如何从Instagram的media_preview原始数据重新创建预览？

Question

如果你从Instagram获得JSON数据,你会发现media_preview关键的女巫价值是一些Base64编码的数据.它看起来像一些非常小的预览二进制数据.也许压缩了.

以这篇文章为例.它只是黑色方块,预览非常小.看看它的JSON: data['graphql']['media_preview'] = "ACoq5miiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKAP/Z"

我无法撤消代码并了解Instagram如何使用这些数据.我该怎么做才能从这个数据中创建一些预览？

我不擅长理解缩小的js,但我认为它在动态创建的画布上绘制了"敏感内容"的模糊预览.

这是一篇帖子,其中包含一些医学上很不敏感的内容供您使用.

更新:我注意到b64解码数据始终以... 00 2A 2A结尾FF D9.

Answer 1

我已经调试了几行代码并为您编译了这个函数。media_preview部分数据如此之小，因为完整的 jpeg 标头已在代码jpegtpl中可用，如我的示例所示：

function ig_media_preview(base64data) {
	var jpegtpl = "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",
		t = atob(base64data),
		p = t.slice(3).split(""),
		o = t.substring(0, 3).split("").map(function(e) {
			return e.charCodeAt(0)
		}),
		c = atob(jpegtpl).split("");
	c[162] = String.fromCharCode(o[1]);
	c[160] = String.fromCharCode(o[2]);
	return base64data ? "data:image/jpeg;base64," + btoa(c.concat(p).join("")) : null
};
      
var data = "ACoq5miiigAooooAKKKKACiiigAooooAKKKKACiiigAooooAKKKKAP/Z";
var uri = ig_media_preview(data);
document.body.insertAdjacentHTML('beforeend', '<img src="' + uri + '">');