base64 string gets written as an invalid image using Node.JS

Question

I have the following code:

var __dirname = '/home/ubuntu/Site/public/uploads/';
var base64Data = '/9j/2wBDABAICAgICBAICAgQEBAQECAYEBAQECggIBggMCgwMDAoMDAwOEhAMDhIODAwQFhASFBQUFBQMEBYYFhQYEhQUFD/2wBDARAQEBAQECgYGChQODA4UFBQUFBQUFBQUA==UFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUP/AABEIADwAUAMBIgACEQEDEQH/xAAfAAABBQEBAQEBAQAAAAAAAAAAAQIDBAUGBwgJCgv/xAC1EAACAQ==AwMCBAMFBQQEAAABfQECAwAEEQUSITFBBhNRYQcicRQygZGhCCNCscEVUtHwJDNicoIJChYXGBkaJSYnKCkqNDU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eA==eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/8QAHwEAAwEBAQEBAQEBAQAAAAAAAAECAw==BAUGBwgJCgv/xAC1EQACAQIEBAMEBwUEBAABAncAAQIDEQQFITEGEkFRB2FxEyIygQgUQpGhscEJIzNS8BVictEKFiQ04SXxFxgZGiYnKCkqNTY3ODk6Q0RFRkdISUpTVFVWVw==WFlaY2RlZmdoaWpzdHV2d3h5eoKDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uLj5OXm5+jp6vLz9PX29/j5+v/aAAwDAQACEQ==AxEAPwDmraLzIyTzkYINUby+njmEKtxH1HqeamkvXs7cxoPnPHPas4lyxZsknrUpGjZNJGsn7+2/4EvcUscjKMMKhViDkZqZJJnXaQSPcUwTAznOAKka2cJukxuPY06C3ELedA==oII+6PepA0074EW0E5x/n8qENu5Hb2zn5RkcGmeQ7zbCCMHmtKKMxuFHPBAPv6/zpJIgX4x+P+f85HpTTFYksFEafLxgdv8AP+fwp5k/doxYfLxz7f5J/P1pbYbUbn8cf59/1g==oYpMxMgP3T1/l/LNMogmt4rsHHUn+p/+tVY6W45DZHfj/PvU43xNkHIB/wA/y/WrEFwrDa/p/TH9Ki5NrlEWnlnLLx/F7f55/Kp7dEbnAwf8/wBTWi1vFOPl55/r/wDX/Wqktg==zQsWA6/eGev+fmoHYfbLHLHiQAsDwD74/wDZiPwBpXRcAx5x/D/T8hg/U1HauXmZF6nt/tf/AK2/SppkJTbGPvfd+nX+QX86ABVV2Mijj7q+4/8Arnim4+bcT+J/n/n1PpU6wA==dm0L7Y/p+v8A49TTCVO4n8f1z/X8TQMVflU9vr/n2x+HvWdJI8E5ZD9Rj/Pt+dX3YKMAdPX/AD+FULv7xYVQE5iOOR/niozCycjt/n+lS22oW8y4Zh0/oP8ACrIiikPB7/1NQA==FWG4kh4z/n/IFXkmiuVKsoOT3Hvj+oqBrX5dw9M/oDUW2WE/Ken/ANf/AAoAnayAkE9vJg+/Uf49f19qvaZZG/Mrx4jaJARHI3Xnt+QH4VRS5BHJ9v5/4ile7bAuIcEo3KH+JQ==PUfy/M0ATyh4hg8jGAPUf/q4+v0qB5SwLMR/j/n/ANmqeS8jZN5YYI6/1/kfxNZ9zdITiPgUDCabPGaqyupB5FJLN71VmmJ71SAhjWVT8oNXrO8uoiMgkA1TYlD8pNPjkc8ZpA==QjTXU224x2x+hFObUVY/Mnf+v/16zS7DvTSzY60Fl57xRjDAdP6f4U2K8BDKH49/pWc8jZojkbJ5osFy1Nc+SxMTkgnlaYb3PIFMVRK3zGnyWsUZUjPLYOTTsK5G1wzUxydhNQ==NNDHGDtFRFR5LH0xTE2f/9k=';
var buffer = new Buffer(base64Data, 'base64');
fs.writeFileSync(__dirname + 'zorro.jpg', buffer, 0, buffer.length);

However the saved image is corrupt and won't open in Finder. What am I doing wrong? Am I missing some header? The base64 string opens perfectly fine as inline data with an img tag.

