scheduler: rate limit IMAP loops

Avoid hitting the server with repeated requests or reconnections if some operation, such as FETCH, keeps failing.

Cargo.lock

@@ -77,6 +77,12 @@ dependencies = [
  "opaque-debug",
 ]
 
+[[package]]
+name = "ahash"
+version = "0.3.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e8fd72866655d1904d6b0997d0b07ba561047d070fbe29de039031c641b61217"
+
 [[package]]
 name = "ahash"
 version = "0.7.2"
@@ -1114,6 +1120,7 @@ dependencies = [
  "fast-socks5",
  "futures",
  "futures-lite",
+ "governor",
  "hex",
  "humansize",
  "image",
@@ -1675,6 +1682,12 @@ version = "0.3.17"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1d3d00f4eddb73e498a54394f228cd55853bdf059259e8e7bc6e69d408892e99"
 
+[[package]]
+name = "futures-timer"
+version = "3.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e64b03909df88034c26dc1547e8970b91f98bdb65165d6a4e9110d94263dbb2c"
+
 [[package]]
 name = "futures-util"
 version = "0.3.17"
@@ -1767,19 +1780,46 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "governor"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "06c5d2f987ee8f6dff3fa1a352058dc59b990e447e4c7846aa7d804971314f7b"
+dependencies = [
+ "dashmap",
+ "futures",
+ "futures-timer",
+ "no-std-compat",
+ "nonzero_ext",
+ "parking_lot",
+ "quanta",
+ "rand 0.8.3",
+ "smallvec",
+]
+
 [[package]]
 name = "half"
 version = "1.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "62aca2aba2d62b4a7f5b33f3712cb1b0692779a56fb510499d5c0aa594daeaf3"
 
+[[package]]
+name = "hashbrown"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e91b62f79061a0bc2e046024cb7ba44b08419ed238ecbd9adbd787434b9e8c25"
+dependencies = [
+ "ahash 0.3.8",
+ "autocfg 1.0.1",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.11.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ab5ef0d4909ef3724cc8cce6ccc8572c5c817592e9285f5464f8e86f8bd3726e"
 dependencies = [
- "ahash",
+ "ahash 0.7.2",
 ]
 
 [[package]]
@@ -1788,7 +1828,7 @@ version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7249a3129cbc1ffccd74857f81464a323a152173cdb134e0fd81bc803b29facf"
 dependencies = [
- "hashbrown",
+ "hashbrown 0.11.2",
 ]
 
 [[package]]
@@ -1982,7 +2022,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bc633605454125dec4b66843673f01c7df2b89479b32e0ed634e43a91cff62a5"
 dependencies = [
  "autocfg 1.0.1",
- "hashbrown",
+ "hashbrown 0.11.2",
 ]
 
 [[package]]
@@ -2320,6 +2360,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "no-std-compat"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b93853da6d84c2e3c7d730d6473e8817692dd89be387eb01b94d7f108ecb5b8c"
+dependencies = [
+ "hashbrown 0.8.2",
+]
+
 [[package]]
 name = "nom"
 version = "4.2.3"
@@ -2354,6 +2403,12 @@ dependencies = [
  "version_check 0.9.3",
 ]
 
+[[package]]
+name = "nonzero_ext"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "44a1290799eababa63ea60af0cbc3f03363e328e58f32fb0294798ed3e85f444"
+
 [[package]]
 name = "num-bigint"
 version = "0.2.6"
@@ -2829,6 +2884,16 @@ dependencies = [
  "tempfile",
 ]
 
+[[package]]
+name = "quanta"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d98dc777a7a39b76b1a26ae9d3f691f4c1bc0455090aa0b64dfa8cb7fc34c135"
+dependencies = [
+ "libc",
+ "winapi",
+]
+
 [[package]]
 name = "quick-error"
 version = "1.2.3"

Cargo.toml

@@ -33,6 +33,7 @@ email = { git = "https://github.com/deltachat/rust-email", branch = "master" }
 encoded-words = { git = "https://github.com/async-email/encoded-words", branch="master" }
 escaper = "0.1.1"
 futures = "0.3.17"
+governor = "0.3.2"
 hex = "0.4.0"
 image = { version = "0.23.5", default-features=false, features = ["gif", "jpeg", "ico", "png", "pnm", "webp", "bmp"] }
 indexmap = "1.7.0"

src/scheduler.rs

@@ -4,6 +4,7 @@ use async_std::{
     channel::{self, Receiver, Sender},
     task,
 };
+use governor;
 
 use crate::config::Config;
 use crate::context::Context;
@@ -70,6 +71,10 @@ async fn inbox_loop(ctx: Context, started: Sender<()>, inbox_handlers: ImapConne
         shutdown_sender,
     } = inbox_handlers;
 
+    let quota = governor::Quota::per_minute(std::num::NonZeroU32::new(1).unwrap())
+        .allow_burst(std::num::NonZeroU32::new(5).unwrap());
+    let rate_limiter = governor::RateLimiter::direct(quota);
+
     let ctx1 = ctx.clone();
     let fut = async move {
         started
@@ -82,6 +87,7 @@ async fn inbox_loop(ctx: Context, started: Sender<()>, inbox_handlers: ImapConne
         let mut jobs_loaded = 0;
         let mut info = InterruptInfo::default();
         loop {
+            rate_limiter.until_ready().await;
             match job::load_next(&ctx, Thread::Imap, &info)
                 .await
                 .ok()
@@ -247,6 +253,10 @@ async fn simple_imap_loop(
 
     let ctx1 = ctx.clone();
 
+    let quota = governor::Quota::per_minute(std::num::NonZeroU32::new(2).unwrap())
+        .allow_burst(std::num::NonZeroU32::new(5).unwrap());
+    let rate_limiter = governor::RateLimiter::direct(quota);
+
     let fut = async move {
         started
             .send(())
@@ -255,6 +265,7 @@ async fn simple_imap_loop(
         let ctx = ctx1;
 
         loop {
+            rate_limiter.until_ready().await;
             fetch_idle(&ctx, &mut connection, folder).await;
         }
     };