// Copyright 2013-2016 The rust-url developers.

//

// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or

// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license

// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your

// option. This file may not be copied, modified, or distributed

// except according to those terms.

//! Parser and serializer for the [`application/x-www-form-urlencoded` syntax](

//! http://url.spec.whatwg.org/#application/x-www-form-urlencoded),

//! as used by HTML forms.

//!

//! Converts between a string (such as an URL’s query string)

//! and a sequence of (name, value) pairs.

#![no_std]

// For forwards compatibility

#[cfg(feature = "std")]

extern crate std as _;

extern crate alloc;

#[cfg(not(feature = "alloc"))]

compile_error!("the `alloc` feature must currently be enabled");

use alloc::borrow::{Borrow, Cow, ToOwned};

use alloc::string::String;

use core::str;

use percent_encoding::{percent_decode, percent_encode_byte};

/// Convert a byte string in the `application/x-www-form-urlencoded` syntax

/// into a iterator of (name, value) pairs.

///

/// Use `parse(input.as_bytes())` to parse a `&str` string.

///

/// The names and values are percent-decoded. For instance, `%23first=%25try%25` will be

/// converted to `[("#first", "%try%")]`.

#[inline]

pub fn parse(input: &[u8]) -> Parse<'_> {

    Parse { input }

}

/// The return type of `parse()`.

#[derive(Copy, Clone)]

pub struct Parse<'a> {

    input: &'a [u8],

}

impl<'a> Iterator for Parse<'a> {

    type Item = (Cow<'a, str>, Cow<'a, str>);

    fn next(&mut self) -> Option<Self::Item> {

        loop {

            if self.input.is_empty() {

                return None;

            }

            let mut split2 = self.input.splitn(2, |&b| b == b'&');

            let sequence = split2.next().unwrap();

            self.input = split2.next().unwrap_or(&[][..]);

            if sequence.is_empty() {

                continue;

            }

            let mut split2 = sequence.splitn(2, |&b| b == b'=');

            let name = split2.next().unwrap();

            let value = split2.next().unwrap_or(&[][..]);

            return Some((decode(name), decode(value)));

        }

    }

}

fn decode(input: &[u8]) -> Cow<'_, str> {

    let replaced = replace_plus(input);

    decode_utf8_lossy(match percent_decode(&replaced).into() {

        Cow::Owned(vec) => Cow::Owned(vec),

        Cow::Borrowed(_) => replaced,

    })

}

/// Replace b'+' with b' '

fn replace_plus(input: &[u8]) -> Cow<'_, [u8]> {

    match input.iter().position(|&b| b == b'+') {

        None => Cow::Borrowed(input),

        Some(first_position) => {

            let mut replaced = input.to_owned();

            replaced[first_position] = b' ';

            for byte in &mut replaced[first_position + 1..] {

                if *byte == b'+' {

                    *byte = b' ';

                }

            }

            Cow::Owned(replaced)

        }

    }

}

impl<'a> Parse<'a> {

    /// Return a new iterator that yields pairs of `String` instead of pairs of `Cow<str>`.

    pub fn into_owned(self) -> ParseIntoOwned<'a> {

        ParseIntoOwned { inner: self }

    }

}

/// Like `Parse`, but yields pairs of `String` instead of pairs of `Cow<str>`.

pub struct ParseIntoOwned<'a> {

    inner: Parse<'a>,

}

impl Iterator for ParseIntoOwned<'_> {

    type Item = (String, String);

    fn next(&mut self) -> Option<Self::Item> {

        self.inner

            .next()

            .map(|(k, v)| (k.into_owned(), v.into_owned()))

    }

}

/// The [`application/x-www-form-urlencoded` byte serializer](

/// https://url.spec.whatwg.org/#concept-urlencoded-byte-serializer).

///

/// Return an iterator of `&str` slices.

pub fn byte_serialize(input: &[u8]) -> ByteSerialize<'_> {

    ByteSerialize { bytes: input }

}

/// Return value of `byte_serialize()`.

