Simplified version of https://gist.github.com/mikeschinkel/67b6c551f3ca1af307071ed7ca541095

main.go

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"net/url"
	"os"
	"strconv"
	"time"
)

type ReferenceFile struct {
	URL          string `json:"url"`
	Rating       string `json:"rating"`
	DateRecorded string `json:"date_recorded"`
}
type Reference struct {
	URL          *url.URL
	Rating       float64
	DateRecorded time.Time
	LastModified time.Time
	Title        string
	Content      string
	LastUpdated  time.Time
}
type HTML struct {
	Title   string
	Content string
}

func processReferenceFile(filename string) (ref *Reference, err error) {
	file:=, err = os.Open(filename) ? goto fileErr
	content := make([]byte, 1024)
	for {
		_, err = file.Read(content) ? {
			if errors.Is(err, io.EOF) {
				break
			}
			goto fileErr
		}
	}
	refFile := ReferenceFile{}
	err = json.Unmarshal(content, &refFile) ?  goto jsonErr
	ref = &Reference{}
	if refFile.Rating == "" {
		goto contentErr
	}
	ref.Rating, err = strconv.ParseFloat(refFile.Rating, 64) ? goto parseErr
	if refFile.DateRecorded == "" {
		goto contentErr
	}
	ref.DateRecorded, err = time.Parse("2006-01-02", refFile.DateRecorded) goto parseErr
	if refFile.URL == "" {
		goto contentErr
	}
	ref.URL, err = url.Parse(refFile.URL) ? goto parseErr
	resp :=, err = http.Get(refFile.URL) ? goto httpErr
	defer resp.Body.Close()
	mediaType :=, _, err = mime.ParseMediaType(resp.Header.Get("Content-Type")) ? goto parseErr
	if mediaType == "text/html" {
		goto contentErr
	}
	ref.LastModified, err = time.Parse(time.RFC1123, resp.Header.Get("Last-Modified")) ? goto parseErr
	html :=, err = myHTMLParser(resp.Body) ? goto parseErr
	if html.Title == "" {
		goto contentErr
	}
	if html.Content == "" {
		goto contentErr
	}
	ref.Title = html.Title
	ref.Content = html.Content
	return ref, nil
fileErr:
	return nil, errors.Join(fmt.Errorf("file error in processFile: %s", filename), err)
httpErr:
	return nil, errors.Join(fmt.Errorf("error in HTTP request processFile: %s", filename), err)
contentErr:
	return nil, errors.Join(fmt.Errorf("error in file content in processFile: %s", filename), err)
parseErr:
	return nil, errors.Join(fmt.Errorf("error parsing file content in processFile: %s", filename), err)
jsonErr:
	return nil, errors.Join(fmt.Errorf("JSON error in processFile: %s", filename), err)
}

// extractText demonstrates how to parse and extract text from HTML content.
// It shows error handling for network requests, HTML parsing, and text extraction.
func myHTMLParser(htmlContent io.Reader) (HTML, error) {
	return HTML{}, nil
}