This error occurs when WinINet / Internet Explorer–era HTTP code asks Windows to retrieve a specific HTTP header from a response, but that header does not exist in the received message.
In plain terms:
“Your code asked for an HTTP header that the server never sent.”
This is a response-parsing / expectation mismatch issue, not a connectivity or DNS problem.
Fact:
is the HRESULT-wrapped form of Win32 error
.
ERROR_HTTP_HEADER_NOT_FOUND simply means:
Correct handling is to treat the header as absent, adjust logic accordingly, and only escalate if your application truly requires that header to function.
In plain terms:
“Your code asked for an HTTP header that the server never sent.”
This is a response-parsing / expectation mismatch issue, not a connectivity or DNS problem.
Error code equivalence (same error, different formats)
| Format | Code |
|---|---|
| Win32 (decimal) |
Code:
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| Win32 (hex) |
Code:
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| HRESULT |
Code:
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| Symbolic name |
Code:
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| Message | The requested header could not be located. |
Code:
Code:
What this error really means
WinINet APIs (for example, querying headers afterHttpSendRequest) do not guarantee that a given header exists.ERROR_HTTP_HEADER_NOT_FOUND simply means:
- The HTTP response is valid
- The request succeeded
- But the specific header name you asked for is absent
Common real-world scenarios that trigger this error
1) The server never sent that header (most common)
Cause- Header is optional (e.g.,
Content-Length,ETag,Location) - Server uses chunked transfer encoding
- Response status doesn’t require that header
- Request succeeds
- Body is present
- Only header lookup fails
- Treat this error as “header not present,” not as a fatal failure
- Make the header optional in your logic
- Use alternate indicators (status code, body length, chunked encoding)
2) Wrong header name or formatting (case, syntax, scope)
Cause- Typo in header name
- Requesting a response header that only exists in requests
- Asking for a header that belongs to redirects or intermediate responses
- Always fails for the same header
- Other headers query successfully
- Verify the exact header name
- Ensure you’re querying response headers, not request-only headers
- Confirm the header applies to the final response, not a redirect step
3) Header exists only for specific status codes (e.g., redirects)
Cause- Code assumes header exists regardless of HTTP status
- Example: querying
Locationon a200 OK
- Works for redirects
- Fails for normal success responses
- Check HTTP status code first
- Only query headers that are valid for that status (e.g.,
Locationonly on 3xx)
4) Proxy or gateway removes or normalizes headers
Cause- Reverse proxy strips headers
- Security gateway removes “unapproved” headers
- Load balancer normalizes responses
- Header present when tested directly
- Missing when accessed through corporate network/VPN
- Capture the actual response headers on the affected network path
- Adjust code to tolerate missing headers
- If the header is required, fix the proxy/server configuration
5) WinINet API misuse or wrong query flags
Cause- Incorrect flags when querying headers
- Asking for raw headers but parsing incorrectly
- Querying before headers are available
- Inconsistent behavior across calls
- Works after retries or refactoring
- Ensure headers are queried after request completion
- Use correct WinINet header query flags
- Don’t assume headers exist unless guaranteed by protocol rules
What this error is NOT
Not a failed HTTP request- Not a server outage
- Not a network error
- Not authentication failure
Real fixes & solutions (correct order matters)
Step 1: Confirm the request actually succeeded
- Check HTTP status code
- Verify response body presence
Step 2: Capture the real response headers
- Use a network trace or logging
- Confirm whether the header is truly absent
Step 3: Make the header optional in logic
- Treat
as a valid “not present” resultCode:
- Only fail if the header is truly required by protocol or design
Step 4: Gate header queries by status code
- Query redirect headers only on 3xx
- Query entity headers only when applicable
Step 5: Fix server/proxy only if the header is mandatory
- Add the header at the server
- Or configure proxy to preserve it
Fast “symptom → fix” mapping
| Symptom | Likely Fix |
|---|---|
| Request works, header lookup fails | Header optional → handle absence gracefully |
| Always fails for one header | Wrong header name/scope → correct query |
| Works on one network only | Proxy stripping → tolerate or reconfigure |
| Redirect logic breaks | Querying header on wrong status → gate by status |
| Code treats this as fatal | Logic bug → handle
Code:
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Related WinINet / HTTP errors (context map)
| Code | Meaning |
|---|---|
|
Code:
| Invalid HTTP response |
|
Code:
| HTTP header not found (this error) |
|
Code:
| Invalid HTTP request |
|
Code:
| Cannot connect to server |
Note
ERROR_HTTP_HEADER_NOT_FOUND is usually not an error condition — it’s a signal.Correct handling is to treat the header as absent, adjust logic accordingly, and only escalate if your application truly requires that header to function.