问题
I am having serious problems decoding the message body of the emails I get using the Gmail API. I want to grab the message content and put the content in a div. I am using a base64 decoder, which I know won't decode emails encoded differently, but I am not sure how to check an email to decide which decoder to use -- emails that say they are utf-8 encoded are successfully decoded by the base64 decoder, but not be a utf-8 decoder.
I've been researching email decoding for several days now, and I've learned that I am a little out of my league here. I haven't done much work with coding around email before. Here is the code I am using to get the emails:
gapi.client.load('gmail', 'v1', function() {
var request = gapi.client.gmail.users.messages.list({
labelIds: ['INBOX']
});
request.execute(function(resp) {
document.getElementById('email-announcement').innerHTML = '<i>Hello! I am reading your <b>inbox</b> emails.</i><br><br>------<br>';
var content = document.getElementById("message-list");
if (resp.messages == null) {
content.innerHTML = "<b>Your inbox is empty.</b>";
} else {
var encodings = 0;
content.innerHTML = "";
angular.forEach(resp.messages, function(message) {
var email = gapi.client.gmail.users.messages.get({
'id': message.id
});
email.execute(function(stuff) {
if (stuff.payload == null) {
console.log("Payload null: " + message.id);
}
var header = "";
var sender = "";
angular.forEach(stuff.payload.headers, function(item) {
if (item.name == "Subject") {
header = item.value;
}
if (item.name == "From") {
sender = item.value;
}
})
try {
var contents = "";
if (stuff.payload.parts == null) {
contents = base64.decode(stuff.payload.body.data);
} else {
contents = base64.decode(stuff.payload.parts[0].body.data);
}
content.innerHTML += '<b>Subject: ' + header + '</b><br>';
content.innerHTML += '<b>From: ' + sender + '</b><br>';
content.innerHTML += contents + "<br><br>";
} catch (err) {
console.log("Encoding error: " + encodings++);
}
})
})
}
});
});
I was performing some checks and debugging, so there's leftover console.log's and some other things that are only there for testing. Still, you can see here what I am trying to do.
What is the best way to decode the emails I pull from the Gmail API? Should I try to put the emails into <script>'s with charset and type attributes matching the encoding content of the email? I believe I remember charset only works with a src attribute, which I wouldn't have here. Any suggestions?
回答1:
For a prototype app I'm writing, the following code is working for me:
var base64 = require('js-base64').Base64;
// js-base64 is working fine for me.
var bodyData = message.payload.body.data;
// Simplified code: you'd need to check for multipart.
base64.decode(bodyData.replace(/-/g, '+').replace(/_/g, '/'));
// If you're going to use a different library other than js-base64,
// you may need to replace some characters before passing it to the decoder.
Caution: these points are not explicitly documented and could be wrong:
The users.messages: get API returns "parsed body content" by default. This data seems to be always encoded in UTF-8 and Base64, regardless of the
Content-TypeandContent-Transfer-Encodingheader.For example, my code had no problem parsing an email with these headers:
Content-Type: text/plain; charset=ISO-2022-JP,Content-Transfer-Encoding: 7bit.The mapping table of the Base64 encoding varies among various implementations. Gmail API uses
-and_as the last two characters of the table, as defined by RFC 4648's "URL and Filename safe Alphabet"1.Check if your Base64 library is using a different mapping table. If so, replace those characters with the ones your library accepts before passing the body to the decoder.
1 There is one supportive line in the documentation: the "raw" format returns "body content as a base64url encoded string". (Thanks Eric!)
回答2:
Use atob to decode the messages in JavaScript (see ref). For accessing your message payload, you can write a function:
var extractField = function(json, fieldName) {
return json.payload.headers.filter(function(header) {
return header.name === fieldName;
})[0].value;
};
var date = extractField(response, "Date");
var subject = extractField(response, "Subject");
referenced from my previous SO Question and
var part = message.parts.filter(function(part) {
return part.mimeType == 'text/html';
});
var html = atob(part.body.data);
If the above does not decode 100% properly, the comments by @cgenco on this answer below may apply to you. In that case, do
var html = atob(part.body.data.replace(/-/g, '+').replace(/_/g, '/'));
回答3:
Here is the solution: Gmail API - "Users.messages: get" method has in response message.payload.body.data parted base64 data, it's separated by "-" symbol. It's not entire base64 encoded text, it's parts of base64 text. You have to try to decode every single part of this or make one mono string by unite and replace "-" symbol. After this you can easily decode it to human text. You can manually check every part here https://www.base64decode.org
回答4:
Please use websafe decoder for decoding gmail emails and attachments. I got blank pages when I used just base64decoder, had to use this: https://www.npmjs.com/package/urlsafe-base64
回答5:
I was also annoyed by this point. I discovered a solution through looking at an extension for VSCode. The solution is really simple:
let body = response.data.payload.body; // the base64 encoded body of a message
body = new Buffer.alloc(
body.data.length,
body.data,
"base64"
).toString(); // the decoded message
It worked for me as I was using gmail.users.messages.get() call of Gmail API.
回答6:
I can easily decode using another tool at https://simplycalc.com/base64-decode.php
In JS: https://www.npmjs.com/package/base64url
In Python 3:
import base64
base64.urlsafe_b64decode(coded_string)
来源：https://stackoverflow.com/questions/24811008/gmail-api-decoding-messages-in-javascript