From 289790235fb0f556d87a84fc960b25ba9bf0f73e Mon Sep 17 00:00:00 2001
From: eltrac <hi@eltr.ac>
Date: Thu, 5 Nov 2026 10:41:31 +0800
Subject: asn: download and map ASN metadata

use jsdelivr CDN
---
 asn/mapping.go | 105 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 go.mod         |   2 ++
 go.sum         |   4 +++
 3 files changed, 111 insertions(+)
 create mode 100644 asn/mapping.go

diff --git a/asn/mapping.go b/asn/mapping.go
new file mode 100644
index 0000000..79372a2
--- /dev/null
+++ b/asn/mapping.go
@@ -0,0 +1,105 @@
+package asn
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+
+	"github.com/adrg/xdg"
+	"github.com/gocarina/gocsv"
+)
+
+const SOURCE string = "https://cdn.jsdelivr.net/gh/ipverse/as-metadata@master/as.csv"
+
+type AsnEntry struct {
+	ASN         int    `csv:"asn"`
+	Handle      string `csv:"handle"`
+	Description string `csv:"description"`
+	CountryCode string `csv:"country-code"`
+}
+
+type AsnMap map[int]AsnEntry
+
+// localPath returns the destination of local copy of asn metadata
+func localPath() string {
+	return filepath.Join(xdg.DataHome, "/audidi/as.csv")
+}
+
+// downloadAsnSource downloads ASN metadata source to disk
+func downloadAsnSource() error {
+	resp, err := http.Get(SOURCE)
+	if err != nil {
+		return fmt.Errorf("error fetching ASN metadata: %s", err)
+	}
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("error fetching ASN metadata: http %d", resp.StatusCode)
+	}
+	defer resp.Body.Close()
+
+	file, err := os.Create(localPath())
+	if err != nil {
+		return fmt.Errorf("can't open file to write ASN metadata: %s", err)
+	}
+
+	if _, err := io.Copy(file, resp.Body); err != nil {
+		return fmt.Errorf("can't copy ASN metadata to file: %s", err)
+	}
+
+	return nil
+}
+
+// useAsnSource returns either a local cached version of
+// ASN source bytes or download from source
+func useAsnSource() ([]byte, error) {
+	path := localPath()
+	os.MkdirAll(filepath.Dir(path), os.ModePerm)
+
+	if info, err := os.Stat(path); os.IsNotExist(err) || info.Size() == 0 {
+		log.Println("downloading ASN metadata...")
+		if err := downloadAsnSource(); err != nil {
+			return nil, err
+		}
+		log.Println("ASN metadata downloaded")
+	}
+
+	bytes, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("can't open file to read ASN metadata: %s", err)
+	}
+
+	return bytes, nil
+}
+
+// parseMetadata parse raw bytes of ASN metadata into readable entries
+func parseMetadata(bytes []byte) ([]AsnEntry, error) {
+	var entries []AsnEntry
+
+	if err := gocsv.UnmarshalBytes(bytes, &entries); err != nil {
+		return nil, fmt.Errorf("can't parse ASN metadata: %s", err)
+	}
+
+	return entries, nil
+}
+
+// GetMapping returns a pointer to ASN-metadata mappings
+func GetMapping() *AsnMap {
+	bytes, err := useAsnSource()
+	if err != nil {
+		log.Fatalln("Failed to load ASN metadata: ", err)
+	}
+
+	entries, err := parseMetadata(bytes)
+	if err != nil {
+		log.Fatalln("Failed to parse ASN metadata (Delete data and retry): ", err)
+	}
+
+	mapping := make(AsnMap)
+	for _, entry := range entries {
+		mapping[entry.ASN] = entry
+	}
+
+	return &mapping
+}
diff --git a/go.mod b/go.mod
index 7507e58..6413654 100644
--- a/go.mod
+++ b/go.mod
@@ -3,7 +3,9 @@ module src.eltr.ac/eltrac/audidi
 go 1.26.5
 
 require (
+	github.com/adrg/xdg v0.5.3 // indirect
 	github.com/gocarina/gocsv v0.0.0-20261101205459-d0dd027dcbfa // indirect
 	github.com/ohler55/ojg v1.28.9 // indirect
 	github.com/x-way/crawlerdetect v0.2.32 // indirect
+	golang.org/x/sys v0.26.0 // indirect
 )
diff --git a/go.sum b/go.sum
index b882144..29a7f15 100644
--- a/go.sum
+++ b/go.sum
@@ -1,6 +1,10 @@
+github.com/adrg/xdg v0.5.3 h1:xRnxJXne7+oWDatRhR1JLnvuccuIeCoBu2rtuLqQB78=
+github.com/adrg/xdg v0.5.3/go.mod h1:nlTsY+NNiCBGCK2tpm09vRqfVzrc2fLmXGpBLF0zlTQ=
 github.com/gocarina/gocsv v0.0.0-20261101205459-d0dd027dcbfa h1:u6dQLh7NdeVIBn4fE4YL9PiHFephNp7t7rUSU+fulro=
 github.com/gocarina/gocsv v0.0.0-20261101205459-d0dd027dcbfa/go.mod h1:5YoVOkjYAQumqlV356Hj3xeYh4BdZuLE0/nRkf2NKkI=
 github.com/ohler55/ojg v1.28.9 h1:VL2vdN1CjniaNABNOFjorAW+/o7eBQDc4z5jO49jkHM=
 github.com/ohler55/ojg v1.28.9/go.mod h1:/Y5dGWkekv9ocnUixuETqiL58f+5pAsUfg5P8e7Pa2o=
 github.com/x-way/crawlerdetect v0.2.32 h1:kmYHC8lk5T91PDETQ3h9pF35GUyrdzmi3KX64jPvHt4=
 github.com/x-way/crawlerdetect v0.2.32/go.mod h1:BPHLsB3FOuiwoWyhAvnqeiUSAEKd34O7BcsTCcxHRj4=
+golang.org/x/sys v0.26.0 h1:KHjCJyddX0LoSTb3J+vWpupP9p0oznkqVk/IfjymZbo=
+golang.org/x/sys v0.26.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
-- 
cgit v1.2.3