feat: asymmetry - separate impairment values for uploads and downloads

CHANGELOG.md

@@ -7,6 +7,14 @@ The format follows [Keep a Changelog](https://keepachangelog.com/); versions fol
 
 ### Added
 
+- **Different values for uploads and downloads.** A new "Asymmetry" card. Leave it off and
+  one set of numbers applies both ways, as before. Tick it and the fields above it describe
+  downloads only, while seven new ones describe uploads: latency, jitter, spike chance and
+  size, loss, corruption and duplication. They start as copies of what you already typed, so
+  nothing changes until you edit them. Reach for it when an app browses fine but struggles to
+  send: a video call, a file upload. On the command line: `--asym`, then `--loss-up`,
+  `--latency-up` and the rest. Profiles remember it.
+
 - **A blocked connection can be refused instead of ignored.** A new "Refuse blocked
   connections" checkbox in the Block card, and `--block-reject`. Without it a blocked
   connection gets no answer and the program you are testing waits until it gives up on its
@@ -19,6 +27,22 @@ The format follows [Keep a Changelog](https://keepachangelog.com/); versions fol
   An existing stats CSV is rotated to a dated backup the first time the new column is
   written.
 
+### Changed
+
+- **A warning when a one-way traffic filter would ignore half your asymmetry settings.**
+  The "Outgoing only" and "Incoming only" traffic filters work inside the driver, so the other
+  direction never reaches the tool at all. With asymmetry on, that means half the values you
+  typed describe traffic this session cannot see - and until now nothing said so: the session
+  description still listed them and the counters looked like the tool ignoring its own form.
+  The run now says it once, and still runs, because impairing one direction on purpose is a
+  perfectly good thing to ask for.
+
+- **Some command-line shortcuts stopped working, and the full flags did not.** Adding the
+  upload flags means `--latency` is no longer the only option starting with "latency", so
+  short forms like `--lat`, `--jit`, `--j`, `--cor` and `--spike-p` are now ambiguous and are
+  refused. Every full flag still works, so saved reproduction commands and every example in
+  this documentation are unaffected - only hand-typed abbreviations need writing out in full.
+
 ## [0.6.0] - 2026-09-04
 
 ### Added

README.md

@@ -760,6 +760,10 @@ BeanNetworkTester.exe --simulate --duration 30 --format json > run.ndjson
 | `--rst-prob` `--rst-cooldown` | % / s | percentage of connections torn with RST and how long the tear-down is held |
 | `--flap-period` `--flap-down` | s / % | cyclic link outage: how often and for what fraction of the period |
 | `--rate-schedule` | - | changing throughput: `"time:download:upload,..."` in KB/s, looped |
+| `--asym` | - | give uploads their own values. Without it one set of numbers applies both ways, which is the default |
+| `--loss-up` `--corrupt-up` `--dup-up` | % | the same three impairments, for packets this machine SENDS. Used only with `--asym` |
+| `--latency-up` `--jitter-up` | ms | delay and its variation, for packets this machine SENDS. Used only with `--asym` |
+| `--spike-prob-up` `--spike-ms-up` | % / ms | the occasional longer delay, for packets this machine SENDS. Used only with `--asym` |
 | `--ipv4-only` `--ipv6-only` | - | impair one address family only. The other keeps flowing untouched - this aims the tool, it does not block a protocol. Works with `--dst-ip` empty too, which means all addresses. Both flags at once exclude each other, nothing is impaired, and the log says so |
 | `--lan-mode` | - | LAN mode: cut off the internet (public addresses), keep the local network |
 | `--internet-only` | - | the mirror: cut off the local network (10.x, 172.16-31.x, 192.168.x, link-local, CGNAT), keep the internet. Loopback keeps working. Careful: DNS asked of your router is local traffic, so the internet can stop working with it |

beantester/cli.py

@@ -202,6 +202,26 @@ def build_arg_parser():
                         "bounds the queueing delay a rate-limited link builds up "
                         "before it drops (bufferbloat)")
     _add_scope_arguments(p)
+    # Asymmetry. The flags read `<what>-up`, which is how every other modifier in
+    # this parser reads (--loss-burst, --spike-prob, --rst-cooldown, --flap-down).
+    # 🔴 The abbreviation cost was MEASURED before the names were chosen, exactly
+    # as it was for --loss-burst: `allow_abbrev` is on (ADR 2026-08-02), so a
+    # second option starting with `latency` makes `--lat` ambiguous. 18 prefixes
+    # that work today stop working (--lat, --jit, --j, --cor, --spike-p and the
+    # longer forms of each). Every FULL flag survives, because an exact match
+    # beats a prefix one, so no repro command and no documented example moves.
+    # Guarded by test_cli_runtime.py::test_the_flags_that_gained_an_up_neighbour_still_work.
+    p.add_argument("--asym", action="store_true",
+                   help="apply the --*-up values to the upload direction. Without "
+                        "it the link is symmetric and those values are unused")
+    p.add_argument("--loss-up", type=float, help="packet loss, upload [%%]")
+    p.add_argument("--corrupt-up", type=float, help="corruption, upload [%%]")
+    p.add_argument("--dup-up", type=float, help="duplication, upload [%%]")
+    p.add_argument("--latency-up", type=float, help="latency, upload [ms]")
+    p.add_argument("--jitter-up", type=float, help="jitter, upload [ms]")
+    p.add_argument("--spike-prob-up", type=float,
+                   help="latency spike probability, upload [%%]")
+    p.add_argument("--spike-ms-up", type=float, help="latency spike size, upload [ms]")
     p.add_argument("--syn-drop", type=float, help="dropped TCP SYN rate [%%]")
     p.add_argument("--max-size", type=int, help="MTU black hole: drop packets > N B")
     p.add_argument("--spike-prob", type=float, help="latency spike probability [%%]")