Adding a custom header or footer in Go with Net/HTTP

In this guide, we'll show you how to add custom headers or footers to a PDF using Go and the Net/HTTP library.

We'll focus this guide on the header parameter, but know that the footer parameter works exactly the same way.

The header parameter is an object that accepts the following parameters:

source: The source of the header. It can be a URL or a raw HTML document. You can also provide some variables that we'll explain at the bottom of this guide.
height: The height of the header. By default, the height is in pixels, but you can also use mm, cm or in as units, like 10mm.
start_at: The page number where the header should start. By default, the header will start at the first page.

NOTE: You must provide the full data in the header/footer, and not via a network request. Loading files such as external CSS, Js or Fonts won't work in the header or footer. Instead, we recommend you to embed them in Base64.

Here's an example:

package main

import (
    "bytes"
    "encoding/base64"
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
)

func main() {
    // Define the API key
    apiKey := "sk_xxxxxxxxxxxx"

    // Define the request parameters
    params := map[string]interface{}{
        "source": "https://en.wikipedia.org/wiki/PDF",
        "header": map[string]interface{}{
            "source":    "<div>Page {{ page }} over a total of {{ total }}. Made on {{ date }}</div>",
            "height":    150,
            "start_at":  2,
        },
    }

    // Marshal the parameters into JSON
    jsonParams, err := json.Marshal(params)
    if err != nil {
        fmt.Println("Error marshaling JSON:", err)
        return
    }

    // Create a new HTTP client
    client := &http.Client{}

    // Create a new request
    req, err := http.NewRequest("POST", "https://api.pdfshift.io/v3/convert/pdf", bytes.NewBuffer(jsonParams))
    if err != nil {
        fmt.Println("Error creating request:", err)
        return
    }

    // Set request headers
    req.Header.Set("Content-Type", "application/json")

    // Set basic authentication header
    auth := "api:" + apiKey
    req.Header.Set("Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(auth)))

    // Perform the request
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error performing request:", err)
        return
    }
    defer resp.Body.Close()

    // Read response body
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        fmt.Println("Error reading response body:", err)
        return
    }

    // Check response status code
    if resp.StatusCode >= 400 {
        fmt.Printf("Request failed with status code %d: %s\n", resp.StatusCode, string(body))
        return
    }

    // Save the PDF document
    err = ioutil.WriteFile("result.pdf", body, 0644)
    if err != nil {
        fmt.Println("Error saving PDF document:", err)
        return
    }

    fmt.Println("The PDF document was generated and saved to result.pdf")
}

The source parameter present in the header/footer accepts a set of variables that will be translated when converting the document.

Here are the properties you can use:

{{ title }}: The title of the document.
{{ url }}: The URL of the document.
{{ page }}: The current page number.
{{ total }}: The total number of pages in the document.
{{ date }}: The current date in the format M/D/YY-H:MM am/pm such as "3/16/24, 2:04 PM".

This will allow you to generate a document that looks more like a printable version of a website, with page number and customized header and footer.

For further details on the header property and its usage, please refer to our dedicated documentation.

We hope this guide was helpful. If you have any questions or noticed any issues on the code above,
feel free to drop us a line.