Scrobbler 2.0 error: Extra content at the end of the document

[lexisother]

Error doesn't come directly from the scrobbler plugin, but rather from libxml.

DEBUG ../audacious-plugins-4.3.1/src/scrobbler2/scrobbler_xml_parsing.cc:11 [prepare_data]: Data received from last.fm:
<?xml version="1.0" encoding="UTF-8"?>
<lfm status="ok">
  <token>rPuYTIpJxRTN6QO-TV0pHhHk8tPETyfP</token>
</lfm>

%%End of data%%
Entity: line 5: parser error : Extra content at the end of the document

^
DEBUG ../audacious-plugins-4.3.1/src/scrobbler2/scrobbler_xml_parsing.cc:16 [prepare_data]: Document not parsed successfully.
DEBUG ../audacious-plugins-4.3.1/src/scrobbler2/scrobbler_xml_parsing.cc:229 [read_token]: Could not read received data from last.fm. What's up?

No idea what's going on here since the XML seems to be perfectly valid. Any ideas?

[radioactiveman]

libxml doesn't care about newlines at the end. For me it looks like an off-by-one error. This patch makes the parsing work.

diff --git a/src/scrobbler2/scrobbler_xml_parsing.cc b/src/scrobbler2/scrobbler_xml_parsing.cc
index 3320a32b0..8e869c41f 100644
--- a/src/scrobbler2/scrobbler_xml_parsing.cc
+++ b/src/scrobbler2/scrobbler_xml_parsing.cc
@@ -10,7 +10,7 @@ static gboolean prepare_data () {
     received_data[received_data_size] = '\0';
     AUDDBG("Data received from last.fm:\n%s\n%%%%End of data%%%%\n", received_data);
 
-    doc = xmlReadMemory(received_data, received_data_size+1, nullptr, nullptr, 0);
+    doc = xmlReadMemory(received_data, received_data_size, nullptr, nullptr, 0);
     received_data_size = 0;
     if (doc == nullptr) {
         AUDDBG("Document not parsed successfully.\n");

I have tested it with this example code. Notice the additional \n\n\n at the end of the XML string.

#include <stdio.h>
#include <string.h>
#include <libxml/parser.h>

/* Compile with gcc -Wall -o lastfm_test lastfm_test.c $(pkg-config --cflags --libs libxml-2.0) */

int main()
{
    const char * received_data =
        "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
        "<lfm status=\"ok\">\n"
        "  <token>Lorem-ipsum-dolor-sit-amet</token>\n"
        "</lfm>\n\n\n";

    size_t received_data_size = strlen(received_data);
    printf("strlen(received_data): %zu\n", received_data_size);

    xmlDocPtr doc = xmlReadMemory(received_data, received_data_size /* + 1 */, NULL, NULL, 0);
    if (!doc)
    {
        printf("Parsing failed\n");
        return -1;
    }

    xmlFreeDoc(doc);

    printf("Parsing successful\n");
    return 0;
}

@jlindgren90: Is this fix valid for you? I wonder why/how this has worked in the past.
Commit audacious-media-player/audacious-plugins@c9246b1 is not the culprit, both functions behave the same in this case.

Edit: Tested on Ubuntu 20.04 with an older libxml2 version (2.9.10). Here received_data_size, received_data_size + 1 and even received_data_size + 10 work. libxml2 seems to be more strict meanwhile.

[jlindgren90]

Perhaps libxml2 used to stop parsing at the null character. Removing the +1 sounds good. Thanks for investigating!

[radioactiveman]

Fixed with audacious-media-player/audacious-plugins@5103ba0, thanks for reporting.