Parse POST body as URL-encoded form data

This matches the format we expect to receive from BSS.

Ref: 90618f5ed0a3784c2e15cc28bd0278c08eef3652 in OpenCHAMI/bss

main.go

@@ -5,7 +5,6 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"io"
 	"net/http"
 	"os"
 	"os/exec"
@@ -103,22 +102,28 @@ func main() {
 func respondNodePost(w http.ResponseWriter, r *http.Request, nodes *SafeUpdatingSlice) {
 	// TODO: Log errors from this?
 	if r.Method == http.MethodPost {
-		// TODO: Add actual validation logic here, once we know our data format
-		// Read (up to 100 chars of) the request body
-		nodeName, err := io.ReadAll(r.Body)
-		if err == nil && len(nodeName) > 0 {
-			// Add our node to the slice, and send a length update to anyone watching
-			nodes.Lock()
-			nodes.slice = append(nodes.slice, string(nodeName))
-			numNodes := len(nodes.slice)
-			nodes.Unlock()
-			log.Debug().Msgf("Buffer updated: %d nodes", numNodes)
-			nodes.length <- numNodes
-			fmt.Fprintf(w, "Acknowledged")
-		} else {
+		// Validate POSTed data; should be of
+		// Content-Type: application/x-www-form-urlencoded
+		err := r.ParseForm()
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			fmt.Fprintf(w, err.Error())
+			return
+		}
+		nodeName := r.FormValue("data")
+		if nodeName == "" {
 			w.WriteHeader(http.StatusBadRequest)
-			fmt.Fprintf(w, "Error reading request body")
+			fmt.Fprintf(w, "data field must not be empty")
+			return
 		}
+		// Add our node to the slice, and send a length update to anyone watching
+		nodes.Lock()
+		nodes.slice = append(nodes.slice, nodeName)
+		numNodes := len(nodes.slice)
+		nodes.Unlock()
+		log.Debug().Msgf("Buffer updated: %d nodes", numNodes)
+		nodes.length <- numNodes
+		fmt.Fprintf(w, "Acknowledged")
 	} else {
 		w.WriteHeader(http.StatusMethodNotAllowed)
 		fmt.Fprintf(w, "This endpoint must be POSTed to")