#[derive(Debug)]

pub struct ByteSerialize<'a> {

    bytes: &'a [u8],

}

fn byte_serialized_unchanged(byte: u8) -> bool {

    matches!(byte, b'*' | b'-' | b'.' | b'0' ..= b'9' | b'A' ..= b'Z' | b'_' | b'a' ..= b'z')

}

impl<'a> Iterator for ByteSerialize<'a> {

    type Item = &'a str;

    fn next(&mut self) -> Option<&'a str> {

        if let Some((&first, tail)) = self.bytes.split_first() {

            if !byte_serialized_unchanged(first) {

                self.bytes = tail;

                return Some(if first == b' ' {

                    "+"

                } else {

                    percent_encode_byte(first)

                });

            }

            let position = tail.iter().position(|&b| !byte_serialized_unchanged(b));

            let (unchanged_slice, remaining) = match position {

                // 1 for first_byte + i unchanged in tail

                Some(i) => self.bytes.split_at(1 + i),

                None => (self.bytes, &[][..]),

            };

            self.bytes = remaining;

            // This unsafe is appropriate because we have already checked these

            // bytes in byte_serialized_unchanged, which checks for a subset

            // of UTF-8. So we know these bytes are valid UTF-8, and doing

            // another UTF-8 check would be wasteful.

            Some(unsafe { str::from_utf8_unchecked(unchanged_slice) })

        } else {

            None

        }

    }

    fn size_hint(&self) -> (usize, Option<usize>) {

        if self.bytes.is_empty() {

            (0, Some(0))

        } else {

            (1, Some(self.bytes.len()))

        }

    }

}

/// The [`application/x-www-form-urlencoded` serializer](

/// https://url.spec.whatwg.org/#concept-urlencoded-serializer).

pub struct Serializer<'a, T: Target> {

    target: Option<T>,

    start_position: usize,

    encoding: EncodingOverride<'a>,

}

pub trait Target {

    fn as_mut_string(&mut self) -> &mut String;

    fn finish(self) -> Self::Finished;

    type Finished;

}

impl Target for String {

    fn as_mut_string(&mut self) -> &mut String {

        self

    }

    fn finish(self) -> Self {

        self

    }

    type Finished = Self;

}

impl Target for &mut String {

    fn as_mut_string(&mut self) -> &mut String {

        self

    }

    fn finish(self) -> Self {

        self

    }

    type Finished = Self;

}

impl<'a, T: Target> Serializer<'a, T> {

    /// Create a new `application/x-www-form-urlencoded` serializer for the given target.

    ///

    /// If the target is non-empty,

    /// its content is assumed to already be in `application/x-www-form-urlencoded` syntax.

    pub fn new(target: T) -> Self {

        Self::for_suffix(target, 0)

    }

    /// Create a new `application/x-www-form-urlencoded` serializer

    /// for a suffix of the given target.

    ///

    /// If that suffix is non-empty,

    /// its content is assumed to already be in `application/x-www-form-urlencoded` syntax.

    /// If `start_position` exceeds the target's length, it is set to the target's length.

    pub fn for_suffix(mut target: T, start_position: usize) -> Self {

        let start_position = start_position.min(target.as_mut_string().len());

        Serializer {

            target: Some(target),

            start_position,

            encoding: None,

        }

    }

Unexecuted instantiation: <form_urlencoded::Serializer<url::UrlQuery>>::for_suffix

Unexecuted instantiation: <form_urlencoded::Serializer<_>>::for_suffix

    /// Remove any existing name/value pair.

    ///

    /// Panics if called after `.finish()`.

    pub fn clear(&mut self) -> &mut Self {

        string(&mut self.target).truncate(self.start_position);

        self

    }

    /// Set the character encoding to be used for names and values before percent-encoding.

    pub fn encoding_override(&mut self, new: EncodingOverride<'a>) -> &mut Self {

        self.encoding = new;

        self

    }

    /// Serialize and append a name/value pair.

    ///

    /// Panics if called after `.finish()`.

    pub fn append_pair(&mut self, name: &str, value: &str) -> &mut Self {

        append_pair(

            string(&mut self.target),

            self.start_position,

            self.encoding,

            name,

            value,

        );

        self

    }

    /// Serialize and append a name of parameter without any value.

    ///

    /// Panics if called after `.finish()`.

    pub fn append_key_only(&mut self, name: &str) -> &mut Self {

        append_key_only(

            string(&mut self.target),

            self.start_position,

            self.encoding,

            name,

        );

        self

    }

    /// Serialize and append a number of name/value pairs.

    ///

    /// This simply calls `append_pair` repeatedly.

    /// This can be more convenient, so the user doesn’t need to introduce a block

    /// to limit the scope of `Serializer`’s borrow of its string.

