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troubleshooting-faq.md

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Frequently asked questions: troubleshooting

I am not getting an image file, what went wrong?

In case of any errors, the server will respond with an HTTP status code other than 200 OK (e.g. 400 Bad Request) and a short plain text message containing the reason for the error.

The server responds with "Post data is not valid JSON!", but I have posted only JSON. How can that be?

Note that there are some subtle differences between objects specified directly in JavaScript and valid JSON. For example, the plot data that could be specified in a JavaScript code snippet as

var myChart = echarts.init(document.getElementById('main'));

// specify chart configuration item and data
var option = {
    title: {
        text: 'ECharts entry example'
    },
    tooltip: {},
    legend: {
        data:['Sales']
    },
    backgroundColor: '#ffffff',
    xAxis: {
        data: ["shirt","cardigan","chiffon shirt","pants","heels","socks"]
    },
    yAxis: {},
    series: [{
        name: 'Sales',
        type: 'bar',
        data: [5, 20, 36, 10, 10, 20]
    }]
};
myChart.setOption(option);

corresponds to the following JSON to generate the same chart on the export server:

{
  "title": {
    "text": "ECharts entry example"
  },
  "tooltip": {},
  "legend": {
    "data": ["Sales"]
  },
  "backgroundColor": "#ffffff",
  "xAxis": {
    "data": ["shirt","cardigan","chiffon shirt","pants","heels","socks"]
  },
  "yAxis": {},
  "series": [{
    "name": "Sales",
    "type": "bar",
    "data": [5, 20, 36, 10, 10, 20]
  }]
}

The notable differences are:

  • no single quote string delimiters, only double quotes are valid string delimiters in JSON
  • names of object members in JSON have to be enclosed in double quotes, too, e.g. name: 'Sales' becomes "name": "Sales"

The message "Fontconfig error: Cannot load default config file" shows up during the first request. What is this about?

This means that the Fontconfig library is missing on your system. It is required to find installed fonts and properly render texts (e. g. for labels) in the generated PNG graphics.

Fontconfig can be installed by typing

apt-get install libfontconfig1

on Debian or Debian-based systems (e. g. Ubuntu).

After the installation of Fontconfig, the export server has to be stopped and then (re-)started with npm start. Otherwise it will not recognize that Fontconfig has been installed.

Text does not render properly in the generated PNG images. How can it be fixed?

That phenomenon is usually an indication that Fontconfig is missing. See the answer to the previous question on how to install Fontconfig.