How do I unescaped, string that has been escaped multiple times in Rust?

I have spent close to an hour on this already, so this is a true case of hitting a wall.

For reasons beyond my control, an internal service I am using hands me a JSON that is in this form

    let dirty_string = r#"\"{\\\"key1\\\":\\\"val1\\\",\\\"key2\\\":\\\"val2\\\"}\""#;

Now obviously this does not look right. My plan it to take this and use serde_json to construct the appropriate struct but that does not work.

I have tried various ways to remove the multiple escapes.

I have tried various form of using replace

This

let to_format = dirty_string.replace("\\\\", r#""#);

gives this

"\\\"{\\\"key1\\\":\\\"val1\\\",\\\"key2\\\":\\\"val2\\\"}\\\"" basically making the matter worse

This let to_format = dirty_string.replace("\\", r#""#); gives this

"\"{\"key1\":\"val1\",\"key2\":\"val2\"}\""

which looks like almost there, but does not work because when I try to parse it into the struct it fails

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
struct Parsed {
    key1: String,
    key2: String
}

let to_struct: Parsed = serde_json::from_str(&to_format).unwrap();
dbg!(to_struct);

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error("invalid type: string \"{\", expected struct Parsed", line: 1, column: 3)', src/main.rs:440:62
stack backtrace:
   0: rust_begin_unwind

So I will really appreciate help here.

How exactly can I successfully removing this annoying back slashes such that it becomes a valid json string that I can then parse to the struct.

You can add quotes and put it through three iterations of serde_json:

let dirty_string = r#"\"{\\\"key1\\\":\\\"val1\\\",\\\"key2\\\":\\\"val2\\\"}\""#;
let s: String = serde_json::from_str(&format!(r#""{}""#, dirty_string)).unwrap();
let s: String = serde_json::from_str(&s).unwrap();
let value: serde_json::Value = serde_json::from_str(&s).unwrap();
println!("{value:#?}");

What you have is a JSON string that was again encoded as JSON, and finally had characters backslash-escaped (smells of PHP's addslashes()). So you need to do these steps in order:

• Strip one set of backslashes, which will produce a new string.
• JSON-decode another String from the new one.
• Finally, JSON-deserialize into the struct.

For example:

use std::error::Error;

use serde::Deserialize;

#[derive(Deserialize, Debug)]
struct Data {
    pub key1: String,
    pub key2: String,
}

fn stripslashes(s: &str) -> Option<String> {
    let mut n = String::new();

    let mut chars = s.chars();

    while let Some(c) = chars.next() {
        n.push(match c {
            '\\' => chars.next()?,
            c => c,
        });
    }

    Some(n)
}

fn main() -> Result<(), Box<dyn Error>> {
    let dirty_string = r#"\"{\\\"key1\\\":\\\"val1\\\",\\\"key2\\\":\\\"val2\\\"}\""#;

    let s = stripslashes(&dirty_string).expect("stripslashes failed");
    let s: String = serde_json::from_str(&s)?;

    let data: Data = serde_json::from_str(&s)?;

    println!("{:?}", data);

    Ok(())
}

This outputs:

Data { key1: "val1", key2: "val2" }