Base64解碼問題

base64 java nodejs decode

undertaker9104 2021-04-28 09:35:24 ‧ 1446 瀏覽

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我有一個Base64 string like this:

String value = "fefWUeQvPgBe/9QaG/RdPnn9PrzQK2VhVwBzAIr7eei9PQrZA2/sXTA/2SCodnTSJn4Lk+ve5kuPGjco4ljYrjNTsrKBAjN6APSHn0BqBce2lOZbm/z29U6j7j79niPbYl/UIc0VTjc0IgRhmNLn1eVvMTuoaGhlwlxUf/+xenC4NmEM2A6y5/DNRheNw6OrmHik/kowpWGQsRNFyXJ2VtzE54nqs9naePBkRlWna/oqBxzA/txtHXn8h/9xTT2caozcU5/R9JayFZq7ZeclzGs2DAACr1TyQwEb9JJpBXr04Zu4rlWLtnSbyflyK3lnSAocma0L6ENnCZoMiN8gUg=="

我利用java去decode:

Base64Utils.decode(value.getBytes())
output:125,-25,-42,81,-28,47,62,0,94,-1,-44,26,27,-12,93,62,121,-3,62,-68,-48,43,101,97,87,0,115,0,-118,-5,121,-24,-67,61,10,-39,3,111,-20,93,48,63,-39,32,-88,118,116,-46,38,126,11,-109,-21,-34,-26,75,-113,26,55,40,-30,88,-40,-82,51,83,-78,-78,-127,2,51,122,0,-12,-121,-97,64,106,5,-57,-74,-108,-26,91,-101,-4,-10,-11,78,-93,-18,62,-3,-98,35,-37,98,95,-44,33,-51,21,78,55,52,34,4,97,-104,-46,-25,-43,-27,111,49,59,-88,104,104,101,-62,92,84,127,-1,-79,122,112,-72,54,97,12,-40,14,-78,-25,-16,-51,70,23,-115,-61,-93,-85,-104,120,-92,-2,74,48,-91,97,-112,-79,19,69,-55,114,118,86,-36,-60,-25,-119,-22,-77,-39,-38,120,-16,100,70,85,-89,107,-6,42,7,28,-64,-2,-36,109,29,121,-4,-121,-1,113,77,61,-100,106,-116,-36,83,-97,-47,-12,-106,-78,21,-102,-69,101,-25,37,-52,107,54,12,0,2,-81,84,-14,67,1,27,-12,-110,105,5,122,-12,-31,-101,-72,-82,85,-117,-74,116,-101,-55,-7,114,43,121,103,72,10,28,-103,-83,11,-24,67,103,9,-102,12,-120,-33,32,82,

接著我試著在nodejs嘗試解碼

Buffer.from(value, 'base64')
output:125,231,214,81,228,47,62,0,94,255,212,26,27,244,93,62,121,253,62,188,208,43,101,97,87,0,115,0,138,251,121,232,189,61,10,217,3,111,236,93,48,63,217,32,168,118,116,210,38,126,11,147,235,222,230,75,143,26,55,40,226,88,216,174,51,83,178,178,129,2,51,122,0,244,135,159,64,106,5,199,182,148,230,91,155,252,246,245,78,163,238,62,253,158,35,219,98,95,212,33,205,21,78,55,52,34,4,97,152,210,231,213,229,111,49,59,168,104,104,101,194,92,84,127,255,177,122,112,184,54,97,12,216,14,178,231,240,205,70,23,141,195,163,171,152,120,164,254,74,48,165,97,144,177,19,69,201,114,118,86,220,196,231,137,234,179,217,218,120,240,100,70,85,167,107,250,42,7,28,192,254,220,109,29,121,252,135,255,113,77,61,156,106,140,220,83,159,209,244,150,178,21,154,187,101,231,37,204,107,54,12,0,2,175,84,242,67,1,27,244,146,105,5,122,244,225,155,184,174,85,139,182,116,155,201,249,114,43,121,103,72,10,28,153,173,11,232,67,103,9,154,12,136,223,32,82

在java取得的output是我想取得的正確值,為何在nodejs decode之後內容會不一樣?
我該如何在nodejs上取得正確的output (跟java output 一樣) ?

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1 個回答

DanSnow

iT邦好手 1 級 ‧ 2021-04-28 10:22:14

最佳解答

Node.js 在顯示時是當成無號數 (unsigned int) 在處理，如果你要讓它變成有號的，你要自己把每個值用 readInt8 讀出來，假設變數叫 buf：

const res = []
for (let i = 0; i < buf.length; ++i) {
  res.push(buf.readInt8(i))
}
// 這邊 res 就是讀完的結果

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undertaker9104 iT邦新手 5 級 ‧ 2021-04-28 10:39:27 檢舉

大大請問一下
因為我要送API的參數必須是Buffer
如果我要將res內容轉為有號的Buffer該怎麼轉呢?

DanSnow iT邦好手 1 級 ‧ 2021-04-28 22:32:41 檢舉

理論上不用轉，因為這是接收端要怎麼去解釋收到的資料的問題，只要確保你的 server 端是以有號數來解釋就行了

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