func create()

in Sources/SwiftDocCUtilities/PreviewServer/RequestHandler/FileRequestHandler.swift [130:189]
41 lines of code
7 McCabe index (conditional complexity)

    func create<ChannelHandler: ChannelInboundHandler>(channelHandler: ChannelHandler) -> RequestHandler
        where ChannelHandler.OutboundOut == HTTPServerResponsePart {

            return { ctx, head in
                // Guards for a valid URL request
                guard let components = URLComponents(string: head.uri) else { throw RequestError(status: .badRequest) }
                
                // Guard that the path is authorized for serving assets
                let mimetype: String
                if let assetMetadata = FileRequestHandler.matchingAssetMetadata(components.path) {
                    mimetype = assetMetadata.mimetype(components.path)
                } else if let topLevelAssetMetadata = FileRequestHandler.matchingTopLevelAssetMetadata(components.path) {
                    mimetype = topLevelAssetMetadata.mimetype
                } else {
                    throw RequestError(status: .unauthorized)
                }
                
                let fileURL = self.rootURL.appendingPathComponent(components.path.removingLeadingSlash)

                // Discard requests to components starting with a period or referring to the user directory
                guard components.path.components(separatedBy: "/")
                    .allSatisfy({ !$0.hasPrefix(".") && $0 != "~" }) else { throw RequestError(status: .unauthorized) }

                var data: Data
                let totalLength: Int
                
                // Read the file contents
                do {
                    data = try Data(contentsOf: fileURL, options: .mappedIfSafe)
                    totalLength = data.count
                } catch {
                    throw RequestError(status: .notFound)
                }

                // Add Range header if neccessary
                var headers = HTTPHeaders()
                let range = head.headers["Range"].first.flatMap(RangeHeader.init)
                if let range = range {
                    data = data.subdata(in: Range<Data.Index>(uncheckedBounds: (lower: range.min, upper: range.max+1)))
                    headers.add(name: "Content-Range", value: "bytes \(range.min)-\(range.max)/\(totalLength)")
                    headers.add(name: "Accept-Ranges", value: "bytes")
                }
                
                // Write the response to the output channel
                var content = ctx.channel.allocator.buffer(capacity: totalLength)
                content.writeBytes(data)

                headers.add(name: "Content-Length", value: "\(data.count)")
                headers.add(name: "Content-Type", value: mimetype)

                // No caching of live preview
                headers.add(name: "Cache-Control", value: "no-store, no-cache, must-revalidate, post-check=0, pre-check=0")
                headers.add(name: "Pragma", value: "no-cache")
                
                let responseHead = HTTPResponseHead(matchingRequestHead: head, status: range != nil ? .partialContent : .ok, headers: headers)
                
                ctx.write(channelHandler.wrapOutboundOut(.head(responseHead)), promise: nil)
                ctx.write(channelHandler.wrapOutboundOut(.body(.byteBuffer(content))), promise: nil)
            }
    }