用Postman模拟free-ocr文件上传POST请求未获预期响应，求排查

Let’s walk through the most likely issues that could be blocking your Postman request from replicating the browser’s successful OCR upload flow:

1. Match Request Headers Exactly #

The server may validate specific headers sent by the browser—missing or mismatched values can cause failures. From your request header screenshot, ensure these are included in Postman:

• Cookie: Copy the session cookie directly from your browser’s DevTools (Network tab > the upload request > Headers section)
• User-Agent: Use the exact same string as your browser (e.g., Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36)
• Referer: Set this to https://www.free-ocr.com/ to match the browser’s context
• Content-Type: Don’t manually set this! Postman auto-generates the correct multipart/form-data; boundary=... header when using form-data, which matches what the browser sends.

2. Verify Form-Data Field Details #

The server expects the file to be uploaded under a specific field name. Cross-check with your browser’s request (DevTools > Network > Form Data tab):

• Confirm the file field name (e.g., file or uploaded_file) and use the exact same name in Postman’s form-data tab
• Ensure no extra, unrequired fields are added to your Postman request that weren’t present in the browser’s upload

3. Check File Constraints #

Free-ocr.com enforces limits on file types and sizes. Double-check:

• Your Postman file uses the same format (PNG, JPG, PDF, etc.) as the one that worked in the browser
• The file size falls within the service’s stated limits (check their website for specifics)

4. Handle Session Validation #

Many services use session cookies to block automated requests. Replicate the browser’s session flow in Postman:

1. Send a GET request to https://www.free-ocr.com/ first
2. Save the cookies returned in this response
3. Enable Postman’s "Automatically send cookies" setting to include these cookies in your POST upload request

5. Disable Auto-Redirects (If Needed) #

Some servers return a redirect after upload, but the OCR text may be in the initial response. Check your browser’s network tab: if the upload request returns the text directly, disable auto-redirects in Postman’s request settings to capture the full response.

6. Compare Raw Requests #

The easiest way to spot discrepancies is to mirror the browser’s request exactly:

1. In Chrome DevTools, right-click the successful upload request > Copy > Copy as cURL
2. Import this cURL command into Postman (File > Import > Paste cURL)
3. Run the imported request—if it works, compare it to your original Postman request to identify missing headers, fields, or settings

内容的提问来源于stack exchange，提问作者Madhur