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Extracting Base64 Encoded Binary File from File Field in multipart/form-data requests

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asked May 13 by rich-c-2789 (17,430 points)

Can you show me how to access the binary file or image used in the form for this question?:

Extracting Form Fields from multipart/form-data requests

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This code extracts the image file associated with the "imagefile" field from the XML request and saves it on the QIE computer.

// 1. Get the content-disposition for the imagefile field using XPath
var contentDisposition = source.getNode("//Part[content-disposition[contains(., 'name=\"imagefile\"')]]/content-disposition");

// 2. Define the pattern to match the filename
var pattern = java.util.regex.Pattern.compile("filename=\"([^\"]+)\"");

// 3. Match the pattern against the text in the content-disposition tag
var matcher = pattern.matcher(contentDisposition);

var filename;
// 4. Check if the pattern is found
if (matcher.find()) {
   // 5. Extract the filename from the matched group
   filename = matcher.group(1);
}

// 6. Get the content for the file using XPath
var fileContent = source.getNode("//Part[content-disposition[contains(., 'name=\"imagefile\"')]]/Content");

// 7. Base64 decode the content direct to a byte[]
var fileBytes = qie.base64DecodeToBytes(fileContent);

// 8. Write the byte[] to a file on disk
qie.writeFile('/Users/dir/Pictures/' + filename, fileBytes);

1. This line fetches the content-disposition for the "imagefile" part in the XML request using XPath. It looks for a Part element where the content-disposition contains the substring 'name="imagefile"', then extracts the content-disposition value from it.

2. Here, a regular expression pattern is defined to match the filename within a content-disposition tag. This pattern looks for the substring 'filename="...', capturing everything within double quotes after the equals sign.

3. This line creates a matcher object by applying the defined regular expression pattern to the content-disposition obtained in the first step. The matcher will be used to find the filename within the content-disposition.

4. This conditional statement checks if the matcher finds a match according to the pattern. If a match is found, the following block of code is executed.

5. If a match is found, this line extracts the filename from the matched group (the portion captured within parentheses in the regular expression pattern) and assigns it to the filename variable.

6. Similar to the first line, this fetches the content of the file from the XML request using XPath. It looks for a Part element where the content-disposition contains the substring 'name="imagefile"', then extracts the Content from it.

7. The content fetched in the previous step is assumed to be Base64 encoded. This line decodes the Base64-encoded content into a byte array.

8. Finally, this line writes the byte array obtained from decoding the file content to a file on disk. The file is written to the directory specified ('/Users/dir/Pictures/') with the filename extracted earlier.

See also:

Extracting Form Fields from multipart/form-data requests

Extracting Base64 Encoded Text File from File Field in multipart/form-data requests

Handling HTTP requests and responses

Processing Requests in mapping nodes via HTTP Listener source node

answered May 13 by rich-c-2789 (17,430 points)
edited May 16 by rich-c-2789
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