Add util to generate random event_id's.

Signed-off-by: Jason Volk <jason@zemos.net>

Cargo.lock

@@ -5285,6 +5285,7 @@ dependencies = [
  "arrayvec",
  "axum",
  "axum-extra",
+ "base64",
  "bytes",
  "bytesize",
  "cargo_toml",

src/core/Cargo.toml

@@ -55,6 +55,7 @@ argon2.workspace = true
 arrayvec.workspace = true
 axum.workspace = true
 axum-extra.workspace = true
+base64.workspace = true
 bytes.workspace = true
 bytesize.workspace = true
 cargo_toml.workspace = true

src/core/utils/rand.rs

@@ -5,6 +5,7 @@ use std::{
 
 use arrayvec::ArrayString;
 use rand::{Rng, seq::SliceRandom, thread_rng};
+use ruma::OwnedEventId;
 
 pub fn shuffle<T>(vec: &mut [T]) {
 	let mut rng = thread_rng();
@@ -31,6 +32,29 @@ pub fn string_array<const LENGTH: usize>() -> ArrayString<LENGTH> {
 	ret
 }
 
+#[must_use]
+pub fn event_id() -> OwnedEventId {
+	use base64::{
+		Engine,
+		alphabet::URL_SAFE,
+		engine::{GeneralPurpose, general_purpose::NO_PAD},
+	};
+
+	let mut binary: [u8; 32] = [0; _];
+	thread_rng().fill(&mut binary);
+
+	let mut encoded: [u8; 43] = [0; _];
+	GeneralPurpose::new(&URL_SAFE, NO_PAD)
+		.encode_slice(binary, &mut encoded)
+		.expect("Failed to encode binary to base64");
+
+	let event_id: &str = str::from_utf8(&encoded)
+		.expect("Failed to convert array of base64 bytes to valid utf8 str");
+
+	OwnedEventId::from_parts('$', event_id, None)
+		.expect("Failed to generate valid random event_id")
+}
+
 #[must_use]
 pub fn truncate_string(mut str: String, range: Range<u64>) -> String {
 	let len = thread_rng()