[Runtime] Improve parameter handling of MIME types in content types (#113)

### Motivation

In service of an upcoming generator PR - to better handle parameters in
MIME types.

This is needed for APIs such as Kubernetes, that has both
`application/json` and `application/json; watch=true` in a single
operation.

### Modifications

Use the more modern `OpenAPIMIMEType` type for parsing and comparing
content types, rather than the old naive logic that ignored parameter
(mis)matches.

### Result

More accurate handling of content types.

### Test Plan

Adapted unit tests.

Author: czechboy0

Sources/OpenAPIRuntime/Conversion/Converter+Server.swift

@@ -56,14 +56,21 @@ extension Converter {
                 // Drop everything after the optional semicolon (q, extensions, ...)
                 value.split(separator: ";")[0].trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
             }
-
         if acceptValues.isEmpty { return }
-        if acceptValues.contains("*/*") { return }
-        if acceptValues.contains("\(substring.split(separator: "/")[0].lowercased())/*") { return }
-        if acceptValues.contains(where: { $0.localizedCaseInsensitiveContains(substring) }) { return }
+        guard let parsedSubstring = OpenAPIMIMEType(substring) else {
+            throw RuntimeError.invalidAcceptSubstring(substring)
+        }
+        // Look for the first match.
+        for acceptValue in acceptValues {
+            // Fast path.
+            if acceptValue == substring { return }
+            guard let parsedAcceptValue = OpenAPIMIMEType(acceptValue) else {
+                throw RuntimeError.invalidExpectedContentType(acceptValue)
+            }
+            if parsedSubstring.satisfies(acceptValue: parsedAcceptValue) { return }
+        }
         throw RuntimeError.unexpectedAcceptHeader(acceptHeader)
     }
-
     /// Retrieves and decodes a path parameter as a URI-encoded value of the specified type.
     ///
     /// - Parameters:
@@ -469,3 +476,27 @@ extension Converter {
         )
     }
 }
+
+fileprivate extension OpenAPIMIMEType {
+    /// Checks if the type satisfies the provided Accept header value.
+    /// - Parameter acceptValue: A parsed Accept header MIME type.
+    /// - Returns: `true` if it satisfies the Accept header, `false` otherwise.
+    func satisfies(acceptValue: OpenAPIMIMEType) -> Bool {
+        switch (acceptValue.kind, self.kind) {
+        case (.concrete, .any), (.concrete, .anySubtype), (.anySubtype, .any):
+            // The response content-type must be at least as specific as the accept header.
+            return false
+        case (.any, _):
+            // Accept: */* -- Any content-type satisfies the accept header.
+            return true
+        case (.anySubtype(let acceptType), .anySubtype(let substringType)),
+            (.anySubtype(let acceptType), .concrete(let substringType, _)):
+            // Accept: type/* -- The content-type should match the partially-specified accept header.
+            return acceptType.lowercased() == substringType.lowercased()
+        case (.concrete(let acceptType, let acceptSubtype), .concrete(let substringType, let substringSubtype)):
+            // Accept: type/subtype -- The content-type should match the concrete type.
+            return acceptType.lowercased() == substringType.lowercased()
+                && acceptSubtype.lowercased() == substringSubtype.lowercased()
+        }
+    }
+}

Sources/OpenAPIRuntime/Errors/RuntimeError.swift

@@ -21,6 +21,7 @@ internal enum RuntimeError: Error, CustomStringConvertible, LocalizedError, Pret
     case invalidServerURL(String)
     case invalidServerVariableValue(name: String, value: String, allowedValues: [String])
     case invalidExpectedContentType(String)
+    case invalidAcceptSubstring(String)
     case invalidHeaderFieldName(String)
     case invalidBase64String(String)
 
@@ -85,6 +86,7 @@ internal enum RuntimeError: Error, CustomStringConvertible, LocalizedError, Pret
             return
                 "Invalid server variable named: '\(name)', which has the value: '\(value)', but the only allowed values are: \(allowedValues.map { "'\($0)'" }.joined(separator: ", "))"
         case .invalidExpectedContentType(let string): return "Invalid expected content type: '\(string)'"
+        case .invalidAcceptSubstring(let string): return "Invalid Accept header content type: '\(string)'"
         case .invalidHeaderFieldName(let name): return "Invalid header field name: '\(name)'"
         case .invalidBase64String(let string):
             return "Invalid base64-encoded string (first 128 bytes): '\(string.prefix(128))'"

Tests/OpenAPIRuntimeTests/Conversion/Test_Converter+Server.swift

@@ -39,25 +39,31 @@ final class Test_ServerConverterExtensions: Test_Runtime {
             .accept: "text/html, application/xhtml+xml, application/xml;q=0.9, image/webp, */*;q=0.8"
         ]
         let multiple: HTTPFields = [.accept: "text/plain, application/json"]
+        let params: HTTPFields = [.accept: "application/json; foo=bar"]
         let cases: [(HTTPFields, String, Bool)] = [
             // No Accept header, any string validates successfully
             (emptyHeaders, "foobar", true),
 
-            // Accept: */*, any string validates successfully
-            (wildcard, "foobar", true),
+            // Accept: */*, any MIME type validates successfully
+            (wildcard, "foobaz/bar", true),
 
             // Accept: text/*, so text/plain succeeds, application/json fails
             (partialWildcard, "text/plain", true), (partialWildcard, "application/json", false),
 
             // Accept: text/plain, text/plain succeeds, application/json fails
-            (short, "text/plain", true), (short, "application/json", false),
+            (short, "text/plain", true), (short, "application/json", false), (short, "application/*", false),
+            (short, "*/*", false),
 
             // A bunch of acceptable content types
             (long, "text/html", true), (long, "application/xhtml+xml", true), (long, "application/xml", true),
             (long, "image/webp", true), (long, "application/json", true),
 
             // Multiple values
             (multiple, "text/plain", true), (multiple, "application/json", true), (multiple, "application/xml", false),
+
+            // Params
+            (params, "application/json; foo=bar", true), (params, "application/json; charset=utf-8; foo=bar", true),
+            (params, "application/json", true), (params, "text/plain", false),
         ]
         for (headers, contentType, success) in cases {
             if success {