    ///

    /// Panics if called after `.finish()`.

    pub fn extend_pairs<I, K, V>(&mut self, iter: I) -> &mut Self

    where

        I: IntoIterator,

        I::Item: Borrow<(K, V)>,

        K: AsRef<str>,

        V: AsRef<str>,

    {

        {

            let string = string(&mut self.target);

            for pair in iter {

                let (k, v) = pair.borrow();

                append_pair(

                    string,

                    self.start_position,

                    self.encoding,

                    k.as_ref(),

                    v.as_ref(),

                );

            }

        }

        self

    }

    /// Serialize and append a number of names without values.

    ///

    /// This simply calls `append_key_only` repeatedly.

    /// This can be more convenient, so the user doesn’t need to introduce a block

    /// to limit the scope of `Serializer`’s borrow of its string.

    ///

    /// Panics if called after `.finish()`.

    pub fn extend_keys_only<I, K>(&mut self, iter: I) -> &mut Self

    where

        I: IntoIterator,

        I::Item: Borrow<K>,

        K: AsRef<str>,

    {

        {

            let string = string(&mut self.target);

            for key in iter {

                let k = key.borrow().as_ref();

                append_key_only(string, self.start_position, self.encoding, k);

            }

        }

        self

    }

    /// If this serializer was constructed with a string, take and return that string.

    ///

    /// ```rust

    /// use form_urlencoded;

    /// let encoded: String = form_urlencoded::Serializer::new(String::new())

    ///     .append_pair("foo", "bar & baz")

    ///     .append_pair("saison", "Été+hiver")

    ///     .finish();

    /// assert_eq!(encoded, "foo=bar+%26+baz&saison=%C3%89t%C3%A9%2Bhiver");

    /// ```

    ///

    /// Panics if called more than once.

    pub fn finish(&mut self) -> T::Finished {

        self.target

            .take()

            .expect("url::form_urlencoded::Serializer double finish")

            .finish()

    }

}

fn append_separator_if_needed(string: &mut String, start_position: usize) {

    if string.len() > start_position {

        string.push('&')

    }

}

fn string<T: Target>(target: &mut Option<T>) -> &mut String {

    target

        .as_mut()

        .expect("url::form_urlencoded::Serializer finished")

        .as_mut_string()

}

fn append_pair(

    string: &mut String,

    start_position: usize,

    encoding: EncodingOverride<'_>,

    name: &str,

    value: &str,

) {

    append_separator_if_needed(string, start_position);

    append_encoded(name, string, encoding);

    string.push('=');

    append_encoded(value, string, encoding);

}

fn append_key_only(

    string: &mut String,

    start_position: usize,

    encoding: EncodingOverride,

    name: &str,

) {

    append_separator_if_needed(string, start_position);

    append_encoded(name, string, encoding);

}

fn append_encoded(s: &str, string: &mut String, encoding: EncodingOverride<'_>) {

    string.extend(byte_serialize(&encode(encoding, s)))

}

pub(crate) fn encode<'a>(encoding_override: EncodingOverride<'_>, input: &'a str) -> Cow<'a, [u8]> {

    if let Some(o) = encoding_override {

        return o(input);

    }

    input.as_bytes().into()

}

// std::ptr::addr_eq was stabilized in rust 1.76. Once we upgrade

// the MSRV we can remove this lint override.

#[allow(ambiguous_wide_pointer_comparisons)]

pub(crate) fn decode_utf8_lossy(input: Cow<'_, [u8]>) -> Cow<'_, str> {

    // Note: This function is duplicated in `percent_encoding/lib.rs`.

    match input {

        Cow::Borrowed(bytes) => String::from_utf8_lossy(bytes),

        Cow::Owned(bytes) => {

            match String::from_utf8_lossy(&bytes) {

                Cow::Borrowed(utf8) => {

                    // If from_utf8_lossy returns a Cow::Borrowed, then we can

                    // be sure our original bytes were valid UTF-8. This is because

                    // if the bytes were invalid UTF-8 from_utf8_lossy would have

                    // to allocate a new owned string to back the Cow so it could

                    // replace invalid bytes with a placeholder.

                    // First we do a debug_assert to confirm our description above.

                    let raw_utf8: *const [u8] = utf8.as_bytes();

                    debug_assert!(core::ptr::eq(raw_utf8, &*bytes));

                    // Given we know the original input bytes are valid UTF-8,

                    // and we have ownership of those bytes, we re-use them and

                    // return a Cow::Owned here.

                    Cow::Owned(unsafe { String::from_utf8_unchecked(bytes) })

                }

                Cow::Owned(s) => Cow::Owned(s),

            }

        }

    }

}

pub type EncodingOverride<'a> = Option<&'a dyn Fn(&str) -> Cow<'_, [u8]>>;