1 files changed, 90 insertions, 0 deletions
diff --git a/lib/response-parser.js b/lib/response-parser.js
new file mode 100644
index 0000000..cb50f0a
--- /dev/null
+++ b/lib/response-parser.js
@@ -0,0 +1,90 @@
+'use strict'
+
+const {Transform} = require('stream')
+const {MESSAGES} = 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 [...].
+// > <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 CRLF = '\r\n'
+const MAX_HEADER_SIZE = 2048 // cutoff
+
+const createResponseParser = () => {
+	let headerParsed = false
+	let peek = Buffer.alloc(0)
+
+	const invalid = () => {
+		peek = null
+		out.destroy(new Error('invalid Gemini request'))
+	}
+
+	const onData = (data) => {
+		if (headerParsed) {
+			out.push(data)
+			return;
+		}
+
+		peek = Buffer.concat([peek, data], peek.length + data.length)
+		if (
+			data.indexOf(CRLF) < 0 &&
+			peek.length < MAX_HEADER_SIZE
+		) return; // keep peeking
+
+		const statusCodeAndSpace = peek.slice(0, 3).toString('utf8')
+		if (!/\d{2} /.test(statusCodeAndSpace)) return invalid()
+		const iCRLF = peek.indexOf(CRLF)
+		if (iCRLF < 0) return invalid()
+
+		let statusCode = parseInt(statusCodeAndSpace)
+		let statusMsg = MESSAGES[statusCode]
+		if (!statusMsg) {
+			statusCode = Math.floor(statusCode / 10) * 10
+			statusMsg = MESSAGES[statusCode]
+			if (!statusMsg) return invalid()
+		}
+
+		const meta = peek.slice(3, iCRLF).toString('utf8').trim()
+
+		headerParsed = true
+		out.emit('header', {
+			statusCode, statusMsg,
+			meta,
+		})
+
+		const iBody = iCRLF + 2
+		if (peek.length > (iBody + 1)) {
+			// `data` contains the beginning of the body
+			out.push(peek.slice(iBody))
+		}
+		peek = null // allow garbage collection
+	}
+
+	const out = new Transform({
+		write: (chunk, _, cb) => {
+			onData(chunk)
+			cb()
+		},
+		writev: (chunks, cb) => {
+			for (let i = 0; i < chunks.length; i++) {
+				onData(chunks[i].chunk)
+			}
+			cb()
+		},
+	})
+	return out
+}
+
+const p = createResponseParser()
+p.on('error', console.error)
+p.on('header', h => console.log('header', h))
+p.on('data', d => console.log('data', d.toString('utf8')))
+const b = str => Buffer.from(str, 'utf8')
+p.write(b('31 gemini://examp'))
+p.write(b('le.org/foo?bar\r\n'))
+
+module.exports = createResponseParser