EDIT: this works in HTML for me:

<img src="data:image/jpg;base64,/9j/2wBDABAICAgICBAICAgQEBAQECAYEBAQECggIBggMCgwMDAoMDAwOEhAMDhIODAwQFhASFBQUFBQMEBYYFhQYEhQUFD/2wBDARAQEBAQECgYGChQODA4UFBQUFBQUFBQUA==UFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUP/AABEIADwAUAMBIgACEQEDEQH/xAAfAAABBQEBAQEBAQAAAAAAAAAAAQIDBAUGBwgJCgv/xAC1EAACAQ==AwMCBAMFBQQEAAABfQECAwAEEQUSITFBBhNRYQcicRQygZGhCCNCscEVUtHwJDNicoIJChYXGBkaJSYnKCkqNDU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eA==eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/8QAHwEAAwEBAQEBAQEBAQAAAAAAAAECAw==BAUGBwgJCgv/xAC1EQACAQIEBAMEBwUEBAABAncAAQIDEQQFITEGEkFRB2FxEyIygQgUQpGhscEJIzNS8BVictEKFiQ04SXxFxgZGiYnKCkqNTY3ODk6Q0RFRkdISUpTVFVWVw==WFlaY2RlZmdoaWpzdHV2d3h5eoKDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uLj5OXm5+jp6vLz9PX29/j5+v/aAAwDAQACEQ==AxEAPwDmraLzIyTzkYINUby+njmEKtxH1HqeamkvXs7cxoPnPHPas4lyxZsknrUpGjZNJGsn7+2/4EvcUscjKMMKhViDkZqZJJnXaQSPcUwTAznOAKka2cJukxuPY06C3ELedA==oII+6PepA0074EW0E5x/n8qENu5Hb2zn5RkcGmeQ7zbCCMHmtKKMxuFHPBAPv6/zpJIgX4x+P+f85HpTTFYksFEafLxgdv8AP+fwp5k/doxYfLxz7f5J/P1pbYbUbn8cf59/1g==oYpMxMgP3T1/l/LNMogmt4rsHHUn+p/+tVY6W45DZHfj/PvU43xNkHIB/wA/y/WrEFwrDa/p/TH9Ki5NrlEWnlnLLx/F7f55/Kp7dEbnAwf8/wBTWi1vFOPl55/r/wDX/Wqktg==zQsWA6/eGev+fmoHYfbLHLHiQAsDwD74/wDZiPwBpXRcAx5x/D/T8hg/U1HauXmZF6nt/tf/AK2/SppkJTbGPvfd+nX+QX86ABVV2Mijj7q+4/8Arnim4+bcT+J/n/n1PpU6wA==dm0L7Y/p+v8A49TTCVO4n8f1z/X8TQMVflU9vr/n2x+HvWdJI8E5ZD9Rj/Pt+dX3YKMAdPX/AD+FULv7xYVQE5iOOR/niozCycjt/n+lS22oW8y4Zh0/oP8ACrIiikPB7/1NQA==FWG4kh4z/n/IFXkmiuVKsoOT3Hvj+oqBrX5dw9M/oDUW2WE/Ken/ANf/AAoAnayAkE9vJg+/Uf49f19qvaZZG/Mrx4jaJARHI3Xnt+QH4VRS5BHJ9v5/4ile7bAuIcEo3KH+JQ==PUfy/M0ATyh4hg8jGAPUf/q4+v0qB5SwLMR/j/n/ANmqeS8jZN5YYI6/1/kfxNZ9zdITiPgUDCabPGaqyupB5FJLN71VmmJ71SAhjWVT8oNXrO8uoiMgkA1TYlD8pNPjkc8ZpA==QjTXU224x2x+hFObUVY/Mnf+v/16zS7DvTSzY60Fl57xRjDAdP6f4U2K8BDKH49/pWc8jZojkbJ5osFy1Nc+SxMTkgnlaYb3PIFMVRK3zGnyWsUZUjPLYOTTsK5G1wzUxydhNQ==NNDHGDtFRFR5LH0xTE2f/9k="/>

Answer 1

I re-encoded your string into proper base64
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==

As to why the base64 encoded data is working on my end, the RFC4648 for base64 states this:

Furthermore, such specifications MAY ignore the pad character, "=", treating it as non-alphabet data, if it is present before the end of the encoded data. If more than the allowed number of pad characters is found at the end of the string (eg, a base 64
string terminated with "==="), the excess pad characters MAY also be
ignored.

