Initial commit.

internal/parser/parser.go

@@ -0,0 +1,136 @@
+package parser
+
+import (
+	"errors"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"go.dev.pztrn.name/hosts-translator/internal/configuration"
+	"go.dev.pztrn.name/hosts-translator/internal/models"
+)
+
+var ErrParserError = errors.New("hosts parser")
+
+// Parser is a controlling structure for hosts file (both parsed and unparsed data).
+type Parser struct {
+	parsedHosts []models.Host
+}
+
+// NewParser creates new hosts file parsing controlling structure.
+func NewParser() *Parser {
+	p := &Parser{}
+	p.initialize()
+
+	return p
+}
+
+// Returns file data as bytes.
+func (p *Parser) getFileData() ([]string, error) {
+	// Before everything we should normalize file path.
+	filePath := configuration.HostsFilePath
+
+	// Replace possible "~" in the beginning as file reading function unable
+	// to expand it. Also we should check only beginning because tilde is actually
+	// a very valid directory or file name.
+	if strings.HasPrefix(filePath, "~") {
+		homeDir, err := os.UserHomeDir()
+		if err != nil {
+			return nil, err
+		}
+
+		filePath = strings.Replace(filePath, "~", homeDir, 1)
+	}
+
+	// Get absolute file path.
+	absolutePath, err := filepath.Abs(filePath)
+	if err != nil {
+		return nil, err
+	}
+
+	log.Println("Reading file data from", absolutePath)
+
+	// Read file data.
+	rawData, err := os.ReadFile(absolutePath)
+	if err != nil {
+		return nil, err
+	}
+
+	data := strings.Split(string(rawData), "\n")
+
+	return data, nil
+}
+
+// GetParsedData returns parsed data slice.
+func (p *Parser) GetParsedData() []models.Host {
+	return p.parsedHosts
+}
+
+// Initializes internal state of parser as well as CLI flags.
+func (p *Parser) initialize() {
+	p.parsedHosts = make([]models.Host, 0)
+}
+
+// Parse parses hosts file into internal representation.
+func (p *Parser) Parse() error {
+	log.Println("Starting hosts file parsing. File located at", configuration.HostsFilePath)
+
+	data, err := p.getFileData()
+	if err != nil {
+		return err
+	}
+
+	for _, line := range data {
+		// We should skip commented lines.
+		if strings.HasPrefix(line, "#") {
+			continue
+		}
+
+		// Every line is a two-or-more-not-empty-strings. First string is always
+		// an IP address.
+		// Also there are a non-zero possibility that line will contain tabs, so as
+		// very first action we should replace them with spaces.
+		if strings.Contains(line, "\t") {
+			line = strings.Replace(line, "\t", " ", -1)
+		}
+
+		lineSplitted := strings.Split(line, " ")
+
+		// As one IP address can be bound to multiple domains we should take care
+		// of that situation by creating multiple Host structures.
+		var address string
+
+		for _, lineData := range lineSplitted {
+			// Also there might be a case when address placed first in line but
+			// line itself has spaces in the beginning.
+			if address == "" && lineData != "" {
+				address = lineData
+
+				continue
+			}
+
+			if lineData == "" {
+				continue
+			}
+
+			domainToAdd := lineData
+
+			if configuration.DomainPostfix != "" && !strings.HasSuffix(domainToAdd, configuration.DomainPostfix) {
+				domainToAdd += "." + configuration.DomainPostfix
+			}
+
+			p.parsedHosts = append(p.parsedHosts, models.Host{
+				Domain:  domainToAdd,
+				Address: address,
+			})
+		}
+	}
+
+	log.Println("Got", len(p.parsedHosts), "domains from hosts file")
+
+	// ToDo: hide under CLI parameter like '-debug'?
+	// log.Printf("%+v\n", p.parsedHosts)
+
+	return nil
+}