resPrepend

The resPrepend protocol is used to insert specified content at the beginning of an existing response body. It only takes effect on status codes that include a response body (such as 200, 500, etc.). Through the resPrepend protocol, you can:

• Add custom content at the beginning of a response.
• Insert debugging information or timestamps.
• Add references to scripts, stylesheets, or other resources.
• Inject environment markers or version information.
• Keep the original response content intact, adding extra content only at the beginning.

Effective Condition: Only takes effect on status codes with a response body.

⚠️ Note: Requests without a response body, such as 204, 304, are not affected.

Rule Syntax

resPrepend supports multiple ways to specify the content to be inserted:

1. Inline Value (Direct Specification)

Write the content to insert directly in the rule, suitable for short text (cannot contain spaces or line breaks).

pattern resPrepend://(value) [lineProps...] [filters...]

Example:

www.example.com/page resPrepend://(<!--Page Start-->)

2. Embedded Value (Using Code Block)

This method is recommended when dealing with complex content containing spaces, line breaks, or when you want to reuse a configuration.

pattern resPrepend://{custom-key} [lineProps...] [filters...]

``` custom-key
<!-- Debug Info -->
<script>
  console.log('Page Load Time:', new Date().toISOString());
</script>
```

3. Referencing a Value from the Values Panel

When the content is large, you can store it in the Values configuration area.

pattern resPrepend://{key-of-values} [lineProps...] [filters...]

Prerequisite: A key named key-of-values with the content to insert as its value must exist in Values.

4. Loading from a File Path or Remote URL

Load the response content to insert from a local file or remote URL.

# Load from a local file
pattern resPrepend:///User/xxx/header.html

# Load from a remote URL
pattern resPrepend://https://cdn.example.com/analytics-script.js

5. Loading from a Temporary File

Use Whistle's temporary file feature when content needs frequent editing.

pattern resPrepend://temp/blank.txt

Steps:

1. In the Rules editor, hold down Command (Mac) / Ctrl (Windows).
2. Click with the mouse on resPrepend://temp/blank.txt.
3. Enter the content to insert in the pop-up editing dialog.
4. Click Save to save.

Parameter Details

Parameter	Required	Description & Examples
pattern	Yes	Expression used to match the request URL. • Supports domains, paths, wildcards, regular expressions. • See Matching Pattern Documentation for details.
value	Yes	The response content to insert, supporting multiple formats: • Local file path • Remote URL • Inline, embedded, Values references
lineProps	No	Sets additional properties for the rule. • Example: lineProps://important can increase this rule's priority. • See lineProps Documentation for details.
filters	No	Optional filter conditions for precise control over when the rule takes effect. • Can match request URL, method, headers, body content. • Can match response status code, headers. • See Filters Documentation for details.

Configuration Examples

Basic Examples

# Add a comment at the beginning of an HTML page
www.example.com/index.html resPrepend://(<!--Page Start Time:-->)

# Add a timestamp before a JSON response
api.example.com/data.json resPrepend://({"timestamp":"2024-01-01T00:00:00Z"})

Example Scenario Analysis

Scenario 1: Inserting Debug Information

``` debug-header
<!-- 
  Debug Info:
  - URL: ${url}
  - Time: ${now}
  - User Agent: ${reqHeaders.user-agent}
-->
```

www.example.com resPrepend://`{debug-header}`

Scenario 2: Adding Page Header Content

# Add a common header
^www.example.com/*.html resPrepend://{custom-html}

``` custom-html
<div class="site-header">Website Header</div>
```

Scenario 3: Injecting Analytics Script

# Add Google Analytics script
www.example.com resPrepend://{google-analytics}
``` google-analytics
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-XXXXX"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());
  gtag('config', 'UA-XXXXX');
</script>
```

Using with Other Protocols

# First add header content, then add footer content
www.example.com/page resPrepend://(<header>) resAppend://(</footer>)

# Use with the file protocol
www.example.com/path resPrepend://(Hello) file://(-test-)

Response Result:

Hello-test-

Using Embedded Values

``` body.txt
Hello world.
```

www.example.com/path resPrepend://{body.txt} file://(-test-)

Response Result:

Hello world.-test-

Loading from a File or Remote URL

# Load from a local file
www.example.com/path1 resPrepend:///User/xxx/test.txt

# Load from a remote URL
www.example.com/path2 resPrepend://https://www.xxx.com/xxx/params.txt

# Use a temporary file
www.example.com/path3 resPrepend://temp/blank.txt

Using with Filters

# Add debug info only for development environment
www.example.com resPrepend://(<!--Development Environment-->) includeFilter://reqH:host=/dev\./

# Add header only for HTML pages
www.example.com resPrepend://{header} resType://html

``` header
<div class="header" />
```

# Determine whether to add content based on response status code
www.example.com/api resPrepend://({"debug":true}) includeFilter://s:200

Advanced Usage

Dynamic Content Insertion

Use template strings to implement dynamic content:

# Insert current timestamp
www.example.com/api resPrepend://`({"timestamp":"${now}"})`

# Insert request information
www.example.com/debug resPrepend://`{req-info}`

``` req-info
<!-- Request Method: ${method}, Path: ${path} -->
```

Combining Multiple Insertions

# Insert multiple content fragments
www.example.com/page resPrepend://{header1} resPrepend://{header2}

``` header1
<div />
```
``` header2
<div id="header2" />
```
# Final result: <div id="header2" /><div id="header1" />[Original Content]

Conditional Insertion

# Insert content only under specific conditions
www.example.com/admin resPrepend://{log.js} includeFilter://reqH:cookie=/admin=true/

```` log.js
<script>console.log('Admin Page')</script>
````

Common Questions

Q: The resPrepend rule is not taking effect.

A: Check:

1. Whether the response status code has a response body (excluding 204, 304, etc.).
2. Whether the rule pattern correctly matches the request URL.
3. Whether the filter conditions are met.
4. Whether other rules are interfering.

Q: How to ensure content is inserted at a specific position?

A:

• resPrepend always inserts content at the very beginning of the response.
• If you need to insert at other positions, consider using resReplace with regular expression replacement.

Q: Can I delete parts of the original response?

A: No. resPrepend only adds content; it does not delete or modify the original content. If you need to delete content, use the resBody protocol.

Differences from resBody

The main distinction between the resPrepend protocol and the resBody protocol lies in the processing method:

• resPrepend: Inserts specified content before the original response content, preserving the original.
• resBody: Replaces the entire response content, without preserving the original.

Related Protocols

1. Replace response content: resBody
   • Completely replaces the response content, without preserving the original.
2. Append content after the response body: resAppend
   • Adds content at the end of the response.
3. Replace request content: reqBody
   • Replaces the request body content sent to the server.
4. Insert content before the request body: reqPrepend
   • Inserts content before the request body.
5. Append content after the request body: reqAppend
   • Adds content at the end of the request body.

Further Reading

• Matching Pattern Documentation: Learn more about URL matching rules.
• Operation Commands Documentation: Learn about multiple ways to load content.
• Filters Documentation: Learn more about filter functionalities.