[utoipa-gen] MediaTypeAttr, Encoding: Parse encodings

Though only in a limited fashion - notable fields are still not
implemented.

Though this does let you do:

```rs
   request_body(
       content(...)
       encoding(
           ("field_name", (
               content_type = "application/json",
               explode = true,
               allow_reserved = true,
           ))
       )
   )
```

Partially addresses #1087

utoipa-gen/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Added
+
+* Add `encoding` support for `request_body` (https://github.com/juhaku/utoipa/pull/1237)
+
 ### Fixed
 
 * Fix tagged enum with flatten fields (https://github.com/juhaku/utoipa/pull/1208)

utoipa-gen/src/path/media_type.rs

@@ -1,4 +1,5 @@
 use std::borrow::Cow;
+use std::collections::BTreeMap;
 
 use proc_macro2::TokenStream;
 use quote::{quote, ToTokens};
@@ -16,19 +17,23 @@ use crate::{parse_utils, AnyValue, Array, Diagnostics, ToTokensDiagnostics};
 use super::example::Example;
 use super::PathTypeTree;
 
+pub mod encoding;
+
+use encoding::Encoding;
+
 /// Parse OpenAPI Media Type object params
 /// ( Schema )
 /// ( Schema = "content/type" )
 /// ( "content/type", ),
-/// ( "content/type", example = ..., examples(..., ...), encoding(...) )
+/// ( "content/type", example = ..., examples(..., ...), encoding(("exampleField" = (...)), ...) )
 #[derive(Default)]
 #[cfg_attr(feature = "debug", derive(Debug))]
 pub struct MediaTypeAttr<'m> {
     pub content_type: Option<parse_utils::LitStrOrExpr>, // if none, true guess
     pub schema: Schema<'m>,
     pub example: Option<AnyValue>,
     pub examples: Punctuated<Example, Comma>,
-    // econding: String, // TODO parse encoding
+    pub encoding: BTreeMap<String, Encoding>,
 }
 
 impl Parse for MediaTypeAttr<'_> {
@@ -105,13 +110,41 @@ impl<'m> MediaTypeAttr<'m> {
             "examples" => {
                 self.examples = parse_utils::parse_comma_separated_within_parenthesis(input)?
             }
-            // // TODO implement encoding support
-            // "encoding" => (),
+            "encoding" => {
+                struct KV {
+                    k: String,
+                    v: Encoding,
+                }
+
+                impl Parse for KV {
+                    fn parse(input: ParseStream) -> syn::Result<Self> {
+                        let key_val;
+
+                        syn::parenthesized!(key_val in input);
+
+                        let k = key_val.parse::<syn::LitStr>()?.value();
+
+                        key_val.parse::<Token![=]>()?;
+
+                        let v = key_val.parse::<Encoding>()?;
+
+                        if !key_val.is_empty() {
+                            key_val.parse::<Comma>()?;
+                        }
+
+                        Ok(KV{k, v})
+                    }
+                }
+
+                let fields = parse_utils::parse_comma_separated_within_parenthesis::<KV>(input)?;
+
+                self.encoding = fields.into_iter().map(|x| (x.k, x.v)).collect();
+            }
             unexpected => {
                 return Err(syn::Error::new(
                     attribute.span(),
                     format!(
-                        "unexpected attribute: {unexpected}, expected any of: example, examples"
+                        "unexpected attribute: {unexpected}, expected any of: example, examples, encoding(...)"
                     ),
                 ))
             }
@@ -151,12 +184,17 @@ impl ToTokensDiagnostics for MediaTypeAttr<'_> {
         } else {
             None
         };
+        let encoding = self
+            .encoding
+            .iter()
+            .map(|(field_name, encoding)| quote!(.encoding(#field_name, #encoding)));
 
         tokens.extend(quote! {
             utoipa::openapi::content::ContentBuilder::new()
                 #schema_tokens
                 #example
                 #examples
+                #(#encoding)*
                 .into()
         });
 

