1 files changed, 69 insertions, 0 deletions
diff --git a/lib/response.js b/lib/response.js
new file mode 100644
index 0000000..ad27c75
--- /dev/null
+++ b/lib/response.js
@@ -0,0 +1,69 @@
+'use strict'
+
+const {Transform} = require('stream')
+const {CODES} = require('./statuses')
+
+// https://gemini.circumlunar.space/docs/spec-spec.txt, 1.3.1
+// > Gemini response headers look like this:
+// > <STATUS><whitespace><META><CR><LF>
+// > <STATUS> is a two-digit numeric status code, as described below in
+// > 1.3.2 and in Appendix 1.
+// > <whitespace> is any non-zero number of consecutive spaces or tabs.
+// > <META> is a UTF-8 encoded string of maximum length 1024, whose
+// > meaning is <STATUS> dependent.
+
+const createResponse = () => {
+	let headerSent = false
+	const _sendHeader = () => {
+		if (typeof res.statusCode !== 'number') {
+			throw new Error('invalid res.statusCode')
+		}
+		const cat = Math.floor(res.statusCode / 10)
+
+		if (cat === 2 && res.mimeType) {
+			res.meta = res.mimeType // todo: validate
+		}
+
+		res.push(`${res.statusCode} ${res.meta}\r\n`)
+		headerSent = true
+
+		if (cat !== 2) res.push(null) // end
+	}
+
+	const sendHeader = (statusCode, meta = '') => {
+		if (headerSent) throw new Error('header already sent')
+		res.statusCode = statusCode
+		res.meta = meta
+		_sendHeader()
+	}
+
+	const write = (chunk, _, cb) => {
+		if (!headerSent) _sendHeader()
+		res.push(chunk)
+		cb(null)
+	}
+
+	const res = new Transform({write})
+	res.statusCode = CODES.SUCCESS
+	res.meta = ''
+	res.mimeType = null
+
+	// API
+	res.sendHeader = sendHeader
+	res.prompt = (promptMsg) => {
+		if (typeof promptMsg !== 'string') {
+			throw new Error('invalid promptMsg')
+		}
+		sendHeader(10, promptMsg)
+		res.push(null)
+	}
+	res.gone = () => {
+		sendHeader(51)
+		res.push(null)
+	}
+	// todo: redirect(), serverUnavailable(), slowDown(), badRequest()
+
+	return res
+}
+
+module.exports = createResponse