Add -cpe flag to download CPE.BIN data

.gitignore

@@ -4,4 +4,5 @@
 
 # Output files
 /EPO.BIN
+/CPE.BIN
 /raw

README.md

@@ -2,17 +2,20 @@
 
 ## About
 
-Retrieve EPO.BIN GPS data from Garmin's servers on any platform that you
-can compile a Go binary for, rather than only those that support Garmin
+Retrieve EPO.BIN and CPE.BIN GPS data from Garmin's servers on any platform that
+you can compile a Go binary for, rather than only those that support Garmin
 Connect. Since Garmin's software doesn't run natively on Linux, it's
 useful there.
 
 EPO.BIN is GPS Extended Prediction Orbit (EPO) satellite data valid for
 7 days, used to help speed up GPS locking on Garmin devices that support
 this.
 
-For Forerunner devices, the file should be copied to
-`GARMIN/REMOTESW/EPO.BIN` on the watch. 
+CPE.BIN is similar to EPO.BIN and used for some Sony GPS chipsets.
+
+For Forerunner and Vivoactive devices, the file should be copied to the following folder on the watch.
+- EPO: `GARMIN/REMOTESW/EPO.BIN`
+- CPE: `Primary/GARMIN/RemoteSW/CPE.BIN` 
 
 ## Alternatives
 
@@ -30,6 +33,7 @@ This [repository](https://github.com/StevenMaude/epo-bin) hosts a daily
 download of `EPO.BIN`.
 
 ## Usage
+Use the `-cpe` flag to download CPE data instead of EPO
 
 ### Download
 

armstrong.go

@@ -22,10 +22,11 @@ import (
 	"log"
 	"net/http"
 	"time"
+	"flag"
 )
 
 // retrieveData makes a HTTP request to get Garmin EPO data and returns the body as []byte if successful.
-func retrieveData() ([]byte, error) {
+func retrieveDataEPO() ([]byte, error) {
 	url := "https://omt.garmin.com/Rce/ProtobufApi/EphemerisService/GetEphemerisData"
 	// Data from https://www.kluenter.de/garmin-ephemeris-files-and-linux/
 	data := []byte("\n-\n\aexpress\u0012\u0005de_DE\u001A\aWindows\"" +
@@ -48,8 +49,8 @@ func retrieveData() ([]byte, error) {
 	return body, nil
 }
 
-// checkDataLength checks the EPO data length; if not as expected, returns an error.
-func checkDataLength(data []byte) error {
+// checkDataLengthEPO checks the EPO data length; if not as expected, returns an error.
+func checkDataLengthEPO(data []byte) error {
 	dataLength := len(data)
 	// Each EPO data set is 2307 bytes long, with the first three bytes to be removed.
 	if dataLength != 28*2307 {
@@ -69,16 +70,16 @@ func cleanEPO(rawEPOData []byte) []byte {
 	return outData
 }
 
-// main retrieves EPO data, checks it, cleans it and writes it to disk.
-func main() {
-	fmt.Println("Retrieving data from Garmin's servers...")
-	rawEPOData, err := retrieveData()
+// Retrieves EPO data, checks it, cleans it and writes it to disk.
+func downloadFileEPO() {
+	fmt.Println("Retrieving EPO data from Garmin's servers...")
+	rawEPOData, err := retrieveDataEPO()
 	if err != nil {
 		log.Fatal(err)
 	}
 
 	fmt.Println("Processing EPO.BIN...")
-	err = checkDataLength(rawEPOData)
+	err = checkDataLengthEPO(rawEPOData)
 	if err != nil {
 		log.Fatal(err)
 	}
@@ -91,3 +92,67 @@ func main() {
 	}
 	fmt.Println("Done! EPO.BIN saved.")
 }
+
+
+// retrieveData makes a HTTP request to get Garmin EPO data and returns the body as []byte if successful.
+func retrieveDataCPE() ([]byte, error) {
+	url := "https://api.gcs.garmin.com/ephemeris/cpe/sony?coverage=WEEKS_1"
+
+	c := &http.Client{
+		Timeout: 20 * time.Second,
+	}
+	resp, err := c.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	body, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	return body, nil
+}
+
+// checkDataLengthCPE errors out of CPE data is empty
+// - CPE internal data format is not yet known
+func checkDataLengthCPE(data []byte) error {
+	dataLength := len(data)
+	if dataLength == 0 {
+		return fmt.Errorf("CPE data has unexpected length of zero")
+	}
+	return nil
+}
+
+// Retrieves CPE data, checks it and writes it to disk.
+func downloadFileCPE() {
+	fmt.Println("Retrieving CPE data from Garmin's servers...\n")
+	rawCPEData, err := retrieveDataCPE()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err = checkDataLengthCPE(rawCPEData)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err = ioutil.WriteFile("CPE.BIN", rawCPEData, 0644)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println("Done! CPE.BIN saved.\n")
+}
+
+
+func main() {
+	var modeCPE bool
+	flag.BoolVar(&modeCPE, "cpe", false, "Download CPE format ephemeris data (instead of EPO)")
+	flag.Parse()
+
+	if modeCPE == true {
+		downloadFileCPE()
+	} else {
+		downloadFileEPO()
+	}
+}