utoipa-gen/src/path/media_type/encoding.rs

@@ -0,0 +1,90 @@
+use proc_macro2::{Ident, TokenStream};
+use quote::{quote, ToTokens};
+use syn::parse::{Parse, ParseStream};
+use syn::{parenthesized, Error, Token};
+
+use crate::parse_utils;
+
+// (content_type = "...", explode = true, allow_reserved = false,)
+#[derive(Default)]
+#[cfg_attr(feature = "debug", derive(Debug))]
+pub struct Encoding {
+    pub(super) content_type: Option<parse_utils::LitStrOrExpr>,
+    // pub(super) headers: BTreeMap<String, Header>,
+    // pub(super) style: Option<ParameterStyle>,
+    pub(super) explode: Option<bool>,
+    pub(super) allow_reserved: Option<bool>,
+    // pub(super) extensions: Option<Extensions>,
+}
+
+impl Parse for Encoding {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let content;
+        parenthesized!(content in input);
+
+        let mut encoding = Encoding::default();
+
+        while !content.is_empty() {
+            let ident = content.parse::<Ident>()?;
+            let attribute_name = &*ident.to_string();
+            match attribute_name {
+                "content_type" => {
+                    encoding.content_type = Some(
+                        parse_utils::parse_next_literal_str_or_expr(&content)?
+                    )
+                }
+                // "headers" => {}
+                // "style" => {}
+                "explode" => {
+                    encoding.explode = Some(
+                        parse_utils::parse_bool_or_true(&content)?
+                    )
+                }
+                "allow_reserved" => {
+                    encoding.allow_reserved = Some(
+                        parse_utils::parse_bool_or_true(&content)?
+                    )
+                }
+                // "extensions"  => {}
+                _ => {
+                    return Err(
+                        Error::new(
+                            ident.span(),
+                            format!("unexpected attribute: {attribute_name}, expected one of: content_type, explode, allow_reserved")
+                        )
+                    )
+                }
+            }
+
+            if !content.is_empty() {
+                content.parse::<Token![,]>()?;
+            }
+        }
+
+        Ok(encoding)
+    }
+}
+
+impl ToTokens for Encoding {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        let content_type = self
+            .content_type
+            .as_ref()
+            .map(|content_type| quote!(.content_type(Some(#content_type))));
+        let explode = self
+            .explode
+            .as_ref()
+            .map(|value| quote!(.explode(Some(#value))));
+        let allow_reserved = self
+            .allow_reserved
+            .as_ref()
+            .map(|allow_reserved| quote!(.allow_reserved(Some(#allow_reserved))));
+
+        tokens.extend(quote! {
+            utoipa::openapi::encoding::EncodingBuilder::new()
+                #content_type
+                #explode
+                #allow_reserved
+        })
+    }
+}

utoipa-gen/src/path/request_body.rs

@@ -1,7 +1,6 @@
 use proc_macro2::{Ident, TokenStream};
 use quote::{quote, ToTokens};
 use syn::parse::ParseStream;
-use syn::punctuated::Punctuated;
 use syn::token::Paren;
 use syn::{parse::Parse, Error, Token};
 
@@ -110,7 +109,7 @@ impl<'r> RequestBodyAttr<'r> {
 impl Parse for RequestBodyAttr<'_> {
     fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
         const EXPECTED_ATTRIBUTE_MESSAGE: &str =
-            "unexpected attribute, expected any of: content, content_type, description, examples, example";
+            "unexpected attribute, expected any of: content, content_type, description, examples, example, encoding";
         let lookahead = input.lookahead1();
 
         if lookahead.peek(Paren) {
@@ -193,9 +192,7 @@ impl Parse for RequestBodyAttr<'_> {
 
             let media_type = MediaTypeAttr {
                 schema: Schema::Default(MediaTypeAttr::parse_schema(input)?),
-                content_type: None,
-                example: None,
-                examples: Punctuated::default(),
+                ..MediaTypeAttr::default()
             };
 
             Ok(RequestBodyAttr {

utoipa-gen/src/path/response.rs

@@ -360,6 +360,7 @@ impl<'r> ResponseValue<'r> {
                 .examples
                 .map(|(examples, _)| examples)
                 .unwrap_or_default(),
+            ..MediaTypeAttr::default()
         };
 
         Self {
@@ -389,6 +390,7 @@ impl<'r> ResponseValue<'r> {
                 .examples
                 .map(|(examples, _)| examples)
                 .unwrap_or_default(),
+            ..MediaTypeAttr::default()
         };
 
         ResponseValue {

utoipa-gen/src/path/response/derive.rs

@@ -649,6 +649,7 @@ impl<'r> EnumResponse<'r> {
                             schema: schema.unwrap_or_else(|| Schema::Default(DefaultSchema::None)),
                             example,
                             examples: examples.unwrap_or_default(),
+                            ..MediaTypeAttr::default()
                         }
                     },
                 )

utoipa-gen/tests/request_body_derive_test.rs

@@ -386,7 +386,7 @@ fn multiple_content_with_examples() {
                     ("example2" = (value = json!("example value"), description = "example value") ),
                     ),
                 ),
-                ( Foo = "text/xml", example = "Value" ) 
+                ( Foo = "text/xml", example = "Value" )
             ),
         ),
         responses(