Why is Spring de-coding + (the plus character) on application/json get requests? and what should I do about it?

Question

I have a Spring application that receives a request like http://localhost/foo?email=foo+bar@example.com. This triggers a controller that roughly looks like this

Answer 1

Original Answer

You are mixing 2 things, a + in the body of the request would mean a space when header has application/x-www-form-urlencoded. The body or content of the request would be dependent on the headers but a request can just have a url and no headers and no body.

So the encoding of a URI cannot be controlled by any headers as such

See the URL Encoding section in https://en.wikipedia.org/wiki/Query_string

Some characters cannot be part of a URL (for example, the space) and some other characters have a special meaning in a URL: for example, the character # can be used to further specify a subsection (or fragment) of a document. In HTML forms, the character = is used to separate a name from a value. The URI generic syntax uses URL encoding to deal with this problem, while HTML forms make some additional substitutions rather than applying percent encoding for all such characters. SPACE is encoded as '+' or "%20".[10]

HTML 5 specifies the following transformation for submitting HTML forms with the "get" method to a web server.1 The following is a brief summary of the algorithm:

Characters that cannot be converted to the correct charset are replaced with HTML numeric character references[11] SPACE is encoded as '+' or '%20' Letters (A–Z and a–z), numbers (0–9) and the characters '*','-','.' and '_' are left as-is All other characters are encoded as %HH hex representation with any non-ASCII characters first encoded as UTF-8 (or other specified encoding) The octet corresponding to the tilde ("~") is permitted in query strings by RFC3986 but required to be percent-encoded in HTML forms to "%7E".

The encoding of SPACE as '+' and the selection of "as-is" characters distinguishes this encoding from RFC 3986.

And you can see the same behaviour on google.com as well from below screenshots

Also you can see the same behaviour in other frameworks as well. Below is an example of Python Flask

So what you are seeing is correct, you are just comparing it with a document which refers to the body content of a request and not the URL

Edit-1: 22nd May

After debugging it seems the decoding doesn't even happen in Spring. I happens in package org.apache.tomcat.util.buf; and the UDecode class

/**
 * URLDecode, will modify the source.
 * @param mb The URL encoded bytes
 * @param query true if this is a query string
 * @throws IOException Invalid %xx URL encoding
 */
public void convert( ByteChunk mb, boolean query )
    throws IOException
{
    int start=mb.getOffset();

And below is where the conversion stuff actually happens

    if( buff[ j ] == '+' && query) {
        buff[idx]= (byte)' ' ;
    } else if( buff[ j ] != '%' ) {

This means that it is an embedded tomcat server which does this translation and spring doesn't even participate in this. There is no config to change this behaviour as seen in the class code. So you have to live with it