Some implementation will ignore the added "=" and some will not.

EDIT: As other has pointed out, your base64 string seems to be many base64 string concatenated together. Here is your string:

/9j/2wBDABAICAgICBAICAgQEBAQECAYEBAQECggIBggMCgwMDAoMDAwOEhAMDhIODAwQFhASFBQUFBQMEBYYFhQYEhQUFD/2wBDARAQEBAQECgYGChQODA4UFBQUFBQUFBQUA==
UFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUP/AABEIADwAUAMBIgACEQEDEQH/xAAfAAABBQEBAQEBAQAAAAAAAAAAAQIDBAUGBwgJCgv/xAC1EAACAQ==
AwMCBAMFBQQEAAABfQECAwAEEQUSITFBBhNRYQcicRQygZGhCCNCscEVUtHwJDNicoIJChYXGBkaJSYnKCkqNDU2Nzg5OkNERUZHSElKU1RVVldYWVpjZGVmZ2hpanN0dXZ3eA==
eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi4+Tl5ufo6erx8vP09fb3+Pn6/8QAHwEAAwEBAQEBAQEBAQAAAAAAAAECAw==
BAUGBwgJCgv/xAC1EQACAQIEBAMEBwUEBAABAncAAQIDEQQFITEGEkFRB2FxEyIygQgUQpGhscEJIzNS8BVictEKFiQ04SXxFxgZGiYnKCkqNTY3ODk6Q0RFRkdISUpTVFVWVw==
WFlaY2RlZmdoaWpzdHV2d3h5eoKDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uLj5OXm5+jp6vLz9PX29/j5+v/aAAwDAQACEQ==
AxEAPwDmraLzIyTzkYINUby+njmEKtxH1HqeamkvXs7cxoPnPHPas4lyxZsknrUpGjZNJGsn7+2/4EvcUscjKMMKhViDkZqZJJnXaQSPcUwTAznOAKka2cJukxuPY06C3ELedA==
oII+6PepA0074EW0E5x/n8qENu5Hb2zn5RkcGmeQ7zbCCMHmtKKMxuFHPBAPv6/zpJIgX4x+P+f85HpTTFYksFEafLxgdv8AP+fwp5k/doxYfLxz7f5J/P1pbYbUbn8cf59/1g==
oYpMxMgP3T1/l/LNMogmt4rsHHUn+p/+tVY6W45DZHfj/PvU43xNkHIB/wA/y/WrEFwrDa/p/TH9Ki5NrlEWnlnLLx/F7f55/Kp7dEbnAwf8/wBTWi1vFOPl55/r/wDX/Wqktg==
zQsWA6/eGev+fmoHYfbLHLHiQAsDwD74/wDZiPwBpXRcAx5x/D/T8hg/U1HauXmZF6nt/tf/AK2/SppkJTbGPvfd+nX+QX86ABVV2Mijj7q+4/8Arnim4+bcT+J/n/n1PpU6wA==
dm0L7Y/p+v8A49TTCVO4n8f1z/X8TQMVflU9vr/n2x+HvWdJI8E5ZD9Rj/Pt+dX3YKMAdPX/AD+FULv7xYVQE5iOOR/niozCycjt/n+lS22oW8y4Zh0/oP8ACrIiikPB7/1NQA==
FWG4kh4z/n/IFXkmiuVKsoOT3Hvj+oqBrX5dw9M/oDUW2WE/Ken/ANf/AAoAnayAkE9vJg+/Uf49f19qvaZZG/Mrx4jaJARHI3Xnt+QH4VRS5BHJ9v5/4ile7bAuIcEo3KH+JQ==
PUfy/M0ATyh4hg8jGAPUf/q4+v0qB5SwLMR/j/n/ANmqeS8jZN5YYI6/1/kfxNZ9zdITiPgUDCabPGaqyupB5FJLN71VmmJ71SAhjWVT8oNXrO8uoiMgkA1TYlD8pNPjkc8ZpA==
QjTXU224x2x+hFObUVY/Mnf+v/16zS7DvTSzY60Fl57xRjDAdP6f4U2K8BDKH49/pWc8jZojkbJ5osFy1Nc+SxMTkgnlaYb3PIFMVRK3zGnyWsUZUjPLYOTTsK5G1wzUxydhNQ==
NNDHGDtFRFR5LH0xTE2f/9k=

Notice how each of base64 string are 136 chracter long. If you decoded each of these base64 and append the result of each decoded base64 into a file, you will get your image.