Yamato
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I'm raising this inquiry to ask for the assistance who know familiar with Fiddler product.
About 9 months ago, in the end of year 2023, the issue occurred.
When a user accesses Web application with the latest Google Chrome, the blank screen (or WSOD) happened.
In order to analyze the cause of this issue, I've decided to install Fiddler to see how HTTP traffic was going about.
However, the issue has never occurred when Fiddler was running and I'm wondering why...
Question#1: Why blank screen in browser never happens while Fidder is running?
Question#2: What's difference when Fiddler is running or not?
Fiddler Version: Progress Telerik Fiddler Classic v5.0.20211.51073
I'd really appreciate it if someone would help to answer this!
Regards,
Yamato
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Jerry
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answered on 10 Sep 2024, 12:14 PM
| edited on 10 Sep 2024, 12:39 PM
It’s interesting that the issue with the blank screen (WSOD) in your web application only occurs when Fiddler isn’t running. Here are some insights into why this might be happening:
Question #1: Why does the blank screen in the browser never happen while Fiddler is running?
When Fiddler is running, it acts as a proxy between your web browser and the internet. This means that all the HTTP/HTTPS traffic between the browser and the server is routed through Fiddler. Here are a few reasons why the issue might not occur when Fiddler is active:
Timing or Race Conditions: Sometimes, web applications have timing issues or race conditions where certain scripts or resources load in a particular order. The additional processing time introduced by Fiddler could be affecting the timing in such a way that it inadvertently resolves the race condition or timing issue.
Caching and Network Conditions: Fiddler might affect caching behavior or network conditions. For example, if the browser cache is invalid or corrupted, Fiddler’s proxy might inadvertently force a fresh request that gets a proper response, bypassing the issue.
Modifications in Traffic: Fiddler might modify or log HTTP headers and traffic in ways that prevent the issue from occurring. For instance, certain headers or request/response transformations done by Fiddler could inadvertently address the underlying issue.
Resource Loading: Sometimes, web applications have issues with specific resources failing to load. Fiddler might be causing the resources to be fetched in a different way, leading to different behavior.
Question #2: What’s the difference when Fiddler is running or not?
When Fiddler is running, the following differences come into play:
Proxy Configuration: Fiddler sets up a proxy configuration that alters how your browser connects to the internet. This can sometimes change the way requests are handled or the responses are processed, which might affect how your application behaves.
Traffic Inspection and Modification: Fiddler allows you to inspect and modify HTTP traffic. This means you can see exactly what requests are being made and what responses are being returned. It might also alter the requests or responses in ways that prevent the issue from manifesting.
Network Latency: Introducing a proxy like Fiddler adds some network latency. This additional latency can affect how resources are loaded and may change the behavior of the application.
SSL/TLS Interception: Fiddler can intercept and decrypt HTTPS traffic. If there are issues related to SSL/TLS handshakes or certificate problems, Fiddler’s handling of these might mitigate the issue.
Steps to Troubleshoot
To further diagnose the problem, you can:
Compare Traffic: Use Fiddler to capture and analyze the HTTP traffic when the application is working correctly versus when it is not. Look for differences in requests, responses, or headers.
Check Console Logs: Examine the browser’s console logs for errors or warnings that might provide clues about the issue.
Isolate the Problem: Try to isolate which part of the application or which resource is causing the blank screen. This can help you understand why Fiddler’s presence might be affecting it.
Network Conditions: Test under various network conditions and configurations to see if the issue persists. It might be related to specific network setups or environmental factors.
Update and Configuration: Ensure that Fiddler and your browser are updated to their latest versions. Sometimes, updating software can resolve unexpected issues.
Question #1: Why does the blank screen in the browser never happen while Fiddler is running?
When Fiddler is running, it acts as a proxy between your web browser and the internet. This means that all the HTTP/HTTPS traffic between the browser and the server is routed through Fiddler. Here are a few reasons why the issue might not occur when Fiddler is active:
Timing or Race Conditions: Sometimes, web applications have timing issues or race conditions where certain scripts or resources load in a particular order. The additional processing time introduced by Fiddler could be affecting the timing in such a way that it inadvertently resolves the race condition or timing issue.
Caching and Network Conditions: Fiddler might affect caching behavior or network conditions. For example, if the browser cache is invalid or corrupted, Fiddler’s proxy might inadvertently force a fresh request that gets a proper response, bypassing the issue.
Modifications in Traffic: Fiddler might modify or log HTTP headers and traffic in ways that prevent the issue from occurring. For instance, certain headers or request/response transformations done by Fiddler could inadvertently address the underlying issue.
Resource Loading: Sometimes, web applications have issues with specific resources failing to load. Fiddler might be causing the resources to be fetched in a different way, leading to different behavior.
Question #2: What’s the difference when Fiddler is running or not?
When Fiddler is running, the following differences come into play:
Proxy Configuration: Fiddler sets up a proxy configuration that alters how your browser connects to the internet. This can sometimes change the way requests are handled or the responses are processed, which might affect how your application behaves.
Traffic Inspection and Modification: Fiddler allows you to inspect and modify HTTP traffic. This means you can see exactly what requests are being made and what responses are being returned. It might also alter the requests or responses in ways that prevent the issue from manifesting.
Network Latency: Introducing a proxy like Fiddler adds some network latency. This additional latency can affect how resources are loaded and may change the behavior of the application.
SSL/TLS Interception: Fiddler can intercept and decrypt HTTPS traffic. If there are issues related to SSL/TLS handshakes or certificate problems, Fiddler’s handling of these might mitigate the issue.
Steps to Troubleshoot
To further diagnose the problem, you can:
Compare Traffic: Use Fiddler to capture and analyze the HTTP traffic when the application is working correctly versus when it is not. Look for differences in requests, responses, or headers.
Check Console Logs: Examine the browser’s console logs for errors or warnings that might provide clues about the issue.
Isolate the Problem: Try to isolate which part of the application or which resource is causing the blank screen. This can help you understand why Fiddler’s presence might be affecting it.
Network Conditions: Test under various network conditions and configurations to see if the issue persists. It might be related to specific network setups or environmental factors.
Update and Configuration: Ensure that Fiddler and your browser are updated to their latest versions. Sometimes, updating software can resolve unexpected issues.