From c51e4f8a7ad0bd518864ffb4a7d4bda26e360cee Mon Sep 17 00:00:00 2001
From: David Ventura <davidventura27@gmail.com>
Date: Thu, 2 May 2024 13:18:28 +0200
Subject: [PATCH] implement rotation via injecting exif headers (#19)

---
 asd.html       | 16 ++++++++--------
 exif.ts        | 28 ++++++++++++++++++++++++++++
 http_server.ts | 37 ++++++++++++++++++++++++++++++++++---
 3 files changed, 70 insertions(+), 11 deletions(-)
 create mode 100644 exif.ts

diff --git a/asd.html b/asd.html
index 50d2a47..87006d4 100644
--- a/asd.html
+++ b/asd.html
@@ -3,8 +3,10 @@
 	<link rel="shortcut icon" href="/favicon.ico">
 	<title>${name}</title>
 	</head><body>
-	<h2>${name}</h2><a href="/camera/${id}"><img src="/camera/${id}"/></a><hr/>
+	<h2>${name}</h2><a href="/camera/${id}"><img style="height: 640px" src="/camera/${id}"/></a><hr/>
 	<button onclick="toggle_audio()" id=audio disabled=true>Audio: disabled</button>
+	<button onclick="fetch('/rotate/${id}')">Rotate</button>
+	<button onclick="fetch('/mirror/${id}')">Mirror</button>
 	<script>
 	const alaw_to_s16_table = [
 	  -5504, -5248, -6016, -5760, -4480, -4224, -4992, -4736, -7552, -7296, -8064, -7808, -6528, -6272, -7040, -6784, -2752,
@@ -49,13 +51,11 @@
 		audio_context.resume();
 
 		const evtSource = new EventSource("/audio/${id}");
-		if (${debug}) {
-			evtSource.onopen = (e) => {
-				console.log("evtsource open");
-			}
-			evtSource.onerror = (e) => {
-				console.log("evtsource error", e);
-			}
+		evtSource.onopen = (e) => {
+			console.log("evtsource open");
+		}
+		evtSource.onerror = (e) => {
+			console.log("evtsource error", e);
 		}
 		let endsAt = 0;
 		let startAt = 0;
diff --git a/exif.ts b/exif.ts
new file mode 100644
index 0000000..c99d54b
--- /dev/null
+++ b/exif.ts
@@ -0,0 +1,28 @@
+// Create a minimal EXIF segment with orientation
+export const createExifOrientation = (orientation: number) => {
+  const tiffHeader = Buffer.from("49492A0008000000", "hex");
+  const ifdEntry = Buffer.concat([
+    Buffer.from("0100", "hex"), // Number of IFD entries
+    Buffer.from("1201030001000000", "hex"), // Tag, Type, Count
+    Buffer.from(orientation.toString(16).padStart(2, "0"), "hex"), // Orientation value
+    Buffer.from("0000", "hex"), // No more IFDs
+    Buffer.from("0000000000", "hex"), // padding??
+  ]);
+
+  const exifData = Buffer.concat([Buffer.from("457869660000", "hex"), tiffHeader, ifdEntry]);
+  const segmentLength = Buffer.from([(exifData.length + 2) >> 8, (exifData.length + 2) & 0xff]);
+  const exifHeader = Buffer.concat([Buffer.from("FFE1", "hex"), segmentLength]);
+
+  return Buffer.concat([exifHeader, exifData]);
+};
+
+export const addExifToJpeg = (jpegData: Buffer, exifSegment: Buffer) => {
+  // Check for existing EXIF (simplified check)
+  if (jpegData.includes(Buffer.from("FFE1", "hex"))) {
+    throw new Error("JPEG already contains EXIF segment");
+  }
+
+  const soiEnd = 2; // After FFD8
+  const modifiedJpeg = Buffer.concat([jpegData.subarray(0, soiEnd), exifSegment, jpegData.subarray(soiEnd)]);
+  return modifiedJpeg;
+};
diff --git a/http_server.ts b/http_server.ts
index 599e1b3..d3e0e33 100644
--- a/http_server.ts
+++ b/http_server.ts
@@ -7,6 +7,7 @@ import { opt } from "./options.js";
 import { discoverDevices } from "./discovery.js";
 import { DevSerial, SendDevStatus } from "./impl.js";
 import { Handlers, makeSession, Session, startVideoStream } from "./session.js";
+import { addExifToJpeg, createExifOrientation } from "./exif.js";
 
 // @ts-expect-error TS2307
 import favicon from "./cam.ico.gz";
@@ -21,6 +22,15 @@ const sessions: Record<string, Session> = {};
 // Text file containing the mapping of camera names.
 const nameFile = "cameras.txt";
 
+// https://sirv.com/help/articles/rotate-photos-to-be-upright/
+const oMap = [1, 8, 3, 6];
+const oMapMirror = [2, 7, 4, 5];
+const orientations = [1, 2, 3, 4, 5, 6, 7, 8].reduce((acc, cur) => {
+  return { [cur]: createExifOrientation(cur), ...acc };
+}, {});
+
+let camSettings: { [key: string]: { orientation: number; mirror: boolean } } = {};
+
 // Reads the mapping of serial numbers to camera names from the text file.
 const cameraNames = Object.assign(
   {},
@@ -90,7 +100,23 @@ export const serveHttp = (opts: opt, port: number, with_audio: boolean) => {
       return;
     }
 
-    if (req.url.startsWith("/camera/")) {
+    if (req.url.startsWith("/rotate/")) {
+      let devId = req.url.split("/")[2];
+      let curPos = camSettings[devId]?.orientation || 0;
+      let nextPos = (curPos + 1) % 4;
+      logger.info(`Rotating ${devId} to ${nextPos}`);
+      camSettings[devId].orientation = nextPos;
+      res.writeHead(204);
+      res.end();
+      return;
+    } else if (req.url.startsWith("/mirror/")) {
+      let devId = req.url.split("/")[2];
+      logger.info(`Mirroring ${devId}`);
+      camSettings[devId].mirror = !camSettings[devId].mirror;
+      res.writeHead(204);
+      res.end();
+      return;
+    } else if (req.url.startsWith("/camera/")) {
       let devId = req.url.split("/")[2];
       logger.info(`Video stream requested for camera ${devId}`);
       let s = sessions[devId];
@@ -151,8 +177,12 @@ export const serveHttp = (opts: opt, port: number, with_audio: boolean) => {
     const header = Buffer.from(`--${BOUNDARY}\r\nContent-Type: image/jpeg\r\n\r\n`);
 
     s.eventEmitter.on("frame", () => {
-      const assembled = Buffer.concat(s.curImage);
-
+      // Add an EXIF header to indicate if the image should be rotated or mirrored
+      let orientation = camSettings[dev.devId].orientation;
+      orientation = camSettings[dev.devId].mirror ? oMapMirror[orientation] : oMap[orientation];
+      const exifSegment = orientations[orientation];
+      const jpegHeader = addExifToJpeg(s.curImage[0], exifSegment);
+      const assembled = Buffer.concat([jpegHeader, ...s.curImage.slice(1)]);
       responses[dev.devId].forEach((res) => {
         res.write(header);
         res.write(assembled);
@@ -175,6 +205,7 @@ export const serveHttp = (opts: opt, port: number, with_audio: boolean) => {
       });
     }
     sessions[dev.devId] = s;
+    camSettings[dev.devId] = { orientation: 0, mirror: false };
   });
 
   logger.info(`Starting HTTP server on port ${port}`);