smtp/mime: look for urls in base64 message

Ticket: 5185

Previously, it was looked for message in plain text, and base64
encoding was only handled for attachments.

This commit also fixes the buffering got such base64 data streamed
into urls finding, by buffering a beginning non-empty line,
and by ensuring that we run extraction on the last line,
even if it had no EOL.

rust/src/mime/smtp.rs

@@ -373,7 +373,9 @@ fn mime_smtp_find_url_strings(ctx: &mut MimeStateSMTP, input_new: &[u8]) {
         } else {
             ctx.decoded_line.extend_from_slice(&input_new[x..]);
         }
-    } // else  no end of line, already buffered for next input...
+    } else if ctx.decoded_line.is_empty() {
+        ctx.decoded_line.extend_from_slice(input_new);
+    }
 }
 
 fn mime_base64_map(input: u8) -> io::Result<u8> {
@@ -614,9 +616,30 @@ fn mime_smtp_parse_line(
                     || ctx.content_type == MimeSmtpContentType::Html
                     || ctx.content_type == MimeSmtpContentType::Message
                 {
-                    mime_smtp_find_url_strings(ctx, full);
+                    match ctx.encoding {
+                        MimeSmtpEncoding::Plain => {
+                            mime_smtp_find_url_strings(ctx, full);
+                        }
+                        MimeSmtpEncoding::QuotedPrintable => {
+                            mime_smtp_find_url_strings(ctx, full);
+                        }
+                        MimeSmtpEncoding::Base64 => {
+                            if unsafe { MIME_SMTP_CONFIG_DECODE_BASE64 } {
+                                if let Some(ref mut decoder) = &mut ctx.decoder {
+                                    if i.len() > MAX_ENC_LINE_LEN {
+                                        warnings |= MIME_ANOM_LONG_ENC_LINE;
+                                    }
+                                    if let Ok(dec) = mime_base64_decode(decoder, i) {
+                                        mime_smtp_find_url_strings(ctx, &dec);
+                                    } else {
+                                        warnings |= MIME_ANOM_INVALID_BASE64;
+                                    }
+                                }
+                            }
+                        }
+                    }
                 }
-                return (MimeSmtpParserResult::MimeSmtpNeedsMore, 0);
+                return (MimeSmtpParserResult::MimeSmtpNeedsMore, warnings);
             }
             match ctx.encoding {
                 MimeSmtpEncoding::Plain => {
@@ -735,6 +758,8 @@ fn mime_smtp_complete(ctx: &mut MimeStateSMTP) {
         ctx.md5_state = MimeSmtpMd5State::MimeSmtpMd5Completed;
         ctx.md5_result = ctx.md5.finalize_reset();
     }
+    // look for url in the last unfinished line
+    mime_smtp_find_url_strings(ctx, &[b'\n']);
 }
 
 #[no_mangle]