	assign overwrite
int|float	assign overwrite
file	assign overwrite
array	assign overwrite

Merge Example

Let’s take body field as an example. The original body value:

// callback function argument: req.body or res.body
{
  body: {
    "k1": 10,
    "k2": "hello",
    "k3": {
      "page": 3
    },
    "k4": [1, 2]
  }
}

The returned body value:

{
  body: {
    "k2": "world",
    "k3": {
      "total": 50
    },
    "k4": [5, 6, 7]
  }
}

The final body value is the merge result of the two maps:

{
  body: {
    "k1": 10,
    "k2": "world",
    "k3": {
      "page": 3,
      "total": 50
    },
    "k4": [5, 6, 7]
  }
}

Assign Example

The original body value is the same with previous example.
The returned body value is handled with function assign:

{
  body: assign({
    "k2": "world",
    "k3": {
      "total": 50
    },
    "k4": [5, 6, 7]
  })
}

The final body value will be the same with the assign argument:

{
  body: {
    "k2": "world",
    "k3": {
      "total": 50
    },
    "k4": [5, 6, 7]
  }
}

Function arguments

req

The argument req represents the incoming HTTP request. The structure of req:

{
  u: array,         // holds Wildcard/Regex submatch strings
  url: string,      // request URL
  method: string,   // request method
  query: map,       // request URL query parameters (string)
  header: map,      // request header key/value pairs (string)
  cookie: map,      // request cookie key/value pairs (string)
  body: string|map, // request body: a string or map
  text: string      // request body as text string

  client_ip: string,   // client IP
  client_addr: string, // client address
}

Note

If you modify req fields, the updated value will be discarded by default. If you assign the updated value and return, it will take effect.

on_request := func(env, req) {
  delete(req.query, "page")  // modify req.query
  return {
    query: assign(req.query) // return with assign
  }
}

res

The argument res represents the response got from remote HTTP request (MapRemote), or the response loaded from local file (MapLocal). The structure of res:

{
  code: int,        // response HTTP status code
  header: map,      // response header key/value pairs (string)
  cookie: map,      // response cookie key/value pairs (string)
  body: string|map, // response body: a string or map
  text: string      // response body as text string
}

Note

If you modify res fields, the updated value will be discarded by default. If you assign the updated value and return, it will take effect.

on_response := func(env, res) {
  delete(res.body, "name")     // modify req.body
  res.body["msg"] = "updated!" // modify req.body
  return {
    body: assign(res.body)     // return with assign
  }
}

env

The argument env is a map, which is designed to get and set enviroment variables.
TODO: under development

Note

You can pass variables between callback functions using env.

Example: Pass variable env.key1 from on_request to on_response, and print its value to Log tab.

on_request := func(env, req) {
  env["key1"] = { "n": 99, "msg": "Hi" }
  return {}
}

on_response := func(env, res) {
  print("env.key1: ", env.key1)
  return {}
}