Refactor DTMF code

Author: tylerlong

src/call-session/index.ts

@@ -4,7 +4,7 @@ import { Buffer } from "node:buffer";
 
 import { RtpHeader, RtpPacket, SrtpSession } from "werift-rtp";
 
-import DTMF from "../dtmf.js";
+import DTMF, { type DTMFChar, isDTMFChar } from "../dtmf.js";
 import {
   type InboundMessage,
   RequestMessage,
@@ -94,9 +94,7 @@ abstract class CallSession extends EventEmitter {
     await this.softphone.send(requestMessage);
   }
 
-  public sendDTMF(
-    char: "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | "*" | "#",
-  ) {
+  public sendDTMF(char: DTMFChar) {
     const payloads = DTMF.charToPayloads(char);
     const timestamp = this.timestamp;
     let first = true;
@@ -128,7 +126,12 @@ abstract class CallSession extends EventEmitter {
 
   public async sendDTMFs(s: string, delay = 500) {
     for (const c of s) {
-      this.sendDTMF(c as any);
+      if (!isDTMFChar(c)) {
+        throw new Error(
+          `Invalid DTMF character: "${c}". Valid characters are 0-9, *, #`,
+        );
+      }
+      this.sendDTMF(c);
       await waitFor({ interval: delay });
     }
   }

src/dtmf.ts

@@ -1,20 +1,31 @@
 import { Buffer } from "node:buffer";
 
+const PHONE_CHARS = [
+  "0",
+  "1",
+  "2",
+  "3",
+  "4",
+  "5",
+  "6",
+  "7",
+  "8",
+  "9",
+  "*",
+  "#",
+] as const;
+
+export type DTMFChar = (typeof PHONE_CHARS)[number];
+
+const VALID_DTMF_SET = new Set<string>(PHONE_CHARS);
+
+export function isDTMFChar(char: string): char is DTMFChar {
+  return VALID_DTMF_SET.has(char);
+}
+
 class DTMF {
-  public static readonly phoneChars = [
-    "0",
-    "1",
-    "2",
-    "3",
-    "4",
-    "5",
-    "6",
-    "7",
-    "8",
-    "9",
-    "*",
-    "#",
-  ];
+  public static readonly phoneChars = PHONE_CHARS;
+
   private static readonly payloads = [
     0x00060000,
     0x000600a0,
@@ -24,11 +35,8 @@ class DTMF {
     0x00860320,
   ];
 
-  public static charToPayloads = (char: string) => {
-    const index = DTMF.phoneChars.indexOf(char[0]);
-    if (index === -1) {
-      throw new Error("invalid phone char");
-    }
+  public static charToPayloads = (char: DTMFChar) => {
+    const index = DTMF.phoneChars.indexOf(char);
     return DTMF.payloads.map((payload) => {
       const temp = payload + index * 0x01000000;
       const buffer = Buffer.alloc(4);
@@ -37,9 +45,12 @@ class DTMF {
     });
   };
 
-  public static payloadToChar = (payload: Buffer) => {
+  public static payloadToChar = (payload: Buffer): DTMFChar | undefined => {
     const intBE = payload.readIntBE(0, 4);
-    const index = (intBE - 0x00060000) / 0x01000000;
+    const index = Math.floor((intBE - 0x00060000) / 0x01000000);
+    if (index < 0 || index >= DTMF.phoneChars.length) {
+      return undefined;
+    }
     return DTMF.phoneChars[index];
   };
 }