fix: Delete uncacheable fits

Delete fits which are uncacheable. Draws from a model
made without setting a random seed will never be retrieved a
second time because the random seed is unavailable. Users
who do want their fits to be cached should set a random seed.

This fix helps solve the problem of the cache growing without limit.
The cache will now grow much slower.

Closes #154

stan/model.py

@@ -218,6 +218,13 @@ def is_iteration_or_elapsed_time_logger_message(msg):
                     for msg in non_standard_logger_messages:
                         text = msg.feature[0].string_list.value[0].replace("info:", "  ")
                         io.error(f"<info>{text}</info>\n")
+
+                # clean up after ourselves when fit is uncacheable (no random seed)
+                if self.random_seed is None:
+                    async with aiohttp.request("DELETE", f"http://{host}:{port}/v1/{fit_name}") as resp:
+                        if resp.status not in {200, 202, 204}:
+                            raise RuntimeError((await resp.json())["message"])
+
             return stan.fit.Fit(
                 stan_outputs,
                 num_chains,

tests/test_fit_cache.py

@@ -0,0 +1,44 @@
+"""Tests related to cached fits."""
+import shutil
+import pathlib
+import random
+
+import stan
+import httpstan.cache
+
+program_code = "parameters {real y;} model {y ~ normal(0,1);}"
+
+
+def cache_path():
+    return pathlib.Path(httpstan.cache.model_directory("models/abcdef")).parent
+
+
+def test_fit_cache():
+    """Test that a fit with a random seed set is cached."""
+
+    cache_size_before = shutil.disk_usage(cache_path()).used
+    print(cache_size_before)
+    # this fit is cacheable
+    random_seed = random.randrange(1, 2 ** 16)
+    normal_posterior = stan.build(program_code, random_seed=random_seed)
+    normal_posterior.sample()
+    cache_size_after = shutil.disk_usage(cache_path()).used
+    print(cache_size_after)
+    assert cache_size_after > cache_size_before
+
+    # fit is now in cache
+    cache_size_before = shutil.disk_usage(cache_path()).used
+    normal_posterior.sample()
+    cache_size_after = shutil.disk_usage(cache_path()).used
+    assert cache_size_before == cache_size_after
+
+
+def test_fit_cache_uncacheable():
+    """Test that a fit with a random seed set is cached."""
+    cache_size_before = shutil.disk_usage(cache_path()).used
+    # this fit is NOT cacheable, should not be saved
+    normal_posterior = stan.build(program_code)
+    normal_posterior.sample()
+    cache_size_after = shutil.disk_usage(cache_path()).used
+    # allow for a 4096 byte difference (an empty directory takes 4K)
+    assert abs(cache_size_before - cache_size_after) <= 4096